bims-auttor 2021-12-05 papers

bims-auttor

Biomed News

on Autophagy and mTOR

Issue of 2021‒12‒05
forty-six papers selected by
Viktor Korolchuk, Newcastle University

Mitochondrial homeostasis is maintained in the absence of autophagy.
Phenotypic Assay Leads to Discovery of Mitophagy Inducers with Therapeutic Potential for Parkinson's Disease.
Vinexin contributes to autophagic decline in brain ageing across species.
The nutrient sensor mTORC1 regulates insulin secretion by modulating ß-cell autophagy.
The complex interplay between ULK1 and protein phosphatases in autophagy regulation.
Attenuation of Obesity Cardiomyopathy by Ulk1/Rab9 Mediated Alternative Mitophagy.
The crystal structure of the FAM134B-GABARAP complex provides mechanistic insights into the selective binding of FAM134 to the GABARAP subfamily.
RPS6 phosphorylation occurs to a greater extent in the periphery of human skeletal muscle fibers, near focal adhesions, after anabolic stimuli.
Role of mammalian target of rapamycin complex 2 in primary and secondary liver cancer.
The unique Akt inhibitor SC66 suppressed AMPK activity and abolished autophagy through the EGFR-p62 pathway.
The caspase-6-p62 axis modulates p62 droplets based autophagy in a dominant-negative manner.
Targeting TBK1 Attenuates LPS-Induced NLRP3 Inflammasome Activation by Regulating of mTORC1 Pathways in Trophoblasts.
Autophagy and antiviral defense.
Dapagliflozin alleviates advanced glycation end product induced podocyte injury through AMPK/mTOR mediated autophagy pathway.
USP10 inhibits the dopamine-induced reactive oxygen species-dependent apoptosis of neuronal cells by stimulating the antioxidant Nrf2 activity.
Targeting neurological abnormalities in lysosomal storage diseases.
Autophagy in Spinocerebellar ataxia type 2, a dysregulated pathway, and a target for therapy.
Amino acid deprivation induces AKT activation by inducing GCN2/ATF4/REDD1 axis.
Role of AMPK mediated pathways in autophagy and aging.
From mouse genetics to targeting the Rag GTPase pathway.
The E2 ubiquitin-conjugating enzyme HIP2 is a crucial regulator of quality control against mutant SOD1 proteotoxicity.
Scutellarin ameliorates hepatic lipid accumulation by enhancing autophagy and suppressing IRE1α/XBP1 pathway.
Quality Control Mechanisms of Mitochondria: Another Important Target for Treatment of Peripheral Neuropathy.
Farrerol Ameliorated Cisplatin-Induced Chronic Kidney Disease Through Mitophagy Induction via Nrf2/PINK1 Pathway.
Decreased efficacy of the ketamine and scopolamine-induced sustained antidepressant-like effects in rats receiving metformin.
SIRT1/mTOR pathway-mediated autophagy dysregulation promotes Pb-induced hepatic lipid accumulation in HepG2 cells.
RUNX1/EGFR pathway contributes to STAT3 activation and tumor growth caused by hyperactivated mTORC1.
Dietary excess regulates absorption and surface of gut epithelium through intestinal PPARα.
Lysosomal Function Impacts the Skeletal Muscle Extracellular Matrix.
Can We Use mTOR Inhibitors for COVID-19 Therapy?
Personalized phosphoproteomics identifies functional signaling.
β-arrestin1 promotes tauopathy by transducing GPCR signaling, disrupting microtubules and autophagy.
Therapeutic Potential of α-Synuclein Evolvability for Autosomal Recessive Parkinson's Disease.
A Conserved Mitochondrial Chaperone-Protease Complex Involved in Protein Homeostasis.
Autophagy: A Promising Target for Triple Negative Breast Cancers.
Mitophagy Disequilibrium, a Prominent Pathological Mechanism in Metabolic Heart Diseases.
Updates on the Genetics of Parkinson's Disease: Clinical Implications and Future Treatment.
Isoforms of autophagy-related proteins: role in glioma progression and therapy resistance.
Anakinra restores cellular proteostasis by coupling mitochondrial redox balance to autophagy.
Chaperon-mediated autophagy can regulate diquat-induced apoptosis by inhibiting α-synuclein accumulation cooperatively with macroautophagy.
The anticancer drug imatinib induces autophagy in Schistosoma mansoni.
Secretion of pro-angiogenic extracellular vesicles during hypoxia is dependent on the autophagy-related protein GABARAPL1.
USP11 regulates autophagy-dependent ferroptosis after spinal cord ischemia-reperfusion injury by deubiquitinating Beclin 1.
Mitochondrial sirtuins, metabolism, and aging.
TORC1 signaling modulates Cdk8-dependent GAL gene expression in Saccharomyces cerevisiae.
Starvation-induced proteasome assemblies in the nucleus link amino acid supply to apoptosis.

Mol Cell Oncol. 2021 ;8(5): 1984162

Mitochondrial homeostasis is maintained in the absence of autophagy.

Christina G Towers.

  Autophagy is a central recycling process, and it plays a complex role in cancer. We discovered that when autophagy is blocked, cancer cells compensate by increasing mitochondrial-derived vesicles. However, there are many unanswered questions remaining, particularly in the context of the dual roles of autophagy in cancer.

Keywords:  Autophagy; cancer; mitochondria; mitochondrial derived vesicles; mitophagy

DOI:  https://doi.org/10.1080/23723556.2021.1984162
ACS Chem Neurosci. 2021 Nov 30.

Phenotypic Assay Leads to Discovery of Mitophagy Inducers with Therapeutic Potential for Parkinson's Disease.

Inés Maestro, Laura R de la Ballina, Anne Simonsen, Patricia Boya, Ana Martinez.

  Mitophagy, the selective degradation of mitochondria by autophagy, involved in important physiological processes and defects in pathways has been reported in pathological conditions, such as neurodegeneration. Thus, mitophagy is an interesting target for drug discovery programs. In this investigation, we used robust phenotypic assay to screen a set of 50 small heterocyclic compounds to identify inducers of mitophagy. We identified two compounds, VP07 and JAR1.39, that induce Parkin-dependent mitophagy. Based on structure-activity relationship studies, we proposed the ability of the compounds to act as light chain 3 (LC3) interactors, similar to cardiolipin or ceramide, triggering mitophagy via Pink1/Parkin. Finally, we show promising therapeutic applicability in a cellular model of Parkinson's disease.

Keywords:  Parkinson’s disease; drug discovery; mitophagy; mitophagy inducers; phenotypic assay

DOI:  https://doi.org/10.1021/acschemneuro.1c00529
Cell Death Differ. 2021 Nov 30.

Vinexin contributes to autophagic decline in brain ageing across species.

So Jung Park, Rebecca A Frake, Cansu Karabiyik, Sung Min Son, Farah H Siddiqi, Carla F Bento, Peter Sterk, Mariella Vicinanza, Mariana Pavel, David C Rubinsztein.

Autophagic decline is considered a hallmark of ageing. The activity of this intracytoplasmic degradation pathway decreases with age in many tissues and autophagy induction ameliorates ageing in many organisms, including mice. Autophagy is a critical protective pathway in neurons and ageing is the primary risk factor for common neurodegenerative diseases. Here, we describe that autophagosome biogenesis declines with age in mouse brains and that this correlates with increased expression of the SORBS3 gene (encoding vinexin) in older mouse and human brain tissue. We characterise vinexin as a negative regulator of autophagy. SORBS3 knockdown increases F-actin structures, which compete with YAP/TAZ for binding to their negative regulators, angiomotins, in the cytosol. This promotes YAP/TAZ translocation into the nucleus, thereby increasing YAP/TAZ transcriptional activity and autophagy. Our data therefore suggest brain autophagy decreases with age in mammals and that this is likely, in part, mediated by increasing levels of vinexin.

DOI: https://doi.org/10.1038/s41418-021-00903-y
Diabetes. 2021 Dec 03. pii: db210281. [Epub ahead of print]

The nutrient sensor mTORC1 regulates insulin secretion by modulating ß-cell autophagy.

Tal Israeli, Yael Riahi, Perla Garzon, Ruy Andrade Louzada, Joao Pedro Werneck-de-Castro, Manuel Blandino-Rosano, Roni Yeroslaviz-Stolper, Liat Kadosh, Sharona Tornovsky-Babeay, Gilad Hacker, Nitzan Israeli, Orly Agmon, Boaz Tirosh, Erol Cerasi, Ernesto Bernal-Mizrachi, Gil Leibowitz.

The dynamic regulation of autophagy in β-cells by cycles of fasting-feeding and its effects on insulin secretion are unknown. In β-cells mTORC1 is inhibited while fasting, and is rapidly stimulated during refeeding by a single amino acid, leucine, and glucose. Stimulation of mTORC1 by nutrients inhibited the autophagy initiator ULK1 and the transcription factor TFEB, thereby preventing autophagy when β-cells are continuously exposed to nutrients. Inhibition of mTORC1 by Raptor knockout mimicked the effects of fasting and stimulated autophagy while inhibiting insulin secretion, whereas moderate inhibition of autophagy under these conditions rescued insulin secretion. These results show that mTORC1 regulates insulin secretion through modulation of autophagy under different nutritional situations. In the fasting state, autophagy is regulated in an mTORC1-dependent manner and its stimulation is required to keep insulin levels low, thereby preventing hypoglycemia. Reciprocally, stimulation of mTORC1 by elevated leucine and glucose, which is common in obesity, may promote hyperinsulinemia by inhibiting autophagy.

DOI: https://doi.org/10.2337/db21-0281
Autophagy. 2021 Nov 28. 1-2

The complex interplay between ULK1 and protein phosphatases in autophagy regulation.

Devanarayanan Siva Sankar, Zehan Hu, Joern Dengjel.

