I-34: Steroid Hormone Signalling at the FetomaternalInterface

Background: Progesterone is indispensable for differentiation of human endometrial stromal cells (HESCs) into decidual cells, a process that critically controls embryo implantation. However, HESCs also abundantly express androgen receptors (AR), yet the role of this member of the superfamily of ligand-dependent transcription factors in the decidual process remains poorly elucidated. Materials and Methods: Laboratory-based analysis of endometrial biopsies and primary endometrial cultures. Results: Although HESCs express both PR and AR, activation of the cAMP pathway is critical to sensitize the cells to progesterone as well as androgens. We demonstrate that cAMP signaling attenuates ligand-dependent sumoylation of both PR and AR, which enables these receptors to become strong transcriptional activators. In fact, decidualization is associated with global hyposumoylation and redistribution of SUMO-1 conjugates into distinct nuclear foci. This altered pattern of global sumoylation is not attributable to impaired maturation of SUMO-1 precursor or altered expression of E1 (SAE1/ SEA2) or E2 (Ubc9) enzymes but coincided with profound changes in the expression of E3 ligases and SUMO-specific proteases. Down-regulation of members of the protein inhibitors of activated STAT (PIAS) family upon decidualization pointed towards a role of these E3 ligases in PR and AR sumoylation. We demonstrate that PIAS1 serves as the E3 SUMO ligase for both PR andAR and that loss of PIAS1 in decidualizing cells is essentialfor steroid hormone signalling By combining small interfering RNA technology with genome-wide expression profiling, we also found that AR and PR regulate the expression of distinct decidual gene networks. Ingenuity pathway analysis implicated a preponderance of AR-induced genes in cytoskeletal organization and cell motility whereas analysis of ARrepressed genes suggested involvement in cell cycle regulation. Functionally, AR depletion prevented differentiation- dependent stress fibre formation and promoted motility and proliferation of decidualizing cells. In comparison, PR depletion perturbed the expression of many more genes, underscoring the importance of this nuclear receptor in diverse cellular functions. However, several PR-dependent genes encode for signaling intermediates and knockdown of PR, but not AR, compromised activation of WNT/β-catenin, TGFβ/SMAD and STAT pathways in decidualizing cells. Conclusion: These findings demonstrate how dynamic changes in the SUMO cycle mediated by the cAMP pathway determine the endometrial responses to progesterone and androgens. We further show that the activated AR and PR exert non-redundant functions during the decidualization process. Whereas the role of AR is centred on cytoskeletal organization and cell cycle regulation, PR regulates HESC differentiation, at least in part, by re-programming growth factor and cytokine signal transduction.