Acts as a synapse-to-nucleus messenger to promote NMDA receptor-mediated excitotoxicity in neurons in a JUN-dependent manner (By similarity). 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 (PubMed:21460222). Might promote apoptosis in T cells (PubMed:21460222). Forms a complex with NMDA receptor zeta subunit GRIN1 and epsilon subunit GRIN2B (PubMed:27458189). Interacts with GRIN1 and GRIN2B (PubMed:27458189). The interaction with GRIN1 is reduced upon NMDA receptor activity (By similarity). Found in a postsynaptic membrane complex with DLG4 and GRIN1 (By similarity). Interacts with DLG4 (via PDZ3 domain and to lesser degree via PDZ2 domain) (By similarity). Found in a complex with JUN and FBXW7 (PubMed:27458189). Interacts with JUN and FBXW7; the interaction inhibits ubiquitination-mediated JUN degradation promoting its phosphorylation and transcriptional activity (PubMed:27458189). Interacts with SRC (PubMed:21460222). Enriched in postsynaptic plasma membrane and postsynaptic densities (PSD). Accumulates in spines along with synapse maturation and colocalizes with DLG4 in a punctate pattern. Translocates from synapses to nuclei following NMDA receptor activity (By similarity). Strongly expressed in brain tissue including the hippocampus, and moderately expressed in esophagus, trachea, lung, ovary, cervix, prostate, testes, thyroid, thymus, lymph nodes and peripheral blood lymphocytes. Up-regulated in peripheral blood leukocytes in response to T-cell receptor stimulation. Palmitoylated. Tyrosine phosphorylated, possibly by SRC.