Involvement of acetylation of ATG4B in controlling autophagy induction

ATG4B, a cysteine protease promoting autophagosome formation by reversibly modifying Atg8-family proteins, plays a vital role in controlling macroautophagy/autophagy initiation in response to stress. However, the molecular mechanism underlying the regulation of ATG4B activity is far from well elucidated. In the current study, we firstly revealed that the acetylation level of ATG4B at lysine residue 39 (K39) is strongly involved in regulating its activity and autophagy. Specifically, SIRT2 deacetylates ATG4B K39, enhancing ATG4B activity and autophagic flux, which can be antagonized by EP300/p300. Starvation treatment contributes to EP300 suppression and SIRT2 activation, promoting the deacetylation of ATG4B K39, which leads to the elevation of ATG4B activity and finally autophagy initiation. Mechanistic investigation showed that starvation reduces CCNE (cyclin E), resulting in the downregulation of the CCNE-CDK2 protein complex, decreasing the phosphorylation of SIRT2 Ser331 and finally activating SIRT2. In addition, we confirmed that SIRT2 promotes autophagy via suppressing acetylation of ATG4B at K39 using sirt2 gene knockout (sirt2^-/-) mice. Collectively, our results have revealed the acetylation-mediated regulation of ATG4B cysteine protease activity in autophagy initiation in response to nutritional deficiency.