SUN-192 Functional Interactions between Estrogen and Relaxin Signaling in the Myometrium

The complex interplay between the steroid hormones progesterone and estrogen (E2), acting through their cognate nuclear receptors, coordinates uterine myometrial contractility. Upon binding E2, estrogen receptor alpha (ERα) binds to regulatory elements across the genome, and promotes the assembly of transcriptional enhancers. The E2-induced ERα (i.e., cistrome) is plastic, and can be reconfigured in response to activation by other cellular signaling pathways. In addition to steroid hormones, the peptide hormone relaxin (Rln), acting via its G-protein coupled receptor, Rxfp1, has numerous, well described roles in the physiology of pregnancy. Interestingly, many of the effects of Rln require, or are augmented by E2 signaling through ERα. However, the extent, and molecular mechanisms by which cross-talk between E2 and Rln is achieved to ensure myometrial function is unknown. We hypothesized that Rln signaling in the myometrium alters or regulates a parturition-specific ERα cistrome that results in a cell-specific and dynamic altered transcriptome that controls downstream biological events. We used myometrial tissue from ovariectomized (ovx) mice treated with E2+Rln or either hormone alone, or from pregnant mice with or without a targeted deletion of Rxfp1. We generated high quality cistromic (ChIP-seq) and transcriptomic (RNA-seq) data sets in the ovx mouse model. The RNA-seq data sets have uncovered a unique transcriptome signature regulated by combined actions of E2 and Rln in the myometrium. In addition, we observed that many of the ERα binding sites were depleted in the presence of Rln, although histone modification associated with active enhancers (i.e., H3K27ac, and H3K4me1) were still enriched at those sites. The reduction in ERα binding is not explained by a reduction in ERα protein, as total ERα protein does not change across these treatments. In contrast, specific phosphorylation sites on ERα regulated by kinases were changed across these treatments. We also observed increased Erk1/2 activation with E2+Rln in the ovx mouse system compared to either hormone alone. Consistent with this observation, myometrial Erk1/2 activation is elevated in late pregnancy in wild type mice, but not in the Rxfp1 KO mouse. Current studies are underway to assess Erk1/2 signaling as a potential downstream mediator of Rln that alters the ERα activity, and also chromatin accessibility to direct the E2/ERa transcriptome signature for appropriate uterine function. This work is supported by theGreenCenterTrainingPrograminReproductiveBiologyScience Research.