Acts as a synapse-to-nucleus messenger to promote NMDA receptor-mediated excitotoxicity in neurons in a JUN-dependent manner (PubMed:27458189). Inhibits ubiquitination-mediated degradation and promotes phosphorylation and transcriptional activity of transcription factor JUN (PubMed:27458189). Might play a redundant role in the regulation of T cell receptor signaling (By similarity). Might promote apoptosis in T cells (By similarity). Forms a complex with NMDA receptor zeta subunit GRIN1 and epsilon subunit GRIN2B (PubMed:27458189). Interacts with GRIN2B (PubMed:27458189). Interacts with GRIN1; the interaction is reduced upon NMDA receptor activity (PubMed:27458189). Found in a postsynaptic membrane complex with DLG4 and GRIN1 (PubMed:15629447, PubMed:27458189). Interacts with DLG4 (via PDZ3 domain and to lesser degree via PDZ2 domain) (PubMed:15629447, PubMed:27458189). Interacts with FBXW7 (PubMed:27458189). Found in a complex with JUN and FBXW7 (By similarity). Interacts with JUN and FBXW7; the interaction inhibits ubiquitination-mediated JUN degradation promoting its phosphorylation and transcriptional activity (By similarity). Interacts with SRC (By similarity). Enriched in postsynaptic plasma membrane and postsynaptic densities (PSD) (PubMed:15629447, PubMed:27458189). Accumulates in spines along with synapse maturation and colocalizes with DLG4 in a punctate pattern (PubMed:15629447). Translocates from synapses to nuclei following NMDA receptor activity (PubMed:27458189). Expressed in brain (PubMed:15629447, PubMed:27458189). Expressed in the cerebral cortex and especially in hippocampal neural cells (at protein level) (PubMed:15629447, PubMed:27458189). Expression detected at postnatal day 7 and expression increases until 4 weeks after birth. Palmitoylated. Tyrosine phosphorylated, possibly by SRC.