The function of TRAF1 (TNF receptor associated factor 1, Ensembl gene identifier ENSG00000056558) is as follows. Adapter molecule that is involved in multiple signaling pathways including the NF-kappa-B and MAPK pathways and thus influences inflammatory and apoptotic responses. Plays a critical role in regulating T-cell activation both through restricting the costimulation-independent activation of NIK in activated T-cells and by promoting the TNFRSF9-induced classical NF-kappa-B pathway (By similarity). Forms a heterotrimer with TRAF2 as part of an E3 ubiquitin-protein ligase complex that mediates ubiquitination of target proteins such as MAP3K14 and gasdermin D/GSDMD (PubMed:40097387). This complex also recruits the antiapoptotic E3 ligases BIRC2 and BIRC3 to TNFRSF1B/TNFR2 (PubMed:19287455). Acts downstream of MAVS within the RIG-I/MAVS antiviral pathway to enhance type I interferon signaling (PubMed:38995016). Regulates osteoclastogenesis by preventing ubiquitination and degradation of MLST8, thereby promoting PI3K-AKT signaling and enhancing oxidative phosphorylation in osteoclasts (By similarity). {ECO:0000250|UniProtKB:P39428, ECO:0000269|PubMed:10692572, ECO:0000269|PubMed:16323247, ECO:0000269|PubMed:18429822, ECO:0000269|PubMed:19287455, ECO:0000269|PubMed:19698991, ECO:0000269|PubMed:20385093, ECO:0000269|PubMed:38995016}. (Microbial infection) Amplifies LMP1-mediated MAP kinase and canonical NF-kappa-B pathway but not non-canonical NF-kappa-B pathway activity. .