Autophagy requires Tip20 in Saccharomyces cerevisiae

Autophagy is a highly conserved intracellular degradation pathway in eukaryotic cells that responds to environmental changes. Genetic analyses have shown that more than 40 autophagy-related genes (ATG) are directly involved in this process in fungi. In addition to Atg proteins, most vesicle transport regulators are also essential for each step of autophagy. The present study showed that one Endoplasmic Reticulum protein in Saccharomyces cerevisiae, Tip20, which controls Golgi-to-ER retrograde transport, was also required for starvation-induced autophagy under high temperature stress. In tip20 conditional mutant yeast, the transport of Atg8 was impaired during starvation, resulting in multiple Atg8 puncta dispersed outside the vacuole that could not be transported to the pre-autophagosomal structure/phagophore assembly site (PAS). Several Atg8 puncta were trapped in ER exit sites (ERES). Moreover, the GFP-Atg8 protease protection assay indicated that Tip20 functions before autophagosome closure. Furthermore, genetic studies showed that Tip20 functions downstream of Atg5 and upstream of Atg1, Atg9 and Atg14 in the autophagy pathway. The present data show that Tip20, as a vesicle transport regulator, has novel roles in autophagy.