Abstract
Accumulating evidence indicates that estrogen regulates diverse but interdependent signaling pathways via estrogen receptor (ER)-dependent and -independent mechanisms. However, molecular relationship between these pathways for gene regulation under the direction of estrogen remains unknown. To address this possibility, our uterine analysis of Wnt/beta-catenin downstream effectors revealed that lymphoid enhancer factor 1 (Lef-1) and T cell factor 3 (Tcf-3) are up-regulated temporally by 17beta-estradiol (E2) in an ER-independent manner. Lef-1 is abundantly up-regulated early (within 2 h), whereas Tcf-3 is predominantly induced after 6 h, and both are sustained through 24 h. Interestingly, activated Lef-1/Tcf-3 molecularly interacted with ERalpha in a time-dependent manner, suggesting they possess a cross talk in the uterus by E2. Moreover, dual immunofluorescence studies confirm their colocalization in uterine epithelial cells after E2. Most importantly, using chromatin immunoprecipitation followed by PCR analyses, we provide evidence for an interesting possibility that ERalpha and Tcf-3/Lef-1 complex occupies at certain DNA regions of estrogen-responsive endogenous gene promoters in the mouse uterus. By selective perturbation of activated Lef-1/Tcf-3 or ERalpha signaling events, we provide in this study novel evidence that cooperative interactions, by these two different classes of transcription factors at the level of chromatin, direct uterine regulation of estrogen-responsive genes. Collectively, these studies support a mechanism that integration of a nonclassically induced beta-catenin/Lef-1/Tcf-3 signaling with ERalpha is necessary for estrogen-dependent endogenous gene regulation in uterine biology.