bims-apauto Biomed News
on Apoptosis and autophagy
Issue of 2022‒02‒06
eight papers selected by
Su Hyun Lee
Seoul National University

  1. Autophagy. 2022 Jan 31. 1-2
      The endoplasmic reticulum (ER) forms a contiguous network of tubules and sheets. When errors in protein folding occur, misfolded proteins accumulate in the ER. Proteostasis can be restored by ER quality control pathways. Reticulophagy is an ER quality control pathway that uses resident autophagy receptors to link an ER domain to the autophagy machinery. We recently showed that the reticulophagy receptor RTN3L recruits the COPII cargo adaptor SEC24C to target disease-causing mutant proinsulin INS2Akita puncta to the lysosome for degradation. When reticulophagy is disrupted and delivery to the lysosome is blocked, large INS2Akita puncta accumulate in the ER. Photobleach analysis revealed that these puncta behave like liquid condensates and not aggregates, as previously suggested. Other reticulophagy substrates that are segregated into tubules behave like INS2Akita, whereas a substrate of the ER sheets receptor, RETREG1/FAM134B, appears to be less fluid. Large INS2Akita puncta also accumulate when ER sheets are proliferated by the loss of LNPK, or by overproduction of the sheets-producing protein, CKAP4/CLIMP63. Restoring the tubular network by overexpressing reticulons reverses this phenotype. Our findings revealed that fluid-like deleterious cargoes are segregated into tubules to prevent them from expanding and affecting cell health while they are waiting to undergo reticulophagy.
    Keywords:  ER structure; Lunapark; SEC24C; misfolded prohormones and neuropeptides; protein quality control; reticulophagy
  2. Autophagy. 2022 Feb 01. 1-17
      Impairments in macroautophagy/autophagy, which degrades dysfunctional organelles as well as long-lived and aggregate proteins, are associated with several cardiomyopathies; however, the regulation of cardiac autophagy remains insufficiently understood. In this regard, ULK1 and ULK2 are thought to play primarily redundant roles in autophagy initiation, but whether their function is developmentally determined, potentially having an impact on cardiac integrity and function remains unknown. Here, we demonstrate that perinatal loss of ULK1 or ULK2 in cardiomyocytes (cU1-KO and cU2-KO mice, respectively) enhances basal autophagy without altering autophagy machinery content while preserving cardiac function. This increased basal autophagy is dependent on the remaining ULK protein given that perinatal loss of both ULK1 and ULK2 in cU1/2-DKO mice impaired autophagy causing age-related cardiomyopathy and reduced survival. Conversely, adult loss of cardiac ULK1, but not of ULK2 (i.e., icU1-KO and icU2-KO mice, respectively), led to a rapidly developing cardiomyopathy, heart failure and early death. icU1-KO mice had impaired autophagy with robust deficits in mitochondrial respiration and ATP synthesis. Trehalose ameliorated autophagy impairments in icU1-KO hearts but did not delay cardiac dysfunction suggesting that ULK1 plays other critical, autophagy-independent, functions in the adult heart. Collectively, these results indicate that cardiac ULK1 and ULK2 are functionally redundant in the developing heart, while ULK1 assumes a more unique, prominent role in the adult heart.Abbreviations: ATG4: autophagy related 4, cysteine peptidase; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG9: autophagy related 9; ATG13: autophagy related 13; CYCS: Cytochrome C; DNM1L, dynamin 1-like; MAP1LC3A: microtubule-associated protein 1 light chain 3 alpha; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; MFN1: mitofusin 1; MFN2: mitofusin 2; MT-CO1: mitochondrially encoded cytochrome c oxidase I; MYH: myosin, heavy polypeptide; NBR1: NBR1 autophagy cargo receptor; NDUFA9: NADH:ubiquinone oxidoreductase subunit A9; OPA1: OPA1, mitochondrial dynamin like GTPase; PPARGC1A, peroxisome proliferator activated receptor, gamma, coactivator 1 alpha; SDHA: succinate dehydrogenase complex, subunit A, flavoprotein (Fp); SQSTM1: sequestosome 1; ULK1: unc-51 like kinase 1; ULK2: unc-51 like kinase 2; UQCRC1: ubiquinol-cytochrome c reductase core protein 1.
