Inhibition of v-raf-dependent c-fos expression and transformation by a kinase-defective mutant of the mitogen-activated protein kinase Erk2.
Receptor-bound growth factors elicit intracellular signals that lead to the phosphorylation and activation of numerous intracellular kinases and transcription factors with consequent changes in patterns of gene expression. Several oncogene products are able to mimic these signals, resulting in cell transformation and proliferation. For example, the introduction of oncogenic forms of Raf-1 kinase into fibroblasts induces transformation and leads to the constitutive expression of, among others, the c-fos proto-oncogene. Here it is shown that the elevation of c-fos promoter activity brought about by v-raf is mediated by TCF/Elk-1, which forms a ternary complex with SRF at the serum response element and is a substrate for mitogen-activating protein kinases in vitro. In NIH 3T3 fibroblasts, v-raf activates Erk2, and overexpression of an interfering mutant of Erk2 both blocks the ability of v-raf to activate the c-fos promoter and suppresses transformation. Mutation of individual mitogen-activating protein kinase phosphoacceptor sites in TCF/Elk-1 also compromises v-raf-activated expression of a Gal-Elk/Gal-chloramphenicol acetyltransferase reporter system. However, in at least one instance the introduction of glutamate, but not aspartate, at a phosphoacceptor site is compatible with activation. These results provide compelling evidence that phosphorylation of TCF/Elk-1 by Erk2 is a major link in the Raf-1 kinase-dependent signal transduction pathway that activates c-fos expression.
Kortenjann
M
M
Max-Planck-Institut für Immunobiologie, Spemann Laboratories, Freiburg, Germany.
Thomae
O
O
Shaw
P E
PE
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000378:metabolism; D017931:DNA Primers; D004268:DNA-Binding Proteins; D016762:Genes, fos; D007700:Kinetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D008969:Molecular Sequence Data; D016296:Mutagenesis; D027384:Oncogene Proteins v-raf; D009857:Oncogenes; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D019908:Proto-Oncogene Proteins c-raf; D015682:Retroviridae Proteins, Oncogenic / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D014157:Transcription Factors; D014162:Transfection; D050807:ets-Domain Protein Elk-1
D017931:DNA Primers; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D015682:Retroviridae Proteins, Oncogenic; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D015500:Chloramphenicol O-Acetyltransferase; D011505:Protein-Tyrosine Kinases; D027384:Oncogene Proteins v-raf; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1