PGR Isoform Modulation via Enhancer Activation Regulates Progesterone Signaling in Human Endometrial Stromal Cells [RNA-Seq]

Progesterone, acting through its isoform receptors PGR-A and PGR-B, is essential for regulating uterus function. The ratio between these isoforms is dynamic and context-dependent, driving distinct transcriptional programs. The upstream mechanisms controlling the PGR isoform balance and their functional impact in the uterus remain poorly understood. In this study, we identified two distal PGR enhancers in endometrial stromal cells located 60 kb and 220 kb upstream of the PGR transcription start site. We found that in comparison to PGR promoter-targeting which favors a PGR-B dominant profile, activation of these enhancers shifts the isoform ratio by increasing PGR-A and decreasing PGR-B expression. Bulk RNA-sequencing revealed that the isoform balance alters the progesterone-regulated transcriptome. PGR-A/B-equivalent cells displayed pro-inflammatory gene signatures, whereas PGR-B-dominant cells exhibited suppression of inflammatory signaling and cell cycle activity. Cut&Run assays identified differential genomic binding patterns associated with each isoform profile, and integration with chromatin interaction maps suggest direct regulation of distinct gene subsets. Upstream, ESR1 indirectly activated the PGR-A isoform dominantly, potentially through cooperation with FOXO1 at the U2 enhancer. This study identifies a novel enhancer-driven mechanism regulating PGR isoform dynamics and sheds light on how their imbalance in the endometrial stroma may reshape progesterone signaling in health and disease.