The kinases MEKK2 and MEKK3 regulate Transforming Growth Factor-β-mediated helper T cell differentiation

Mitogen-activated protein kinases (MAPKs) are key mediators of the T cell receptor (TCR) signals but their roles in T helper (Th) cell differentiation are unclear. Here we showed that the MAPK kinase kinases MEKK2 (encoded by Map3k2) and MEKK3 (encoded by Map3k3),negatively regulated transforming growth factor-beta (TGF-beta)-mediated Th cell differentiation.Map3k2-/-Map3k3Lck-Cre/- mice showed an abnormal accumulation of regulatory T (Treg) and Th17 cells in the periphery, consistent with Map3k2-/-Map3k3Lck-Cre/- naïve CD4+ T cells' differentiation into Treg and Th17 cells with a higher frequency than wild-type (WT) cells after TGF-beta stimulation in vitro. In addition, Map3k2-/-Map3k3Lck-Cre/- mice developed more severe experimental autoimmune encephalomyelitis. Map3k2-/-Map3k3Lck-Cre/- T cells exhibited impaired phosphorylation of the SMAD2 and SMAD3 proteins at their linker regions, which negatively regulated the TGF-beta responses in T cells. Thus, the crosstalk between TCR-induced MAPK and the TGF-beta signaling pathways is important in regulating Th cell differentiation. CD4+CD62L-CD44+ cells were FACS sorted from C57BL/6 Lck-Cre MEKK2 KO MEKK3F/-(dKO) or C57BL/6 WT mice