    Keywords:  Age-related cardiomyopathy; MAP1LC3; NBR1; SQSTM1; dilated cardiomyopathy; heart failure; mitochondria; mitophagy
  3. J Cell Sci. 2022 Jan 31. pii: jcs.259138. [Epub ahead of print]
      Cell migration is a complex process underlying physiological and pathological processes such as brain development and cancer metastasis. The autophagy-linked FYVE protein (ALFY), an autophagy adaptor protein known to promote clearance of protein aggregates, has been implicated in brain development and neural migration during cerebral cortical neurogenesis in mice. However, a specific role of ALFY in cell motility and extracellular matrix adhesion during migration has not been investigated. Here we reveal a novel role for ALFY in the endocytic pathway and in cell migration. We show that ALFY localizes to RAB5 and EEA1 positive early endosomes in a PtdIns(3)P dependent manner and is highly enriched in cellular protrusions at the leading and lagging edge of migrating cells. We find that cells lacking ALFY have reduced attachment and altered protein levels and glycosylation of integrins, resulting in the inability to form a proper leading edge and loss of directional cell motility.
    Keywords:  ALFY; Endosome; Focal adhesion; Integrin; Migration; WDFY3
  4. Autophagy. 2022 Jan 31. 1-15
      Deubiquitination plays an important role in the regulation of the crosstalk between macroautophagy/autophagy and innate immune signaling, yet its regulatory mechanisms are not fully understood. Here we identify the deubiquitinase OTUD7B as a negative regulator of antiviral immunity by targeting IRF3 (interferon regulatory factor 3) for selective autophagic degradation. Mechanistically, OTUD7B interacts with IRF3, and activates IRF3-associated cargo receptor SQSTM1/p62 (sequestosome 1) by removing its K63-linked poly-ubiquitin chains at lysine 7 (K7) to enhance SQSTM1 oligomerization. Moreover, viral infection increased the expression of OTUD7B, which forms a negative feedback loop by promoting IRF3 degradation to balance type I interferon (IFN) signaling. Taken together, our study reveals a specific role of OTUD7B in mediating the activation of cargo receptors in a substrate-dependent manner, which could be a potential target against excessive immune responses.Abbreviations: Baf A1: bafilomycin A1; CGAS: cyclic GMP-AMP synthase; DDX58/RIG-I: DExD/H-box helicase 58; DSS: dextran sodium sulfate; DUBs: deubiquitinating enzymes; GFP: green fluorescent protein; IFN: interferon; IKKi: IKBKB/IkappaB kinase inhibitor; IRF3: interferon regulatory factor 3; ISGs: interferon-stimulated genes; MAVS: mitochondrial antiviral signaling protein; MOI: multiplicity of infection; PAMPs: pathogen-associated molecular patterns; SeV: Sendai virus; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK binding kinase 1; Ub: ubiquitin; WT: wild-type; VSV: vesicular stomatitis virus.
    Keywords:  Antiviral immunity; cargo receptor; deubiquitination; selective autophagy; type I interferon signaling
  5. Mol Cell. 2022 Jan 25. pii: S1097-2765(22)00002-8. [Epub ahead of print]
      The mTOR complex 1 (mTORC1) is an essential metabolic hub that coordinates cellular metabolism with the availability of nutrients, including amino acids. Sestrin2 has been identified as a cytosolic leucine sensor that transmits leucine status signals to mTORC1. In this study, we identify an E3 ubiquitin ligase RING finger protein 167 (RNF167) and a deubiquitinase STAMBPL1 that function in concert to control the polyubiquitination level of Sestrin2 in response to leucine availability. Ubiquitination of Sestrin2 promotes its interaction with GATOR2 and inhibits mTORC1 signaling. Bioinformatic analysis reveals decreased RNF167 expression and increased STAMBPL1 expression in gastric and colorectal tumors. Knockout of STAMBPL1 or correction of the heterozygous STAMBPL1 mutation in a human colon cancer cell line suppresses xenograft tumor growth. Lastly, a cell-permeable peptide that blocks the STAMBPL1-Sestrin2 interaction inhibits mTORC1 and provides a potential option for cancer therapy.
