E3 ubiquitin-protein ligase that promotes the ubiquitination of various substrates (PubMed:23645206, PubMed:25165885). In turn, participates in the regulation of many biological processes including cell cycle, apoptosis, osteoclastogenesis as well as innate or adaptive immunity (PubMed:25165885, PubMed:28708287). Acts as negative regulator of NF-kappa-B-dependent transcription by promoting the ubiquitination and stabilization of the NF-kappa-B inhibitor TNFAIP3 (PubMed:25165885). May promote the ubiquitination of TRAF6 as well (PubMed:28708287). Acts also as a negative regulator of T-cell activation (PubMed:25165885). Inhibits cellular dsRNA responses and interferon production by targeting MAVS component for proteasomal degradation (PubMed:25165885). Ubiquitinates the CDK inhibitor CDKN1A leading to its degradationand probably also CDKN1B and CDKN1C (PubMed:23645206). This activity stimulates cell cycle G1-to-S phase transition and suppresses cellular senescence. May play a role in spermatogenesis. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with XAF1, the interaction increases XAF1 stability and proapoptotic effects, and may regulate IFN signaling. Expressed in numerous tissues, including skin, CD4 lymphocytes and dendritic cells. Highest levels in testis. Autoubiquitinated. Polyubiquitinated in the presence of E2 enzymes UBE2D1, UBE2D2 and UBE2D3, but only monoubiquitinated in the presence of UBE2E1.