  ULK1 kinase is the gatekeeper of canonical macroautophagy (hereafter referred to as autophagy) phosphorylating an array of substrates critical for autophagosome biogenesis. To uncover if ULK1 has broader functions also regulating subsequent steps of autophagosome turnover, i.e., maturation, lysosomal fusion, and degradation, we performed a set of unbiased phosphoproteomic experiments employing mouse and human cells in combination with genetic and environmental perturbations. We characterized more than 1,000 potential ULK1 target sites of which many affect proteins known to be involved in all phases of the autophagosome life cycle. To better understand which of these 1,000 phosphosites were directly phosphorylated by ULK1, in contrast to downstream kinases being activated or phosphatases being inhibited by ULK1, we developed a proteome-scale in vitro kinase assay and characterized 187 phosphosites on 157 proteins as bona fide ULK1 target sites. Interestingly, our results highlight an intricate crosstalk between ULK1 and protein phosphatases. Focusing on STRN (striatin), a regulatory subunit of PPP2/PP2A (protein phosphatase 2), we identified a positive feedback loop linked to ULK1 and promoting autophagy.

Keywords:  Feedback; STRIPAK; STRN; ULK1; in vitro kinase assay; kinase; phosphatase; phosphoproteomics; phosphorylation; striatin

DOI:  https://doi.org/10.1080/15548627.2021.2002546
Circ Res. 2021 Dec 03. 129(12): 1122-1124

Attenuation of Obesity Cardiomyopathy by Ulk1/Rab9 Mediated Alternative Mitophagy.

Inna Rabinovich-Nikitin, Rachel C Cogan, Lorrie A Kirshenbaum.



Keywords:  Editorials; autophagy; cardiomyopathies; diet, high-fat; mitochondria; mitophagy; obesity

DOI:  https://doi.org/10.1161/CIRCRESAHA.121.320365
FEBS Open Bio. 2021 Dec 01.

The crystal structure of the FAM134B-GABARAP complex provides mechanistic insights into the selective binding of FAM134 to the GABARAP subfamily.

Junfeng Zhao, Zhiwei Li, Jianchao Li.

  The mammalian Atg8 family (Atg8s proteins) consists of two subfamilies: GABARAP and LC3. All members can bind to the LC3-interacting region (LIR) or Atg8-interacting motif (AIM) and participate in multiple steps of autophagy. The endoplasmic reticulum (ER) autophagy receptor FAM134B contains an LIR motif that can bind to Atg8s, but whether it can differentially bind to the two subfamilies and, if so, the structural basis for this preference remain unknown. Here we found that FAM134B bound to the GABARAP subfamily more strongly than to the LC3 subfamily. We then solved the crystal structure of the FAM134B-GABARAP complex and demonstrated that FAM134B used both its LIR core and the C-terminal helix to bind to GABARAP. We further showed that these properties might be conserved in FAM134A or FAM134C. The structure also allowed us to identify the structural determinants for the binding selectivity. Our work may be valuable for studying the differential functions of GABARAP and LC3 subfamilies in ER-phagy in the future.

Keywords:  Atg8; Autophagy; FAM134B; GABARAP; LC3 interacting region/Atg8 interacting motif

DOI:  https://doi.org/10.1002/2211-5463.13340
Am J Physiol Cell Physiol. 2021 Dec 01.

RPS6 phosphorylation occurs to a greater extent in the periphery of human skeletal muscle fibers, near focal adhesions, after anabolic stimuli.

Nathan Hodson, Michael Mazzulla, Maksym N H Holowaty, Dinesh Kumbhare, Daniel R Moore.

  Following anabolic stimuli (mechanical loading and/or amino acid provision) the mechanistic target of rapamycin complex 1 (mTORC1), a master regulator of protein synthesis, translocates toward the cell periphery. However, it is unknown if mTORC1-mediated phosphorylation events occur in these peripheral regions or prior to translocation (i.e. in central regions). We therefore aimed to determine the cellular location of a mTORC1-mediated phosphorylation event, RPS6Ser240/244, in human skeletal muscle following anabolic stimuli. Fourteen young, healthy males either ingested a protein-carbohydrate beverage (0.25g/kg protein, 0.75g/kg carbohydrate) alone (n=7;23±5yrs;76.8±3.6kg;13.6±3.8%BF, FED) or following a whole-body resistance exercise bout (n=7;22±2yrs;78.1±3.6kg;12.2±4.9%BF, EXFED). Vastus lateralis muscle biopsies were obtained at rest (PRE) and 120 and 300min following anabolic stimuli. RPS6Ser240/244 phosphorylation measured by immunofluorescent staining or immunoblot was positively correlated (r=0.76, p<0.001). Peripheral staining intensity of p-RPS6Ser240/244 increased above PRE in both FED and EXFED at 120min (~54% and ~138% respectively, p<0.05) but was greater in EXFED at both post-stimuli time points (p<0.05). The peripheral-central ratio of p-RPS6240/244 staining displayed a similar pattern, even when corrected for total RPS6 distribution, suggesting RPS6 phosphorylation occurs to a greater extent in the periphery of fibers. Moreover, p-RPS6Ser240/244 intensity within paxillin-positive regions, a marker of focal adhesion complexes, was elevated at 120min irrespective of stimulus (p=0.006) before returning to PRE at 300min. These data confirm that RPS6Ser240/244 phosphorylation occurs in the region of human muscle fibers to which mTOR translocates following anabolic stimuli and identifies focal adhesion complexes as a potential site of mTORC1 regulation in vivo.

Keywords:  Focal Adhesions; RPS6; Resistance Exercise; Skeletal muscle; mTOR

DOI:  https://doi.org/10.1152/ajpcell.00357.2021
World J Gastrointest Oncol. 2021 Nov 15. 13(11): 1632-1647

Role of mammalian target of rapamycin complex 2 in primary and secondary liver cancer.

Katharina Joechle, Jessica Guenzle, Claus Hellerbrand, Pavel Strnad, Thorsten Cramer, Ulf Peter Neumann, Sven Arke Lang.

  The mammalian target of rapamycin (mTOR) acts in two structurally and functionally distinct protein complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Upon deregulation, activated mTOR signaling is associated with multiple processes involved in tumor growth and metastasis. Compared with mTORC1, much less is known about mTORC2 in cancer, mainly because of the unavailability of a selective inhibitor. However, existing data suggest that mTORC2 with its two distinct subunits Rictor and mSin1 might play a more important role than assumed so far. It is one of the key effectors of the PI3K/AKT/mTOR pathway and stimulates cell growth, cell survival, metabolism, and cytoskeletal organization. It is not only implicated in tumor progression, metastasis, and the tumor microenvironment but also in resistance to therapy. Rictor, the central subunit of mTORC2, was found to be upregulated in different kinds of cancers and is associated with advanced tumor stages and a bad prognosis. Moreover, AKT, the main downstream regulator of mTORC2/Rictor, is one of the most highly activated proteins in cancer. Primary and secondary liver cancer are major problems for current cancer therapy due to the lack of specific medical treatment, emphasizing the need for further therapeutic options. This review, therefore, summarizes the role of mTORC2/Rictor in cancer, with special focus on primary liver cancer but also on liver metastases.

Keywords:  Cholangiocellular carcinoma; Hepatocellular carcinoma; Liver cancer; Liver metastases; Mammalian target of rapamycin; Mammalian target of rapamycin complex 2; Rictor

DOI:  https://doi.org/10.4251/wjgo.v13.i11.1632
Cell Biol Int. 2021 Dec 02.

The unique Akt inhibitor SC66 suppressed AMPK activity and abolished autophagy through the EGFR-p62 pathway.

Bolin Hou, Erwei Li, Jingnan Liang, Shuchun Liu, Huaiyi Yang, Ling Liu, Xuejun Jiang.

  Akt is usually considered to be a negative regulator of both autophagy and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling. In the present study, we found that SC66, a pyridine-based allosteric Akt inhibitor, suppressed basal and H2 O2 -induced autophagy concurrent with decreased phosphorylation and activity of AMPK. SC66 treatment led to the formation of a high molecular weight (HMW) form of SQSTM1/p62 (p62), which is an autophagic substrate and is essential for selective autophagy. Moreover, we observed that SC66 inhibited the binding of p62 and microtubule-associated protein light chain 3 (LC3). The immunoprecipitation results revealed the interaction between p62 and epidermal growth factor receptor (EGFR), and knockdown of EGFR reversed SC66-mediated autophagy inhibition without affecting the phosphorylation of acetyl-CoA carboxylase (ACC), a well-known substrate of AMPK. SC66 increased the interaction between EGFR and Beclin 1 and markedly decreased the association of EGFR with VPS34, a critical protein for autophagy induction. Collectively, the data presented here indicate that EGFR-p62 pathway plays a critical role in Akt-mediated positive regulation of autophagy. This article is protected by copyright. All rights reserved.

Keywords:  AMPK; EGFR; SC66; autophagy; p62

DOI:  https://doi.org/10.1002/cbin.11732
Cell Death Differ. 2021 Dec 03.

The caspase-6-p62 axis modulates p62 droplets based autophagy in a dominant-negative manner.

Evelina Valionyte, Yi Yang, Sophie A Griffiths, Amelia T Bone, Elizabeth R Barrow, Vikram Sharma, Boxun Lu, Shouqing Luo.

SQSTM1/p62, as a major autophagy receptor, forms droplets that are critical for cargo recognition, nucleation, and clearance. p62 droplets also function as liquid assembly platforms to allow the formation of autophagosomes at their surfaces. It is unknown how p62-droplet formation is regulated under physiological or pathological conditions. Here, we report that p62-droplet formation is selectively blocked by inflammatory toxicity, which induces cleavage of p62 by caspase-6 at a novel cleavage site D256, a conserved site across human, mouse, rat, and zebrafish. The N-terminal cleavage product is relatively stable, whereas the C-terminal product appears undetectable. Using a variety of cellular models, we show that the p62 N-terminal caspase-6 cleavage product (p62-N) plays a dominant-negative role to block p62-droplet formation. In vitro p62 phase separation assays confirm this observation. Dominant-negative regulation of p62-droplet formation by caspase-6 cleavage attenuates p62 droplets dependent autophagosome formation. Our study suggests a novel pathway to modulate autophagy through the caspase-6-p62 axis under certain stress stimuli.

