During macroautophagy, conjugation of ATG12 to ATG5 is essential for LC3 lipidation and autophagosome formation. Additionally, ATG12 has ATG5-independent functions in diverse processes including ...mitochondrial fusion and mitochondrial-dependent apoptosis. In this study, we investigated the regulation of free ATG12. In stark contrast to the stable ATG12-ATG5 conjugate, we find that free ATG12 is highly unstable and rapidly degraded in a proteasome-dependent manner. Surprisingly, ATG12, itself a ubiquitin-like protein, is directly ubiquitinated and this promotes its proteasomal degradation. As a functional consequence of its turnover, accumulation of free ATG12 contributes to proteasome inhibitor-mediated apoptosis, a finding that may be clinically important given the use of proteasome inhibitors as anticancer agents. Collectively, our results reveal a novel interconnection between autophagy, proteasome activity, and cell death mediated by the ubiquitin-like properties of ATG12.
Cancer cells rely on lysosome-dependent degradation to recycle nutrients that serve their energetic and biosynthetic needs. Despite great interest in repurposing the antimalarial hydroxychloroquine ...as a lysosomal inhibitor in clinical oncology trials, the mechanisms by which hydroxychloroquine and other lysosomal inhibitors induce tumor-cell cytotoxicity remain unclear. In this issue of theJCI, Bhardwaj et al. demonstrate that DC661, a dimeric form of chloroquine that inhibits palmitoyl-protein thioesterase 1 (PPT1), promoted lysosomal lipid peroxidation, resulting in lysosomal membrane permeabilization and tumor cell death. Remarkably, this lysosomal cell death pathway elicited cell-intrinsic immunogenicity and promoted T lymphocyte-mediated tumor cell clearance. The findings provide the mechanistic foundation for the potential combined use of immunotherapy and lysosomal inhibition in clinical trials.
Autophagy is an evolutionarily conserved lysosomal degradation process that is crucial for adaptation to stress as well as in cellular homeostasis. In cancer, our current understanding has uncovered ...multifaceted roles for autophagy in tumor initiation and progression. Although genetic evidence corroborates a critical role for autophagy as a tumor suppressor mechanism, autophagy can also promote the survival and fitness of advanced tumors subject to stress, which has important implications during breast cancer progression and metastasis. Here, I discuss the mechanisms and the evidence underlying these diverse roles for autophagy in cancer and speculate on specific circumstances in which autophagy can be most effectively targeted for breast cancer treatment.
The ubiquitin-like molecule ATG12 is required for the early steps of autophagy. Recently, we identified ATG3, the E2-like enzyme required for LC3 lipidation during autophagy, as an ATG12 conjugation ...target. Here, we demonstrate that cells lacking ATG12-ATG3 have impaired basal autophagic flux, accumulation of perinuclear late endosomes, and impaired endolysosomal trafficking. Furthermore, we identify an interaction between ATG12-ATG3 and the ESCRT-associated protein Alix (also known as PDCD6IP) and demonstrate that ATG12-ATG3 controls multiple Alix-dependent processes including late endosome distribution, exosome biogenesis and viral budding. Similar to ATG12-ATG3, Alix is functionally required for efficient basal, but not starvation-induced, autophagy. Overall, these results identify a link between the core autophagy and ESCRT machineries and uncover a role for ATG12-ATG3 in late endosome function that is distinct from the canonical role of either ATG in autophagosome formation.
