bims-unfpre 2023-10-29 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2023‒10‒29
thirteen papers selected by
Susan Logue, University of Manitoba

Non-canonical activation of IRE1α during Candida albicans infection enhances macrophage fungicidal activity.
Fundamental and Applicative Aspects of the Unfolded Protein Response in Yeasts.
Adaptive responses of neuronal cells to chronic endoplasmic reticulum (ER) stress.
Loss of STIM2 in colorectal cancer drives growth and metastasis through metabolic reprogramming and PERK-ATF4 endoplasmic reticulum stress pathway.
Potential mechanism of TMEM2/CD44 in endoplasmic reticulum stress‑induced neuronal apoptosis in a rat model of traumatic brain injury.
Synergistic anticancer activity of cisplatin combined with tannic acid enhances apoptosis in lung cancer through the PERK-ATF4 pathway.
Identification of the role of endoplasmic reticulum stress genes in endometrial cancer and their association with tumor immunity.
Identification and functional coordination analysis of gene co-expression networks in different tissues of XBP1 cartilage-specific deficient mice.
USP7 attenuates endoplasmic reticulum stress-induced apoptotic cell death through deubiquitination and stabilization of FBXO7.
Angiotensin II type-2 receptor attenuates liver fibrosis progression by suppressing IRE1α-XBP1 pathway.
Apoptotic Effect of Gallic Acid via Regulation of p-p38 and ER Stress in PANC-1 and MIA PaCa-2 Cells Pancreatic Cancer Cells.
Endoplasmic Reticulum Stress Promotes the Expression of TNF-α in THP-1 Cells by Mechanisms Involving ROS/CHOP/HIF-1α and MAPK/NF-κB Pathways.
The biological function of cytoplasm-translocated ENDOG (endonuclease G).

bioRxiv. 2023 Oct 02. pii: 2023.10.02.560560. [Epub ahead of print]

Non-canonical activation of IRE1α during Candida albicans infection enhances macrophage fungicidal activity.

Michael J McFadden, Mack B Reynolds, Britton C Michmerhuizen, Faith M Anderson, Mary X D O'Riordan, Teresa R O'Meara.

Infection by intracellular pathogens can trigger activation of the IRE1α branch of the unfolded protein response (UPR), which then modulates innate immunity and infection outcomes during bacterial or viral infection. However, the mechanisms by which infection activates IRE1α have not been fully elucidated. While recognition of microbe-associated molecular patterns can activate IRE1α, it is unclear whether this depends on the canonical role of IRE1α in detecting misfolded proteins. Here, we report that Candida albicans infection of macrophages results in IRE1α activation through C-type lectin receptor signaling, reinforcing a role for IRE1α as a central regulator of host responses to infection by a broad range of pathogens. However, IRE1α activation was not preceded by protein misfolding in response to either C. albicans infection or lipopolysaccharide treatment, implicating a non-canonical mode of IRE1α activation after recognition of microbial patterns. Investigation of the phenotypic consequences of IRE1α activation in macrophage antimicrobial responses revealed that IRE1α activity enhances the fungicidal activity of macrophages. Macrophages lacking IRE1α activity displayed inefficient phagolysosomal fusion, enabling C. albicans to evade fungal killing and escape the phagosome. Together, these data provide mechanistic insight for the non-canonical activation of IRE1α during infection, and reveal central roles for IRE1α in macrophage antifungal responses.

DOI: https://doi.org/10.1101/2023.10.02.560560
J Fungi (Basel). 2023 Oct 05. pii: 989. [Epub ahead of print]9(10):

Fundamental and Applicative Aspects of the Unfolded Protein Response in Yeasts.

Yuki Ishiwata-Kimata, Yukio Kimata.

