SUN-150 Progesterone Receptor Mediates Gene Regulation in the Ovary Through Facilitating Glucocorticoid Receptor Action

Abstract Disclosure: T. Dinh: None. R.L. Robker: None. D.L. Russell: None. Steroid receptors activated by progesterone (PGR), androgen (AR) and glucocorticoid (GR), are transcription factors that share a canonical DNA binding sequence (nuclear receptor response element - NRE). In the ovary, PGR is the key determinant of ovulation and regulates crucial ovulatory genes through extensive cooperation with other transcription factors. The roles of AR and GR in ovulation, on the other hand, remain elusive. In particular, it is unknown whether they contribute to PGR action in the ovary. Through qPCR, Western blot and immunofluorescence we showed that all three steroid receptors were present in ovarian granulosa cells during mid-ovulation, where PGR largely exerts influence as a transcription factor. To elucidate the relationship between AR, GR and PGR in the ovary, we characterised and contrasted the chromatin binding profiles of PGR, AR and GR using ChIP-seq in granulosa cells from mice undergoing in vivo hormone stimulation for ovulation. More than half of all AR and GR chromatin binding was located at constitutively accessible chromatin sites, and in particular within close proximity (<1 kb) to transcription start sites. In response to ovulatory hormones, PGR and GR gained novel binding sites, whereas chromatin interaction by AR was largely repressed. Interestingly, while AR showed a strong binding preference for the canonical NRE sequence, PGR and GR favoured non-canonical motifs that correspond to other transcription factor families, including AP-1, CEBP and RUNX. Integration of the AR and GR cistromes with PGR showed that two-thirds of PGR binding sites were co-bound by AR and/or GR, indicating substantial interaction between all three steroid receptors. Importantly, LH-induced PGR and GR co-binding had a significant effect on LH- and PGR-dependent gene activation that was observed specifically in the ovary, as shown through RNA-seq analysis of ovulatory or PGR knockout mice. PGR recruited to pre-accessible, constitutively AR/GR-bound chromatin sites had little contribution to ovulatory gene regulation. Unexpectedly, ATAC-seq and ChIP-seq on PGR knockout mice showed that PGR was required for LH-dependent chromatin accessibility as well as GR recruitment to these sites. Our findings indicate a novel role of PGR that has not been described in other tissue contexts, in which PGR facilitates GR binding and chromatin remodelling of promoters, thereby activating ovulatory genes. Therefore, this illustrates the multi-faceted relationship between steroid receptors in the ovary, which helps to explain how steroid receptors cooperatively mediate gene expression during ovulation. Presentation: Sunday, July 13, 2025