Introduction: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a novel coronavirus (nCoV) that causes viral pneumonia known as Coronavirus Disease 2019 (COVID- 19). It can infect ...people of all age groups, and various clinical conditions are strong indicators of co-morbidities in COVID- 19. The presence of co-morbidities is crucial in determining the clinical outcome of coronavirus infections. Therefore, it is crucial to understand the demographic profile and associated risk factors of COVID-19 in this geographical region. Aim: To assess the association between SARS-CoV-2 infection and demographic characteristics and co-morbidities. Materials and Methods: A retrospective cohort study was conducted at the National Accreditation Board for Testing and Calibration Laboratories (NABL)-accredited Virology Service Laboratory (VSL) of Tripura Medical College and Dr. BR Ambedkar Memorial Teaching Hospital, Agartala, Tripura, India. All the required data was collected between May 2021 and October 2022, and data analysis was carried out from February to March 2023. After obtaining Indian Council of Medical Research (ICMR) approval, real-time Reverse Transcriptase-Polymerase Chain Reaction (rRT-PCR) was used for the detection of SARS-CoV-2 RNA. A total of 10,263 samples were included in the study. RNA extraction was performed using the viral Ribonucleic Acid (RNA) extraction Miniprep Kit protocol manufactured by MDI Membrane Technologies, and RT-PCR was conducted according to the Indian Council of Medical Research (ICMR)-approved DiAGSureTM nCoV-19 Detection Assay (Multiplex, TaqMan based) protocol developed by GCC BIOTECH. The findings were based on demographic parameters such as age group and gender distribution. Results were expressed as proportions and percentages, and statistical analysis was done by Chi-square test in Statistical Package for Social Sciences (SPSS) version 20.0. Results: Out of the 10,263 registered patients, 1471 (14.33%) were confirmed to have SARS-CoV-2 infection. The most affected age group was found to be between 21 and 40 years, with 524 (35.62%) cases. Males, 927 (63.02%) were more frequently infected than females, 544 (36.98%). Among all the SARS-CoV-2 infected patients, co-morbidities were found in 254 (17.26%) cases, and the association between co-morbidities and the rRT- PCR test results was found to be statistically significant, with a p-value=0.01. Conclusion: The highest number of SARS-CoV-2 patients were found in the age group of 21 to 40 years, predominantly among males. Patients with co-morbidities showed a significant association with SARS-CoV-2 infection. Diabetes was found to be the most prevalent risk factor among all the patients.
Su et al. demonstrate that upon inhibiting autophagy, an intracellular nutrient recycling pathway, pancreatic ductal adenocarcinoma cells upregulate NRF2-mediated transcription of macropinocytosis ...pathway components, thereby triggering an alternate route for tumors to scavenge nutrients from extracellular sources. Accordingly, the combined inhibition of autophagy and macropinocytosis may improve cancer treatment.
Su et al. demonstrate that upon inhibiting autophagy, an intracellular nutrient recycling pathway, pancreatic ductal adenocarcinoma cells upregulate NRF2-mediated transcription of macropinocytosis pathway components, thereby triggering an alternate route for tumors to scavenge nutrients from extracellular sources. Accordingly, the combined inhibition of autophagy and macropinocytosis may improve cancer treatment.
The molecular events regulating the elimination of cells to create a hollow lumen during tissue development are poorly understood. By using an in vitro morphogenesis model in which MCF-10A human ...mammary epithelial cells form hollow acini-like structures, we have observed both caspase-mediated apoptosis and autophagy associated with cells that are lost during lumen formation. Here, we show that the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mediates induction of autophagic processes associated with lumen formation. TRAIL is up-regulated during morphogenesis of MCF-10A mammary epithelial cells in 3D basement-membrane cultures and inhibition of TRAIL signaling during morphogenesis blocks the formation of autophagic vacuoles. In addition, treatment with exogenous TRAIL induces extensive autophagy in monolayer and 3D cultures. When combined with inhibition of caspase 3 activity (by Bcl- X L overexpression), inhibition of TRAIL-induced autophagy results in luminal filling. Thus, TRAIL regulates an autophagic program during acinar morphogenesis, which together with caspase-mediated apoptotic events, results in lumen formation during MCF-10A morphogenesis.
Autophagy promotes protein degradation, and therefore has been proposed to maintain amino acid pools to sustain protein synthesis during metabolic stress. To date, how autophagy influences the ...protein synthesis landscape in mammalian cells remains unclear. Here, we utilize ribosome profiling to delineate the effects of genetic ablation of the autophagy regulator, ATG12, on translational control. In mammalian cells, genetic loss of autophagy does not impact global rates of cap dependent translation, even under starvation conditions. Instead, autophagy supports the translation of a subset of mRNAs enriched for cell cycle control and DNA damage repair. In particular, we demonstrate that autophagy enables the translation of the DNA damage repair protein BRCA2, which is functionally required to attenuate DNA damage and promote cell survival in response to PARP inhibition. Overall, our findings illuminate that autophagy impacts protein translation and shapes the protein landscape.
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