  Upon the dysfunction or functional shortage of the endoplasmic reticulum (ER), namely, ER stress, eukaryotic cells commonly provoke a protective gene expression program called the unfolded protein response (UPR). The molecular mechanism of UPR has been uncovered through frontier genetic studies using Saccharomyces cerevisiae as a model organism. Ire1 is an ER-located transmembrane protein that directly senses ER stress and is activated as an RNase. During ER stress, Ire1 promotes the splicing of HAC1 mRNA, which is then translated into a transcription factor that induces the expression of various genes, including those encoding ER-located molecular chaperones and protein modification enzymes. While this mainstream intracellular UPR signaling pathway was elucidated in the 1990s, new intriguing insights have been gained up to now. For instance, various additional factors allow UPR evocation strictly in response to ER stress. The UPR machineries in other yeasts and fungi, including pathogenic species, are another important research topic. Moreover, industrially beneficial yeast strains carrying an enforced and enlarged ER have been produced through the artificial and constitutive induction of the UPR. In this article, we review canonical and up-to-date insights concerning the yeast UPR, mainly from the viewpoint of the functions and regulation of Ire1 and HAC1.

Keywords:  endoplasmic reticulum; stress response; unfolded protein response; yeast

DOI:  https://doi.org/10.3390/jof9100989
Redox Biol. 2023 Oct 20. pii: S2213-2317(23)00344-0. [Epub ahead of print]67 102943

Adaptive responses of neuronal cells to chronic endoplasmic reticulum (ER) stress.

Thu Nguyen Minh Pham, Natarajan Perumal, Caroline Manicam, Marion Basoglu, Stefan Eimer, Dominik C Fuhrmann, Claus U Pietrzik, Albrecht M Clement, Hagen Körschgen, Jana Schepers, Christian Behl.

  Accumulation of misfolded proteins or perturbation of calcium homeostasis leads to endoplasmic reticulum (ER) stress and is linked to the pathogenesis of neurodegenerative diseases. Hence, understanding the ability of neuronal cells to cope with chronic ER stress is of fundamental interest. Interestingly, several brain areas uphold functions that enable them to resist challenges associated with neurodegeneration. Here, we established novel clonal mouse hippocampal (HT22) cell lines that are resistant to prolonged (chronic) ER stress induced by thapsigargin (TgR) or tunicamycin (TmR) as in vitro models to study the adaption to ER stress. Morphologically, we observed a significant increase in vesicular und autophagosomal structures in both resistant lines and 'giant lysosomes', especially striking in TgR cells. While autophagic activity increased under ER stress, lysosomal function appeared slightly impaired; in both cell lines, we observed enhanced ER-phagy. However, proteomic analyses revealed that various protein clusters and signaling pathways were differentially regulated in TgR versus TmR cells in response to chronic ER stress. Additionally, bioenergetic analyses in both resistant cell lines showed a shift toward aerobic glycolysis ('Warburg effect') and a defective complex I of the oxidative phosphorylation (OXPHOS) machinery. Furthermore, ER stress-resistant cells differentially activated the unfolded protein response (UPR) comprising IRE1α and ATF6 pathways. These findings display the wide portfolio of adaptive responses of neuronal cells to chronic ER stress. ER stress-resistant neuronal cells could be the basis to uncover molecular modulators of adaptation, resistance, and neuroprotection as potential pharmacological targets for preventing neurodegeneration.

Keywords:  Aerobic glycolysis; ER stress resistance; ER-Phagy; Giant lysosomes; Neuroprotection; Warburg effect

DOI:  https://doi.org/10.1016/j.redox.2023.102943
bioRxiv. 2023 Oct 03. pii: 2023.10.02.560521. [Epub ahead of print]

Loss of STIM2 in colorectal cancer drives growth and metastasis through metabolic reprogramming and PERK-ATF4 endoplasmic reticulum stress pathway.

Trayambak Pathak, J Cory Benson, Martin T Johnson, Ping Xin, Ahmed Emam Abdelnaby, Vonn Walter, Walter A Koltun, Gregory S Yochum, Nadine Hempel, Mohamed Trebak.