DOI: https://doi.org/10.1038/s41418-021-00912-x
Front Immunol. 2021 ;12 743700

Targeting TBK1 Attenuates LPS-Induced NLRP3 Inflammasome Activation by Regulating of mTORC1 Pathways in Trophoblasts.

Sohee Lee, Jiha Shin, Jong-Seok Kim, Jongdae Shin, Sung Ki Lee, Hwan-Woo Park.

  Pathological maternal inflammation and abnormal placentation contribute to several pregnancy-related disorders, including preterm birth, intrauterine growth restriction, and preeclampsia. TANK-binding kinase 1 (TBK1), a serine/threonine kinase, has been implicated in the regulation of various physiological processes, including innate immune response, autophagy, and cell growth. However, the relevance of TBK1 in the placental pro-inflammatory environment has not been investigated. In this study, we assessed the effect of TBK1 inhibition on lipopolysaccharide (LPS)-induced NLRP3 inflammasome activation and its underlying mechanisms in human trophoblast cell lines and mouse placenta. TBK1 phosphorylation was upregulated in the trophoblasts and placenta in response to LPS. Pharmacological and genetic inhibition of TBK1 in trophoblasts ameliorated LPS-induced NLRP3 inflammasome activation, placental inflammation, and subsequent interleukin (IL)-1 production. Moreover, maternal administration of amlexanox, a TBK1 inhibitor, reversed LPS-induced adverse pregnancy outcomes. Notably, TBK1 inhibition prevented LPS-induced NLRP3 inflammasome activation by targeting the mammalian target of rapamycin complex 1 (mTORC1). Thus, this study provides evidence for the biological significance of TBK1 in placental inflammation, suggesting that amlexanox may be a potential therapeutic candidate for treating inflammation-associated pregnancy-related complications.

Keywords:  NLRP3 inflammasome; TBK1; mTORC1; maternal inflammation; placenta; trophoblast

DOI:  https://doi.org/10.3389/fimmu.2021.743700
IUBMB Life. 2021 Dec 03.

Autophagy and antiviral defense.

Po-Yuan Ke.

  Targeting intracellular components for lysosomal degradation by autophagy not only maintains cellular homeostasis but also counteracts the effects of external stimuli, including invading pathogens. Among various kinds of pathogens, viruses have been extensively shown to induce autophagy to benefit viral growth in infected cells and to modulate host defense responses, such as innate antiviral immunity. Recently, numerous lines of evidence have implied that virus-induced autophagy triggers multilayer mechanisms to regulate the innate antiviral response of host cells, thus promoting a balance in virus-host cell interactions. In this review, the detailed mechanisms underlying autophagy and the innate antiviral immune response are first described. Then, I summarize the current information regarding the diverse functional role(s) of autophagy in the control of antiviral defenses against different types of viral infections. Moreover, the physiological significance of autophagy-regulated antiviral responses on the viral life cycle and the potential autophagy alterations induced by virus-associated antiviral signaling is further discussed.

Keywords:  antiviral response; autophagy; host defense; innate immunity; selective autophagy; virus

DOI:  https://doi.org/10.1002/iub.2582
Cell Signal. 2021 Nov 29. pii: S0898-6568(21)00295-3. [Epub ahead of print]90 110206

Dapagliflozin alleviates advanced glycation end product induced podocyte injury through AMPK/mTOR mediated autophagy pathway.

Lei Yang, Baozhu Liang, Jingxin Li, Xiaoyan Zhang, Hong Chen, Jia Sun, Zhen Zhang.

  Excessive accumulation of advanced glycation end products (AGEs) contributes to autophagy interruption on podocytes and insufficient autophagy on podocytes is accountable to podocyte injury and eventually accelerates the advancement of DN. SGLT2 inhibitors have been confirmed excellent renoprotection in DN whereas the mechanism for such benefit is not fully illustrated. Here, we report dapagliflozin, an SGLT2 inhibitor, ameliorated the pro-inflammatory cytokines release and apoptosis level concomitant with increasing Synaptopodin level on AGE-induced podocytes. Furthermore, dapagliflozin manifested autophagy promotion on AGE-induced podocytes as evident by the upregulated Beclin and LC3II/LC3I ratio levels attendant with the shrunk p62 level. However, The protective effect of dapagliflozin was blunted by 3-MA, an autophagy inhibitor. Additionally, the effect of dapagliflozin on autophagy was relevant to the regulation of the AMPK-mTOR signal pathway. Taken together, dapagliflozin effectively mitigated AGE-induced podocyte injury through AMPK-mTOR mediated upregulation of autophagy. It may offer a novel mechanism to further elucidate the renoprotective effect on SGLT2 inhibitors.

Keywords:  Advanced glycation end product; Autophagy; Dapagliflozin; Podocyte; SGLT2

DOI:  https://doi.org/10.1016/j.cellsig.2021.110206
J Biol Chem. 2021 Nov 24. pii: S0021-9258(21)01257-6. [Epub ahead of print] 101448

USP10 inhibits the dopamine-induced reactive oxygen species-dependent apoptosis of neuronal cells by stimulating the antioxidant Nrf2 activity.

Junya Sango, Taichi Kakihana, Masahiko Takahashi, Yoshinori Katsuragi, Sergei Anisimov, Masaaki Komatsu, Masahiro Fujii.

  Nrf2 is an antioxidant transcriptional activator in many types of cells, and its dysfunction plays key roles in a variety of human disorders, including Parkinson's disease (PD). PD is characterized by the selective loss of dopaminergic neurons in PD-affected brain regions. Dopamine treatment of neuronal cells stimulates the production of reactive oxygen species (ROS) and increases ROS-dependent neuronal apoptosis. In this study, we found that the ubiquitin-specific protease 10 (USP10) protein reduces dopamine-induced ROS production of neuronal cells and ROS-dependent apoptosis by stimulating the antioxidant activity of Nrf2. USP10 interacted with the Nrf2 activator p62, increased the phosphorylation of p62, increased the interaction of p62 with the Nrf2 inhibitor Keap1, and stimulated Nrf2 antioxidant transcriptional activity. In addition, USP10 augmented dopamine-induced Nrf2 translation. Taken together, these results indicate that USP10 is a key regulator of Nrf2 antioxidant activity in neuronal cells and suggest that USP10 activators are promising therapeutic agents for oxidative stress-related diseases, including PD.

Keywords:  Keap1; Nrf2; Parkinson's disease; ROS; USP10; apoptosis; dopamine; p62

DOI:  https://doi.org/10.1016/j.jbc.2021.101448
Trends Pharmacol Sci. 2021 Nov 27. pii: S0165-6147(21)00222-4. [Epub ahead of print]

Targeting neurological abnormalities in lysosomal storage diseases.

Raquel van Gool, Anthony Tucker-Bartley, Edward Yang, Nicholas Todd, Frank Guenther, Benjamin Goodlett, Walla Al-Hertani, Olaf A Bodamer, Jaymin Upadhyay.

  Central nervous system (CNS) abnormalities and corresponding neurological and psychiatric symptoms are frequently observed in lysosomal storage disorders (LSDs). The genetic background of individual LSDs is indeed unique to each illness. However, resulting defective lysosomal function within the CNS can transition normal cellular processes (i.e., autophagy) into aberrant mechanisms, facilitating overlapping downstream consequences including neurocircuitry dysfunction, neurodegeneration as well as sensory, motor, cognitive, and psychological symptoms. Here, the neurological and biobehavioral phenotypes of major classes of LSDs are discussed alongside therapeutic strategies in development that aim to tackle neuropathology among other disease elements. Finally, focused ultrasound blood-brain barrier opening is proposed to enhance therapeutic delivery thereby overcoming the key hurdle of central distribution of disease modifying therapies in LSDs.

Keywords:  autophagy; central nervous system abnormalities; lysosomal storage disease; neurological symptoms; psychiatric symptoms

DOI:  https://doi.org/10.1016/j.tips.2021.11.005
Cell Death Dis. 2021 Nov 29. 12(12): 1117

Autophagy in Spinocerebellar ataxia type 2, a dysregulated pathway, and a target for therapy.

Adriana Marcelo, Inês T Afonso, Ricardo Afonso-Reis, David V C Brito, Rafael G Costa, Ana Rosa, João Alves-Cruzeiro, Benedita Ferreira, Carina Henriques, Rui J Nobre, Carlos A Matos, Luís Pereira de Almeida, Clévio Nóbrega.

Spinocerebellar ataxia type 2 (SCA2) is an incurable and genetic neurodegenerative disorder. The disease is characterized by progressive degeneration of several brain regions, resulting in severe motor and non-motor clinical manifestations. The mutation causing SCA2 disease is an abnormal expansion of CAG trinucleotide repeats in the ATXN2 gene, leading to a toxic expanded polyglutamine segment in the translated ataxin-2 protein. While the genetic cause is well established, the exact mechanisms behind neuronal death induced by mutant ataxin-2 are not yet completely understood. Thus, the goal of this study is to investigate the role of autophagy in SCA2 pathogenesis and investigate its suitability as a target for therapeutic intervention. For that, we developed and characterized a new striatal lentiviral mouse model that resembled several neuropathological hallmarks observed in SCA2 disease, including formation of aggregates, neuronal marker loss, cell death and neuroinflammation. In this new model, we analyzed autophagic markers, which were also analyzed in a SCA2 cellular model and in human post-mortem brain samples. Our results showed altered levels of SQSTM1 and LC3B in cells and tissues expressing mutant ataxin-2. Moreover, an abnormal accumulation of these markers was detected in SCA2 patients' striatum and cerebellum. Importantly, the molecular activation of autophagy, using the compound cordycepin, mitigated the phenotypic alterations observed in disease models. Overall, our study suggests an important role for autophagy in the context of SCA2 pathology, proposing that targeting this pathway could be a potential target to treat SCA2 patients.

