bims-apauto 2023-07-23 papers

Issue of 2023–07–23
five papers selected by
Su Hyun Lee, Harvard University

Autophagy. 2023 Jul 20.

Noncanonical autophagy is a new strategy to inhibit HSV-1 through STING1 activation.

Zhihua Zheng, Man Zhao, Hao Shan, Dongmei Fang, Zuyi Jin, Jiuge Tang, Zhiping Liu, Liang Hong, Peiqing Liu, Min Li.

STING1 (stimulator of interferon response cGAMP interactor 1) plays an essential role in immune responses for virus inhibition via inducing the production of type I interferon, inflammatory factors and macroautophagy/autophagy. In this study, we found that STING1 activation could induce not only canonical autophagy but also non-canonical autophagy (NCA) which is independent of the ULK1 or BECN1 complexes to form MAP1LC3/LC3-positive structures. Whether STING1-induced NCA has similar characters and physiological functions to canonical autophagy is totally unknown. Different from canonical autophagy, NCA could increase single-membrane structures and failed to degrade long-lived proteins, and could be strongly suppressed by interrupting vacuolar-type H+-translocating ATPase (V-ATPase) activity. Importantly, STING1-induced NCA could effectively inhibit DNA virus HSV-1 in cell model. Moreover, STING1[1-340], a STING1 mutant lacking immunity and inflammatory response due to deletion of the tail end of STING1, could degrade virus through NCA alone, suggesting that the antiviral effect of activated STING1 could be separately mediated by inherent immunity, canonical autophagy, and NCA. In addition, the translocation and dimerization of STING1 do not rely on its immunity function and autophagy pathway. Similar to canonical autophagy, LC3-positive structures of NCA induced by STING1 could finally fuse with lysosomes, and the degradation of HSV-1 could be reverted by inhibition of lysosome function, suggesting that the elimination of DNA virus via NCA still requires the lysosome pathway. Collectively, we proved that besides its classical immunity function and canonical autophagy pathway, STING1-induced NCA is also an efficient antiviral pathway for the host cell.

Keywords: HSV-1; STING1; autophagy; inherent immunity; lysosome degradation; noncanonical autophagy

DOI: https://doi.org/10.1080/15548627.2023.2237794

Autophagy Rep. 2022 ;1(1): 65-69

Driving arginine catabolism to activate systemic autophagy.

Yiming Zhang, Brian N Finck, Brian J DeBosch.

Macroautophagy/autophagy is a conserved cellular self-digestive mechanism to catabolize superfluous or damaged cellular components to maintain cell homeostasis. Impaired autophagy underlies multiple pathophysiological states, including aging, neurodegenerative, inflammatory, and metabolic diseases. Intermittent fasting and caloric restriction are effective means by which to activate autophagy, yet relatively few people can sustain such intensive interventions in real-world settings. Moreover, current pharmacotherapies do not yet fully exploit autophagic flux as a target mechanism. Here, we discuss recent work, which demonstrates that arginine catabolism is a tractable process to activate autophagy with utility to treat obesity and its complications. Hepatocyte-specific transgenic activation of arginine catabolism, or systemic administration of an anti-tumor pharmacotherapy, pegylated arginine deiminase, each promote energy expenditure and insulin sensitivity, and reduce dyslipidemia and hepatic steatosis in obese mice. These effects depend upon hepatocyte Fgf21, and whole-body Becn1 expression. The data suggest that hepatocyte and systemic arginine catabolism drive autophagy, and identify an index pharmacological agent to leverage this process.

DOI: https://doi.org/10.1080/27694127.2022.2040763

Proc Natl Acad Sci U S A. 2023 07 25. 120(30): e2306152120

Homeostatic regulation of ribosomal proteins by ubiquitin-independent cotranslational degradation.

Donghong Ju, Li Li, Youming Xie.

