Estrogen receptor-mediated activation of the serum response element in MCF-7 cells through MAPK-dependent phosphorylation of Elk-1

17 beta -Estradiol (E2) induces c-fos protooncogene expression in MCF-7 hum an breast cancer cells, and deletion analysis of the c-fas promoter showed that the serum response element (SRE) at -325 to -296 was E2-responsive. Th e mechanism of ligand-activated estrogen receptor alpha (ER alpha)-dependen t activation of gene expression through the SRE was determined by mutationa l analysis of the promoter, analysis of mitogen-activated protein kinase (M APK) pathway activation by E2, and transforming growth factor alpha (TGF-al pha) as a positive control. In addition, ER alpha -negative MDA-MB-231 brea st cancer and Chinese hamster ovary cells were used as reference cell lines , The results showed that transcriptional activation of the SRE by E2 was d ue to ER alpha activation of the MAPK pathway and increased binding of the serum response factor and Elk-1 to the SRE. Subsequent studies with dominan t negative Elk-1, wild type, and variant GAL4-Elk-1. fusion proteins confir med that phosphorylation of Elk-1 at serines 383 and 389 in the C-terminal region of Elk-1 is an important downstream target associated with activatio n of an SRE by E2. Both E2 (ER alpha -dependent) and,growth factors (ER alp ha -independent) activated the SRE in breast cancer cells via the Ras/MAPK pathway; however, in ER-negative CHO cells that do not express a receptor f or TGF-alpha, only hormone-induced activation was observed in cells transfe cted with ER alpha.