Hanlon M, Sturgill TW, Sealy L

Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.

The serum response element (SRE) of the c-fos promoter is a convergence point for mitogenic signaling pathways. Several transcription factors regulate SRE, including serum response factor (SRF), ternary complex factors, and CCAAT/enhancer-binding protein-beta (C/EBPbeta). C/EBPbeta can interact with both SRF and the ternary complex factor family member Elk-1, but only in response to activated Ras. Transactivation of the SRE by C/EBPbeta is also greatly stimulated by Ras. The Ras effectors that signal to C/EBPbeta are unknown. In this report, we demonstrate that a consensus MAPK site in C/EBPbeta is necessary for Ras stimulation of both C/EBPbeta-SRF interaction and transactivation of the SRE by C/EBPbeta. To dissect signaling pathways activated downstream of Ras, different Ras effector constructs were analyzed. We show that activated forms of Raf and phosphatidylinositol 3-kinase stimulate C/EBPbeta-SRF interaction. We also show a novel selectivity for the MAPK family member ERK2, where dominant-negative ERK2, but not dominant-negative ERK1, blocks Ras stimulation of C/EBPbeta-SRF interaction. In addition, recombinant C/EBPbeta protein is phosphorylated by ERK2, but not by ERK1, in vitro. Finally, we demonstrate a requirement for p90(Rsk2) in regulation of C/EBPbeta-SRF interaction. These data show that multiple Ras effectors are required to regulate C/EBPbeta and SRF association.

Mesh Terms:
1-Phosphatidylinositol 3-Kinase, 3T3 Cells, Animals, Binding Sites, CCAAT-Enhancer-Binding Protein-beta, DNA-Binding Proteins, Enzyme Activation, Genes, Dominant, Immunoblotting, Mice, Mitogen-Activated Protein Kinase 1, Mitogen-Activated Protein Kinase 3, Mitogen-Activated Protein Kinases, Models, Biological, Mutation, Plasmids, Protein Binding, Proto-Oncogene Proteins, Recombinant Proteins, Ribosomal Protein S6 Kinases, Serum Response Factor, Signal Transduction, Threonine, Transcription Factors, Transcriptional Activation, Transfection, ets-Domain Protein Elk-1

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