DOI: https://doi.org/10.1038/s41419-021-04404-1
Cell Death Dis. 2021 Dec 03. 12(12): 1127

Amino acid deprivation induces AKT activation by inducing GCN2/ATF4/REDD1 axis.

Hyeon-Ok Jin, Sung-Eun Hong, Ji-Young Kim, Se-Kyeong Jang, In-Chul Park.

Amino acid availability is sensed by various signaling molecules, including general control nonderepressible 2 (GCN2) and mechanistic target of rapamycin complex 1 (mTORC1). However, it is unclear how these sensors are associated with cancer cell survival under low amino acid availability. In the present study, we investigated AKT activation in non-small cell lung cancer (NSCLC) cells deprived of each one of 20 amino acids. Among the 20 amino acids, deprivation of glutamine, arginine, methionine, and lysine induced AKT activation. AKT activation was induced by GCN2/ATF4/REDD1 axis-mediated mTORC2 activation under amino acid deprivation. In CRISPR-Cas9-mediated REDD1-knockout cells, AKT activation was not induced by amino acid deprivation, indicating that REDD1 plays a major role in AKT activation under amino acid deprivation. Knockout of REDD1 sensitized cells cultured under glutamine deprivation conditions to radiotherapy. Taken together, GCN2/ATF4/REDD1 axis induced by amino acid deprivation promotes cell survival signal, which might be a potential target for cancer therapy.

DOI: https://doi.org/10.1038/s41419-021-04417-w
Biochimie. 2021 Nov 24. pii: S0300-9084(21)00271-6. [Epub ahead of print]

Role of AMPK mediated pathways in autophagy and aging.

Yuchen Ge, Min Zhou, Cui Chen, Xiaojian Wu, Xiaobo Wang.

  AMPK is an important kinase regulating energy homeostasis and also a key protein involved in a variety of signal transduction pathways. It plays a vitally regulatory role in cellular senescence. Activation of AMPK can delay or block the aging process, which is of great significance in the treatment of cardiovascular diseases and other aging related diseases, and provides a potential target for new indications such as Alzheimer's disease. Therefore, AMPK signaling pathway plays an important role in aging research. The in-depth study of AMPK activators will provide more new directions for the treatment of age-related maladies and the development of innovative drugs. Autophagy is a process that engulfs and degrades own cytoplasm or organelles. Thereby, meeting the metabolic demands and updating certain organelles of the cell has become a hotspot in the field of anti-aging in recent years. AMPK plays an important role between autophagy and senescence. In our review, the relationship among AMPK signaling, autophagy and aging will be clarified through the interaction between AMPK and mTOR, ULK1, FOXO, p53, SIRT1, and NF -κB.

Keywords:  AMPK; Aging; Autophagy; Disease; Signaling pathways

DOI:  https://doi.org/10.1016/j.biochi.2021.11.008
Mol Cell Oncol. 2021 ;8(5): 1979370

From mouse genetics to targeting the Rag GTPase pathway.

Ana Ortega-Molina, Alejo Efeyan.

  The identification of the Rag GTPases initiated the deciphering of the molecular puzzle of nutrient signaling to the mechanistic target of rapamycin (mTOR), and spurred interest in targeting this pathway to combat human disease. Recent mouse genetic studies have provided pathophysiological insight and pointed to potential indications for inhibitors of the Rag GTPase pathway.

Keywords:  B cells; Mtor; Rag GTPases; nutrients; lymphoma; mice; small molecules

DOI:  https://doi.org/10.1080/23723556.2021.1979370
Biochim Biophys Acta Mol Basis Dis. 2021 Nov 29. pii: S0925-4439(21)00249-0. [Epub ahead of print] 166316

The E2 ubiquitin-conjugating enzyme HIP2 is a crucial regulator of quality control against mutant SOD1 proteotoxicity.

Yeong Jin Tak, Seongman Kang.

  Mutations in superoxide dismutase 1 (SOD1) leading to the formation of intracellular protein aggregates cause amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder characterized by a selective degeneration of motor neurons. The ALS-linked mutant SOD1 emerged as a possible target for ubiquitin-proteasome system (UPS)-mediated degradation. We aimed to elucidate the role of huntingtin interaction protein 2 (HIP2), an E2 ubiquitin-conjugating enzyme, in the proteotoxicity of mutant SOD1 aggregates. We found that HIP2 interacts with mutant SOD1, but not wild-type SOD1, and is upregulated in response to mutant SOD1 expression. Upregulation of HIP2 protein was observed in the spinal cord of 16-week-old SOD1-G93A transgenic mice. HIP2 further modified mutant SOD1 proteins via K48-linked polyubiquitination and degraded mutant SOD1 proteins through the UPS. Upregulation of HIP2 protected cells from mutant SOD1-induced toxicity. Taken together, our findings demonstrate that HIP2 is a crucial regulator of quality control against the proteotoxicity of mutant SOD1. Our results suggest that modulating HIP2 may represent a novel therapeutic strategy for the treatment of ALS.

Keywords:  ALS; HIP2; Protein aggregates; Proteotoxicity; SOD1; UPS

DOI:  https://doi.org/10.1016/j.bbadis.2021.166316
Phytother Res. 2021 Dec 02.

Scutellarin ameliorates hepatic lipid accumulation by enhancing autophagy and suppressing IRE1α/XBP1 pathway.

Xueying Zhang, Zhaojiong Huo, Huiling Luan, Yihai Huang, Yanhui Shen, Liang Sheng, Jiangyu Liang, Feihua Wu.

  Nonalcoholic fatty liver disease is the most prevalent liver disease characterized by excessive lipid accumulation in hepatocytes. Endoplasmic reticulum (ER) stress and autophagy play an important role in lipid accumulation. In this study, scutellarin (Scu) was examined in palmitic acid-treated HepG2 cells and C57/BL6 mice fed a high-fat diet (HFD). Scu reduced intracellular lipid content and inhibited sterol regulatory element binding protein-1c (SREBP-1c)-mediated lipid synthesis and fatty acid translocase-mediated lipid uptake in HepG2 cells. Additionally, Scu restored impaired autophagy and inhibited excessive activation of ER stress in vivo and in vitro. Moreover, Scu upregulated forkhead box O transcription factor 1-mediated autophagy by inhibiting inositol-requiring enzyme 1α (IRE1α)/X-box-binding protein 1 (XBP1) branch activation, while XBP1s overexpression exacerbated the lipid accumulation and impaired autophagy in HepG2 cells and also weakened the positive effects of Scu. Furthermore, Scu attenuated ER stress by activating autophagy, ultimately downregulating SREBP-1c-mediated lipid synthesis, and autophagy inhibitors offset these beneficial effects. Scu inhibited the crosstalk between autophagy and ER stress and downregulated saturated fatty acid-induced lipid accumulation in hepatocytes. These findings demonstrate that Scu ameliorates hepatic lipid accumulation by enhancing autophagy and suppressing ER stress via the IRE1α/XBP1 pathway.

Keywords:  XBP1s; autophagy; endoplasmic reticulum stress; nonalcoholic fatty liver disease; scutellarin

DOI:  https://doi.org/10.1002/ptr.7344
DNA Cell Biol. 2021 Dec 01.

Quality Control Mechanisms of Mitochondria: Another Important Target for Treatment of Peripheral Neuropathy.

Te Zhang, Jiannan Li, Guoqing Zhao.

  Mitochondria provide energy for various cellular activities and are involved in the regulating of several physiological and pathological processes. Mitochondria constitute a dynamic network regulated by numerous quality control mechanisms; for example, division is necessary for mitochondria to develop, and fusion dilutes toxins produced by the mitochondria. Mitophagy removes damaged mitochondria. The etiologies of peripheral neuropathy include congenital and acquired diseases, and the pathogenesis varies; however, oxidative stress caused by mitochondrial damage is the accepted pathogenesis of peripheral neuropathy. Regulation and control of mitochondrial quality might point the way toward potential treatments for peripheral neuropathy. This article will review mitochondrial quality control mechanisms, their involvement in peripheral nerve diseases, and their potential therapeutic role.

Keywords:  mitochondria; mitochondrial dynamics; mitophagy; pain; peripheral neuropathy

DOI:  https://doi.org/10.1089/dna.2021.0529
Front Pharmacol. 2021 ;12 768700

Farrerol Ameliorated Cisplatin-Induced Chronic Kidney Disease Through Mitophagy Induction via Nrf2/PINK1 Pathway.

Ning Ma, Zhentong Wei, Jianqiang Hu, Wenjing Gu, Xinxin Ci.

  Previously, Our study has showed that farrerol can activate Nrf2 and ameliorate cisplatin-induced acute kidney injury (AKI). Mitophagy reportedly can prevent diabetic nephropathy, cisplatin-induced AKI and other related nephropathy. In this study, we evaluated the correlation between mitophagy and the protective effect of the Nrf2 activator farrerol on cisplatin-induced CKD by using C57BL/6 wild-type and Nrf2 knockout mice. We confirmed that Nrf2 and PINK1/Parkin-mediated mitophagy was significantly increased on the 3rd day of cisplatin stimulation but was reduced on the 38th day of cisplatin stimulation. Similar to previous results, farrerol activated Nrf2 on the 38th day of cisplatin administration, subsequently stimulating the Nrf2-targeted antioxidant enzymes HO-1 and NQO1. In addition, farrerol triggered PINK1/Parkin-mediated mitophagy by recruiting the receptor proteins LC3 and p62/SQSTM1, thereby eliminating damaged mitochondria. Furthermore, genetic deletion of Nrf2 reduced PINK1/Parkin-mediated mitophagy activation and led to increased renal tubular necrosis and renal fibrosis. We also found that farrerol alleviated inflammation and renal fibrosis by inhibiting p-NF-κB/NLRP3 and TGF-β/Smad signaling. These data indicated that farrerol effectively inhibited cisplatin-induced inflammation and renal fibrosis by activating Nrf2 and PINK1/Parkin-mediated mitophagy, which provides a potential novel therapeutic target for CKD.

