bims-lysosi 2021-09-05 papers

bims-lysosi

Biomed News

on Lysosomes and signaling

Issue of 2021–09–05
thirty papers selected by
Stephanie Fernandes, Max Planck Institute for Biology of Ageing

A proteomic view on lysosomes.
Targeted disruption of GAK stagnates autophagic flux by disturbing lysosomal dynamics.
The CACNA1A Mutant Disrupts Lysosome Calcium Homeostasis in Cerebellar Neurons and the Resulting Endo-Lysosomal Fusion Defect Can be Improved by Calcium Modulation.
Epidermal Lamellar Body Biogenesis: Insight Into the Roles of Golgi and Lysosomes.
Deathly triangle for pancreatic β-cells: Hippo pathway-MTORC1-autophagy.
LncRNA coordinates Hippo and mTORC1 pathway activation in cancer.
MPS I: early diagnosis, bone disease and treatment, where are we now?
Transformable amyloid-beta mimetic peptide amphiphiles for lysosomal disruption in non-small cell lung cancer.
Lowering mTORC1 Drives CAR-Ts Home in Acute Myeloid Leukemia.
mTORC2 is an important target for simvastatin-associated toxicity in C2C12 cells and mouse skeletal muscle - roles of Rap1 geranylgeranylation and mitochondrial dysfunction.
Detecting lysosomal storage disorders by glycomic profiling using liquid chromatography mass spectrometry.
Aberrant mTOR/autophagy/Nurr1 signaling is critical for TSC-associated tumor development.
The Akt-mTOR pathway drives myelin sheath growth by regulating cap-dependent translation.
The Akt-mTOR network at the interface of hematopoietic stem cell homeostasis.
A modified density gradient proteomic-based method to analyze endolysosomal proteins in cardiac tissue.
Autophagy in major human diseases.
Neuromyelitis optica (NMO)-IgG-driven organelle reorganization in human iPSC-derived astrocytes.
Lymphangioleiomyomatosis: pathogenesis, clinical features, diagnosis, and management.
Self-assemblies of Rab- and Arf-family small GTPases on lipid bilayers in membrane tethering.
Divergent regulation of inflammatory cytokines by mTORC1 in THP-1-derived macrophages and intestinal epithelial Caco-2 cells.
Lysosomes in acute myeloid leukemia: potential therapeutic targets?
LAMP2 Cardiomyopathy: Consequences of Impaired Autophagy in the Heart.
Chloroquine Increases Osteoclast Activity in vitro but does not Improve the Osteopetrotic Bone Phenotype of ADO2 Mice.
The trans-SNARE complex VAMP4/Stx6/Stx7/Vti1b is a key regulator of Golgi to late endosome MT1-MMP transport in macrophages.
Identification of genetic modifiers of murine hepatic β-glucocerebrosidase activity.
Enhancing Acsl4 in absence of mTORC2/Rictor drove β-cell dedifferentiation via inhibiting FoxO1 and promoting ROS production.
β-Galactosylceramidase in cancer: friend or foe?
Regulation of lipid homeostasis by the TBC protein dTBC1D22 via modulation of the small GTPase Rab40 to facilitate lipophagy.
BMP2K phosphorylates AP-2 and regulates clathrin-mediated endocytosis.
Organelle-specific regulation of ferroptosis.

Mol Omics. 2021 Sep 03.

A proteomic view on lysosomes.

Pathma Muthukottiappan, Dominic Winter.

Lysosomes are the main degradative organelles of almost all eukaryotic cells. They fulfil a crucial function in cellular homeostasis, and impairments in lysosomal function are connected to a continuously increasing number of pathological conditions. In recent years, lysosomes are furthermore emerging as control centers of cellular metabolism, and major regulators of cellular signaling were shown to be activated at the lysosomal surface. To date, >300 proteins were demonstrated to be located in/at the lysosome, and the lysosomal proteome and interactome is constantly growing. For the identification of these proteins, and their involvement in cellular mechanisms or disease progression, mass spectrometry (MS)-based proteomics has proven its worth in a large number of studies. In this review, we are recapitulating the application of MS-based approaches for the investigation of the lysosomal proteome, and their application to a diverse set of research questions. Numerous strategies were applied for the enrichment of lysosomes or lysosomal proteins and their identification by MS-based methods. This allowed for the characterization of the lysosomal proteome, the investigation of lysosome-related disorders, the utilization of lysosomal proteins as biomarkers for diseases, and the characterization of lysosome-related cellular mechanisms. While these >60 studies provide a comprehensive picture of the lysosomal proteome across several model organisms and pathological conditions, various proteomics approaches have not been applied to lysosomes yet, and a large number of questions are still left unanswered.

DOI: https://doi.org/10.1039/d1mo00205h
Int J Mol Med. 2021 Oct;pii: 195. [Epub ahead of print]48(4):

Targeted disruption of GAK stagnates autophagic flux by disturbing lysosomal dynamics.

Masaya Miyazaki, Masaki Hiramoto, Naoharu Takano, Hiroko Kokuba, Jun Takemura, Mayumi Tokuhisa, Hirotsugu Hino, Hiromi Kazama, Keisuke Miyazawa.

  The autophagy‑lysosome system allows cells to adapt to environmental changes by regulating the degradation and recycling of cellular components, and to maintain homeostasis by removing aggregated proteins and defective organelles. Cyclin G‑associated kinase (GAK) is involved in the regulation of clathrin‑dependent endocytosis and cell cycle progression. In addition, a single nucleotide polymorphism at the GAK locus has been reported as a risk factor for Parkinson's disease. However, the roles of GAK in the autophagy‑lysosome system are not completely understood, thus the present study aimed to clarify this. In the present study, under genetic disruption or chemical inhibition of GAK, analyzing autophagic flux and observing morphological changes of autophagosomes and autolysosomes revealed that GAK controlled lysosomal dynamics via actomyosin regulation, resulting in a steady progression of autophagy. GAK knockout (KO) in A549 cells impaired autophagosome‑lysosome fusion and autophagic lysosome reformation, which resulted in the accumulation of enlarged autophagosomes and autolysosomes during prolonged starvation. The stagnation of autophagic flux accompanied by these phenomena was also observed with the addition of a GAK inhibitor. Furthermore, the addition of Rho‑associated protein kinase (ROCK) inhibitor or ROCK1 knockdown mitigated GAK KO‑mediated effects. The results suggested a vital role of GAK in controlling lysosomal dynamics via maintaining lysosomal homeostasis during autophagy.

Keywords:  Rho‑associated protein kinase; actomyosin; autophagic lysosome reformation; autophagosome‑lysosome fusion; autophagy; cyclin G‑associated kinase

DOI:  https://doi.org/10.3892/ijmm.2021.5028
Neurochem Res. 2021 Sep 02.

