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, TRAF3, TRAF5, TRAF6, IKKA and NF-kappa-B2/P100. Interacts with PELI3. Interacts with NIBP; the interaction is direct. Interacts with ARRB1 and ARRB2. Interacts with GRB10. Interacts with ZFP91 (By similarity). Interacts with NLRP12; this interaction promotes proteasomal degradation of MAP3K14. Directly interacts with DDX3X (By similarity). Interacts (via C-terminus and kinase domain) with PPPC3A (via N-terminus) and PPP3CB (PubMed:26029823). Phosphorylation at Thr-561 is required to activates its kinase activity and 'Lys-63'-linked polyubiquitination. Phosphorylated by CHUK/IKKA leading to MAP3K14 destabilization (By similarity). Autophosphorylated. 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 (By similarity). Mice display the alymphoplasia phenotype (aly), which is characterized by systemic absence of lymph nodes and Peyer patches and disorganized splenic and thymic structures with immunodeficiency. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.