SKF-82958 Is a Subtype-selective Estrogen Receptor-α (ERα) Agonist That Induces Functional Interactions between ERα and AP-1

The transcriptional activity of estrogen receptors (ERs) can be regulated by ligands as well as agents such as dopamine, which stimulate intracellular signaling pathways able to communicate with these receptors. We examined the ability of SKF-82958 (SKF), a previously characterized full dopamine D1 receptor agonist, to stimulate the transcriptional activity of ERα and ERβ. Treatment of HeLa cells with SKF-82958 stimulated robust ERα-dependent transcription from an estrogen-response element-E1b-CAT reporter in the absence of estrogen, and this was accompanied by increased receptor phosphorylation. However, induction of ERβ-directed gene expression under the same conditions was negligible. In our cell model, SKF treatment did not elevate cAMP levels nor enhance transcription from a cAMP-response element-linked reporter. Control studies revealed that SKF-82958, but not dopamine, competes with 17β-estradiol for binding to ERα or ERβ with comparable relative binding affinities. Therefore, SKF-82958 is an ERα-selective agonist. Transcriptional activation of ERα by SKF was more potent than expected from its relative binding activity, and further examination revealed that this synthetic compound induced expression of an AP-1 target gene in a tetradecanoylphorbol-13-acetate-response element (TRE)-dependent manner. A putative TRE site upstream of the estrogen-response element and the amino-terminal domain of the receptor contributed to, but were not required for, SKF-induced expression of an ERα-dependent reporter gene. Overexpression of the AP-1 protein c-Jun, but not c-Fos, strongly enhanced SKF-induced ERα target gene expression but only when the TRE was present. These studies provide information on the ability of a ligand that weakly stimulates ERα to yield strong stimulation of ERα-dependent gene expression through cross-talk with other intracellular signaling pathways producing a robust combinatorial response within the cell.