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). {ECO:0000250|UniProtKB:P0C6T3, ECO:0000250|UniProtKB:Q3V0I2, ECO:0000269|PubMed:21460222, ECO:0000269|PubMed:27458189}. This is the function of PRR7 (proline rich 7, synaptic, Ensembl gene identifier ENSG00000131188).