Keywords:  Nrf2; PINK1; acute kidney injury; chronic kidney disease; mitophagy

DOI:  https://doi.org/10.3389/fphar.2021.768700
Pharmacol Rep. 2021 Nov 30.

Decreased efficacy of the ketamine and scopolamine-induced sustained antidepressant-like effects in rats receiving metformin.

Han-Wen Chuang, I-Hua Wei, Chun-Te Li, Chih-Chia Huang.

  BACKGROUND: Metformin is the most widely used drug for treating type 2 diabetes mellitus (DM), which frequently co-occurs with depressive disorders. Thus, patients with depression are likely to receive metformin. Metformin activates AMP-activated kinase (AMPK), which inhibits mechanistic target of rapamycin complex 1 (mTORC1) signaling. mTORC1 activation is essential for the antidepressant effects of ketamine and scopolamine. Thus, we hypothesized that metformin may attenuate ketamine- or scopolamine-induced antidepressant efficacies by blocking their mTORC1 activation.METHODS: We assessed the acute and sustained antidepressant-like actions of ketamine and scopolamine in male Sprague-Dawley rats subjected to the forced swim test with or without metformin pretreatment. The expressions of AMPK, mTORC1, and brain-derived neurotrophic factor (BDNF) in their prefrontal cortex were assessed.
RESULTS: Metformin (50 mg/kg) attenuated the sustained, but not acute, antidepressant-like effects of ketamine (10 mg/kg) and scopolamine (25 μg/kg). Although metformin reduced mTORC1 downstream activated P70S6K, it did not significantly alter mTORser2448 activation and even increased BDNF expression. Notably, ketamine, scopolamine, and metformin all exerted significant antidepressant-like actions, as evidenced by increased AMPK phosphorylation and BDNF expression.
CONCLUSIONS: Metformin-induced attenuation of sustained antidepressant-like effects are not directly dependent on AMPK-deactivated mTORC1. Our results indicate the complexity of interactions between AMPK, BDNF, and mTORC1. Further research, including mechanistic studies, is warranted to comprehensively evaluate the application of metformin in patients receiving mTORC1-based antidepressants.

Keywords:  AMPK; BDNF; Ketamine; Metformin; Scopolamine; mTOR

DOI:  https://doi.org/10.1007/s43440-021-00342-z
Environ Toxicol. 2021 Nov 29.

SIRT1/mTOR pathway-mediated autophagy dysregulation promotes Pb-induced hepatic lipid accumulation in HepG2 cells.

Yanan Zhao, Ankang Mao, Ranran Zhang, Shuang Guan, Jing Lu.

  Lead (Pb) is a common and toxic metal pollutant in the ecological environment and has drawn significant attention due to its presence in various channels, including the use of lead-based paint, mineral extraction and smelting, exhaust gas from gasoline combustion. Autophagy is an essential catabolic pathway and blocked autophagy may result in abnormal lipid metabolism in liver. A body of evidence demonstrates that Pb exposure causes abnormal lipid droplet (LDs) accumulation in the liver, but the mechanism remains unknown. Here, we investigated whether Pb induced lipid accumulation by regulating autophagy in HepG2 cells. In this study, we found that Pb (50 μM) blocked the autophagy flux mainly by transcription factor EB (TFEB)-mediated impairment of lysosome formation and activity. Then we demonstrated that the dense lipid accumulation was observed upon Pb exposure, and induction of autophagy by the autophagy activator rapamycin (Rap) alleviated Pb-induced lipid accumulation, while suppression of autophagy by chloroquine (CQ) exacerbated Pb-induced lipid accumulation, suggested that Pb-induced autophagy blockage might be responsible for lipid accumulation. Moreover, we demonstrated that the SIRT1/mTOR pathway participated in Pb-induced autophagy dysregulation, leading to Pb-induced hepatic lipid accumulation. In summary, these results revealed a new insight into the relationship between Pb-caused autophagy dysregulation and lipid accumulation for the first time and highlight autophagy as a novel therapeutic target against Pb-induced hepatic lipid accumulation which supplying the theoretical basis and potential strategies for the intervention and treatment of Pb-related disease.

Keywords:  HepG2 cells; SIRT1/mTOR; autophagy; lead; lipid accumulation

DOI:  https://doi.org/10.1002/tox.23420
Mol Ther Oncolytics. 2021 Dec 17. 23 387-401

RUNX1/EGFR pathway contributes to STAT3 activation and tumor growth caused by hyperactivated mTORC1.

Wei Lin, Xiaofeng Wan, Anjiang Sun, Meng Zhou, Xu Chen, Yanling Li, Zixi Wang, Hailiang Huang, Hongwu Li, Xianguo Chen, Juan Hua, Xiaojun Zha.

  Loss of function of tuberous sclerosis complex 1 or 2 (TSC1 or TSC2) leads to the activation of mammalian target of rapamycin complex 1 (mTORC1). Hyperactivated mTORC1 plays a critical role in tumor growth, but the underlying mechanism is still not completely elucidated. Here, by analyzing Tsc1- or Tsc2-null mouse embryonic fibroblasts, rat Tsc2-null ELT3 cells, and human cancer cells, we present evidence for the involvement of epidermal growth factor receptor (EGFR) as a downstream target of mTORC1 in tumor growth. We show that mTORC1 leads to increased EGFR expression through upregulation of runt-related transcriptional factor 1 (RUNX1). Knockdown of EGFR impairs proliferation and tumoral growth of Tsc-deficient cells, while overexpression of EGFR promotes the proliferation of the control cells. Moreover, the mTOR signaling pathway has been shown to be positively correlated with EGFR in human cancers. In addition, we demonstrated that EGFR enhances cell growth through activation of signal transducer and activator of transcription 3 (STAT3). We conclude that activation of the RUNX1/EGFR/STAT3 signaling pathway contributes to tumorigenesis caused by hyperactivated mTORC1 and should be targeted for the treatment of mTORC1-related tumors, particularly TSC.

Keywords:  EGFR; RUNX1; STAT3; mTOR; tuberous sclerosis complex; tumorigenesis

DOI:  https://doi.org/10.1016/j.omto.2021.10.009
Nat Commun. 2021 Dec 02. 12(1): 7031

Dietary excess regulates absorption and surface of gut epithelium through intestinal PPARα.

Ozren Stojanović, Jordi Altirriba, Dorothée Rigo, Martina Spiljar, Emilien Evrard, Benedek Roska, Salvatore Fabbiano, Nicola Zamboni, Pierre Maechler, Françoise Rohner-Jeanrenaud, Mirko Trajkovski.

Intestinal surface changes in size and function, but what propels these alterations and what are their metabolic consequences is unknown. Here we report that the food amount is a positive determinant of the gut surface area contributing to an increased absorptive function, reversible by reducing daily food. While several upregulated intestinal energetic pathways are dispensable, the intestinal PPARα is instead necessary for the genetic and environment overeating-induced increase of the gut absorptive capacity. In presence of dietary lipids, intestinal PPARα knock-out or its pharmacological antagonism suppress intestinal crypt expansion and shorten villi in mice and in human intestinal biopsies, diminishing the postprandial triglyceride transport and nutrient uptake. Intestinal PPARα ablation limits systemic lipid absorption and restricts lipid droplet expansion and PLIN2 levels, critical for droplet formation. This improves the lipid metabolism, and reduces body adiposity and liver steatosis, suggesting an alternative target for treating obesity.

DOI: https://doi.org/10.1038/s41467-021-27133-7
J Dev Biol. 2021 Nov 23. pii: 52. [Epub ahead of print]9(4):

Lysosomal Function Impacts the Skeletal Muscle Extracellular Matrix.

Elizabeth C Coffey, Mary Astumian, Sarah S Alrowaished, Claire Schaffer, Clarissa A Henry.

  Muscle development and homeostasis are critical for normal muscle function. A key aspect of muscle physiology during development, growth, and homeostasis is modulation of protein turnover, the balance between synthesis and degradation of muscle proteins. Protein degradation depends upon lysosomal pH, generated and maintained by proton pumps. Sphingolipid transporter 1 (spns1), a highly conserved gene encoding a putative late endosome/lysosome carbohydrate/H+ symporter, plays a pivotal role in maintaining optimal lysosomal pH and spns1-/- mutants undergo premature senescence. However, the impact of dysregulated lysosomal pH on muscle development and homeostasis is not well understood. We found that muscle development proceeds normally in spns1-/- mutants prior to the onset of muscle degeneration. Dysregulation of the extracellular matrix (ECM) at the myotendinous junction (MTJ) coincided with the onset of muscle degeneration in spns1-/- mutants. Expression of the ECM proteins laminin 111 and MMP-9 was upregulated. Upregulation of laminin 111 mitigated the severity of muscle degeneration, as inhibition of adhesion to laminin 111 exacerbated muscle degeneration in spns1-/- mutants. MMP-9 upregulation was induced by tnfsf12 signaling, but abrogation of MMP-9 did not impact muscle degeneration in spns1-/- mutants. Taken together, these data indicate that dysregulated lysosomal pH impacts expression of ECM proteins at the myotendinous junction.

Keywords:  basement membrane; lysosomal myopathy; myotendinous junction; skeletal muscle; spinster; zebrafish

DOI:  https://doi.org/10.3390/jdb9040052
Comb Chem High Throughput Screen. 2021 Nov 30.

Can We Use mTOR Inhibitors for COVID-19 Therapy?