The CACNA1A Mutant Disrupts Lysosome Calcium Homeostasis in Cerebellar Neurons and the Resulting Endo-Lysosomal Fusion Defect Can be Improved by Calcium Modulation.

Feng Zhu, Yunping Miao, Min Cheng, Xiaodi Ye, Aiying Chen, Gaoli Zheng, Xuejun Tian.

  Mutations in P/Q type voltage gated calcium channel (VGCC) lead severe human neurological diseases such as episodic ataxia 2, familial hemiplegic migraine 1, absence epilepsy, progressive ataxia and spinocerebellar ataxia 6. The pathogenesis of these diseases remains unclear. Mice with spontaneous mutation in the Cacna1a gene encoding the pore-forming subunit of P/Q type VGCC also exhibit ataxia, epilepsy and neurodegeneration. Based on the previous work showing that the P/Q type VGCC in neurons regulates lysosomal fusion through its calcium channel activity on lysosomes, we utilized CACNA1A mutant mice to further investigate the mechanism by which P/Q-type VGCCs regulate lysosomal function and neuronal homeostasis. We found CACNA1A mutant neurons have reduced lysosomal calcium storage without changing the resting calcium concentration in cytoplasm and the acidification of lysosomes. Immunohistochemistry and transmission electron microscopy reveal axonal degeneration due to lysosome dysfunction in the CACNA1A mutant cerebella. The calcium modulating drug thapsigargin, by depleting the ER calcium store, which locally increases the calcium concentration can alleviate the defective lysosomal fusion in mutant neurons. We propose a model that in cerebellar neurons, P/Q-type VGCC maintains the integrity of the nervous system by regulating lysosomal calcium homeostasis to affect lysosomal fusion, which in turn regulates multiple important cellular processes such as autophagy and endocytosis. This study helps us to better understand the pathogenesis of P/Q-type VGCC related neurodegenerative diseases and provides a feasible direction for future pharmacological treatment.

Keywords:  Calcium homeostasis; LAMP1; Lysosome; Neurodegeneration; P/Q-type voltage gated calcium channel

DOI:  https://doi.org/10.1007/s11064-021-03438-3
Front Cell Dev Biol. 2021 ;9 701950

Epidermal Lamellar Body Biogenesis: Insight Into the Roles of Golgi and Lysosomes.

Sarmistha Mahanty, Subba Rao Gangi Setty.

  Epidermal lamellar bodies (eLBs) are secretory organelles that carry a wide variety of secretory cargo required for skin homeostasis. eLBs belong to the class of lysosome-related organelles (LROs), which are cell-type-specific organelles that perform diverse functions. The formation of eLBs is thought to be related to that of other LROs, which are formed either through the gradual maturation of Golgi/endosomal precursors or by the conversion of conventional lysosomes. Current evidence suggests that eLB biogenesis presumably initiate from trans-Golgi network and receive cargo from endosomes, and also acquire lysosome characteristics during maturation. These multistep biogenesis processes are frequently disrupted in human skin disorders. However, many gaps remain in our understanding of eLB biogenesis and their relationship to skin diseases. Here, we describe our current understanding on eLB biogenesis with a focus on cargo transport to this LRO and highlight key areas where future research is needed.

Keywords:  Golgi; epidermal lamellar body; epidermis; lysosome; lysosome-related organelle

DOI:  https://doi.org/10.3389/fcell.2021.701950
Autophagy. 2021 Sep 01. 1-3

Deathly triangle for pancreatic β-cells: Hippo pathway-MTORC1-autophagy.

Amin Ardestani, Kathrin Maedler.

  A progressive decline in the macroautophagic/autophagic flux is a hallmark of pancreatic β-cell failure in type 2 diabetes (T2D) but the responsible intrinsic factors and underlying molecular mechanisms are incompletely understood. A stress-sensitive multicomponent cellular loop of the Hippo pathway kinase LATS2 (large tumor suppressor 2), MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) and autophagy regulates β-cell survival and metabolic adaptation. Chronic metabolic stress leads to LATS2 hyperactivation which then induces MTORC1, subsequently impairing the cellular autophagic flux and consequently triggering β-cell death. Reciprocally, under physiological conditions, autophagy controls β-cell survival by lysosomal degradation of LATS2. These signaling cross-talks and the interaction between autophagy and LATS2 are important for the regulation of β-cell turnover and functional compensation under metabolic stress.

Keywords:  Autophagy; LATS2; MTORC1; beta cells; diabetes; type 2 diabetes

DOI:  https://doi.org/10.1080/15548627.2021.1972404
Cell Death Dis. 2021 Aug 30. 12(9): 822

LncRNA coordinates Hippo and mTORC1 pathway activation in cancer.

Shugeng Zhang, Shuhang Liang, Dehai Wu, Hongrui Guo, Kun Ma, Lianxin Liu.

The Hippo and mammalian target of rapamycin complex 1 (mTORC1) pathways are the two predominant pathways that regulate tumour growth and metastasis. Therefore, we explored the potential crosstalk between these two functionally relevant pathways to coordinate their tumour growth-control functions. We found that a Hippo pathway-related long noncoding RNA, HPR, directly interacts with Raptor, an essential component of mTORC1, to upregulate mTORC1 activation by impairing the phosphorylation of Raptor by AMPK. Knockdown or knockout of HPR in breast cancer and cholangiocarcinoma cells led to a reduction in tumour growth. Compared with HPR WT cells, HPR-overexpressing cells exhibited nuclear accumulation of YAP1, and significantly blocked the downregulation of mTORC1 signalling induced by energy stress. Thus, our study reveals a direct link between the Hippo and mTORC1 pathways in the control of tumour growth.

DOI: https://doi.org/10.1038/s41419-021-04112-w
J Inherit Metab Dis. 2021 Sep 03.

MPS I: early diagnosis, bone disease and treatment, where are we now?

Sandra D K Kingma, An I Jonckheere.

  Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder characterized by α-L-iduronidase deficiency. Patients present with a broad spectrum of disease severity ranging from the most severe phenotype (Hurler) with devastating neurocognitive decline, bone disease and early death to intermediate (Hurler-Scheie) and more attenuated (Scheie) phenotypes, with a normal life expectancy. The most severely affected patients are preferably treated with haematopoietic stem cell transplantation, which halts the neurocognitive decline. Patients with more attenuated phenotypes are treated with enzyme replacement therapy. There are several challenges to be met in the treatment of MPS I patients. Firstly, to optimize outcome, early recognition of the disease and clinical phenotype is needed to guide decisions on therapeutic strategies. Secondly, there is thus far no effective treatment available for MPS I bone disease. The pathophysiological mechanisms behind bone disease are largely unknown, limiting the development of effective therapeutic strategies. This article is a state of the art that comprehensively discusses 3 of the most urgent open issues in MPS I: early diagnosis of MPS I patients, pathophysiology of MPS I bone disease, and emerging therapeutic strategies for MPS I bone disease. This article is protected by copyright. All rights reserved.

Keywords:  Mucopolysaccharidosis type I; bone disease; growth factors; lysosomal storage disorder; newborn screening; pathophysiology; phenotype; treatment

DOI:  https://doi.org/10.1002/jimd.12431
Biomaterials. 2021 Aug 21. pii: S0142-9612(21)00434-8. [Epub ahead of print]277 121078

Transformable amyloid-beta mimetic peptide amphiphiles for lysosomal disruption in non-small cell lung cancer.

Christopher M Baehr, Lu Zhang, Yi Wu, Andras Domokos, Wenwu Xiao, Lei Wang, Kit S Lam.

  Non-small cell lung cancer (NSCLC) is the largest contributor to cancer mortality in the United States. Traditional chemotherapies are toxic and prone to the development of drug-resistance. Recently, several drug candidates were shown to induce lysosomal membrane permeabilization (LMP) in aggressive cancers. This has led to increased interest in lysosome dysregulation as a therapeutic target. However, approaches are needed to overcome two limitations of current lysosomal inhibitors: low specificity and potency. Here, we report the development of a transformable nanomaterial which is triggered to induce LMP of lysosomes in NSCLC. The nanomaterial consists of peptide amphiphiles, which self-assemble into nanoparticles, colocalize with the lysosome, and change conformation to nanofibrils due to lysosomal pH shift, which leads to the disruption of the lysosome, cell death, and cisplatin sensitization. We have found that this cell-penetrating transformable peptide nanoparticle (CPTNP) was cytotoxic to NSCLC cells in the low-micromolar range and it synergized cisplatin cytotoxicity four-fold. Moreover, we demonstrate CPTNP's promising antitumor effect in mouse xenograft models with limited toxicity when given in combination with low dose cisplatin chemotherapy. This is the first example of enhanced LMP via transformable peptide nanomaterial and offers a promising new strategy for cancer therapy.

Keywords:  Amyloid-beta; Cisplatin; Lysosomal targeting; Nanofibers; Nanoparticles; Non-small cell lung cancer

DOI:  https://doi.org/10.1016/j.biomaterials.2021.121078
Clin Cancer Res. 2021 Sep 01. pii: clincanres.2574.2021. [Epub ahead of print]

Lowering mTORC1 Drives CAR-Ts Home in Acute Myeloid Leukemia.

Abhishek Maiti, Naval G Daver.

Cellular therapies have demonstrated limited efficacy thus far in acute myeloid leukemia (AML). A recent study shows that mTORC1 activation down-regulated CXCR4 reducing marrow infiltration of EpCAM-targeting CAR-T cells in AML. Abrogating mTOR signaling by co-treatment with mTOR inhibitors during IL2-mediated ex vivo expansion upregulated CXCR4 and bolstered bone marrow migration and AML elimination by CAR-T cells.

DOI: https://doi.org/10.1158/1078-0432.CCR-21-2574
Biochem Pharmacol. 2021 Aug 27. pii: S0006-2952(21)00366-X. [Epub ahead of print] 114750

mTORC2 is an important target for simvastatin-associated toxicity in C2C12 cells and mouse skeletal muscle - roles of Rap1 geranylgeranylation and mitochondrial dysfunction.

Gerda M Sanvee, Leonie Hitzfeld, Jamal Bouitbir, Stephan Krähenbühl.

  Statins decrease the serum LDL-cholesterol concentration and reduce the risk for cardiovascular diseases but can cause myopathy, which may be related to mTORC inhibition. In the current study, we investigated which mTORC is inhibited by simvastatin and by which mechanisms. In C2C12 myoblasts and myotubes and mouse gastrocnemius, simvastatin was cytotoxic and inhibited S6rp and Akt Ser473 phosphorylation, indicating inhibition of mTORC1 and mTORC2, respectively. In contrast to simvastatin, the mTORC1 inhibitor rapamycin did not inhibit mTORC2 activity and was not cytotoxic. Like simvastatin, knock-down of Rictor, an essential component of mTORC2, impaired Akt Ser473 and S6rp phosphorylation and was cytotoxic for C2C12 myoblasts, suggesting that mTORC2 inhibition is an important myotoxic mechanism. The investigation of the mechanism of mTORC2 inhibition showed that simvastatin impaired Ras farnesylation, which was prevented by farnesol but without restoring mTORC2 activity. In comparison, Rap1 knock-down reduced mTORC2 activity and was cytotoxic for C2C12 myoblasts. Simvastatin impaired Rap1 geranylgeranylation and function, which was prevented by geranylgeraniol. In addition, simvastatin and the complex III inhibitor antimycin A caused mitochondrial superoxide accumulation and impaired the activity of mTORC2, which could partially be prevented by the antioxidant MitoTEMPO. In conclusion, mTORC2 inhibition is an important mechanism of simvastatin-induced myotoxicity. Simvastatin inhibits mTORC2 by impairing geranylgeranylation of Rap1 and by inducing mitochondrial dysfunction.

Keywords:  Akt/PKB; Rap1; Rictor; geranylgeranylation; mTORC1; mTORC2; mitochondrial function; simvastatin

DOI:  https://doi.org/10.1016/j.bcp.2021.114750
Mol Genet Metab. 2021 Aug 21. pii: S1096-7192(21)00770-8. [Epub ahead of print]

Detecting lysosomal storage disorders by glycomic profiling using liquid chromatography mass spectrometry.

Justin Mak, Tina M Cowan.

   BACKGROUND: Urine and plasma biomarker testing for lysosomal storage disorders by liquid chromatography mass spectrometry (LC-MS) currently requires multiple analytical methods to detect the abnormal accumulation of oligosaccharides, mucopolysaccharides, and glycolipids. To improve clinical testing efficiency, we developed a single LC-MS method to simultaneously identify disorders of oligosaccharide, mucopolysaccharide, and glycolipid metabolism with minimal sample preparation.
METHODS: We created a single chromatographic method for separating free glycans and glycolipids in their native form, using an amide column and high pH conditions. We used this glycomic profiling method both in untargeted analyses of patient and control urines using LC ion-mobility high-resolution MS (biomarker discovery), and targeted analyses of urine, serum, and dried blood spot samples by LC-MS/MS (clinical validation).
RESULTS: Untargeted glycomic profiling revealed twenty biomarkers that could identify and subtype mucopolysaccharidoses. We incorporated these with known oligosaccharide and glycolipid biomarkers into a rapid test that identifies at least 27 lysosomal storage disorders, including oligosaccharidoses, mucopolysaccharidoses, sphingolipidoses, glycogen storage disorders, and congenital disorders of glycosylation and de-glycosylation. In a validation set containing 115 urine samples from patients with lysosomal storage disorders, all were unambiguously distinguished from normal controls, with correct disease subtyping for 88% (101/115) of cases. Glucosylsphingosine was reliably elevated in dried blood spots from Gaucher disease patients with baseline resolution from galactosylsphingosine.
CONCLUSION: Glycomic profiling by liquid chromatography mass spectrometry identifies a range of lysosomal storage disorders. This test can be used in clinical evaluations to rapidly focus a diagnosis, as well as to clarify or support additional gene sequencing and enzyme studies.

