Targeted disruption of the MKK4 gene causes embryonic death, inhibition of c-Jun NH2-terminal kinase activation, and defects in AP-1 transcriptional activity

MKK4 is a member of the mitogen-activated protein kinase kinase group of dual specificity protein kinases that functions as an activator of the c-Jun NH2-terminal kinase (JNK) in vitro. To examine the function of MKK4 in vivo, we investigated the effect of targeted disruption of the MKK4 gene, Crosses of heterozygous MKK4 (+/-) mice demonstrated that homozygous knockout (-/-) animals die before embryonic day 14, indicating that the MKK4 gene is required for viability, The role of MKK4 in JNK activation was examined by investigation of cultured MKK4 (+/+) and MKK4 (-/-) cells, Disruption of the MKK4 gene blocked JNK activation caused by: (i) the mitogen-activated protein kinase kinase kinase MEKK1, and (ii) treatment with anisomycin or heal shock, In contrast, JNK activation caused by other fornls of environmental stress (UV-C radiation and osmotic shock) was partially inhibited in MKK4 (-/-) cells, Regulated AP-I transcriptional activity, a target of the JNK signal transduction pathway, was also selectively blocked in MKK4 (-/-) cells, Complementation studies demonstrated that the defective AP-1 transcriptional activity was restored by transfection of MKK4 (-/-) tells with an MKK4 expression vector, These data establish that MKK4 is a JNK activator in vivo and demonstrate that MKK4 is an essential component of the JNK signal transduction pathway.