Differential activation of mitogen-activated protein kinases by palytoxin and ouabain, two ligands for the Na+,K+-ATPase.
We previously demonstrated that the marine toxin and skin tumor promoter palytoxin activates the stress-activated protein kinase/c-Jun N-terminal kinase (JNK), but not the extracellular signal-regulated kinase (ERK), which is typically activated by mitogenic agents. JNK, ERK, and p38, another stress-activated protein kinase, are members of the mitogen-activated protein (MAP) kinase family of serine/threonine kinases, which coordinate the transmission of various signals through the cell. The Na+,K+-ATPase is the putative palytoxin receptor. Therefore, we hypothesized that the Na+,K+-ATPase inhibitor ouabain might also stimulate signaling pathways that activate MAP kinases. Using HeLa and COS7 cells, we found that, although there are similarities between the protein kinase cascades by which palytoxin and ouabain activate JNK, there are also significant differences between the activation of specific MAP kinases by palytoxin and ouabain. Transient expression of dominant negative mutants indicates that ouabain, like palytoxin, activates JNK through a protein kinase cascade that involves the JNK kinase SEK1 but does not require the GTPase Ras. Palytoxin activates JNK and p38 to a greater extent than ouabain. By contrast, ouabain activates ERK to a greater extent than palytoxin. Ouabain blocked palytoxin-stimulated activation of JNK and p38, but not anisomycin-stimulated activation of these kinases, supporting the conclusion that ouabain and palytoxin bind to the same site on the Na+,K+-ATPase. These results suggest that the Na+,K+-ATPase can differentially mediate the activation of MAP kinases by two diverse ligands, palytoxin and ouabain.
Li
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School of Public Health, University of Minnesota, Minneapolis 55455, USA.
Wattenberg
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D000178:Acrylamides / Q000494:pharmacology*; D000818:Animals; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003064:Cnidarian Venoms; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases; D008024:Ligands; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D010042:Ouabain / Q000494:pharmacology*; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins / Q000378:metabolism; D000095702:Polyether Toxins
D000178:Acrylamides; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D003064:Cnidarian Venoms; D004791:Enzyme Inhibitors; D048031:JNK Mitogen-Activated Protein Kinases; D008024:Ligands; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D010042:Ouabain; D011494:Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase; D048051:p38 Mitogen-Activated Protein Kinases; D018631:ras Proteins; C482559:MAP2K4 protein, human; C010272:palytoxin; D000095702:Polyether Toxins