MLK-3 activates the SAPK/JNK and p38/RK pathways via SEK1 and MKK3/6.
Mixed lineage kinase-3 (MLK-3) is a 97 kDa serine/threonine kinase with multiple interaction domains, including a Cdc42 binding motif, but unknown function. Cdc42 and the related small GTP binding protein Rac1 can activate the SAPK/JNK and p38/RK stress-responsive kinase cascades, suggesting that MLK-3 may have a role in upstream regulation of these pathways. In support of this role, we demonstrate that MLK-3 can specifically activate the SAPK/JNK and p38/RK pathways, but has no effect on the activation of ERKs. Immunoprecipitated MLK-3 catalyzed the phosphorylation of SEK1 in vitro, and co-transfected MLK-3 induced phosphorylation of SEK1 and MKK3 at sites required for activation, suggesting direct regulation of these protein kinases. Furthermore, interactions between MLK-3 and SEK and MLK-3 and MKK6 were observed in co-precipitation experiments. Finally, kinase-dead mutants of MLK-3 blocked activation of the SAPK pathway by a newly identified mammalian analog of Ste20, germinal center kinase, but not by MEKK, suggesting that MLK-3 functions to activate the SAPK/JNK and p38/RK cascades in response to stimuli transduced by Ste20-like kinases.
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LA
Ontario Cancer Institute, Toronto, Canada.
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Y L
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Kiefer
F
F
Chan
J
J
Iscove
N
N
Woodgett
J R
JR
Lassam
N J
NJ
D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048670:MAP Kinase Kinase 4; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D000097767:Mitogen-Activated Protein Kinase Kinase Kinase 11
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048670:MAP Kinase Kinase 4; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D000097767:Mitogen-Activated Protein Kinase Kinase Kinase 11; C482530:MAP2K3 protein, human; C482559:MAP2K4 protein, human