Keywords:  Biomarker discovery; Glycomics; Inborn errors of metabolism; Liquid chromatography mass spectrometry; Lysosomal storage disorders; Metabolomics

DOI:  https://doi.org/10.1016/j.ymgme.2021.08.006
Biochem Cell Biol. 2021 Aug 31. 1-8

Aberrant mTOR/autophagy/Nurr1 signaling is critical for TSC-associated tumor development.

Ying Wang, Chunjia Li, Yanzhuo Zhang, Xiaojun Zha, Hongbing Zhang, Zhongdong Hu, Chengai Wu.

  Tuberous sclerosis complex (TSC), an inherited neurocutaneous disease, is caused by mutations in either the TSC1 or TSC2 gene. This genetic disorder is characterized by the growth of benign tumors in the brain, kidneys, and other organs. As a member of the orphan nuclear receptor family, nuclear receptor related 1 (Nurr1) plays a vital role in some neuropathological diseases and several types of benign or malignant tumors. Here, we explored the potential regulatory role of TSC1/2 signaling in Nurr1 and the effect of Nurr1 in TSC-related tumors. We found that Nurr1 expression was drastically decreased by the disruption of the TSC1/2 complex in Tsc2-null cells, genetically modified mouse models of TSC, cortical tubers of TSC patients, and kidney tumor tissue obtained from a TSC patient. Deficient TSC1/2 complex downregulated Nurr1 expression in an mTOR-dependent manner. Moreover, hyperactivation of mTOR reduced Nurr1 expression via suppression of autophagy. In addition, Nurr1 overexpression inhibited cell proliferation and suppressed cell cycle progression. Therefore, TSC/mTOR/autophagy/Nurr1 signaling is partially responsible for the tumorigenesis of TSC. Taken together, Nurr1 may be a novel therapeutic target for TSC-associated tumors, and Nurr1 agonists or reagents that induce Nurr1 expression may be used for the treatment of TSC.

Keywords:  Nurr1; autophagie; autophagy; cell proliferation; cible de la rapamycine mTOR; mechanistic target of rapamycin; prolifération cellulaire; sclérose tubéreuse de Bourneville; tuberous sclerosis complex

DOI:  https://doi.org/10.1139/bcb-2021-0017
J Neurosci. 2021 Sep 02. pii: JN-RM-0783-21. [Epub ahead of print]

The Akt-mTOR pathway drives myelin sheath growth by regulating cap-dependent translation.

Karlie N Fedder-Semmes, Bruce Appel.

In the vertebrate central nervous system, oligodendrocytes produce myelin, a specialized membrane, to insulate and support axons. Individual oligodendrocytes wrap multiple axons with myelin sheaths of variable lengths and thicknesses. Myelin grows at the distal ends of oligodendrocyte processes and multiple lines of work have provided evidence that mRNAs and RNA binding proteins localize to myelin, together supporting a model where local translation controls myelin sheath growth. What signal transduction mechanisms could control this? One strong candidate is the Akt-mTOR pathway, a major cellular signaling hub that coordinates transcription, translation, metabolism, and cytoskeletal organization. Here, using zebrafish as a model system, we found that Akt-mTOR signaling promotes myelin sheath growth and stability during development. Through cell-specific manipulations to oligodendrocytes, we show that the Akt-mTOR pathway drives cap-dependent translation to promote myelination and that restoration of cap-dependent translation is sufficient to rescue myelin deficits in mTOR loss-of-function animals. Moreover, an mTOR-dependent translational regulator was phosphorylated and co-localized with mRNA encoding a canonically myelin-translated protein in vivo and bioinformatic investigation revealed numerous putative translational targets in the myelin transcriptome. Together, these data raise the possibility that Akt-mTOR signaling in nascent myelin sheaths promotes sheath growth via translation of myelin-resident mRNAs during development.SIGNIFICANCE STATEMENTIn the brain and spinal cord oligodendrocytes extend processes that tightly wrap axons with myelin, a protein and lipid rich membrane that increases electrical impulses and provides trophic support. Myelin membrane grows dramatically following initial axon wrapping in a process that demands protein and lipid synthesis. How protein and lipid synthesis is coordinated with the need for myelin to be generated in certain locations remains unknown. Our study reveals that the Akt-mTOR signaling pathway promotes myelin sheath growth by regulating protein translation. Because we found translational regulators of the Akt-mTOR pathway in myelin, our data raise the possibility Akt-mTOR activity regulates translation in myelin sheaths to deliver myelin on demand to the places it is needed.

DOI: https://doi.org/10.1523/JNEUROSCI.0783-21.2021
Exp Hematol. 2021 Aug 28. pii: S0301-472X(21)00289-7. [Epub ahead of print]

The Akt-mTOR network at the interface of hematopoietic stem cell homeostasis.

Feng Wu, Zhe Chen, Jingbo Liu, Yu Hou.

  Hematopoietic stem cells (HSCs) are immature blood cells that exhibit multi-lineage differentiation capacity. Homeostasis is critical for HSC potential and life-long hematopoiesis, and HSC homeostasis is tightly governed by both intrinsic molecular networks and microenvironmental signals. The evolutionarily conserved serine/threonine protein kinase B (PKB, also referred to as Akt) -mammalian target of rapamycin (mTOR) pathway is universal to nearly all multicellular organisms and plays an integral role in most cellular processes. Emerging evidence has revealed a central role of the Akt-mTOR network in HSC homeostasis, as it responses to multiple intracellular and extracellular signals and regulates various downstream targets, eventually affecting several cellular processes, including the cell cycle, mitochondrial metabolism, and protein synthesis. The dysregulated Akt-mTOR signaling greatly affects HSC self-renewal, maintenance, differentiation, survival, and autophagy, and aging, as well as transformation of HSCs to leukemia stem cells (LSCs). Here, we review recent works and provide an advanced understanding of how the Akt-mTOR network regulates HSC homeostasis, thus offering insights for future clinical applications.

Keywords:  Akt-mTOR; Hematopoietic stem cells; Homeostasis; Leukemia stem cells

DOI:  https://doi.org/10.1016/j.exphem.2021.08.009
iScience. 2021 Sep 24. 24(9): 102949

A modified density gradient proteomic-based method to analyze endolysosomal proteins in cardiac tissue.

Thamali Ayagama, Samuel J Bose, Rebecca A Capel, David A Priestman, Georgina Berridge, Roman Fischer, Antony Galione, Frances M Platt, Holger Kramer, Rebecca A B Burton.

