Trs20, Trs23, Trs31 and Bet5 participate in autophagy through GTPase Ypt1 in Saccharomyces cerevisiae

Abstract

TRAPP (transport protein particle) is a large, highly conserved, multi-subunit complex. Four types of TRAPP complexes (I, II, III and most recently IV) have been identified in Saccharomyces cerevisiae. Studies on the roles of TRAPP II, TRAPP III and TRAPP IV specific subunits (Trs130, Trs85 and Trs33) have demonstrated that TRAPP II, TRAPP III and TRAPP IV activate the small GTPases that regulate autophagy. Up to now, the roles of the common TRAPP subunits have been well studied in vesicle transport. However, the roles of the common TRAPP subunits and their relationship to Ypt/Rab GTPases in autophagy are not clear. In this paper, we examined Trs20, Trs23, Trs31, and Bet5 (the common TRAPP subunits), which are required for starvation-induced autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway. During autophagy, GFP-Atg8 accumulates as single or multiple dots and is not recruited into the pre-autophagosomal structures (PAS) in trs20ts, trs23ts, trs31ts and bet5ts mutant cells. Furthermore, these dots are linked to the endoplasmic reticulum in mutant cells. Additionally, overexpression of Ypt1, but not Ypt31, suppresses the autophagy defect in trs20ts, trs23ts, trs31ts and bet5ts mutant cells. Based on these results, we concluded that Trs20, Trs23, Trs31, and Bet5 are required for autophagy, and that these common TRAPP subunits regulate autophagy partially through GTPase Ypt1, but not Ypt31.

Keywords

• autophagy
• TRAPP
• common TRAPP subunits
• Ypt1
• Ypt31