The endoplasmic reticulum (ER) stores large amounts of calcium (Ca 2+ ), and the controlled release of ER Ca 2+ regulates a myriad of cellular functions. Although altered ER Ca 2+ homeostasis is known to induce ER stress, the mechanisms by which ER Ca 2+ imbalance activate ER stress pathways are poorly understood. Stromal-interacting molecules STIM1 and STIM2 are two structurally homologous ER-resident Ca 2+ sensors that synergistically regulate Ca 2+ influx into the cytosol through Orai Ca 2+ channels for subsequent signaling to transcription and ER Ca 2+ refilling. Here, we demonstrate that reduced STIM2, but not STIM1, in colorectal cancer (CRC) is associated with poor patient prognosis. Loss of STIM2 causes SERCA2-dependent increase in ER Ca 2+ , increased protein translation and transcriptional and metabolic rewiring supporting increased tumor size, invasion, and metastasis. Mechanistically, STIM2 loss activates cMyc and the PERK/ATF4 branch of ER stress in an Orai-independent manner. Therefore, STIM2 and PERK/ATF4 could be exploited for prognosis or in targeted therapies to inhibit CRC tumor growth and metastasis.Highlights: STIM2 regulates ER Ca 2+ homeostasis independently of Orai and SOCE. STIM2 downregulation in colorectal cancer cells causes enhanced ER Ca 2+ and is associated with poor patient prognosis. STIM2 downregulation induces PERK/ATF4 dependent ER stress in colorectal cancer.Increased ER stress drives colorectal cancer metabolic reprogramming, growth, and metastasis.

DOI: https://doi.org/10.1101/2023.10.02.560521
Int J Mol Med. 2023 Dec;pii: 119. [Epub ahead of print]52(6):

Potential mechanism of TMEM2/CD44 in endoplasmic reticulum stress‑induced neuronal apoptosis in a rat model of traumatic brain injury.

Muyao Wu, Chaoyu Wang, Yating Gong, Yaqian Huang, Lei Jiang, Min Zhang, Rong Gao, Baoqi Dang.

  Traumatic brain injury (TBI) can lead to the disruption of endoplasmic reticulum (ER) homeostasis in neurons and induce ER stress. Transmembrane protein 2 (TMEM2) may regulate ER stress through the p38/ERK signaling pathway, independent of the classic unfolded protein response (UPR) pathway. The present study examined the expression of TMEM2 following TBI in a rat model, in an aim to determine whether the mitogen‑activated protein kinase (MAPK) signaling pathway is controlled by TMEM2/CD44 to mitigate secondary brain injury. For this purpose, 89 Sprague‑Dawley rats were used to establish the model of TBI, and TMEM2 siRNA was used to silence TMEM2. Western blot analysis, immunofluorescence, TUNEL assay and Fluoro‑Jade C staining, the wet‑dry method and behavioral scoring were used for analyses. The results revealed that TMEM2 was activated following TBI in rats. The silencing of TMEM2 resulted in a significant increase in the levels of p38 and ERK (components of MAPK signaling), while brain edema, neuronal apoptosis and degeneration were significantly aggravated. TBI increased TMEM2/CD44‑aggravated brain edema and neurological impairment, possibly by regulating ERK and p38 signaling. TMEM2/CD44 may thus be a target for the prevention and control of TBI.

Keywords:  CD44; MAPK pathway; endoplasmic reticulum stress; transmembrane protein 2; traumatic brain injury

DOI:  https://doi.org/10.3892/ijmm.2023.5322
Eur J Med Res. 2023 Oct 27. 28(1): 462

Synergistic anticancer activity of cisplatin combined with tannic acid enhances apoptosis in lung cancer through the PERK-ATF4 pathway.

Xiang Zheng, Lei Yang, Wei Zhai, Nana Geng, Zhimin Zhang, Xueying Li, Mingsong Wu.

  BACKGROUND: Cisplatin (CDDP) is a common anticancer drug whose side effects limit its clinical applications. Tannins (TA) are plant-derived polyphenols that inhibit tumor growth in different types of cancer. Here, we evaluated the anticancer effect of TA combined with CDDP on lung cancer cell lines (GLC-82 and H1299) and investigated the underlying molecular mechanism of endoplasmic reticulum (ER) stress-induced apoptosis.METHODS: Cell lines were treated with CDDP, TA, and CDDP + TA, and the effect of the combination was assessed using MTT assay and observed under light and fluorescence microscopes. Cell apoptosis was detected by flow cytometry, and the levels of ERS apoptosis pathway related genes were valuated by qRT-PCR and western blotting. The effects of the drug combination on the tumors of nude mice injected with H1299 cells were investigated, and the expression of key factors in the ER stress apoptotic pathway was investigated.
RESULTS: The combination of CDDP and TA significantly inhibited lung cancer cell viability indicating a synergistic antitumoral effect. The mRNA and protein expression levels of key ER stress factors in the CDDP + TA group were considerably higher than those in the CDDP and TA groups, the tumor volume in tumor-bearing mice was the smallest, and the number of apoptotic cells and the protein expression levels of the key ER stress in the combination group were considerably higher.
CONCLUSIONS: The combination of TA and CDDP may produce synergistic antitumoral effects mediated by the PERK-ATF4-CHOP apoptotic axis, suggesting a novel adjuvant treatment for lung cancer.

