Associates with the adapter-like complex 4 (AP-4) and may therefore play a role in vesicular trafficking of proteins at the trans-Golgi network (PubMed:30262884). Signaling adapter which plays a role in neuronal differentiation (PubMed:15024033). Involved in regulation of NGF-dependent neurite outgrowth (PubMed:15024033). May play a role in neuronal vesicular trafficking, specifically involving pre-synaptic membrane proteins (By similarity). Seems to be involved in signaling pathways that are regulated by the prolonged activation of MAPK (PubMed:15024033). Can regulate the polyubiquitination of IKBKG and thus may be involved in regulation of the NF-kappa-B pathway (PubMed:19365808). {ECO:0000250|UniProtKB:Q8BG26, ECO:0000269|PubMed:15024033, ECO:0000269|PubMed:19365808, ECO:0000269|PubMed:30262884}. This is the function of RUSC1 (RUN and SH3 domain containing 1, ENSG00000160753).