GSK3-TIP60-ULK1 Signaling Pathway Links Growth Factor Deprivation to Autophagy

Abstract

Acetylation and Autophagy Autophagy allows cells to digest their own components when necessary to survive stressful conditions. Lin et al. (p. 477) and Yi et al. (p. 474) describe signaling mechanisms in mammalian cells and yeast, respectively, by which autophagy is regulated by protein acetylation. In mammalian cells deprived of serum, the acetyltransferase TIP60 was activated by phosphorylation by the protein kinase GSK3 (glycogen synthase kinase 3). TIP60's target appeared to be a protein kinase central to autophagy regulation, ULK1. This activating pathway was required for autophagy in the absence of serum, but was not needed for autophagy in cells deprived of glucose. In the yeast Saccharomyces cerevisiae starved of nitrogen, another acetylation mechanism was uncovered. Starvation led to activation of the histone acetyltransferase Esa1, which acetylated the protein Atg3, a key component of the autophagy machinery, thus increasing its interaction with another autophagy protein, Atg8.