Keywords:  Cisplatin; Combination drugs; Endoplasmic reticulum stress; Lung cancer; Tannins

DOI:  https://doi.org/10.1186/s40001-023-01420-z
BMC Med Genomics. 2023 10 25. 16(1): 261

Identification of the role of endoplasmic reticulum stress genes in endometrial cancer and their association with tumor immunity.

Tang Ansu Zhang, Qian Zhang, Jun Zhang, Rong Zhao, Rui Shi, Sitian Wei, Shuangge Liu, Qi Zhang, Hongbo Wang.

  BACKGROUND: Endometrial cancer (EC) is one of the worldwide gynecological malignancies. Endoplasmic reticulum (ER) stress is the cellular homeostasis disturbance that participates in cancer progression. However, the mechanisms of ER Stress on EC have not been fully elucidated.METHOD: The ER Stress-related genes were obtained from Gene Set Enrichment Analysis (GSEA) and GeneCards, and the RNA-seq and clinical data were downloaded from The Cancer Genome Atlas (TCGA). The risk signature was constructed by the Cox regression and the least absolute shrinkage and selection operator (LASSO) analysis. The significance of the risk signature and clinical factors were tested by time-dependent receiver operating characteristic (ROC) curves, and the selected were to build a nomogram. The immunity correlation was particularly analyzed, including the related immune cells, pathways, and immune checkpoints. Functional enrichment, potential chemotherapies, and in vitro validation were also conducted.
RESULT: An ER Stress-based risk signature, consisting of TRIB3, CREB3L3, XBP1, and PPP1R15A was established. Patients were randomly divided into training and testing groups with 1:1 ratio for subsequent calculation and validation. Based on risk scores, high- and low-risk subgroups were classified, and low-risk subgroup demonstrated better prognosis. The Area Under Curve (AUC) demonstrated a reliable predictive capability of the risk signature. The majority of significantly different immune cells and pathways were enriched more in low-risk subgroup. Similarly, several typical immune checkpoints, expressed higher in low-risk subgroup. Patients of the two subgroups responded differently to chemotherapies.
CONCLUSION: We established an ER Stress-based risk signature that could effectively predict EC patients' prognosis and their immune correlation.

Keywords:  Bioinformatic analysis; Endometrial cancer; Endoplasmic reticulum stress; Immune infiltration; Prognosis; Risk signature

DOI:  https://doi.org/10.1186/s12920-023-01679-5
Cell Signal. 2023 Oct 22. pii: S0898-6568(23)00344-3. [Epub ahead of print]113 110929

Identification and functional coordination analysis of gene co-expression networks in different tissues of XBP1 cartilage-specific deficient mice.

Xiaoli Li, Yiming Pan, Kaiwen Liu, Yuyou Yang, Yuanlan Ye, Qingbo Xu, Mengtian Fan, Fengjin Guo.

  Abnormal differentiation and proliferation of chondrocytes leads to various diseases related to growth and development. The process of chondrocyte differentiation involves a series of complex cellular and molecular interactions. X-box binding protein 1 (XBP1), an essential molecule of the unfolded protein response (UPR) in Endoplasmic Reticulum (ER) stress, participated in cartilage development and causes other related diseases. We previously reported that XBP1 deficiency in cartilage impacts the function and associated diseases of many different tissues including cartilage. However, how differential expression of genes modulates the roles of cartilage and other tissues when XBP1 is lack of in chondrocytes remains unclear. We aimed to screen for differentially expressed (DE) genes in cartilage, brain, heart, and muscle by high-throughput sequencing in XBP1 cartilage-specific knockout (CKO) mice. Further, gene co-expression networks were constructed by weighted gene co-expression network analysis (WGCNA) algorithm and pivot genes were identified in the above four tissues. Protein detection, Hematoxylin-eosin (HE) staining and immunohistochemistry (IHC) experiments have proved that these differentially co-expressed genes participate in the downstream regulatory pathway of different tissues and affect tissue function.Significantly differentially expressed mRNAs [differentially expressed genes (DEGs)] were identified between XBP1 CKO mice and controls in cartilage, brain, heart, and muscle tissues, including 610, 126, 199 and 219 DEGs, respectively. 39 differentially co-expressed genes were identified in the above four tissues, and they were important pivot genes. Comprehensive analysis discovered that XBP1 deficiency in cartilage influences the difference of co-expressed genes between cartilage and other different tissues. These differentially co-expressed genes participate in downstream regulatory pathways of different tissues and affect tissue functions. Collectively, our conclusions may contribute potential biomarkers and molecular mechanisms for the mutual modulation between cartilage and different tissues and the diagnosis and treatment of diseases caused by abnormalities in different tissues. The analysis also provides meaningful insights for future genetic discoveries.