Ina Y Aneva, Solomon Habtemariam, Maciej Banach, Parames C Sil, Kasturi Sarkar, Adeleh Sahebnasagh, Mohammad Amjad Kamal, Maryam Khayatkashani, Hamid Reza Khayat Kashani.

  Infection by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) provokes acute inflammation due to extensive replication of the virus in the epithelial cells of the upper and lower respiratory system. The mammalian target of rapamycin (mTOR) is a l signalling protein with critical functions in cell growth, metabolism, and proliferation. It is known for its regulatory functions in protein synthesis and angiogenesis cascades. The structure of mTOR consists of two distinct complexes (mTORC1 and mTORC2) with diverse functions at different levels of the signaling pathway. By activating mRNA translation, the mTORC1 plays a key role in regulating protein synthesis and cellular growth. On the other hand, the functions of mTORC2 are mainly associated with cell proliferation and survival. By using an appropriate inhibitor at the right time, mTOR modulation could provide immunosuppressive opportunities as antirejection regimens in organ transplantation as well as in the treatment of autoimmune diseases and solid tumours. The mTOR has an important role in the inflammatory process, too. Inhibitors of mTOR might indeed be promising agents in the treatment of viral infections. They have further been successfully used in patients with severe influenza A/H1N1 pneumonia and acute respiratory failure. The officially accepted mTOR inhibitors that have undergone clinical testing are sirolimus, everolimus, temsirolimus, and tacrolimus. Thus, further studies on mTOR inhibitors for SARS-CoV-2 infection or COVID-19 therapy are well merited.

Keywords:  COVID-19; SARS-CoV-2; everolimus; mTOR inhibitors; rapamycin; sirolimus; temsirolimus

DOI:  https://doi.org/10.2174/1386207325666211130140923
Nat Biotechnol. 2021 Dec 02.

Personalized phosphoproteomics identifies functional signaling.

Elise J Needham, Janne R Hingst, Benjamin L Parker, Kaitlin R Morrison, Guang Yang, Johan Onslev, Jonas M Kristensen, Kurt Højlund, Naomi X Y Ling, Jonathan S Oakhill, Erik A Richter, Bente Kiens, Janni Petersen, Christian Pehmøller, David E James, Jørgen F P Wojtaszewski, Sean J Humphrey.

Protein phosphorylation dynamically integrates environmental and cellular information to control biological processes. Identifying functional phosphorylation amongst the thousands of phosphosites regulated by a perturbation at a global scale is a major challenge. Here we introduce 'personalized phosphoproteomics', a combination of experimental and computational analyses to link signaling with biological function by utilizing human phenotypic variance. We measure individual subject phosphoproteome responses to interventions with corresponding phenotypes measured in parallel. Applying this approach to investigate how exercise potentiates insulin signaling in human skeletal muscle, we identify both known and previously unidentified phosphosites on proteins involved in glucose metabolism. This includes a cooperative relationship between mTOR and AMPK whereby the former directly phosphorylates the latter on S377, for which we find a role in metabolic regulation. These results establish personalized phosphoproteomics as a general approach for investigating the signal transduction underlying complex biology.

DOI: https://doi.org/10.1038/s41587-021-01099-9
Life Sci Alliance. 2022 Mar;pii: e202101183. [Epub ahead of print]5(3):

β-arrestin1 promotes tauopathy by transducing GPCR signaling, disrupting microtubules and autophagy.

Jung-Aa Woo, Yan Yan, Teresa R Kee, Sara Cazzaro, Kyle C McGill Percy, Xinming Wang, Tian Liu, Stephen B Liggett, David E Kang.

G protein-coupled receptors (GPCRs) have been shown to play integral roles in Alzheimer's disease pathogenesis. However, it is unclear how diverse GPCRs similarly affect Aβ and tau pathogenesis. GPCRs share a common mechanism of action via the β-arrestin scaffolding signaling complexes, which not only serve to desensitize GPCRs by internalization, but also mediate multiple downstream signaling events. As signaling via the GPCRs, β2-adrenergic receptor (β2AR), and metabotropic glutamate receptor 2 (mGluR2) promotes hyperphosphorylation of tau, we hypothesized that β-arrestin1 represents a point of convergence for such pathogenic activities. Here, we report that β-arrestins are not only essential for β2AR and mGluR2-mediated increase in pathogenic tau but also show that β-arrestin1 levels are increased in brains of Frontotemporal lobar degeneration (FTLD-tau) patients. Increased β-arrestin1 in turn drives the accumulation of pathogenic tau, whereas reduced ARRB1 alleviates tauopathy and rescues impaired synaptic plasticity and cognitive impairments in PS19 mice. Biochemical and cellular studies show that β-arrestin1 drives tauopathy by destabilizing microtubules and impeding p62/SQSTM1 autophagy flux by interfering with p62 body formation, which promotes pathogenic tau accumulation.

DOI: https://doi.org/10.26508/lsa.202101183
Parkinsons Dis. 2021 ;2021 6318067

Therapeutic Potential of α-Synuclein Evolvability for Autosomal Recessive Parkinson's Disease.

Jianshe Wei, Gilbert Ho, Yoshiki Takamatsu, Eliezer Masliah, Makoto Hashimoto.

The majority of Parkinson's disease (PD) is sporadic in elderly and is characterized by α-synuclein (αS) aggregation and other alterations involving mitochondria, ubiquitin-proteasome, and autophagy. The remaining are familial PD associated with gene mutations of either autosomal dominant or recessive inheritances. However, the former ones are similar to sporadic PD, and the latter ones are accompanied by impaired mitophagy during the reproductive stage. Since no radical therapies are available for PD, the objective of this paper is to discuss a mechanistic role for amyloidogenic evolvability, a putative physiological function of αS, among PD subtypes, and the potential relevance to therapy. Presumably, αS evolvability might benefit familial PD due to autosomal dominant genes and also sporadic PD during reproduction, which may manifest as neurodegenerative diseases through antagonistic pleiotropy mechanism in aging. Indeed, there are some reports describing that αS prevents apoptosis and mitochondrial alteration under the oxidative stress conditions, notwithstanding myriads of papers on the neuropathology of αS. Importantly, β-synuclein (βS), the nonamyloidogenic homologue of αS, might buffer against evolvability of αS protofibrils associated with neurotoxicity. Finally, it is intriguing to predict that increased αS evolvability through suppression of βS expression might protect against autosomal recessive PD. Collectively, further studies are warranted to better understand αS evolvability in PD pathogenesis, leading to rational therapy development.

DOI: https://doi.org/10.1155/2021/6318067
Front Mol Biosci. 2021 ;8 767088

A Conserved Mitochondrial Chaperone-Protease Complex Involved in Protein Homeostasis.

Mauro Serricchio, Peter Bütikofer.

  Mitochondria are essential organelles involved in cellular energy production. The inner mitochondrial membrane protein stomatin-like protein 2 (SLP-2) is a member of the SPFH (stomatin, prohibitin, flotilin, and HflK/C) superfamily and binds to the mitochondrial glycerophospholipid cardiolipin, forming cardiolipin-enriched membrane domains to promote the assembly and/or stabilization of protein complexes involved in oxidative phosphorylation. In addition, human SLP-2 anchors a mitochondrial processing complex required for proteolytic regulation of proteins involved in mitochondrial dynamics and quality control. We now show that deletion of the gene encoding the Trypanosoma brucei homolog TbSlp2 has no effect on respiratory protein complex stability and mitochondrial functions under normal culture conditions and is dispensable for growth of T. brucei parasites. In addition, we demonstrate that TbSlp2 binds to the metalloprotease TbYme1 and together they form a large mitochondrial protein complex. The two proteins negatively regulate each other's expression levels by accelerating protein turnover. Furthermore, we show that TbYme1 plays a role in heat-stress resistance, as TbYme1 knock-out parasites displayed mitochondrial fragmentation and loss of viability when cultured at elevated temperatures. Unbiased interaction studies uncovered putative TbYme1 substrates, some of which were differentially affected by the absence of TbYme1. Our results support emerging evidence for the presence of mitochondrial quality control pathways in this ancient eukaryote.

Keywords:  Yme1; cardiolipin; membrane proteins; mitochondria; mitochondrial stress response; prohibitin; stomatin-like protein 2; trypanosoma

DOI:  https://doi.org/10.3389/fmolb.2021.767088
Pharmacol Res. 2021 Nov 26. pii: S1043-6618(21)00590-9. [Epub ahead of print] 106006

Autophagy: A Promising Target for Triple Negative Breast Cancers.

Yomna S Abd El-Aziz, Josef Gillson, Patric J Jansson, Sumit Sahni.

  Triple negative breast cancer (TNBC) is the most aggressive type of breast cancers which constitutes about 15% of all breast cancer cases and characterized by negative expression of hormonal receptors and human epidermal growth factor receptor 2 (HER2). Thus, endocrine and HER2 targeted therapies are not effective toward TNBCs, and they mainly rely on chemotherapy and surgery for treatment. Despite recent advances in chemotherapy, 40% of TNBC patients develop a metastatic relapse and recurrence. Therefore, understanding the molecular profile of TNBC is warranted to identify targets that can be selected for the development of a new and effective therapeutic approach. Autophagy is an internal defensive mechanism that allows the cells to survive under different stressors. It has been well known that autophagy exerts a crucial role in cancer progression. The critical role of autophagy in TNBC progression is emerging in recent years. This review will discuss autophagic pathway, how autophagy affects TNBC progression and recent therapeutic approaches that can target autophagy as a new treatment modality.

Keywords:  Autophagy; Autophagy Inhibitors; Triple negative breast cancer

DOI:  https://doi.org/10.1016/j.phrs.2021.106006
Diabetes Metab Syndr Obes. 2021 ;14 4631-4640

Mitophagy Disequilibrium, a Prominent Pathological Mechanism in Metabolic Heart Diseases.

