Calmodulin Is a Selective Modulator of Estrogen Receptors

Abstract

Abstract In the search for differences between ERα and ERβ, we analyzed the interaction of both receptors with calmodulin (CaM) and demonstrated that ERα but not ERβ directly interacts with CaM. Using transiently transfected HeLa cells, we examined the effect of the CaM antagonist N-(6-aminohexyl)-5-chloro-naphthalene sulfonilamide hydrochloride (W7) on the transactivation properties of ERα and ERβ in promoters containing either estrogen response elements or activator protein 1 elements. Transactivation by ERα was dose-dependently inhibited by W7, whereas that of ERβ was not inhibited or even activated at low W7 concentrations. In agreement with these results, transactivation of an estrogen response element containing promoter in MCF-7 cells (which express a high ERα/ERβ ratio) was also inhibited by W7. In contrast, transactivation in T47D cells (which express a low ERα/ERβ ratio) was not affected by this CaM antagonist. The sensitivity of MCF-7 cells to W7 was abolished when cells were transfected with increasing amounts of ERβ, indicating that the sensitivity to CaM antagonists of estrogen-responsive tissues correlates with a high ERα/ERβ ratio. Finally, substitution of lysine residues 302 and 303 of ERα for glycine rendered a mutant ERα unable to interact with CaM whose transactivation activity became insensitive to W7. Our results indicate that CaM antagonists are selective modulators of ER able to inhibit ERα-mediated activity, whereas ERβ actions were not affected or even potentiated by W7.