Deacetylation of ATG7 drives the induction of macroautophagy and LC3-associated microautophagy

SIRT5-mediated desuccinylation of PPA2 enhances HIF-1alpha-dependent adaptation to hypoxic stress and colorectal cancer metastasis

Metastasis is the primary cause of death in patients with colorectal cancer (CRC). Hypoxia is a hallmark of solid tumors that promotes cellular metabolic adaptation and dissemination. However, the mechanisms linking hypoxia-regulated metabolic adaptation to CRC metastasis remain unclear. Here, we found that inorganic pyrophosphatase 2 (PPA2) suppresses metastatic progression of CRC via its phosphatase function. PPA2 expression levels are reduced in CRC specimen and correlate with enhanced response to hypoxia by promoting hypoxia-inducible factor-1 (HIF-1) signaling to promote CRC cell glycolysis and dissemination. Mechanistically, PPA2 decreases HIF-1alpha stability through non-canonical ubiquitin-mediated proteasomal degradation via recruitment of E3 ligase NEDD4. Furthermore, PPA2 directly dephosphorylates NEDD4 at threonine 758 residue, resulting in its activation. Under hypoxic stress, NAD-dependent protein deacetylase sirtuin-5 promotes the dissociation of PPA2 and NEDD4 by inducing PPA2 desuccinylation at lysine 176, contributing to the improved stability of HIF-1alpha under hypoxic conditions. Our findings reveal a tumor-suppressive role of PPA2 in HIF-1alpha-dependent colorectal cancer, providing a potential therapeutic target and prognostic strategy.

The role of autophagy in fibrosis: Mechanisms, progression and therapeutic potential (Review)

Various forms of tissue damage can lead to fibrosis, an abnormal reparative reaction. In the industrialized countries, 45% of deaths are attributable to fibrotic disorders. Autophagy is a highly preserved process. Lysosomes break down organelles and cytoplasmic components during autophagy. The cytoplasm is cleared of pathogens and dysfunctional organelles, and its constituent components are recycled. With the growing body of research on autophagy, it is becoming clear that autophagy and its associated mechanisms may have a role in the development of numerous fibrotic disorders. However, a comprehensive understanding of autophagy in fibrosis is still lacking and the progression of fibrotic disease has not yet been thoroughly investigated in relation to autophagy‑associated processes. The present review focused on the latest findings and most comprehensive understanding of macrophage autophagy, endoplasmic reticulum stress‑mediated autophagy and autophagy‑mediated endothelial‑to‑mesenchymal transition in the initiation, progression and treatment of fibrosis. The article also discusses treatment strategies for fibrotic diseases and highlights recent developments in autophagy‑targeted therapies.

A double-edged sword in antiviral defence: ATG7 binding dicer to promote virus replication

RNA interference (RNAi) and autophagy are two pivotal biological processes that regulate virus replication. This study explored the complex relationship between autophagy and RNAi in controlling influenza virus replication. Initially, we reported that influenza virus (H9N2) infection increases the viral load and the expression of autophagy markers while inhibiting the RNAi pathway. Subsequent studies employing autophagy enhancer and inhibitor treatments confirmed that avian influenza virus (AIV, H9N2) promotes viral replication by enhancing autophagy pathways. Further analysis revealed that ATG7, an autophagy protein, can interact with dicer to affect its antiviral functions. Finally, we discovered that infection with other avian RNA viruses, including infectious bursal disease virus (IBDV) and infectious bronchitis virus (IBV), induced the upregulation of ATG7, which blocked the RNAi pathway to facilitate virus replication. Our findings suggested that virus infection might trigger the upregulation of autophagy and downregulation of the RNAi pathway, revealing a complex interaction between these two biological processes in the defence against viral replication.

Enhanced therapeutic efficacy of anti-PD-1 blockade by targeting LAMP2A inhibits lysosomal degradation of STING and TBK1

Rationale: LAMP2A is a key translocase in chaperone-mediated autophagy (CMA), and the STING/TBK1 axis is crucial in antitumor immunity. This study explored the complex mechanisms by which CMA regulates the STING/TBK1 degradation and whether targeting LAMP2A could enhance the efficacy of PD-1 monoclonal antibodies. Methods: The expression of STING and TBK1 was detected after treatment with various inhibitors of protein degradation pathways. Confocal microscopy was used to detect the localization of STING and TBK1 in lysosomes. R software was used to analyze LAMP2A expression and prognosis. The biological function of LAMP2A was examined by in vitro and in vivo experiments. Results: Through in vitro and in vivo experiments and a review of clinical specimens, we identified STING/TBK1 as a novel substrate of CMA. Downregulation of LAMP2A enhanced IFNβ production and cellular antiviral response by inhibiting CMA-mediated degradation of STING and TBK1. Based on these observations, further in vivo experiments confirmed that the LAMP2A loss combined with PD-1 monoclonal antibodies significantly stimulated the activation of infiltrating CD8+ T cells, thereby inhibiting tumor growth. Also, non-responder head and neck squamous cell carcinoma (HNSCC) patients undergoing neoadjuvant immuno-chemotherapy had higher levels of LAMP2A and lower levels of PD-L1 expression in their tumor tissues. Conclusions: Our study has revealed a prospective combination therapy, in which diclofenac functioning as a LAMP2A inhibitor, enhances the anti-tumor efficacy of PD-1 monoclonal antibody by inhibiting the degradation of STING and TBK1.