Keywords:  Brain; Cartilage; Co-expressed genes; Heart; Muscle; Transcriptome analysis; XBP1

DOI:  https://doi.org/10.1016/j.cellsig.2023.110929
PLoS One. 2023 ;18(10): e0290371

USP7 attenuates endoplasmic reticulum stress-induced apoptotic cell death through deubiquitination and stabilization of FBXO7.

Su Hyoun Lee, Kwang Chul Chung.

Parkinson's disease (PD) is a common neurodegenerative disease (NDD) characterized by the loss of dopaminergic neurons in the substantia nigra. Similar to other NDDs, the buildup of toxic protein aggregates in PD leads to progressive neuronal loss, culminating in neurodegeneration. Accumulating evidence indicates that alterations in subcellular organelles, particularly the endoplasmic reticulum (ER), are critically involved in pathological neurodegenerative events in NDDs, including PD. Mutations in the F-box only protein 7 (FBXO7 or PARK15) gene have been found to cause early onset autosomal recessive familiar PD. FBXO7 functions as an adaptor protein in the Skp1-Cullin1-F-box protein (SCF) E3 ubiquitin ligase complex, which promotes substrate ubiquitination. Although FBXO7 is involved in the ubiquitination of various target proteins, little is known about the upstream regulatory mechanism of FBXO7 and/or its modulator(s). Ubiquitin specific protease 7 (USP7) is a deubiquitinating enzyme that regulates the balance between protein synthesis and degradation by removing ubiquitin from target substrates. The role of USP7 in various types of cancer is well-established; however, its role in NDDs has not been elucidated to date. In this study, we identified that USP7 acts as a novel regulator of FBXO7, positively regulating the stability of FBXO7 through Lys48-linked deubiquitination. Moreover, USP7 was found to mitigate ER stress-induced cytotoxicity and apoptosis by preventing the proteasomal degradation of FBXO7. Taken together, our study suggests that the functional relationship between FBXO7 and USP7 may play a crucial role in ER stress-induced apoptosis and the pathogenesis of PD.

DOI: https://doi.org/10.1371/journal.pone.0290371
Cell Signal. 2023 Oct 20. pii: S0898-6568(23)00350-9. [Epub ahead of print] 110935

Angiotensin II type-2 receptor attenuates liver fibrosis progression by suppressing IRE1α-XBP1 pathway.

Yue An, Changyong Xu, Wenmin Liu, Ji Jiang, Pengfei Ye, Mei Yang, Weihua Zhu, Jingjing Yu, Manman Yu, Wuyi Sun, Jian Hong, Huan Qiu, Wei Wei, Shihao Zhang.

  The renin-angiotensin system (RAS) has been recognized as a crucial contributor to the development of liver fibrosis, and AT2R, an essential component of RAS, is involved in the progression of liver fibrosis. However, the underlying mechanisms by which AT2R modulates liver fibrosis remain elusive. Here, we report that AT2R was induced to be highly expressed during the progression of liver fibrosis, and the elevated AT2R attenuates liver fibrosis by suppressing IRE1α-XBP1 pathway. In this study, we found that AT2R is not expressed in the no cirrhotic adult liver, but is induced expression during liver fibrosis in both cirrhotic patients and fibrotic mice models. Upregulated AT2R inhibits the activation and proliferation of hepatic stellate cells (HSCs). In addition, our study showed that during liver fibrosis, AT2R deletion increased the dimerization activation of IRE1α and promoted XBP1 splicing, and the spliced XBP1s could promote their transcription by binding to the AT2R promoter and repress the IRE1α-XBP1 axis, forming an AT2R-IRE1α-XBP1 negative feedback loop. Importantly, the combination treatment of an AT2R agonist and an endoplasmic reticulum stress (ER stress) alleviator significantly attenuated liver fibrosis in a mouse model of liver fibrosis. Therefore, we conclude that the AT2R-IRE1α signaling pathway can regulate the progression of liver fibrosis, and AT2R is a new potential therapeutic target for treating liver fibrosis.

