Estrogen receptor phosphorylation by MAPK . R S THOMAS and others 181 Figure 6 Effect of MAPK signaling activators and inhibitors on ERa activity. (A) NIH3T3 cells were co-transfected with ERE-3-TATA-luc, pRL-TK, and the wild-type ERa expression vector (ERa), or versions in which S104, S106, and S118 were substituted by alanine (4/6/18A) or glutamic acid (4/6/18E), as indicated. Cells were additionally co-transfected with empty expression vector (K) or expression vectors for Ras-V12, Raf-CAAX, or Raf-S621A, as shown. Cells were treated and luciferase assays carried out as for Fig. 4. (B) COS-1 cells were transfected with ERE-3-TATA-luc, pRL-TK, and the wild- type ERa expression vector (ERa) or versions with alanine or glutamic acid substitutions, as indicated. Cells were pre-incubated with U0126 (10 mM), 16 h following transfection, as indicated, for 1 h prior to addition of OHT, and harvested for luciferase assays 7 h later. www.endocrinology-journals.org Journal of Molecular Endocrinology (2008) 40, 173–184