Kinase Suppressor of Ras Inhibits the Activation of Extracellular Ligand-regulated (ERK) Mitogen-activated Protein (MAP) Kinase by Growth Factors, Activated Ras, and Ras Effectors

doi:10.1074/jbc.273.13.7743

Kinase Suppressor of Ras Inhibits the Activation of Extracellular Ligand-regulated (ERK) Mitogen-activated Protein (MAP) Kinase by Growth Factors, Activated Ras, and Ras Effectors*

From the Eppley Institute for Research in Cancer and Allied Diseases, ^‖Department of Biochemistry and Molecular Biology and the ^¶Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6805 and the ^‡Department of Molecular Genetics and Microbiology, State University of New York at Stony Brook, Stony Brook, New York 11794

Abstract

Kinase suppressor of Ras (KSR) is a loss-of-function allele that suppresses the rough eye phenotype of activated Ras in Drosophila and the multivulval phenotype of activated Ras in Caenorhabditis elegans. Genetic and biochemical studies suggest that KSR is a positive regulator of Ras signaling that functions between Ras and Raf or in a pathway parallel to Raf. We examined the effect of mammalian KSR expression on the activation of extracellular ligand-regulated (ERK) mitogen-activated protein (MAP) kinase in fibroblasts. Ectopic expression of KSR inhibited the activation of ERK MAP kinase by insulin, phorbol ester, or activated alleles of Ras, Raf, and mitogen and extracellular-regulated kinase. Expression of deletion mutants of KSR demonstrated that the KSR kinase domain was necessary and sufficient for the inhibitory effect of KSR on ERK MAP kinase activity. KSR inhibited cell transformation by activated Ras^Val-12 but had no effect on the ability of Ras^Val-12 to induce membrane ruffling. These data indicate that KSR is a potent modulator of a signaling pathway essential to normal and oncogenic cell growth and development.

Footnotes

↵* This work was supported by Grants DK52809 (to R. E. L.) and CA55360 (to D. B.-S.) from the National Institutes of Health, BE-260 from the American Cancer Society (to R. E. L.), 98-28 from the Nebraska Department of Health and Human Services (to R. E. L.), and P30 CA36727 from the National Cancer Institute to the Eppley Institute.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.
↵§ Contributed equally to the results of this work.
↵** To whom correspondence should be addressed: Eppley Cancer Institute, University of Nebraska Medical Center, 600 S. 42nd St., Omaha, NE 68198-6805. Tel.: 402-559-8290; Fax: 402-559-4651; E-mail: rlewis{at}unmc.edu.
↵1 The abbreviations used are: MEK, mitogen and extracellular-regulated kinase; ERK, extracellular ligand-regulated kinase; KSR, kinase suppressor of Ras; MAP, mitogen-activated protein; PMA, phorbol 12-myristate 13-acetate; Raf-CAAX, c-Raf-1 kinase targeted to the plasma membrane by a carboxyl-terminal lipid modification signal from Ha-Ras; MEKEE, constitutively active MEK; PCR, polymerase chain reaction.
- Received December 19, 1997.
- Revision received January 21, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.