Keywords:  AT2R; ER stress; IRE1α; Liver fibrosis; RAS

DOI:  https://doi.org/10.1016/j.cellsig.2023.110935
Int J Mol Sci. 2023 Oct 16. pii: 15236. [Epub ahead of print]24(20):

Apoptotic Effect of Gallic Acid via Regulation of p-p38 and ER Stress in PANC-1 and MIA PaCa-2 Cells Pancreatic Cancer Cells.

Jeong Woo Kim, Jinwon Choi, Moon Nyeo Park, Bonglee Kim.

  Pancreatic cancer (PC) is currently recognized as the seventh most prevalent cause of cancer-related mortality among individuals of both genders. It is projected that a significant number of individuals will succumb to this disease in the forthcoming years. Extensive research and validation have been conducted on both gemcitabine and 5-fluorouracil as viable therapeutic options for PC. Nevertheless, despite concerted attempts to enhance treatment outcomes, PC continues to pose significant challenges in terms of achieving effective treatment alone through chemotherapy. Gallic acid, an endogenous chemical present in various botanical preparations, has attracted considerable attention due to its potential as an anticancer agent. The results of the study demonstrated that gallic acid exerted a decline in cell viability that was dependent on its concentration. Furthermore, it efficiently suppressed cell proliferation in PC cells. This study observed a positive correlation between gallic acid and the production of reactive oxygen species (ROS). Additionally, it confirmed the upregulation of proteins associated with the protein kinase-like endoplasmic reticulum kinase (PERK) pathway, which is one of the pathways involved in endoplasmic reticulum (ER) stress. Moreover, the administration of gallic acid resulted in verified alterations in the transmission of mitogen-activated protein kinase (MAPK) signals. Notably, an elevation in the levels of p-p38, which represents the phosphorylated state of p38 MAPK was detected. The scavenger of reactive oxygen species (ROS), N-Acetyl-L-cysteine (NAC), has shown inhibitory effects on phosphorylated p38 (p-p38), whereas the p38 inhibitor SB203580 inhibited C/EBP homologous protein (CHOP). In both instances, the levels of PARP have been successfully reinstated. In other words, the study discovered a correlation between endoplasmic reticulum stress and the p38 signaling pathway. Consequently, gallic acid induces the activation of both the p38 pathway and the ER stress pathway through the generation of ROS, ultimately resulting in apoptosis. The outcomes of this study provide compelling evidence to support the notion that gallic acid possesses considerable promise as a viable therapeutic intervention for pancreatic cancer.

Keywords:  ER stress; ROS; apoptosis; gallic acid; p38 pathway; pancreatic cancer

DOI:  https://doi.org/10.3390/ijms242015236
Int J Mol Sci. 2023 Oct 14. pii: 15186. [Epub ahead of print]24(20):

Endoplasmic Reticulum Stress Promotes the Expression of TNF-α in THP-1 Cells by Mechanisms Involving ROS/CHOP/HIF-1α and MAPK/NF-κB Pathways.

Nadeem Akhter, Ajit Wilson, Hossein Arefanian, Reeby Thomas, Shihab Kochumon, Fatema Al-Rashed, Mohamed Abu-Farha, Ashraf Al-Madhoun, Fahd Al-Mulla, Rasheed Ahmad, Sardar Sindhu.

