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 th at homozygous knockout (-/-) animals die before embryonic day 14, indi cating 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 activat ion 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 ra diation 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 transcr iptional activity was restored by transfection of MKK4 (-/-) tells wit h an MKK4 expression vector, These data establish that MKK4 is a JNK a ctivator in vivo and demonstrate that MKK4 is an essential component o f the JNK signal transduction pathway.