Lymphotoxin beta-activated kinase which seems to be exclusively involved in the activation of NF-kappa-B and its transcriptional activity. Promotes proteolytic processing of NFKB2/P100, which leads to activation of NF-kappa-B via the non-canonical pathway. Could act in a receptor-selective manner. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with TRAF2, TRAF5, TRAF6, IKKA and NFKB2/P100 (By similarity). Interacts with TRAF3 and PELI3. Interacts with NIBP; the interaction is direct. Interacts with ARRB1 and ARRB2. Interacts with GRB10. Interacts with ZFP91. Interacts with NLRP12; this interaction promotes proteasomal degradation of MAP3K14. Directly interacts with DDX3X (PubMed:30341167). Interacts (via C-terminus and kinase domain) with PPPC3A (via N-terminus) and PPP3CB (By similarity). Weakly expressed in testis, small intestine, spleen, thymus, peripheral blood leukocytes, prostate, ovary and colon. Autophosphorylated. Phosphorylation at Thr-559 is required to activates its kinase activity and 'Lys-63'-linked polyubiquitination. Phosphorylated by CHUK/IKKA leading to MAP3K14 destabilization. Ubiquitinated. Undergoes both 'Lys-48'- and 'Lys-63'-linked polyubiquitination. 'Lys-48'-linked polyubiquitination leads to its degradation by the proteasome, while 'Lys-63'-linked polyubiquitination stabilizes and activates it. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.