Yunhao Li, Ningning Zheng, Xudong Ding.

  With overall food intake among the general population as high as ever, metabolic syndrome (MetS) has become a global epidemic and is responsible for many serious life-threatening diseases, especially heart failure. In multiple metabolic disorders, maintaining a dynamic balance of mitochondrial number and function is necessary to prevent the overproduction of reactive oxygen species (ROS), which has been proved to be one of the important mechanisms of cardiomyocyte injury due to the mismatching of oxygen consumption and mitochondrial population and finally to heart failure. Mitophagy is a process that eliminates damaged or redundant mitochondria. It is mediated by a series of signaling molecules, including PINK, parkin, BINP3, FUNDC1, CTSD, Drp1, Rab9 and mTOR. Meanwhile, increasing evidence also showed that the interaction between ferroptosis and mitophagy interfered with mitochondrial homeostasis. This review will focus on these essential molecules and pathways of mitophagy and cell homeostasis affected by hypoxia and other stimuli in metabolic heart diseases.

Keywords:  BNIP3; Bcl-2/E1B19kDa-interacting protein; FUN14 domain-containing protein 1; FUNDC1; PINK; PTEN induced putative kinase; ferroptosis; metabolic heart diseases; metabolic syndrome; mitophagy; parkin

DOI:  https://doi.org/10.2147/DMSO.S336882
Acta Neurol Taiwan. 2021 Sep 30. 30(3) 83-93

Updates on the Genetics of Parkinson's Disease: Clinical Implications and Future Treatment.

Yung-Tsai Chu, Chun-Hwei Tai, Chin-Hsien Lin, Ruey-Meei Wu.

Parkinson' disease (PD) is a common neurodegenerative disease with the pathological hallmark of alpha-synuclein aggregation within dopaminergic neurons. The etiology of PD comes from a complex interplay between genetic and environmental factors. Though most cases of PD are sporadic; a family history of PD is found in approximately 15% of patients. Pathogenic mutations are found in 5% to 10% of individuals with either familial or sporadic PD. In recent decades, because of the advent of next generation sequencing, more than 25 genes have been identified as causative genes in PD. These findings allow better understanding of the pathogenesis of PD, including aberrant alpha-synuclein homeostasis, defective mitochondrial functions, and impairment of the ubiquitin-proteasome and autophagy-lysosome pathways. Among the PD-causative genes, LRRK2 mutation is the most frequent mutation in autosomal dominant PD and Parkin mutation is prevalent in patients with autosomal recessive or early onset PD. Several genetic epidemiology studies in Asians have revealed a distinctive mutation spectrum from Western populations, reinforcing the importance of ethnic differences in PD. Proper genetic testing is recommended for patients with early onset, a strong family history, or associated red flag clinical features. Considering that clinical trials of disease-modifying therapy targeting patients with specific mutations are ongoing and we are in the era of precision medicine, this review highlights recent updates of genetic findings in patients with PD, focusing on Asian populations and practical recommendations for genetic testing. Keywords: Parkinson's disease, Genetics.
Mol Cell Biochem. 2021 Dec 01.

Isoforms of autophagy-related proteins: role in glioma progression and therapy resistance.

Elizaveta Belyaeva, Rajesh Kumar Kharwar, Ilya V Ulasov, Irina Karlina, Petr Timashev, Reza Mohammadinejad, Arbind Acharya.

  Autophagy is the process of recycling and utilization of degraded organelles and macromolecules in the cell compartments formed during the fusion of autophagosomes with lysosomes. During autophagy induction the healthy and tumor cells adapt themselves to harsh conditions such as cellular stress or insufficient supply of nutrients in the cell environment to maintain their homeostasis. Autophagy is currently seen as a form of programmed cell death along with apoptosis and necroptosis. In recent years multiple studies have considered the autophagy as a potential mechanism of anticancer therapy in malignant glioma. Although, subsequent steps in autophagy development are known and well-described, on molecular level the mechanism of autophagosome initiation and maturation using autophagy-related proteins is under investigation. This article reviews current state about the mechanism of autophagy, its molecular pathways and the most recent studies on roles of autophagy-related proteins and their isoforms in glioma progression and its treatment.

Keywords:  Autophagy; Glioblastoma; Isoforms; Tumor resistance

DOI:  https://doi.org/10.1007/s11010-021-04308-w
J Clin Invest. 2021 Nov 30. pii: e144983. [Epub ahead of print]

Anakinra restores cellular proteostasis by coupling mitochondrial redox balance to autophagy.

Frank L van de Veerdonk, Giorgia Renga, Marilena Pariano, Marina M Bellet, Giuseppe Servillo, Francesca Fallarino, Antonella De Luca, Rossana G Iannitti, Danilo Piobbico, Marco Gargaro, Giorgia Manni, Fiorella D'Onofrio, Claudia Stincardini, Luigi Sforna, Monica Borghi, Marilena Castelli, Stefania Pieroni, Vasileios Oikonomou, Valeria R Villella, Matteo Puccetti, Stefano Giovagnoli, Roberta Galarini, Carolina Barola, Luigi Maiuri, Della-Fazia Maria Agnese, Barbara Cellini, Vincenzo Talesa, Charles A Dinarello, Claudio Costantini, Luigina Romani.

  Autophagy selectively degrades aggregation-prone misfolded proteins caused by defective cellular proteostasis. However, the complexity of autophagy may prevent the full appreciation of how its modulation could be used as a therapeutic strategy in disease management. Here we define a molecular pathway through which recombinant interleukin-1 receptor antagonist (IL-1Ra, anakinra) affects cellular proteostasis independently from the IL-1 receptor (IL-1R1). Anakinra promoted H2O2-driven autophagy through a xenobiotic sensing pathway involving the aryl hydrocarbon receptor that, activated through the indoleamine 2,3-dioxygenase 1-kynurenine pathway, transcriptionally activates NADPH Oxidase 4 independent of the IL-1R1. By coupling the mitochondrial redox balance to autophagy, anakinra improved the dysregulated proteostasis network in murine and human cystic fibrosis. We anticipate that anakinra may represent a therapeutic option in addition to its IL-1R1 dependent anti-inflammatory properties by acting at the intersection of mitochondrial oxidative stress and autophagy with the capacity to restore conditions in which defective proteostasis leads to human disease.

Keywords:  Autophagy; Fungal infections; Infectious disease; Inflammation

DOI:  https://doi.org/10.1172/JCI144983
Food Chem Toxicol. 2021 Nov 27. pii: S0278-6915(21)00739-0. [Epub ahead of print] 112706

Chaperon-mediated autophagy can regulate diquat-induced apoptosis by inhibiting α-synuclein accumulation cooperatively with macroautophagy.

Hong Ju Kim, Hyun Chul Koh.

  α-Synuclein, which is associated with Parkinson's disease, is cleared by the ubiquitin-proteasome system and autophagy lysosome system. Chaperon-mediated autophagy (CMA) and macroautophagy are major subtypes of autophagy and play a critical role in pesticide-induced α-synucleinopathy. In this study, we explored the role of CMA in diquat (DQ)-induced α-synucleinopathy and characterized the relationship between CMA and macroautophagy in the clearance of pathologic α-synuclein for the prevention of DQ neurotoxicity. DQ was cytotoxic to SH-SY5Y cells in a concentration-dependent manner, as shown by decreased cell viability and increased cytotoxicity. DQ treatment was also found to induce autophagy such as CMA and macroautophagy by monitoring the expression of Lamp2A and microtubule-associated protein 1A/1B light chain 3B (LC3-II) respectively. Following DQ treatment, SH-SY5Y cells were found to have induced phosphorylated and detergent-insoluble α-synuclein deposits, and MG132, a proteasome inhibitor, effectively potentiated both CMA and macroautophagy for preventing α-synuclein aggregation. Interestingly, CMA impairment by Lamp2A-knock down decreased the LC3II expression compared to in DQ-treated cells transfected with control siRNA. In Lamp2-knock down cells, pathologic α-synuclein was increased 12 h after DQ treatment, but there was no change observed at 24 h. In DQ-treated cells, macroautophagy by 3-methyladenine and bafilomycin inhibition increased Lamp2A expression, indicating an increase in CMA activity. In addition, CMA modulation affected apoptosis, and inhibiting lysosome activity by NH4Cl increased apoptosis in DQ-treated cells. An increase in autophagy was confirmed to compensate for the decrease in lysosome activity. Pretreatment with z-VAD-fmk, a pan-caspase inhibitor, significantly enhanced the macroautophagy response of DQ-exposed cells without alterations in Lamp2A expression. Our results suggest that CMA can regulate DQ-induced α-synucleinopathy cooperatively with macroautophagy, and crosstalk between macroautophagy and CMA plays an important role in DQ-induced cytotoxicity. Taken together, autophagy modulation may be a useful treatment strategy in pesticide-induced neurodegenerative disorders through preventing α-synucleinopathy.

Keywords:  Apoptosis; Chaperon-mediated autophagy; Diquat (DQ); Macroautophagy; α-synucleinopathy

DOI:  https://doi.org/10.1016/j.fct.2021.112706
Int J Parasitol. 2021 Nov 24. pii: S0020-7519(21)00312-X. [Epub ahead of print]

The anticancer drug imatinib induces autophagy in Schistosoma mansoni.

Mudassar N Mughal, Christoph G Grevelding, Simone Haeberlein.

  Schistosomiasis, caused by schistosome parasites, is a neglected tropical disease affecting humans and animals. There is no vaccine available yet, and fear of upcoming resistance against the only widely used drug, praziquantel, is omnipresent. Previously, we showed that imatinib (Gleevec), an anticancer drug, affected schistosome physiology and caused the death of adult Schistosoma mansoni in vitro. Here, we present the first known evidence that one effect of imatinib is the induction of autophagy in S. mansoni. Furthermore, worms co-treated with imatinib and bafilomycin A1, a late-phase autophagy inhibitor, reversed imatinib-induced autophagy and its antischistosomal effects as revealed by phenotypic and molecular analyses.