Ribosomes are the workplace for protein biosynthesis. Protein production required for normal cell function is tightly linked to ribosome abundance. It is well known that ribosomal genes are actively transcribed and ribosomal messenger RNAs (mRNAs) are rapidly translated, and yet ribosomal proteins have relatively long half-lives. These observations raise questions as to how homeostasis of ribosomal proteins is controlled. Here, we show that ribosomal proteins, while posttranslationally stable, are subject to high-level cotranslational protein degradation (CTPD) except for those synthesized as ubiquitin (Ub) fusion precursors. The N-terminal Ub moiety protects fused ribosomal proteins from CTPD. We further demonstrate that cotranslational folding efficiency and expression level are two critical factors determining CTPD of ribosomal proteins. Different from canonical posttranslational degradation, we found that CTPD of all the ribosomal proteins tested in this study does not require prior ubiquitylation. This work provides insights into the regulation of ribosomal protein homeostasis and furthers our understanding of the mechanism and biological significance of CTPD.

Keywords: cotranslational protein degradation; proteasomal degradation; protein degradation; ribosomal proteins; ubiquitin-independent protein degradation

DOI: https://doi.org/10.1073/pnas.2306152120

Autophagy. 2023 Jul 16.

Mitofissin: a novel mitochondrial fission protein that facilitates mitophagy.

Tomoyuki Fukuda, Kentaro Furukawa, Tatsuro Maruyama, Nobuo N Noda, Tomotake Kanki.

Mitophagy is a selective form of autophagy that targets dysfunctional or superfluous mitochondria for degradation. During mitophagy, specific selective autophagy receptors (SARs) mark a portion of mitochondria to recruit the autophagy-related (Atg) machinery and nucleate a phagophore. The phagophore expands and surrounds the mitochondrial cargo, forming an autophagosome. Fission plays a crucial role in separating the targeted portion of mitochondria from the main body to sequester it within the autophagosome. Our recent study, utilizing fission and budding yeasts as model systems, has identified Atg44 as a mitochondrial fission factor that generates mitochondrial fragments suitable for phagophore engulfment. Atg44 resides in the mitochondrial intermembrane space (IMS) and interacts with lipid membranes, with the capacity of mediating membrane fragility and fission. Based on our findings, we propose the term mitofissin to refer to Atg44 and its homologous proteins, which might participate in diverse cellular processes requiring membrane remodeling across various species.

Keywords: Atg44; autophagy; mitochondria; mitochondrial fission; mitofissin; mitophagy; yeast

DOI: https://doi.org/10.1080/15548627.2023.2237343

Mol Cell. 2023 Jul 12. pii: S1097-2765(23)00475-6. [Epub ahead of print]

UBR5 forms ligand-dependent complexes on chromatin to regulate nuclear hormone receptor stability.

Nuclear hormone receptors (NRs) are ligand-binding transcription factors that are widely targeted therapeutically. Agonist binding triggers NR activation and subsequent degradation by unknown ligand-dependent ubiquitin ligase machinery. NR degradation is critical for therapeutic efficacy in malignancies that are driven by retinoic acid and estrogen receptors. Here, we demonstrate the ubiquitin ligase UBR5 drives degradation of multiple agonist-bound NRs, including the retinoic acid receptor alpha (RARA), retinoid x receptor alpha (RXRA), glucocorticoid, estrogen, liver-X, progesterone, and vitamin D receptors. We present the high-resolution cryo-EMstructure of full-length human UBR5 and a negative stain model representing its interaction with RARA/RXRA. Agonist ligands induce sequential, mutually exclusive recruitment of nuclear coactivators (NCOAs) and UBR5 to chromatin to regulate transcriptional networks. Other pharmacological ligands such as selective estrogen receptor degraders (SERDs) degrade their receptors through differential recruitment of UBR5 or RNF111. We establish the UBR5 transcriptional regulatory hub as a common mediator and regulator of NR-induced transcription.

Keywords: HECT-E3 ligases; nuclear receptors; protein degradation; structural biology; ubiquitin ligases

DOI: https://doi.org/10.1016/j.molcel.2023.06.028