Regulation of Expression of Cytokine Signal Transducer STAT3 by C/EBPbeta Contributes to Human Endometrial Stromal Decidualization.

Abstract

The human endometrium is a dynamic tissue that undergoes proliferation, differentiation and shedding during each menstrual cycle. The sequential actions of ovarian steroids estrogen (E) and progesterone (P) induce a unique endometrial stromal differentiation and remodeling process, known as predecidualization, which is a prerequisite for successful implantation. The molecular pathways underlying this hormonally induced cellular transformation event remain poorly understood. We have recently identified C/EBPβ, a CCAAT box-binding transcription factor, as a unique regulator of decidualization in mice. In this study, using an in vitro decidualization system in which primary human endometrial stromal cells (HESC) undergo decidualization upon addition of E, P, and a cyclic AMP analog, we established that C/EBPβ plays an essential role in human stromal differentiation. Attenuation of endogenous C/EBPβ function by a dominant negative mutant of this transcription factor blocked the decidualization process. Similar results were obtained by siRNA-mediated down regulation of C/EBPβin HESCs. In order to identify the molecular pathways regulated by C/EBPβ during decidualization, we performed gene expression profiling experiments using normal and C/EBP β-deficient HESCs. Our studies revealed that several key regulators of decidualization, such as BMP2 and Wnt4, operate downstream of C/EBP beta. We also identified the interleukin 11 receptor alpha (IL-11Ralpha) and the signal transducer and activator of transcription 3 (STAT3) as prominent downstream targets of C/EBPβ. STAT3 mediates the signaling by several cytokines including IL11. Chromatin immunoprecipitation experiments indicated that C/EBPβ controls the expression of STAT3 by directly interacting with its promoter. siRNA-mediated down regulation of STAT3 expression in HESCs resulted in significantly reduced differentiation of these cells, indicating an important role for this cytokine signal transducer in the decidualization process. Collectively, our observations established that C/EBPβis a central regulator of human endometrial stromal differentiation. This study further revealed that STAT3 is a critical downstream mediator of the function of C/EBPβ, providing a novel link between C/EBPβ and cytokine signaling pathways that regulate endometrial functions during decidualization. (Supported by NIH grant U54 HD55787). (poster)