Estrogen Receptor β (ERβ1) Transactivation Is Differentially Modulated by the Transcriptional Coregulator Tip60 in a cis-Acting Element-dependent Manner

Background: The interactions between estrogen receptor ␤ (ER␤1) and different coregulators are responsible for the distinct functions of ER␤1.Results: Tip60 enhances ER␤1 transactivation at the AP-1 site but inhibits it at ERE sites.Conclusion: Tip60 is either a coactivator or a corepressor for ER␤1 in a regulatory element-dependent manner.Significance: Tip60 is the first multifaceted coregulator of the transcriptional activity of ER␤1 that has been identified. Estrogen receptor (ER)␤1 and ER␣ have overlapping and distinct functions despite their common use of estradiol as the physiological ligand.These attributes are explained in part by their differential utilization of coregulators and ligands.Although Tip60 has been shown to interact with both receptors, its regulatory role in ER␤1 transactivation has not been defined.In this study, we found that Tip60 enhances transactivation of ER␤1 at the AP-1 site but suppresses its transcriptional activity at the estrogen-response element (ERE) site in an estradiol-independent manner.However, different estrogenic compounds can modify the Tip60 action.The corepressor activity of Tip60 at the ERE site is abolished by diarylpropionitrile, genistein, equol, and bisphenol A, whereas its coactivation at the AP-1 site is augmented by fulvestrant (ICI 182,780).GRIP1 is an important tethering mediator for ERs at the AP-1 site.We found that coexpression of GRIP1 synergizes the action of Tip60.Although Tip60 is a known acetyltransferase, it is unable to acetylate ER␤1, and its coregulatory functions are independent of its acetylation activity.In addition, we showed the co-occupancy of ER␤1 and Tip60 at ERE and AP-1 sites of ER␤1 target genes.Tip60 differentially regulates the endogenous expression of the target genes by modulating the binding of ER␤1 to the cis-regulatory regions.Thus, we have identified Tip60 as the first dualfunction coregulator of ER␤1.Estrogen normally exerts its effects via two main receptor subtypes, estrogen receptor (ER) 2 ␣ and ␤ (ER␤1) (1).These receptors function as transcription factors and regulate gene expression either by binding directly to estrogen-response elements (EREs) within the regulatory region of target genes (2, 3) or by interacting with other transcription factors, such as AP-1, NFB, and Sp1 (4, 5).The activation of ERs is controlled by interplay between the binding of ligands and coregulators (coactivators and corepressors) (6).Most ER signaling pathways require ligand binding because ligands are able to induce the dimerization of ERs and conformational changes in receptors and thus to increase the potency of coactivator recruitment (7).However, studies of the ligand-independent regulation of ER␤1 by coregulators are limited to previous findings demonstrating this mode of action for SRC1 and GRIP1 (8, 9).Global transcriptional profiling also reveals that unliganded ER␤1 regulates a significant number of target genes (10, 11).These findings, taken together, have stimulated significant interest in the topic of ligand-independent action.Coregulators regulate the activity of transcription factors through several mechanisms, including post-translational modification.Activities of ERs are regulated, for example, by acetylation, phosphorylation, and ubiquitination (12-14).A putative acetylation motif is present in many hormone receptors conserved among different species (13, 15), revealing that acetylation is a common regulatory mechanism of receptor activity.ER␣ is acetylated by p300 and SRC1 (16, 17), whereas its hormone sensitivity and transactivation are regulated by acetylation (17).Moreover, acetylation of ER␣ modulates or is modulated by other post-translational modifications, such as ubiquitination and phosphorylation (18, 19).However, acetylation of ER␤1 has not yet been reported.Alternatively, coregulators can act as scaffold proteins to allow tethering of ERs and * This work was supported, in whole or in part, by National Institutes of Health Grants R01CA015776, R01DK061084, R01ES015584, U01ES019480, U01ES020988, and P30ES006096 from NIEHS (to S. M. H.).