Autophagy-regulating protease Atg4: structure, function, regulation and inhibition.
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ABSTRACT:
SUBMITTER: Maruyama T
PROVIDER: S-EPMC5799747 | biostudies-literature | 2017 Sep
REPOSITORIES: biostudies-literature
Publications
Autophagy-regulating protease Atg4: structure, function, regulation and inhibition.
Maruyama Tatsuro T Noda Nobuo N NN
The Journal of antibiotics 20170913
Autophagy is an intracellular degradation system that contributes to cellular homeostasis through degradation of various targets such as proteins, organelles and microbes. Since autophagy is related to various diseases such as infection, neurodegenerative diseases and cancer, it is attracting attention as a new therapeutic target. Autophagy is mediated by dozens of autophagy-related (Atg) proteins, among which Atg4 is the sole protease that regulates autophagy through the processing and deconjug ...[more]
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Project description:Autophagy is a membrane-trafficking process whereby double-membrane vesicles called autophagosomes engulf and deliver intracellular material to the vacuole for degradation. Atg4 is a cysteine protease with an essential function in autophagosome formation. Mounting evidence suggests that reactive oxygen species may play a role in the control of autophagy and could regulate Atg4 activity but the precise mechanisms remain unclear. In this study, we showed that reactive oxygen species activate autophagy in the model yeast Saccharomyces cerevisiae and unraveled the molecular mechanism by which redox balance controls Atg4 activity. A combination of biochemical assays, redox titrations, and site-directed mutagenesis revealed that Atg4 is regulated by oxidoreduction of a single disulfide bond between Cys338 and Cys394. This disulfide has a low redox potential and is very efficiently reduced by thioredoxin, suggesting that this oxidoreductase plays an important role in Atg4 regulation. Accordingly, we found that autophagy activation by rapamycin was more pronounced in a thioredoxin mutant compared with wild-type cells. Moreover, in vivo studies indicated that Cys338 and Cys394 are required for the proper regulation of autophagosome biogenesis, since mutation of these cysteines resulted in increased recruitment of Atg8 to the phagophore assembly site. Thus, we propose that the fine-tuning of Atg4 activity depending on the intracellular redox state may regulate autophagosome formation.
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Project description:Hydrogen sulfide is a signaling molecule that regulates essential processes for plant performance, such as autophagy. In Arabidopsis thaliana, hydrogen sulfide negatively regulates autophagy independently of reactive oxygen species, but the underlying mechanism remains to be understood. To determine whether persulfidation, an emergent posttranslational modification, has a main role in the control of autophagy by sulfide, we have used a proteomic approach targeting ATG4, a cysteine protease that plays a crucial role in autophagy progression. We showed that AtATG4a from A. thaliana, which is the predominant ATG4 protease in this plant species, contains a specific site for persulfidation, the residue Cys170, included in the characteristic catalytic triad Cys-His-Asp of cysteine proteases. We tested whether persulfidation regulates the activity of ATG4 by setting up a heterologous assay using the Chlamydomonas reinhardtii CrATG8 protein as a substrate. Our findings demonstrate that sulfide significantly inactivates AtATG4a cleavage activity in a reversible manner. The biological significance of the reversible inhibition of the ATG4 protease by sulfide is supported by our findings in Arabidopsis leaves under both basal and autophagy-inducing conditions. We also observed a significant increase in the overall ATG4 activity in Arabidopsis under nitrogen starvation and osmotic stress, which is inhibited by sulfide. Therefore, our data strongly suggest that the negative regulation of autophagy by sulfide is mediated, at least, by the specific persulfidation of the protease ATG4.
2020-12-14 | PXD019802 | Pride
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Project description:Autophagy is a highly conserved biological process during which double membrane bound autophagosomes carry intracellular cargo material to the vacuole or lysosome for degradation and/or recycling. Autophagosome biogenesis requires Autophagy 4 (Atg4) cysteine protease-mediated processing of ubiquitin-like Atg8 proteins. Unlike single Atg4 and Atg8 genes in yeast, the Arabidopsis genome contains two Atg4 (AtAtg4a and AtAtg4b) and nine Atg8 (AtAtg8a-AtAtg8i) genes. However, we know very little about specificity of different AtAtg4s for processing of different AtAtg8s. Here, we describe a unique bioluminescence resonance energy transfer-based AtAtg8 synthetic substrate to assess AtAtg4 activity in vitro and in vivo. In addition, we developed a unique native gel assay of superhRLUC catalytic activity assay to monitor cleavage of AtAtg8s in vitro. Our results indicate that AtAtg4a is the predominant protease and that it processes AtAtg8a, AtAtg8c, AtAtg8d, and AtAtg8i better than AtAtg4b in vitro. In addition, kinetic analyses indicate that although both AtAtg4s have similar substrate affinity, AtAtg4a is more active than AtAtg4b in vitro. Activity of AtAtg4s is reversibly inhibited in vitro by reactive oxygen species such as H2O2. Our in vivo bioluminescence resonance energy transfer analyses in Arabidopsis transgenic plants indicate that the AtAtg8 synthetic substrate is efficiently processed and this is AtAtg4 dependent. These results indicate that the synthetic AtAtg8 substrate is used efficiently in the biogenesis of autophagosomes in vivo. Transgenic Arabidopsis plants expressing the AtAtg8 synthetic substrate will be a valuable tool to dissect autophagy processes and the role of autophagy during different biological processes in plants.
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Project description:Autophagy is a dynamic process by which intracellular damaged macromolecules and organelles are degraded and recycled for the synthesis of new cellular components. Basal autophagy in the kidney acts as a quality control system and is vital for cellular metabolic and organelle homeostasis. Under pathological conditions, autophagy facilitates cellular adaptation; however, activation of autophagy in response to renal injury may be insufficient to provide protection, especially under dysregulated conditions. Kidney-specific deletion of Atg genes in mice has consistently demonstrated worsened acute kidney injury (AKI) outcomes supporting the notion of a pro-survival role of autophagy. Recent studies have also begun to unfold the role of autophagy in progressive renal disease and subsequent fibrosis. Autophagy also influences tubular cell death in renal injury. In this review, we reported the current understanding of autophagy regulation and its role in the pathogenesis of renal injury. In particular, the classic mammalian target of rapamycin (mTOR)-dependent signaling pathway and other mTOR-independent alternative signaling pathways of autophagy regulation were described. Finally, we summarized the impact of autophagy activation on different forms of cell death, including apoptosis and regulated necrosis, associated with the pathophysiology of renal injury. Understanding the regulatory mechanisms of autophagy would identify important targets for therapeutic approaches.
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