Phosphorylation of OTUB1 promotes autophagy initiation under starvation.

Eukaryotes initiate autophagy in response to environmental challenges such as nutrient deprivation. However, the mechanisms governing autophagy initiation remain incompletely understood. Here, we demonstrated that OTUB1 phosphorylation plays a key role in starvation-induced autophagy initiation. Specifically, ERK phosphorylates OTUB1 at S118 during starvation. This phosphorylation enables competitive binding of ANXA2 to OTUB1, disrupting its interaction with TRIM29 and enhancing OTUB1 stability. Stabilized OTUB1 upregulated DEPTOR, thereby inhibiting mTOR and inducing autophagy. Furthermore, in vivo studies reveal that fasting-induced OTUB1-mTOR-autophagy axis counteracted Western diet-mediated mTOR activation by restoring ERK-dependent OTUB1 phosphorylation, ultimately ameliorating MASLD progression. Collectively, this study uncovers a phosphorylation-dependent regulatory mechanism controlling OTUB1's function in nutrient deficiency-triggered autophagy initiation, providing cellular and molecular evidence supporting the therapeutic potential of fasting in alleviating MASLD.