ATG4B is a core protein and essential for cleaving precursor MAP1LC3/LC3 or deconjugating lipidated LC3-II to drive the formation of autophagosomes. The protein stability and activity of ATG4B regulated by post-translational modification (ubiquitination) will directly affect macroautophagy/autophagy. However, the mechanism involved in ATG4B ubiquitination is largely unclear. In this study, a new E3 ligase of ATG4B, UBE3C, was identified by mass spectra. UBE3C mainly assembles K33-branched ubiquitin chains on ATG4B at Lys119 without causing ATG4B degradation. In addition, the increased ubiquitination of ATG4B caused by UBE3C overexpression inhibits autophagy flux in both normal and starvation conditions, which might be due to the reduced activity of ATG4B and ATG4B-LC3 interaction. This reduction could be reversed once the lysine 119 of ATG4B was mutated to arginine. More important, under starvation conditions the interaction between ATG4B and UBE3C apparently decreased followed by the removal of the K33-branched ubiquitin chain of ATG4B. Thus, starvation-induced autophagy could be partially suppressed by an increased ubiquitination level of ATG4B. In conclusion, our research reveals a novel modification mode of ATG4B in which UBE3C can fine tune ATG4B activity by specific ubiquitination regulating autophagy without causing ATG4B degradation.
Ovarian aging is a natural process characterized by a decline in both the quantity and quality of oocytes, which subsequently leads to diminished fertility, particularly in women over the age of 35. Given the societal trend toward postponing childbirth, it is imperative to understand the molecular mechanisms that underpin ovarian aging to address infertility issues. Melatonin (MT) is recognized for its therapeutic potential in mitigating ovarian aging; however, the specific epigenetic mechanisms involved, particularly concerning m 6 A methylation, remain inadequately defined. Our investigation demonstrates that MT mitigates ovarian aging in murine models, significantly decreasing m 6 A methylation levels. In vitro analyses of ovarian granulosa (KGN) cells reveals a marked increase in YTHDF2 expression, with differentially methylated genes being notably enriched in the polyubiquitination pathway. Further examination shows that YTHDF2 enhances the expression of the E3 ligase UBE3C by modulating the m 6 A methylation of UBE3C mRNA, thereby reducing the expression of the P53 senescence factor and alleviating the effects of ovarian aging.
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