  The importance of lysosomes in cardiac physiology and pathology is well established, and evidence for roles in calcium signaling is emerging. We describe a label-free proteomics method suitable for small cardiac tissue biopsies based on density-separated fractionation, which allows study of endolysosomal (EL) proteins. Density gradient fractions corresponding to tissue lysate; sarcoplasmic reticulum (SR), mitochondria (Mito) (1.3 g/mL); and EL with negligible contamination from SR or Mito (1.04 g/mL) were analyzed using Western blot, enzyme activity assay, and liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis (adapted discontinuous Percoll and sucrose differential density gradient). Kyoto Encyclopedia of Genes and Genomes, Reactome, Panther, and Gene Ontology pathway analysis showed good coverage of RAB proteins and lysosomal cathepsins (including cardiac-specific cathepsin D) in the purified EL fraction. Significant EL proteins recovered included catalytic activity proteins. We thus present a comprehensive protocol and data set of guinea pig atrial EL organelle proteomics using techniques also applicable for non-cardiac tissue.

Keywords:  Biochemistry; Biological sciences; Omics; Porcine cardiology; Proteomics; Systems biology

DOI:  https://doi.org/10.1016/j.isci.2021.102949
EMBO J. 2021 Aug 30. e108863

Autophagy in major human diseases.

Daniel J Klionsky, Giulia Petroni, Ravi K Amaravadi, Eric H Baehrecke, Andrea Ballabio, Patricia Boya, José Manuel Bravo-San Pedro, Ken Cadwell, Francesco Cecconi, Augustine M K Choi, Mary E Choi, Charleen T Chu, Patrice Codogno, Maria Isabel Colombo, Ana Maria Cuervo, Vojo Deretic, Ivan Dikic, Zvulun Elazar, Eeva-Liisa Eskelinen, Gian Maria Fimia, David A Gewirtz, Douglas R Green, Malene Hansen, Marja Jäättelä, Terje Johansen, Gábor Juhász, Vassiliki Karantza, Claudine Kraft, Guido Kroemer, Nicholas T Ktistakis, Sharad Kumar, Carlos Lopez-Otin, Kay F Macleod, Frank Madeo, Jennifer Martinez, Alicia Meléndez, Noboru Mizushima, Christian Münz, Josef M Penninger, Rushika M Perera, Mauro Piacentini, Fulvio Reggiori, David C Rubinsztein, Kevin M Ryan, Junichi Sadoshima, Laura Santambrogio, Luca Scorrano, Hans-Uwe Simon, Anna Katharina Simon, Anne Simonsen, Alexandra Stolz, Nektarios Tavernarakis, Sharon A Tooze, Tamotsu Yoshimori, Junying Yuan, Zhenyu Yue, Qing Zhong, Lorenzo Galluzzi, Federico Pietrocola.

  Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Keywords:  aging; cancer; inflammation; metabolic syndromes; neurodegeneration

DOI:  https://doi.org/10.15252/embj.2021108863
FASEB J. 2021 Oct;35(10): e21894

Neuromyelitis optica (NMO)-IgG-driven organelle reorganization in human iPSC-derived astrocytes.

Sukhee Cho, Hyein Lee, Minkyo Jung, Kirim Hong, Seung-Hwa Woo, Young-Sam Lee, Byoung Joon Kim, Mi Young Jeon, Jinsoo Seo, Ji Young Mun.

  Neuromyelitis optica (NMO) is an autoimmune disease that primarily targets astrocytes. Autoantibodies (NMO-IgG) against the water channel protein, aquaporin 4 (AQP4), are a serologic marker in NMO patients, and they are known to be responsible for the pathophysiology of the disease. In the brain, AQP4 is mainly expressed in astrocytes, especially at the end-feet, where they form the blood-brain barrier. Following the interaction between NMO-IgG and AQP4 in astrocytes, rapid AQP4 endocytosis initiates pathogenesis. However, the cellular and molecular mechanisms of astrocyte destruction by autoantibodies remain largely elusive. We established an in vitro human astrocyte model system using induced pluripotent stem cells (iPSCs) technology in combination with NMO patient-derived serum and IgG to elucidate the cellular and functional changes caused by NMO-IgG. Herein, we observed that NMO-IgG induces structural alterations in mitochondria and their association with the endoplasmic reticulum (ER) and lysosomes at the ultrastructural level, which potentially leads to impaired mitochondrial functions and dynamics. Indeed, human astrocytes display impaired mitochondrial bioenergetics and autophagy activity in the presence of NMO-IgG. We further demonstrated NMO-IgG-driven ER membrane deformation into a multilamellar structure in human astrocytes. Together, we show that NMO-IgG rearranges cellular organelles and alter their functions and that our in vitro system using human iPSCs offers previously unavailable experimental opportunities to study the pathophysiological mechanisms of NMO in human astrocytes or conduct large-scale screening for potential therapeutic compounds targeting astrocytic abnormalities in patients with NMO.

Keywords:  astrocytes; autophagy; endoplasmic reticulum; human iPSC; lysosome; metabolic flux; mitochondria; neuromyelitis optica (NMO)

DOI:  https://doi.org/10.1096/fj.202100637R
Lancet Respir Med. 2021 Aug 27. pii: S2213-2600(21)00228-9. [Epub ahead of print]

Lymphangioleiomyomatosis: pathogenesis, clinical features, diagnosis, and management.

Cormac McCarthy, Nishant Gupta, Simon R Johnson, Jane J Yu, Francis X McCormack.

Lymphangioleiomyomatosis (LAM) is a slowly progressive, low-grade, metastasising neoplasm of women, characterised by infiltration of the lung parenchyma with abnormal smooth muscle-like cells, resulting in cystic lung destruction. The invading cell in LAM arises from an unknown source and harbours mutations in tuberous sclerosis complex (TSC) genes that result in constitutive activation of the mechanistic target of rapamycin (mTOR) pathway, dysregulated cellular proliferation, and a programme of frustrated lymphangiogenesis, culminating in disordered lung remodelling and respiratory failure. Over the past two decades, all facets of LAM basic and clinical science have seen important advances, including improved understanding of molecular mechanisms, novel diagnostic and prognostic biomarkers, effective treatment strategies, and comprehensive clinical practice guidelines. Further research is needed to better understand the natural history of LAM; develop more powerful diagnostic, prognostic, and predictive biomarkers; optimise the use of inhibitors of mTOR complex 1 in the treatment of LAM; and explore novel approaches to the development of remission-inducing therapies.

DOI: https://doi.org/10.1016/S2213-2600(21)00228-9
Biophys Rev. 2021 Aug;13(4): 531-539

Self-assemblies of Rab- and Arf-family small GTPases on lipid bilayers in membrane tethering.

Joji Mima.

