Abstract

The Transport protein particle (TRAPP) complexes are molecular machines that function in various membrane transport processes including the secretory pathway. Recently, one form of the TRAPP complex, TRAPPIII, has been shown to be involved in autophagy, a cellular recycling process that delivers cytoplasmic components to lysosomes for degradation. Mutations in TrappC11, one subunit in TRAPPIII, have been reported to be associated with muscular dystrophy and intellectual disability. To understand mutated TrappC11 could lead to the phenotypes, I employed BioID to identify TrappC11 interacting proteins. To perform BioID, I constructed TrappC11 fused to BirA*, a biotin ligase that catalyzes the biotinylation of proteins within proximity to the fusion protein. The biotinylated proteins were then isolated and identified by mass spectrometry. The BioID approach revealed the autophagy-related proteins Atg2A, Atg2B, WDR45, p62/SQSTM1, and NBR1 as potential TrappC11 interacting partners, suggesting the involvement of TrappC11 in autophagy. Consistently, transient and stable knockdown of TrappC11 in HeLa cells both resulted in an accumulation of autophagosomes in non-starved cells as well as an increase of cellular lipid droplets. The distribution of lysosomes was also effected by the TrappC11 knockdown. Moreover, expression of eGFP-TrappC11 resulted in the formation of cytoplasmic puncta that partially overlapped with p62/SQSTM1, consistent with the BioID data that suggested an interaction between TrappC11 and this selective autophagy receptor. Taken together, my data indicate that TrappC11 might have an important role in non-starvation induced autophagy.