Alpha-Arrestin Regulation Of Autophagy

Cells adapt to changes in their environment through a selective relocalization of their proteome. This reorganization is imperative for cell survival and is regulated, in part, by a highly conserved family of protein trafficking adapters called the α-arrestins. To help us identify specific regulators of the α-arrestins and to aid in defining new α-arrestin functions, we generated and utilized the Saccharomyces cerevisiae Ubiquitin Interactome (ScUbI) library, a unique subset of the deletion collection that contains knockout strains for all non-essential genes annotated as being important for ubiquitination or ubiquitin interaction. We used this library to screen for factors that altered the ability of α-arrestins to confer resistance to the TORC1-inhibiting drug, rapamycin, and found that the most enriched functional category from the screen to be the autophagy gene family, or ATG genes. The ATG genes encode the machinery or regulators of the self-degradative process of autophagy, which is the process whereby cells recycle damaged components or reclaim nutrients during starvation. Defects in autophagy are linked to many human diseases, neurodegenerative diseases, cancer, and most notably aging. We have defined a genetic network that links α-arrestins to autophagy. To elucidate the functional connections between α-arrestins to this pathway, we employed live cell imaging and biochemical analyses with GFP-Atg8 and Pho8∆60, each of which are established readouts of autophagic flux, and demonstrate that this is impaired in the absence of select α-arrestins. Electron micrographs suggest a defect in autophagosome biogenesis associated with the loss of α-arrestins, further supported by biochemical and live-cell imaging experiments. How then does loss of α-arrestins lead to impaired autophagosome production? We find defects in lipid droplet maintenance in α-arrestin mutants suggesting the balance of neutral lipids, a key source of membrane during autophagosome biogenesis, is disrupted when α-arrestins are lost. These data support an exciting novel role for α-arrestins as regulators of autophagy, expanding their known suite of functions in sensing and responding to nutrient stress.