Regulation of a c-Jun Amino-terminal Kinase/Stress-activated Protein Kinase Cascade by a Sodium-dependent Signal Transduction Pathway

doi:10.1074/jbc.272.38.23905

Regulation of a c-Jun Amino-terminal Kinase/Stress-activated Protein Kinase Cascade by a Sodium-dependent Signal Transduction Pathway*

From the ^‡Division of Environmental and Occupational Health, School of Public Health, University of Minnesota, Minneapolis, Minnesota 55455, the ^§Department of Biological Sciences, Columbia University, New York, New York 10027, and the ^¶Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138

Abstract

Palytoxin is a novel skin tumor promoter that does not activate protein kinase C. Previous studies demonstrated that palytoxin stimulates a sodium-dependent signaling pathway that activates the c-Jun NH₂-terminal kinase/stress-activated protein kinase (JNK) in Swiss 3T3 fibroblasts. In this study we show that a JNK kinase known as the stress-activated protein kinase/extracellular signal-regulated kinase-1 (SEK1) plays an important role in the regulation of JNK by palytoxin. We found that palytoxin stimulates the sustained activation of both JNK and SEK1 in COS7 and HeLa cells. Transiently expressed SEK1 isolated from palytoxin-treated cells can phosphorylate and activate JNK, which, in turn, can phosphorylate c-Jun. Furthermore, expression of a dominant negative mutant of SEK1 blocks activation of JNK by palytoxin. Sodium appears to play an important role in the regulation of JNK and SEK1 by palytoxin. Activation of JNK and SEK1 by palytoxin, but not anisomycin, requires extracellular sodium. Complementary studies showed that the sodium ionophore gramicidin can mimic palytoxin by regulating JNK and SEK1 through a sodium-dependent mechanism. Collectively, these results demonstrate that palytoxin stimulates a sodium-dependent signaling pathway that activates the SEK1/JNK/c-Jun protein kinase cascade.

Footnotes

↵* This work was supported in part by National Institutes of Health Grant CA 72498-01, a Pharmaceutical Research and Manufacturers of America Foundation Research Starter Grant, and funds from the Grant-in-Aid program of the Office of the Vice President for Research at the University of Minnesota.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‖ To whom correspondence should be addressed: Division of Environmental and Occupational Health, University of Minnesota, Box 807 Mayo, 420 Delaware St. S.E., Minneapolis, MN 55455.
↵1 The abbreviations used are: TPA, 12-O-tetradecanoylphorbol-13-acetate; JNK, c-Jun NH₂-terminal kinase or stress-activated protein kinase; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; TNF-α, tumor necrosis factor α; SEK1, stress-activated protein kinase/extracellular signal-regulated kinase-1; DMEM, Dulbecco’s modified Eagle’s medium; PDBu, phorbol 12,13-dibutyrate; GST, glutathione S-transferase; HA, hemagglutinin; DTT, dithiothreitol; PMSF, phenylmethylsulfonyl fluoride; PAGE, polyacrylamide gel electrophoresis; MKK and MEK, mitogen-activated protein kinase kinase; MEKK, MEK kinase; SPRK, src-homology 3 domain-containing proline-rich kinase.
↵2 D. W. Kuroki and E. V. Wattenberg, unpublished results.
- Received April 4, 1997.
- Revision received July 7, 1997.