Foxl2, a Forkhead Transcription Factor, Modulates Nonclassical Activity of the Estrogen Receptor-α

Abstract

Foxl2 is a forkhead transcription factor required for ovary development and ovarian follicle maturation. In this report, we identified and characterized a functional relationship between Foxl2 expression and estrogen receptor (ER)-alpha signaling. We show that Foxl2 has no effect on classical ERalpha-mediated transcription, which occurs through canonical estrogen response elements. However, Foxl2 suppresses ERalpha signaling through nonclassical tethered transcriptional pathways. Specifically, the selective ER modulator tamoxifen stimulates activator protein-1 (AP1)-dependent transcription via the ERalpha, and this enhancement is blocked by Foxl2. Two lines of evidence suggest that Foxl2 suppression is mediated by physical interactions with ERalpha rather than direct action at AP1 binding sites. First, ERalpha is coimmunoprecipitated with Foxl2. Second, activation of a upstream activating sequence (UAS) reporter by Gal4-cJun in the presence of ERalpha and tamoxifen was blocked by Foxl2, demonstrating suppression in the absence of an AP1 site. Cyclooxygenase-2 (COX2), which is required for ovulation, was identified through expression profiling as a candidate physiological target for nonclassical ERalpha signaling and thus modulation by ERalpha/Foxl2 interactions. This possibility was confirmed by two sets of experiments. COX2 protein levels were induced by ERalpha in the presence of tamoxifen, and protein expression was suppressed by Foxl2. In addition, ERalpha stimulation of the COX2 promoter was repressed by Foxl2. We conclude that ERalpha and Foxl2 interact and that Foxl2 selectively suppresses ERalpha-mediated transcription of AP1-regulated genes. These data provide a potential point of convergence for ERalpha and Foxl2 to regulate ovarian development and function.