Plays a role in intracellular protein trafficking and degradation (PubMed:11707463, PubMed:14570915, PubMed:15358775). May regulate CFTR chloride currents and acid-induced ASIC3 currents by modulating cell surface expression of both channels (By similarity). May also regulate the intracellular trafficking of the ADR1B receptor (PubMed:15358775). May play a role in autophagy (By similarity). Together with MARCHF2 mediates the ubiquitination and lysosomal degradation of CFTR (PubMed:23818989). Overexpression results in CFTR intracellular retention and lysosomaldegradation in the lysosomes (PubMed:11707463, PubMed:14570915). Homooligomer (By similarity). Interacts with FZD5 (By similarity). Interacts with FZD8 (PubMed:16882988). Interacts with GRID2 and BECN1 (By similarity). Interacts with CSPG5 (By similarity). Interacts with CLCN3 (By similarity). Interacts with STX6 (PubMed:11384996). Interacts with CFTR (PubMed:11707463). Interacts with ASIC3 (PubMed:15317815). Interacts with GOLGA3 (PubMed:15951434). Interacts with NLGN1 (PubMed:16882988). Interacs with RHOQ (PubMed:15546864). Interacts with MARCHF2; the interaction leads to CFTR ubiquitination and degradation (PubMed:23818989). Interacts with ADRB1 (PubMed:15358775). May interact with CACNG2 (By similarity). Enriched in synaptosomal and postsynaptic densities (PSD) fractions. Expressed in cell bodies and dendrites of Purkinje cells. Localized at the trans-Golgi network (TGN) of spermatids and the medulla of round spermatides. Ubiquitously expressed. The PDZ domain mediates interactions with FZD5, FZD8, ASIC3, GRID2, CLCN3 (By similarity). Mediates also interaction with CFTR and ADRB1. The coiled-coil region probably mediates association to membranes, targeting to the Golgi, and interactions with GOLGA3, and STX6. May also mediate interaction with RHOQ (By similarity). A chromosomal aberration involving GOPC is found in a glioblastoma multiforme sample. An intra-chromosomal deletion del(6)(q21q21) is responsible for the formation of GOPC-ROS1 chimeric protein which has a constitutive receptor tyrosine kinase activity.