Component of a protein kinase signal transduction cascade (PubMed:11784851). Activates the ERK and JNK kinase pathways by phosphorylation of MAP2K1 and MAP2K4 (PubMed:11784851). May phosphorylate the MAPK8/JNK1 kinase (By similarity). Activates CHUK and IKBKB, the central protein kinases of the NF-kappa-B pathway (PubMed:11784851). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by autophosphorylation on Thr-1381 and Thr-1393 following oligomerization. Binds both upstream activators and downstream substrates in multimolecular complexes through its N-terminus. Oligomerizes after binding MAP4K2 or TRAF2. Interacts (via the kinase catalytic domain) with STK38 (By similarity). Interacts with GRIPAP1 (PubMed:17761173). Most highly expressed in spleen, kidney and lung. Autophosphorylated. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.