    Keywords:  Sestrin2; amino acid sensing; colorectal cancer; mTOR; tumorigenesis; ubiquitination
  6. Autophagy. 2022 Jan 31. 1-13
      Obesity is a common comorbidity in patients with asthma, and obese asthma patients present the most refractory phenotype among patients with severe asthma. Similar to the observations in non-obese asthma patients, clinical studies have revealed heterogeneity in obese asthma patients, including the occurrences of T helper (Th)2-high and Th2-low phenotypes. However, the mechanisms underlying obesity-related asthma are not completely understood. Though macroautophagy/autophagy is involved in asthma and obesity, its role in obesity-associated asthma is unknown. We hypothesized that autophagy is involved in the pathogenesis of obese asthma. For our investigations, we used high-fat diet-induced Atg5 (autophagy related 5)-deficient mice and epithelial cell-specific atg5-/- (Scgb1a1/CCSP-atg5-/-) obesity-induced mice. House dust mite (HDM)-sensitized atg5-/- obese mice exhibited marked eosinophilic inflammation and airway hyper-reactivity (AHR), compared to wild-type (WT) obese mice. Analyses of atg5-/- obese mice showed increased levels of Th2 cells but not ILC2s together with elevated expression of Th2 cytokines in the lung. In response to the HDM challenge, activated epithelial autophagy was observed in lean but not obese WT mice. Epithelium-specific deletion of Atg5 induced eosinophilic inflammation in Scgb1a1/CCSP-atg5-/- obese mice, and genetic analyses of epithelial cells from HDM-immunized atg5-/- obesity-induced mice showed an elevated expression of thymic stromal lymphopoietin (TSLP) and IL33. Notably, HDM-sensitized atg5-/- mice developed TSLP- and IL33-dependent eosinophilic inflammation and AHR. Our results suggest that autophagy contributes to the exacerbation of eosinophilic inflammation in obese asthma. Modulations of autophagy may be a therapeutic target in obesity-associated asthma.
    Keywords:  Asthma; IL33; autophagy; corticosteroid resistance; eosinophil inflammation; obesity; thymic stromal lymphopoietin
  7. Cell Mol Life Sci. 2022 Feb 03. 79(2): 116
      Esophageal cancer (EC) is one of the most incident and lethal tumors worldwide. Although surgical resection is an important approach in EC treatment, late diagnosis, metastasis and recurrence after surgery have led to the management of adjuvant and neoadjuvant therapies over the past few decades. In this scenario, 5-fluorouracil (5-FU) and cisplatin (CISP), and more recently paclitaxel (PTX) and carboplatin (CBP), have been traditionally used in EC treatment. However, chemoresistance to these agents along EC therapeutic management represents the main obstacle to successfully treat this malignancy. In this sense, despite the fact that most of chemotherapy drugs were discovered several decades ago, in many cases, including EC, they still represent the most affordable and widely employed treatment approach for these tumors. Therefore, this review summarizes the main mechanisms through which the response to the most widely chemotherapeutic agents used in EC treatment is impaired, such as drug metabolism, apoptosis resistance, cancer stem cells (CSCs), cell cycle, autophagy, energetic metabolism deregulation, tumor microenvironment and epigenetic modifications.
    Keywords:  5-Fluorouracil; Chemoresistance; Cisplatin; Esophageal cancer; Molecular mechanisms; Paclitaxel
  8. Nat Commun. 2022 Feb 03. 13(1): 674
      Conductin/axin2 is a scaffold protein negatively regulating the pro-proliferative Wnt/β-catenin signaling pathway. Accumulation of scaffold proteins in condensates frequently increases their activity, but whether condensation contributes to Wnt pathway inhibition by conductin remains unclear. Here, we show that the Gαi2 subunit of trimeric G-proteins induces conductin condensation by targeting a polymerization-inhibiting aggregon in its RGS domain, thereby promoting conductin-mediated β-catenin degradation. Consistently, transient Gαi2 expression inhibited, whereas knockdown activated Wnt signaling via conductin. Colorectal cancers appear to evade Gαi2-induced Wnt pathway suppression by decreased Gαi2 expression and inactivating mutations, associated with shorter patient survival. Notably, the Gαi2-activating drug guanabenz inhibited Wnt signaling via conductin, consequently reducing colorectal cancer growth in vitro and in mouse models. In summary, we demonstrate Wnt pathway inhibition via Gαi2-triggered conductin condensation, suggesting a tumor suppressor function for Gαi2 in colorectal cancer, and pointing to the FDA-approved drug guanabenz for targeted cancer therapy.