Plays a role in endoplasmic reticulum to Golgi apparatus trafficking at a very early stage (PubMed:21525244). Maintains together with TBC1D14 the cycling pool of ATG9 required for initiation of autophagy (PubMed:26711178). Involved in collagen secretion (PubMed:32095531). {ECO:0000269|PubMed:21525244, ECO:0000269|PubMed:26711178, ECO:0000269|PubMed:32095531}. This is the function of TRAPPC8 (trafficking protein particle complex subunit 8, Ensembl gene identifier ENSG00000153339).