MEKK7, known as TAK1 for transforming growth factor (TGF) beta-activated kinase-1, is a MLK (MAP3K) type protein kinase which is associated with several signaling pathways. The protein contains a N-terminal protein kinase domain preceeded by a short regulatory motif and followed by a C-terminal extension of unknown function. TAK1 is activated by TGF beta and tumor necrosis factor (TNF). Further, TAK1 binding proteins, TAB-1 and -2, bind to the N-terminal regulatory motif and couple TAK1 to additional upstream signals, including the human X chromosome-linked inhibitor of apoptosis. TAK1 regulates the JNK cascade by phosphorylating MKK4/MAP2K4 and p38 cascades by phosphorylating MEK3/MAP2K3 and MKK6/MAP2K6. TAK1 also has been implicated in interleukin-1 (IL-1) signaling to JNKs via direct activation by IL-1 or by forming a complex with TRAF6, TAB1 and TAB2. At least four protein isoforms, resulting from alternatively spliced transcript variants, have been identified - 491, 518, 579 and 606 amino acids.Synonyms: Mitogen-activated protein kinase kinase kinase 7, TAK-1, TAK1, TGF-beta-activated kinase 1, Transforming growth factor-beta-activated kinase 1