The cGAS-STING pathway activates transcription factor TFEB to stimulate lysosome biogenesis and pathogen clearance

Induction of autophagy is an ancient function of the cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway through which autophagic cargoes are delivered to lysosomes for degradation. However, whether lysosome function is also modulated by the cGAS-STING pathway remains unknown. Here, we discovered that the cGAS-STING pathway upregulated lysosomal activity by stimulating lysosome biogenesis independently of the downstream protein kinase TANK-binding kinase 1 (TBK1). STING activation enhanced lysosome biogenesis through inducing the nuclear translocation of transcription factor EB (TFEB) as well as its paralogs transcription factor E3 (TFE3) and microphthalmia-associated transcription factor (MITF). STING-induced lipidation of GABA type A receptor-associated protein (GABARAP), an autophagy-related protein, on STING vesicles was responsible for TFEB activation. Membrane-bound GABARAP sequestered the GTPase-activating protein folliculin (FLCN) and FLCN-interacting protein (FNIP) complex to block its function toward the Rag GTPases Ras-related GTP-binding C and D (RagC and RagD), abolishing mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent phosphorylation and inactivation of TFEB. Functionally, STING-induced lysosome biogenesis within cells facilitated the clearance of cytoplasmic DNA and invading pathogens. Thus, our findings reveal that induction of lysosome biogenesis is another important function of the cGAS-STING pathway.

Lysosomal control of the cGAS-STING signaling

The cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway has a crucial role in combating pathogen infection. However, its aberrant activation is involved in several human disorders. Lysosomes are emerging as key negative regulators of cGAS-STING signaling. Here, we discuss the lysosomal control of cGAS-STING signaling and its implication in human disorders.

Macrophage Perspectives in Liver Diseases: Programmed Death, Related Biomarkers, and Targeted Therapy

Macrophages, as important immune cells of the organism, are involved in maintaining intrahepatic microenvironmental homeostasis and can undergo rapid phenotypic changes in the injured or recovering liver. In recent years, the crucial role of macrophage-programmed cell death in the development and regression of liver diseases has become a research hotspot. Moreover, macrophage-targeted therapeutic strategies are emerging in both preclinical and clinical studies. Given the macrophages' vital role in complex organismal environments, there is tremendous academic interest in developing novel therapeutic strategies that target these cells. This review provides an overview of the characteristics and interactions between macrophage polarization, programmed cell death, related biomarkers, and macrophage-targeted therapies. It aims to deepen the understanding of macrophage immunomodulation and molecular mechanisms and to provide a basis for the treatment of macrophage-associated liver diseases.

6PPD induced cardiac dysfunction in zebrafish associated with mitochondrial damage and inhibition of autophagy processes

The compound 6PPD is widely acknowledged for its antioxidative properties; however, concerns regarding its impact on aquatic organisms have spurred comprehensive investigations. In our study, we advanced our comprehension by revealing that exposure to 6PPD could induce cardiac dysfunction, myocardial injury and DNA damage in adult zebrafish. Furthermore, our exploration unveiled that the exposure of cardiomyocytes to 6PPD resulted in apoptosis and mitochondrial injury, as corroborated by analyses using transmission electron microscopy and flow cytometry. Significantly, our study demonstrated the activation of the autophagy pathway in both the heart of zebrafish and cardiomyocytes, as substantiated by transmission electron microscopy and immunofluorescent techniques. Importantly, the increased the expression of P62 in the heart and cardiomyocytes suggested an inhibition of the autophagic process. The reduction in autophagy flux was also verified through in vivo experiments involving the infection of mCherry-GFP-LC3. We further identified that the fusion of autophagosomes and lysosomes was impaired in the 6PPD treatment group. In summary, our findings indicated that the impaired fusion of autophagosomes and lysosomes hampered the autophagic degradation process, leading to apoptosis and ultimately resulting in cardiac dysfunction and myocardial injury. This study discovered the crucial role of the autophagy pathway in regulating 6PPD-induced cardiotoxicity. SYNOPSIS: 6PPD exposure inhibited the autophagic degradation process and induced mitochondrial injury and apoptosis in the heart of adult zebrafish.