Synonyms:IC53, Background:Probable tumor suppressor initially identified as a CDK5R1 interactor controlling cell proliferation(PubMed:12054757, PubMed:12737517). Negatively regulates NF-kappa-B-mediated gene transcription through the control of RELA phosphorylation(PubMed:17785205, PubMed:20228063). Also regulates mitotic G2/M transition checkpoint and mitotic G2 DNA damage checkpoint(PubMed:15790566, PubMed:19223857). Through its interaction with CDKN2A/ARF and MDM2 may induce MDM2-dependent p53/TP53 ubiquitination, stabilization and activation in the nucleus, thereby promoting G1 cell cycle arrest and inhibition of cell proliferation(PubMed:16173922). May play a role in the unfolded protein response, mediating the ufmylation of multiple proteins in response to endoplasmic reticulum stress(PubMed:23152784). May also play a role in the rupture of the nuclear envelope during apoptosis(PubMed:23478299). May regulate MAPK14 activity by regulating its dephosphorylation by PPM1D/WIP1(PubMed:21283629). (Microbial infection) May be negatively regulated by hepatitis B virus large envelope protein mutant pre-s2 to promote mitotic entry.