Mitogen-activated protein kinase kinase kinase kinase 2, also known as B lymphocyte serine/threonine-protein kinase, Germinal center kinase, MAPK/ERK kinase kinase kinase 2, MEK kinase kinase 2, Rab8-interacting protein and MAP4K2, is a cytoplasm and peripheral membrane protein which belongs to the protein kinase superfamily, STE Ser/Thr protein kinase family and STE20 subfamily. MAP4K2 contains one CNH domain and one protein kinase domain. Although this kinase is found in many tissues, its expression in lymphoid follicles is restricted to the cells of germinal centre, where it may participate in B-cell differentiation. MAP4K2 can be activated by TNF-alpha, and has been shown to specifically activate MAP kinases. It is also found to interact with TNF receptor-associated factor 2 (TRAF2), which is involved in the activation of MAP3K1 / MEKK1. MAP4K2 enhances MAP3K1 oligomerization, which may relieve amino-terminal mediated MAP3K1 autoinhibition and lead to activation following autophosphorylation. It may also play a role in the regulation of vesicle targeting or fusion.