Adapter protein that plays essential roles in both innate and adaptive immunity. Plays a crucial role in the regulation of thymocyte development (PubMed:26195727). Mechanistically, mediates TCR-stimulated activation through recruiting MAP2K1/MEK1 to the Golgi and, thereby, facilitating the interaction of MAP2K1/MEK1 with its activator BRAF (PubMed:26195727). Also plays an essential role in regulatory T-cell stability and function by recruiting the serine-threonine phosphatase catalytic subunit (PPP2CA) to the lysosome, thereby facilitating the interaction of PP2Ac with the mTORC1 component RPTOR and restricting glycolytic metabolism (PubMed:30115741). Positively regulates TLR4 signaling activity in macrophage-mediated inflammation by acting as a molecular clamp to facilitate LPS-induced translocation of TLR4 to lipid rafts (PubMed:30115741). In response to viral infection, facilitates the recruitment of TRAF3 to MAVS within mitochondria leading to IRF3 activation and interferon production (PubMed:30115741). However, participates in the maintenance of immune homeostasis and the prevention of overzealous innate immunity by promoting 'Lys-48'-dependent ubiquitination of TBK1 (By similarity). Interacts (via its coiled-coil domain) with TRAF3 (via isoleucine zipper). Interacts with MAP2K1 (By similarity). Interacts with PPP2CA; this interaction targets PPP2CA to the lysosomes (By similarity). Interacts with MAVS (By similarity). Interacts with TBK1 (By similarity). Accumulates on the mitochondria after virus infection. Expressed in bone marrow, spleen and thymus. Not detected in heart, kidney and liver. Knockout mice have considerably lower frequencies of CD4(+) and CD8(+) single positive thymocytes, and concomitantly higher frequencies of double positive thymocytes (PubMed:26195727). TRAF3IP3 deletion also affects regulatory T-cell transcriptional programs and stability (PubMed:30115741). In addition, mice show a severely compromised potential to induce interferon production and are vulnerable to RNA virus infection (PubMed:31390091). Sequencing errors.