A distinct feed-forward mechanism between GREB1 and steroid receptors dictates hormone-dependent GREB1 action in endometrial function and dysfunction
The cellular responses to the steroid hormones, estrogen (E2), and progesterone (P4) are governed by their cognate receptor's transcriptional output. Although multiple mechanisms including the tissue-specific coactivators dictate these transcriptional signatures, the feed-forward mechanisms, that evolved to coordinate the cell-type specific transcriptional fulcrums for steroid receptors are not yet identified. In this report, we found that a common feed-forward mechanism between GREB1 and steroid receptors governs the differential effect of GREB1 on steroid hormones in a physiological or pathological context. We found that in physiological (receptive) endometrium, GREB1 is essential for progesterone but not estrogenic responses, whereas in endometriosis, an E2-dependent endometrial pathology, it pre-dominantly mediates estrogenic actions. Specifically, the deletion of GREB1 curtails endometrial receptivity and decidualization, owing to impaired P4-dependent stromal cell proliferation. In contrast, GREB1 is not required for E2-mediated epithelial proliferation of the receptive uterus. Of mechanism, in receptive endometrium, progesterone-induced GREB1 physically interacts with the progesterone receptor on chromatin and functions as a cofactor in a positive feedback mechanism to selectively regulate P4-responses. In pathological conditions (endometriosis), ablation of GREB1 led to the development of smaller endometriotic lesions in mice and reduced E2-driven proliferation of human endometriotic cells. Moreover, E2-induced GREB1 modulated the E2-dependent target gene expression in a feed-forward mechanism. Collectively, acting as a downstream effector, GREB1 governs either P4-responses or E2-responses depending on the physiological or pathological setting. Importantly, this differential action of GREB1 is exerted by a common feed-forward mechanism between GREB1 and steroid receptors, which conceptually advances our understanding of the mechanism(s) that underlie the distinct cell- and tissue-specific actions of steroid hormones. Overall design: Cut n Run for GREB1 binding in human endometrial stromal cells