  Small GTPases of the Ras superfamily, which include Ras-, Rho-, Rab-, Arf-, and Ran-family isoforms, are generally known to function as a nucleotide-dependent molecular switch in eukaryotic cells. In the GTP-loaded forms, they selectively recruit their cognate interacting proteins or protein complexes, termed "effectors," to the cytoplasmic face of subcellular membrane compartments, thereby switching on the downstream effector functions, which are vital for fundamental cellular events, such as cell proliferation, cytoskeletal organization, and intracellular membrane trafficking. Nevertheless, in addition to acting as the classic nucleotide-dependent switches for the effectors, recent studies have uncovered that small GTPases themselves can be self-assembled specifically into homo-dimers or higher-order oligomers on membranes, and these assembly processes are likely responsible for their physiological functions. This Review focuses particularly on the self-assembly processes of Rab- and Arf-family isoforms during membrane tethering, the most critical step to ensure the fidelity of membrane trafficking. A summary of the current experimental evidence for self-assemblies of Rab and Arf small GTPases on lipid bilayers in chemically defined reconstitution system is provided.

Keywords:  Arf; Membrane tethering; Membrane trafficking; Rab; Ras; Small GTPase

DOI:  https://doi.org/10.1007/s12551-021-00819-4
Life Sci. 2021 Aug 31. pii: S0024-3205(21)00907-3. [Epub ahead of print] 119920

Divergent regulation of inflammatory cytokines by mTORC1 in THP-1-derived macrophages and intestinal epithelial Caco-2 cells.

Harleen Kaur, Anjeza Erickson, Régis Moreau.

   AIMS: The sustained activation of intestinal mechanistic target of rapamycin complex 1 (mTORC1) brought about by repeated mucosal insult or injury has been linked to escalation of gut inflammatory response, which may progress to damage the epithelium if not controlled. This study investigated the role of mTORC1 in the response of macrophage and enterocyte to inflammatory stimuli.
MATERIALS AND METHODS: We genetically manipulated human THP-1 monocytes and epithelial intestinal Caco-2 cells to generate stable cell lines with baseline, low or high mTORC1 kinase activity. The effects of THP-1 macrophage secretions onto Caco-2 cells were investigated by means of conditioned media transfer experiments.
KEY FINDINGS: The priming of mTORC1 for activation promoted lipopolysaccharide (LPS)-mediated THP-1 macrophage immune response as evidenced by the stimulation of inflammatory mediators (TNFα, IL-6, IL-8, IL-1β and IL-10). The treatment of THP-1 macrophages with LPS more than the manipulated level of mTORC1 activity of macrophages determined whether cytokine gene expression was induced in Caco-2 cells. LPS carry over was not responsible for the stimulation of Caco-2 cells' cytokine response. Knocking down Raptor in Caco-2 cells or treating Caco-2 cells with rapamycin enhanced Caco-2 TNFα gene expression revealing the anti-inflammatory role of a functional mTORC1 in intestinal epithelial cells exposed to macrophage-derived pro-inflammatory stimuli.
SIGNIFICANCE: Taken together, mTORC1 differentially impacts the immune responses of THP-1-derived macrophages and Caco-2 epithelial cells when placed in a pro-inflammatory microenvironment.

Keywords:  Cell differentiation; Endotoxin; Gut innate immunity; Interleukin; Rapamycin; Tuberous sclerosis complex

DOI:  https://doi.org/10.1016/j.lfs.2021.119920
Leukemia. 2021 Aug 30.

Lysosomes in acute myeloid leukemia: potential therapeutic targets?

Sreoshee Rafiq, Sharon L McKenna, Sylviane Muller, Mario P Tschan, Magali Humbert.

Lysosomes, since their discovery, have been primarily known for degrading cellular macromolecules. However, in recent studies, they have begun to emerge as crucial regulators of cell homeostasis. They are at the crossroads of catabolic and anabolic pathways and are intricately involved in cellular trafficking, nutrient signaling, energy metabolism, and immune regulation. Their involvement in such essential cellular functions has renewed clinical interest in targeting the lysosome as a novel way to treat disease, particularly cancer. Acute myeloid leukemia (AML) is an aggressive blood cancer with a low survival probability, particularly in older patients. The genomic landscape of AML has been extensively characterized but few targeted therapies (with the exception of differentiation therapy) can achieve a long-term cure. Therefore, there is an unmet need for less intensive and more tolerable therapeutic interventions. In this review, we will give an overview on the myriad of functions performed by lysosomes and their importance in malignant disease. Furthermore, we will discuss their relevance in hematopoietic cells and different ways to potentially target them in AML.

DOI: https://doi.org/10.1038/s41375-021-01388-x
J Am Heart Assoc. 2021 Aug 28. e018829

LAMP2 Cardiomyopathy: Consequences of Impaired Autophagy in the Heart.

Ronny Alcalai, Michael Arad, Hiroko Wakimoto, Dor Yadin, Joshua Gorham, Libin Wang, Elia Burns, Barry J Maron, William C Roberts, Tetsuo Konno, David A Conner, Antonio R Perez-Atayde, Jon G Seidman, Christine E Seidman.

  Background Human mutations in the X-linked lysosome-associated membrane protein-2 (LAMP2) gene can cause a multisystem Danon disease or a primary cardiomyopathy characterized by massive hypertrophy, conduction system abnormalities, and malignant ventricular arrhythmias. We introduced an in-frame LAMP2 gene exon 6 deletion mutation (denoted L2Δ6) causing human cardiomyopathy, into mouse LAMP2 gene, to elucidate its consequences on cardiomyocyte biology. This mutation results in in-frame deletion of 41 amino acids, compatible with presence of some defective LAMP2 protein. Methods and Results Left ventricular tissues from L2Δ6 and wild-type mice had equivalent amounts of LAMP2 RNA, but a significantly lower level of LAMP2 protein. By 20 weeks of age male mutant mice developed left ventricular hypertrophy which was followed by left ventricular dilatation and reduced systolic function. Cardiac electrophysiology and isolated cardiomyocyte studies demonstrated ventricular arrhythmia, conduction disturbances, abnormal calcium transients and increased sensitivity to catecholamines. Myocardial fibrosis was strikingly increased in 40-week-old L2Δ6 mice, recapitulating findings of human LAMP2 cardiomyopathy. Immunofluorescence and transmission electron microscopy identified mislocalization of lysosomes and accumulation of autophagosomes between sarcomeres, causing profound morphological changes disrupting the cellular ultrastructure. Transcription profile and protein expression analyses of L2Δ6 hearts showed significantly increased expression of genes encoding activators and protein components of autophagy, hypertrophy, and apoptosis. Conclusions We suggest that impaired autophagy results in cardiac hypertrophy and profound transcriptional reactions that impacted metabolism, calcium homeostasis, and cell survival. These responses define the molecular pathways that underlie the pathology and aberrant electrophysiology in cardiomyopathy of Danon disease.

