title: MEK kinase 3 directly activates MKK6 and MKK7, specific activators of the p38 and c-Jun NH2-terminal kinases.
abstract: Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase kinase 3 (MEKK3) activates the c-Jun NH2-terminal kinase (JNK) pathway, although no substrates for MEKK3 have been identified. We have examined the regulation by MEKK3 of MAPK kinase 7 (MKK7) and MKK6, two novel MAPK kinases specific for JNK and p38, respectively. Coexpression of MKK7 with MEKK3 in COS-7 cells enhanced MKK7 autophosphorylation and its ability to activate recombinant JNK1 in vitro. MKK6 autophosphorylation and in vitro activation of p38alpha were also observed following coexpression of MKK6 with MEKK3. MEKK2, a closely related homologue of MEKK3, also activated MKK7 and MKK6 in COS-7 cells. Importantly, immunoprecipitates of either MEKK3 or MEKK2 directly activated recombinant MKK7 and MKK6 in vitro. These data identify MEKK3 as a MAPK kinase kinase specific for MKK7 and MKK6 in the JNK and p38 pathways. We have also examined whether MEKK3 or MEKK2 activates p38 in intact cells using MAPK-activated protein kinase-2 (MAPKAPK2) as an affinity ligand and substrate. Anisomycin, sorbitol, or the expression of MEKK3 in HEK293 cells enhanced MAPKAPK2 phosphorylation, whereas MEKK2 was less effective. Furthermore, MAPKAPK2 phosphorylation induced by MEKK3 or cellular stress was abolished by the p38 inhibitor SB-203580, suggesting that MEKK3 is coupled to p38 activation in intact cells.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester School of Medicine, P. O. Box 138, Medical Sciences Building, University Road, Leicester LE1 9HN, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Deacon
authors.forename: J L
authors.initials: JL
authors.lastname: Blank
mesh_terms: D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D048688:MAP Kinase Kinase 7; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D013012:Sorbitol / Q000494:pharmacology; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D013012:Sorbitol; D000841:Anisomycin; D011494:Protein Kinases; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D048688:MAP Kinase Kinase 7; C482530:MAP2K3 protein, human; C482566:MAP2K6 protein, human; C482569:MAP2K7 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases