FIG. 4.

CIA is a potent and specific ERα transcriptional activator. (A) A luciferase reporter gene linked with various hormone-responsive promoters (2C-vERE-TKLuc, 3C-TREpal-TKLuc, and MMTV-Luc) was transfected into COS-1 cells along with expression vectors for CIA, ERα, TRα, and PR in the combinations shown. Results are expressed as fold induction over the reporter alone in the presence of the appropriate ligand (ERα, 10⁻⁸ M E₂; TRα, 10⁻⁸ M 3-iodothyronine; PR, 10⁻⁸ M progesterone). (B) Ligand-dependent activation of ERα on the pS2-Luc reporter gene is enhanced by cotransfection of CIA. No effect of CIA is observed on the pS2 promoter when its ERE site is mutated (pS2-Luc ΔERE).