Keywords:  Danon disease; autophagy; calcium transients; cardiomyopathy; mouse model

DOI:  https://doi.org/10.1161/JAHA.120.018829
Bone. 2021 Aug 28. pii: S8756-3282(21)00326-4. [Epub ahead of print] 116160

Chloroquine Increases Osteoclast Activity in vitro but does not Improve the Osteopetrotic Bone Phenotype of ADO2 Mice.

Imranul Alam, Rita L Gerard-O'Riley, Dena Acton, Sara L Hardman, Jung Min Hong, Angela Bruzzaniti, Michael J Econs.

  Autosomal Dominant Osteopetrosis type II (ADO2) is a bone disease of impaired osteoclastic bone resorption that usually results from heterozygous missense mutations in the chloride channel 7 (CLCN7) gene. We created mouse models of ADO2 by introducing a knock-in (p.G213R) mutation in the Clcn7 gene, which is analogous to one of the common mutations (G215R) found in humans. The mutation leads to severe osteopetrosis and lethality in homozygous mice but produces substantial phenotypic variability in heterozygous mice on different genetic backgrounds that phenocopy the human disease of ADO2. ADO2 is an osteoclast-intrinsic disease, and lysosomal enzymes and proteins are critical for osteoclast activity. Chloroquine (CQ) is known to affect lysosomal trafficking, intracellular signaling and the lysosomal and vesicular pH, suggesting it might improve ADO2 osteoclast function. We tested this hypothesis in cell culture studies using osteoclasts derived from wild-type (WT or ADO2+/+) and ADO2 heterozygous (ADO2+/-) mice and found that CQ and its metabolite desethylchloroquine (DCQ), significantly increased ADO2+/- osteoclasts bone resorption activity in vitro, whereas bone resorption of ADO2+/+ osteoclasts was increased only by DCQ. In addition, we exploited our unique animal model of ADO2 on 129 background to identify the effect of CQ for the treatment of ADO2. Female ADO2 mice at 8 weeks of age were treated with 5 doses of CQ (1, 2.5, 5, 7.5 and 10 mg/kg BW/day) via drinking water for 6 months. Bone mineral density and bone micro-architecture were analyzed by longitudinal in-vivo DXA and micro-CT at baseline, 3 and 6 months. Serum bone biomarkers (CTX, TRAP and P1NP) were also analyzed at these time points. CQ treatment at the doses tested failed to produce any significant changes of aBMD, BMC (whole body, femur and spine) and trabecular BV/TV (distal femur) in ADO2 mice compared to the control group (water only). Further, levels of bone biomarkers were not significantly changed due to CQ treatment in these mice. Our findings indicate that while CQ increased osteoclast activity in vitro, it did not improve the osteopetrotic bone phenotypes in ADO2 heterozygous mice.

Keywords:  Bone phenotypes; Chloride channel 7; Chloroquine; Osteoclast; Osteopetrosis

DOI:  https://doi.org/10.1016/j.bone.2021.116160
Traffic. 2021 Sep 02.

The trans-SNARE complex VAMP4/Stx6/Stx7/Vti1b is a key regulator of Golgi to late endosome MT1-MMP transport in macrophages.

Zoe Elizabeth West, Savannah Margaret Aitcheson, Annalese Barbara Trudy Semmler, Rachael Zoe Murray.

  The activity of the matrix metalloproteinase (MMP) MT1-MMP is strictly regulated by expression and cellular location. In macrophages LPS activation leads to the upregulation of MT1-MMP and this need to be at the cell surface for them to degrade the dense extracellular matrix (ECM) components to create a path to migrate into injured and infected tissues. Fixed and live imaging shows newly made MT1-MMP is packaged into vesicles that traffic to and fuse with LBPA+ LAMP1+ late endosomes en route to the surface. The R-SNARE VAMP4, found on Golgi-derived vesicles that traffic to late endosomes, forms a trans-SNARE complex with the Q-SNARE complex Stx6/Stx7/Vti1b. The Stx6/Stx7/Vti1b complex has been shown to be upregulated in lipopolysaccharide (LPS)-activated cells to increase trafficking of key cytokines through the classical pathway and now we show here its upregulation also plays a role in the late endosomal pathway of MT1-MMP trafficking. Depletion of any of the SNAREs in this complex reduces surface MT1-MMP and gelatin degradation. Conversely, overexpression of the Stx6/Stx7/Vti1b components increases surface MT1-MMP levels. This suggest that Stx6/Stx7/Vti1b is a key Q-SNARE complex in macrophages during an immune response and in partnership with VAMP4 it regulates transport of newly made MT1-MMP. This article is protected by copyright. All rights reserved.

Keywords:  MT1-MMP; SNARE; Stx6; Stx7; VAMP4; Vti1b; late endosome; macrophage; trafficking

DOI:  https://doi.org/10.1111/tra.12813
Biochem Biophys Rep. 2021 Dec;28 101105

Identification of genetic modifiers of murine hepatic β-glucocerebrosidase activity.

Anyelo Durán, Boris Rebolledo-Jaramillo, Valeria Olguin, Marcelo Rojas-Herrera, Macarena Las Heras, Juan F Calderón, Silvana Zanlungo, David A Priestman, Frances M Platt, Andrés D Klein.

  The acid β-glucocerebrosidase (GCase) enzyme cleaves glucosylceramide into glucose and ceramide. Loss of function variants in the gene encoding for GCase can lead to Gaucher disease and Parkinson's disease. Therapeutic strategies aimed at increasing GCase activity by targeting a modulating factor are attractive and poorly explored. To identify genetic modifiers, we measured hepatic GCase activity in 27 inbred mouse strains. A genome-wide association study (GWAS) using GCase activity as a trait identified several candidate modifier genes, including Dmrtc2 and Arhgef1 (p=2.1x10-7), and Grik5 (p=2.1x10-7). Bayesian integration of the gene mapping with transcriptomics was used to build integrative networks. The analysis uncovered additional candidate GCase regulators, highlighting modules of the acute phase response (p=1.01x10-8), acute inflammatory response (p=1.01x10-8), fatty acid beta-oxidation (p=7.43x10-5), among others. Our study revealed previously unknown candidate modulators of GCase activity, which may facilitate the design of therapies for diseases with GCase dysfunction.

Keywords:  Gaucher disease; Inbred strains; Modifier genes; Parkinson's disease; Systems genetics; β-glucocerebrosidase

DOI:  https://doi.org/10.1016/j.bbrep.2021.101105
Biochim Biophys Acta Mol Basis Dis. 2021 Aug 26. pii: S0925-4439(21)00194-0. [Epub ahead of print] 166261

Enhancing Acsl4 in absence of mTORC2/Rictor drove β-cell dedifferentiation via inhibiting FoxO1 and promoting ROS production.

Canqi Cui, Tingting Li, Yun Xie, Jie Yang, Chenyang Fu, Yixuan Qiu, Linyan Shen, Qicheng Ni, Qidi Wang, Aifang Nie, Guang Ning, Weiqing Wang, Yanyun Gu.