  Obesity and metabolic syndrome involve chronic low-grade inflammation called metabolic inflammation as well as metabolic derangements from increased endotoxin and free fatty acids. It is debated whether the endoplasmic reticulum (ER) stress in monocytic cells can contribute to amplify metabolic inflammation; if so, by which mechanism(s). To test this, metabolic stress was induced in THP-1 cells and primary human monocytes by treatments with lipopolysaccharide (LPS), palmitic acid (PA), or oleic acid (OA), in the presence or absence of the ER stressor thapsigargin (TG). Gene expression of tumor necrosis factor (TNF)-α and markers of ER/oxidative stress were determined by qRT-PCR, TNF-α protein by ELISA, reactive oxygen species (ROS) by DCFH-DA assay, hypoxia-inducible factor 1-alpha (HIF-1α), p38, extracellular signal-regulated kinase (ERK)-1,2, and nuclear factor kappa B (NF-κB) phosphorylation by immunoblotting, and insulin sensitivity by glucose-uptake assay. Regarding clinical analyses, adipose TNF-α was assessed using qRT-PCR/IHC and plasma TNF-α, high-sensitivity C-reactive protein (hs-CRP), malondialdehyde (MDA), and oxidized low-density lipoprotein (OX-LDL) via ELISA. We found that the cooperative interaction between metabolic and ER stresses promoted TNF-α, ROS, CCAAT-enhancer-binding protein homologous protein (CHOP), activating transcription factor 6 (ATF6), superoxide dismutase 2 (SOD2), and nuclear factor erythroid 2-related factor 2 (NRF2) expression (p ≤ 0.0183),. However, glucose uptake was not impaired. TNF-α amplification was dependent on HIF-1α stabilization and p38 MAPK/p65 NF-κB phosphorylation, while the MAPK/NF-κB pathway inhibitors and antioxidants/ROS scavengers such as curcumin, allopurinol, and apocynin attenuated the TNF-α production (p ≤ 0.05). Individuals with obesity displayed increased adipose TNF-α gene/protein expression as well as elevated plasma levels of TNF-α, CRP, MDA, and OX-LDL (p ≤ 0.05). Our findings support a metabolic-ER stress cooperativity model, favoring inflammation by triggering TNF-α production via the ROS/CHOP/HIF-1α and MAPK/NF-κB dependent mechanisms. This study also highlights the therapeutic potential of antioxidants in inflammatory conditions involving metabolic/ER stresses.

Keywords:  CHOP; ER stress; HIF-1α; MAPK/NF-κB; ROS; TNF-α; inflammation; metabolic stress; metabolic syndrome; obesity

DOI:  https://doi.org/10.3390/ijms242015186
Autophagy. 2023 Oct 27. 1-3

The biological function of cytoplasm-translocated ENDOG (endonuclease G).

Wenjun Wang, Jianshuang Li, Qinghua Zhou.

  ENDOG, a mitochondrial intermembrane space located endonuclease, participates in DNA fragmentation and apoptosis by translocating to the nucleus. ENDOG can also relocate to the mitochondrial matrix, where it regulates mitochondrial genome cleavage. However, the biological function of cytoplasm-translocated ENDOG remains unclear. Our previous study reported that starvation induces the release of ENDOG from mitochondria to the cytoplasm, promoting macroautophagy/autophagy in a process conserved across species. We demonstrate that ENDOG can be phosphorylated by GSK3B, which enhances ENDOG binding to YWHAG/14-3-3γ, and leads to the release of TSC2 and PIK3C3/VPS34 from YWHAG/14-3-3γ, followed by MTORC1 pathway suppression and autophagy initiation. Additionally, we recently reported that ENDOG can also activate the MTORC2-AKT-ACLY signaling axis by promoting the release of RICTOR and TSC2 from YWHAG/14-3-3γ, resulting in acetyl-CoA production. Furthermore, cytoplasmic ENDOG can translocate to the endoplasmic reticulum, where it binds with HSPA5/BIP to release ERN1/IRE1a-EIF2AK3/PERK to activate the endoplasmic reticulum stress response, eventually promoting lipid synthesis. Collectively, ENDOG will be released from the mitochondrial intermembrane space, and translocated to the mitochondrial matrix, cytoplasm, and nucleus during different stress stimulation, where it digests DNA or interacts with crucial proteins to regulate different biological functions, including apoptosis, autophagy, mitophagy, and lipid synthesis.

Keywords:  Autophagy; ENDOG; MTORC1; MTORC2; endoplasmic reticulum

DOI:  https://doi.org/10.1080/15548627.2023.2271750