Serine/threonine kinase which acts as an essential component of the MAP kinase signal transduction pathway. Plays an important role in the cascades of cellular responses evoked by changes in the environment. Mediates signal transduction of TRAF6, various cytokines including interleukin-1 (IL-1), transforming growth factor-beta (TGFB), TGFB-related factors like BMP2 and BMP4, toll-like receptors (TLR), tumor necrosis factor receptor CD40 and B-cell receptor (BCR) (PubMed:10748100, PubMed:16157589, PubMed:21183079, PubMed:29291351). Ceramides are also able to activate MAP3K7/TAK1. Once activated, acts as an upstream activator of the MKK/JNK signal transduction cascade and the p38 MAPK signal transduction cascade through the phosphorylation and activation of several MAP kinase kinases like MAP2K1/MEK1, MAP2K3/MKK3, MAP2K6/MKK6 and MAP2K7/MKK7. These MAP2Ks in turn activate p38 MAPKs, c-jun N-terminal kinases (JNKs) and I-kappa-B kinase complex (IKK). Both p38 MAPK and JNK pathways control the transcription factors activator protein-1 (AP-1), while nuclear factor-kappa B is activated by IKK (PubMed:16157589, PubMed:8533096, PubMed:29291351). MAP3K7 activates also IKBKB and MAPK8/JNK1 in response to TRAF6 signaling and mediates BMP2-induced apoptosis (PubMed:10748100). In osmotic stress signaling, plays a major role in the activation of MAPK8/JNK1, but not that of NF-kappa-B. Promotes TRIM5 capsid-specific restriction activity (By similarity). Phosphorylates RIPK1 at 'Ser-321' which positively regulates RIPK1 interaction with RIPK3 to promote necroptosis but negatively regulates RIPK1 kinase activity and its interaction with FADD to mediate apoptosis (PubMed:28842570). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by pro-inflammatory cytokines and in response to physical and chemical stresses, including osmotic stress, oxidative stress, arsenic and ultraviolet light irradiation. Activated by 'Lys-63'-linked polyubiquitination and by autophosphorylation. Association with TAB1/MAP3K7IP1 and TAB2/MAP3K7IP2 promotes activation through autophosphorylation, whereas PPM1B/PP2CB, PP2A and PPP6C dephosphorylation leads to inactivation. Can form homodimer (By similarity). Binds both upstream activators and downstream substrates in multimolecular complexes (By similarity). Interacts with TAB1/MAP3K7IP1, TAB2/MAP3K7IP2 and TAB3/MAP3K7IP3 (By similarity). Identified in the TRIKA2 complex composed of MAP3K7/TAK1, TAB1/MAP3K7IP1 and TAB2/MAP3K7IP2 (By similarity). Interacts with PPM1L and PPM1B/PP2CB (PubMed:12556533). Interaction with PP2A and PPP6C leads to its repressed activity (By similarity). Interacts with TRAF6 and TAB1/MAP3K7IP1; during IL-1 signaling (By similarity). Interacts with TAOK1 and TAOK2; interaction with TAOK2 interferes with MAP3K7 interaction with IKKA, thus preventing NF-kappa-B activation (By similarity). Interacts with DYNC2I2 (via WD domains) (By similarity). Interacts with CYLD and RBCK1 (PubMed:17548520). Interacts with TGFBR1; induces MAP3K7/TAK1 activation by TRAF6 (By similarity). Interacts with MAPK8IP1 and SMAD6 (PubMed:10748100, PubMed:17709393). Interacts with isoform 1 of VRK2 (PubMed:17709393). Interacts with DAB2; the interaction is induced by TGF-beta stimulation and may mediate TGF-beta stimulated JNK activation (By similarity). Interacts with TRIM5 (By similarity). Part of a complex containing ITCH, NDFIP1 and MAP3K7 (PubMed:25632008). Interacts with PLEKHM1 (via N- and C-terminus) (PubMed:27777970). Interacts with TRIM8 (By similarity). Found in a complex with SH3RF1, RAC2, MAP2K7/MKK7, MAPK8IP1/JIP1, MAPK8/JNK1 and MAPK9/JNK2 (PubMed:27084103). Interacts with SASH1 (By similarity). Interacts with RIPK1 (PubMed:31519887). Although the majority of MAP3K7/TAK1 is found in the cytosol, when complexed with TAB1/MAP3K7IP1 and TAB2/MAP3K7IP2, it is also localized at the cell membrane. Association with TAB1/MAP3K7IP1 promotes autophosphorylation and subsequent activation. Association with TAB2/MAP3K7IP2, itself associated with free unanchored Lys-63 polyubiquitin chain, promotes autophosphorylation and subsequent activation of MAP3K7. Dephosphorylation at Thr-187 by PP2A and PPP6C leads to inactivation (By similarity). 'Lys-48'-linked polyubiquitination at Lys-72 is induced by TNFalpha, and leads to proteasomal degradation (PubMed:16157589). Undergoes 'Lys-48'-linked polyubiquitination catalyzed by ITCH (PubMed:25632008). 'Lys-63'-linked polyubiquitination at Lys-158 by TRIM8 does not lead to proteasomal degradation but contributes to autophosphorylation and activation. Deubiquitinated by CYLD, a protease that selectively cleaves 'Lys-63'-linked ubiquitin chains (PubMed:17548520, PubMed:29291351). Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.