Regulates the endosomal recycling back to the neuronal plasma membrane, possibly by connecting early and late recycling endosomal domains and promoting segregation of recycling endosomes from early endosomal membranes. Involved in the localization of recycling endosomes to dendritic spines, thereby playing a role in the maintenance of dendritic spine morphology. Required for the activity-induced AMPA receptor recycling to dendrite membranes and for long-term potentiation and synaptic plasticity. Functions as a scaffold protein in neurons to facilitate MAP3K1/MEKK1-mediated activation of the JNK1 kinase by phosphorylation, possibly by bringing MAP3K1/MEKK1 and JNK1 in close proximity. Interacts with GRIP1, GRIP2 and AMPA receptors (PubMed:10896157). Interacts (via C-terminus) with MAPK8/JNK1 and with MAP3K1/MEKK1; the interaction promotes MAP3K1-mediated phosphorylation of MAPK8 (PubMed:17761173). Interacts (via N-terminus) with RAB4A (in GTP-bound form) (PubMed:20098723). Interacts (via C-terminus) with STX12 (PubMed:20098723). Localizes to recycling endosomal tubules that are emanating from early endosomes. Expressed in the central nervous system; especially in neurons. Proteolytically cleaved by caspase-3 (PubMed:10896157). A minor C-terminal proteolytic fragment of 30 kDa is produced (PubMed:10896157). Proteolytic cleavage is required for JNK signaling activation (PubMed:17761173).