ERK2-and p90(Rsk2)-dependent pathways regulate the CCAAT/enhancer-binding protein-beta interaction with serum response factor

The serum response element (SRE) of the c-fos promoter is a convergence poi nt for mitogenic signaling pathways. Several transcription factors regulate SRE, including serum response factor (SRF), ternary complex factors, and C CAAT/enhancer-binding protein-beta (C/ EBP beta). C/EBP beta can interact w ith both SRF and the ternary complex factor family member Elk-1, but only i n response to activated Ras. Transactivation of the SRE by C/EBP beta is al so greatly stimulated by Ras. The Ras effectors that signal to C/EBP beta a re unknown. In this report, we demonstrate that a consensus MAPK site in C/ EBP beta is necessary for Ras stimulation of both C/EBP beta -SRF interacti on and transactivation of the SRE by C/EBP beta. To dissect signaling pathw ays activated downstream of Ras, different Ras effector constructs were ana lyzed. We show that activated forms of Raf and phosphatidylinositol 3-kinas e stimulate C/EBP beta -SRF interaction. We also show a novel selectivity f or the MAPK family member ERK2, where dominant-negative ERK2, but not domin ant-negative ERK1, blocks Ras stimulation of C/EBP beta -SRF interaction. I n addition, recombinant C/EBP beta protein is phosphorylated by ERK2, but n ot by ERK1, in vitro. Finally, we demonstrate a requirement for p90(Rsk2) i n regulation of C/EBP beta -SRF interaction. These data show that multiple Ras effectors are required to regulate C/EBP beta and SRF association.