Keywords:  Autophagy; Bafilomycin A1; Cathepsins; Imatinib; LC3B; Schistosoma mansoni

DOI:  https://doi.org/10.1016/j.ijpara.2021.10.008
J Extracell Vesicles. 2021 Dec;10(14): e12166

Secretion of pro-angiogenic extracellular vesicles during hypoxia is dependent on the autophagy-related protein GABARAPL1.

Tom G Keulers, Sten F Libregts, Joel E J Beaumont, Kim G Savelkouls, Johan Bussink, Hans Duimel, Ludwig Dubois, Marijke I Zonneveld, Carmen López-Iglesias, Karel Bezstarosti, Jeroen A Demmers, Marc Vooijs, Marca Wauben, Kasper M A Rouschop.

  Tumour hypoxia is a hallmark of solid tumours and contributes to tumour progression, metastasis development and therapy resistance. In response to hypoxia, tumour cells secrete pro-angiogenic factors to induce blood vessel formation and restore oxygen supply to hypoxic regions. Extracellular vesicles (EVs) are emerging as mediators of intercellular communication in the tumour microenvironment. Here we demonstrate that increased expression of the LC3/GABARAP protein family member GABARAPL1, is required for endosomal maturation, sorting of cargo to endosomes and the secretion of EVs. Silencing GABARAPL1 results in a block in the early endosomal pathway and impaired secretion of EVs with pro-angiogenic properties. Tumour xenografts of doxycycline inducible GABARAPL1 knockdown cells display impaired vascularisation that results in decreased tumour growth, elevated tumour necrosis and increased therapy efficacy. Moreover, our data show that GABARAPL1 is expressed on the EV surface and targeting GABARAPL1+ EVs with GABARAPL1 targeting antibodies results in blockade of pro-angiogenic effects in vitro. In summary, we reveal that GABARAPL1 is required for EV cargo loading and secretion. GABARAPL1+ EVs are detectable and targetable and are therefore interesting to pursue as a therapeutic target.

Keywords:  GABARAPL1; autophagy; exosomes; extracellular vesicles; hypoxia

DOI:  https://doi.org/10.1002/jev2.12166
Cell Death Differ. 2021 Nov 27.

USP11 regulates autophagy-dependent ferroptosis after spinal cord ischemia-reperfusion injury by deubiquitinating Beclin 1.

Yuluo Rong, Jin Fan, Chengyue Ji, Zhuanghui Wang, Xuhui Ge, Jiaxing Wang, Wu Ye, Guoyong Yin, Weihua Cai, Wei Liu.

Spinal cord ischemia-reperfusion injury (SCIRI) is a serious trauma that can lead to loss of sensory and motor function. Ferroptosis is a new form of regulatory cell death characterized by iron-dependent accumulation of lipid peroxides. Ferroptosis has been studied in various diseases; however, the exact function and molecular mechanism of ferroptosis in SCIRI remain unknown. In this study, we demonstrated that ferroptosis is involved in the pathological mechanism of SCIRI. Inhibition of ferroptosis could promote the recovery of motor function in mice after SCIRI. In addition, we found that ubiquitin-specific protease 11 (USP11) was significantly upregulated in neuronal cells after hypoxia-reoxygenation and in the spinal cord in mice with I/R injury. Knockdown of USP11 in vitro and KO of USP11 in vivo (USP11-/Y) significantly decreased neuronal cell ferroptosis. In mice, this promotes functional recovery after SCIRI. In contrast, in vitro, USP11 overexpression leads to classic ferroptosis events. Overexpression of USP11 in mice resulted in increased ferroptosis and poor functional recovery after SCIRI. Interestingly, upregulating the expression of USP11 also appeared to increase the production of autophagosomes and to cause substantial autophagic flux, a potential mechanism through which USP11 may enhance ferroptosis. The decreased autophagy markedly weakened the ferroptosis mediated by USP11 and autophagy induction had a synergistic effect with USP11. Importantly, USP11 promotes autophagy activation by stabilizing Beclin 1, thereby leading to ferroptosis. In conclusion, this study shows that ferroptosis is closely associated with SCIRI, and that USP11 plays a key role in regulating ferroptosis and additionally identifies USP11-mediated autophagy-dependent ferroptosis as a promising target for the treatment of SCIRI.

DOI: https://doi.org/10.1038/s41418-021-00907-8
J Genet Genomics. 2021 Nov 29. pii: S1673-8527(21)00358-1. [Epub ahead of print]

Mitochondrial sirtuins, metabolism, and aging.

Zhejun Ji, Guang-Hui Liu, Jing Qu.

  Maintaining metabolic homeostasis is essential for cellular and organismal health throughout life. Of the multiple signaling pathways that regulate metabolism, such as PI3K/AKT, mTOR, AMPK, and sirtuins, mammalian sirtuins also play unique roles in aging. By understanding how sirtuins regulate metabolic processes, we can start to understand how they slow down or accelerate biological aging. Here, we review the biology of SIRT3, SIRT4, and SIRT5, known as the mitochondrial sirtuins due to their localization in the mitochondrial matrix. First, we will focus on canonical pathways that regulate metabolism more broadly and how these are integrated with aging regulation. Then, we will summarize the current knowledge about functional differences between SIRT3, SIRT4, and SIRT5 in metabolic control and integration in signaling networks. Finally, we will discuss how mitochondrial sirtuins regulate processes associated with aging and oxidative stress, calorie restriction and disease.

Keywords:  Metabolism and aging regulation; Mitochondrial sirtuins; SIRT3; SIRT4; SIRT5; age-related diseases

DOI:  https://doi.org/10.1016/j.jgg.2021.11.005
Genetics. 2021 Oct 05. pii: iyab168. [Epub ahead of print]

TORC1 signaling modulates Cdk8-dependent GAL gene expression in Saccharomyces cerevisiae.

Riley Horvath, Nicole Hawe, Cindy Lam, Konstantin Mestnikov, Mariam Eji-Lasisi, John Rohde, Ivan Sadowski.

  Cdk8 of the RNA polymerase II mediator kinase complex regulates gene expression by phosphorylating sequence-specific transcription factors. This function is conserved amongst eukaryotes, but the signals and mechanisms regulating Cdk8 activity and phosphorylation of its substrates are unknown. Full induction of the GAL genes in yeast requires phosphorylation of the transcriptional activator Gal4 by Cdk8. We used a screen to identify regulators of the Cdk8-dependent phosphorylation on Gal4, from which we identified multiple mutants with defects in TORC1 signaling. One mutant, designated gal four throttle 1 (gft1) was identified as a recessive allele of hom3, encoding aspartokinase, and mutations in hom3 caused effects typical of inhibition of TORC1, including rapamycin sensitivity and enhanced nuclear localization of the TORC1-responsive transcription factor Gat1. Mutations in hom3 also inhibit phosphorylation of Gal4 in vivo at the Cdk8-dependent site on Gal4, as did mutations of tor1, but these mutations did not affect activity of Cdk8 assayed in vitro. Disruption of cdc55, encoding a regulatory subunit of the TORC1-regulated protein phosphatase PP2A, suppressed the effect of hom3 and tor1 mutations on GAL expression, and also restored phosphorylation of Gal4 at the Cdk8-dependent site in vivo. These observations demonstrate that TORC1 signaling regulates GAL induction through the activity of PP2A/Cdc55 and suggest that Cdk8-dependent phosphorylation of Gal4 is opposed by PP2A/Cdc55 dephosphorylation. These results provide insight into how induction of transcription by a specific inducer can be modulated by global nutritional signals through regulation of Cdk8-dependent phosphorylation.

Keywords:   GAL genes; Cdc55; Cdk8; Gal4; PP2A; Tor; phosphorylation; transcription; yeast

DOI:  https://doi.org/10.1093/genetics/iyab168
Nat Commun. 2021 Nov 30. 12(1): 6984

Starvation-induced proteasome assemblies in the nucleus link amino acid supply to apoptosis.

Maxime Uriarte, Nadine Sen Nkwe, Roch Tremblay, Oumaima Ahmed, Clémence Messmer, Nazar Mashtalir, Haithem Barbour, Louis Masclef, Marion Voide, Claire Viallard, Salima Daou, Djaileb Abdelhadi, Daryl Ronato, Mohammadjavad Paydar, Anaïs Darracq, Karine Boulay, Nicolas Desjardins-Lecavalier, Przemyslaw Sapieha, Jean-Yves Masson, Mikhail Sergeev, Benjamin H Kwok, Laura Hulea, Frédérick A Mallette, Eric Milot, Bruno Larrivée, Hugo Wurtele, El Bachir Affar.

Eukaryotic cells have evolved highly orchestrated protein catabolic machineries responsible for the timely and selective disposal of proteins and organelles, thereby ensuring amino acid recycling. However, how protein degradation is coordinated with amino acid supply and protein synthesis has remained largely elusive. Here we show that the mammalian proteasome undergoes liquid-liquid phase separation in the nucleus upon amino acid deprivation. We termed these proteasome condensates SIPAN (Starvation-Induced Proteasome Assemblies in the Nucleus) and show that these are a common response of mammalian cells to amino acid deprivation. SIPAN undergo fusion events, rapidly exchange proteasome particles with the surrounding milieu and quickly dissolve following amino acid replenishment. We further show that: (i) SIPAN contain K48-conjugated ubiquitin, (ii) proteasome inhibition accelerates SIPAN formation, (iii) deubiquitinase inhibition prevents SIPAN resolution and (iv) RAD23B proteasome shuttling factor is required for SIPAN formation. Finally, SIPAN formation is associated with decreased cell survival and p53-mediated apoptosis, which might contribute to tissue fitness in diverse pathophysiological conditions.

DOI: https://doi.org/10.1038/s41467-021-27306-4