  Rapamycin insensitive companion of mechanistic target of Rapamycin (Rictor), the key component of mTOR complex 2 (mTORC2), controls both β-cell proliferation and function. We sought to study whether long chain acyl-CoA synthetase 4 (Acsl4) worked downstream of Rictor/mTORC2 to maintain β-cell functional mass. We found Acsl4 was positively regulated by Rictor at transcriptional and posttranslational levels in mouse β-cell. Infecting adenovirus expressing Acsl4 in β-cell-specific-Rictor-knockout (βRicKO) islets and Min6 cells knocking down Rictor with lentivirus-expressing siRNA-oligos targeting Rictor(siRic), recovered the β-cell dysplasia but not dysfunction. Cell bioenergetic experiment performed with Seahorse XF showed that Acsl4 could not rescue the dampened glucose oxidation in Rictor-lacking β-cell, but further promoted lipid oxidation. Transposase-Accessible Chromatin (ATAC) and H27K3Ac chromatin immunoprecipitation (ChIP) sequencing studies reflected the epigenetic elevated molecular signature for β-cell dedifferentiation and mitigated oxidative defense/response. These results were confirmed by the observations of elevated acetylation and ubiquitination of FoxO1, increased protein levels of Gpx1 and Hif1an, excessive reactive oxygen species (ROS) production and diminished MafA in Acsl4 overexpressed Rictor-lacking β-cells. Antioxidant treatment significantly recovered MafA level and insulin content. Inducing lipid oxidation alone could not mimic the effect of Acsl4 in Rictor lacking β-cell. Our study suggested that Acsl4 function in β-cell was context dependent and might facilitate β-cell dedifferentiation with attenuated Rictor/mTORC2 activity or insulin signaling via posttranslational inhibiting FoxO1 and epigenetically enhancing ROS induced MafA degradation.

Keywords:  Acsl4; FoxO1; MafA; Pancreatic β-cell; ROS; mTORC2; β-Cell dedifferentiation

DOI:  https://doi.org/10.1016/j.bbadis.2021.166261
Trends Cancer. 2021 Aug 26. pii: S2405-8033(21)00160-6. [Epub ahead of print]

β-Galactosylceramidase in cancer: friend or foe?

Marco Presta.

  Lysosomal β-galactosylceramidase (GALC) removes β-galactose from β-galactosylceramide, thus generating the oncosuppressor metabolite ceramide. Recent observations have shown that GALC may exert opposite effects on tumor growth and differentiation, questioning its contribution to the sphingolipid metabolism in cancer cells and its role in tumor progression.

Keywords:  ceramide; lipidomics; melanoma; sphingolipids; β-galactosylceramidase

DOI:  https://doi.org/10.1016/j.trecan.2021.08.001
Cell Rep. 2021 Aug 31. pii: S2211-1247(21)00975-X. [Epub ahead of print]36(9): 109541

Regulation of lipid homeostasis by the TBC protein dTBC1D22 via modulation of the small GTPase Rab40 to facilitate lipophagy.

Xiuying Duan, Lingna Xu, Yawen Li, Lijun Jia, Wei Liu, Wenxia Shao, Vafa Bayat, Weina Shang, Liquan Wang, Jun-Ping Liu, Chao Tong.

  The regulation of lipid homeostasis is not well understood. Using forward genetic screening, we demonstrate that the loss of dTBC1D22, an essential gene that encodes a Tre2-Bub2-Cdc16 (TBC) domain-containing protein, results in lipid droplet accumulation in multiple tissues. We observe that dTBC1D22 interacts with Rab40 and exhibits GTPase activating protein (GAP) activity. Overexpression of either the GTP- or GDP-binding-mimic form of Rab40 results in lipid droplet accumulation. We observe that Rab40 mutant flies are defective in lipid mobilization. The lipid depletion induced by overexpression of Brummer, a triglyceride lipase, is dependent on Rab40. Rab40 mutant flies exhibit decreased lipophagy and small size of autolysosomal structures, which may be due to the defective Golgi functions. Finally, we demonstrate that Rab40 physically interacts with Lamp1, and Rab40 is required for the distribution of Lamp1 during starvation. We propose that dTBC1D22 functions as a GAP for Rab40 to regulate lipophagy.

Keywords:  Drosophila; GTPase-activating proteins (GAPs); Golgi; Rab GTPase; Rab40; TBC domain-containing protein; autophagy; lipophagy; lysosome

DOI:  https://doi.org/10.1016/j.celrep.2021.109541
Traffic. 2021 Sep 03.

BMP2K phosphorylates AP-2 and regulates clathrin-mediated endocytosis.

Shikha T Ramesh, Kolaparamba V Navyasree, Sneha Sah, Anjitha B Ashok, Nishada Qathoon, Suryasikha Mohanty, Rajeeb K Swain, Perunthottathu K Umasankar.

Phosphorylation of the central adaptor protein complex, AP-2 is pivotal for clathrin-mediated endocytosis (CME). Here, we uncover the role of an uncharacterized kinase (BMP-2 inducible kinase- BMP2K) in AP-2 phosphorylation. We demonstrate that BMP2K can phosphorylate AP-2 in vitro and in vivo. Functional impairment of BMP2K impedes AP-2 phosphorylation leading to defects in clathrin-coated pit (CCP) morphology and cargo internalization. BMP2K engages AP-2 via its extended C-terminus and this interaction is important for its CCP localization and function. Notably, endogenous BMP2K levels decline upon functional impairment of AP-2 indicating AP-2 dependent BMP2K stabilization in cells. Further, functional inactivation of BMP2K in zebrafish embryos yields gastrulation phenotypes which mirror AP-2 loss-of-function suggesting physiological relevance of BMP2K in vertebrates. Together, our findings propose involvement of a novel kinase in AP-2 phosphorylation and in the operation of CME. This article is protected by copyright. All rights reserved.

DOI: https://doi.org/10.1111/tra.12814
Cell Death Differ. 2021 Aug 31.

Organelle-specific regulation of ferroptosis.

Xin Chen, Rui Kang, Guido Kroemer, Daolin Tang.

Ferroptosis, a cell death modality characterized by iron-dependent lipid peroxidation, is involved in the development of multiple pathological conditions, including ischemic tissue damage, infection, neurodegeneration, and cancer. The cellular machinery responsible for the execution of ferroptosis integrates multiple pro-survival or pro-death signals from subcellular organelles and then 'decides' whether to engage the lethal process or not. Here, we outline the evidence implicating different organelles (including mitochondria, lysosomes, endoplasmic reticulum, lipid droplets, peroxisomes, Golgi apparatus, and nucleus) in the ignition or avoidance of ferroptosis, while emphasizing their potential relevance for human disease and their targetability for pharmacological interventions.

DOI: https://doi.org/10.1038/s41418-021-00859-z