Female Reproductive Tract

Role of FOXO1A in the Regulation of Insulin Like Growth Factor Binding Protein-1 in Human Endometrial Cells: Interaction with Progesterone Receptor

Abstract
Insulin-like growth factor binding protein 1 (IGFBP1) is a major secretory product of the decidualized endometrium. In this study, we investigated the role of two transcription factors, progesterone receptor (PGR) and a member of the forkhead box class O family of transcription factors, FOXO1A, in the regulation of the IGFBP1 gene in endometrial cells. Human endometrial fibroblasts (HuF) expressed FOXO1A, progesterone receptor A (PGRA) and progesterone receptor B (PGRB) proteins while the endometrial adenocarcinoma cell line, HEC- 1B cells expressed only FOXO1A and no detectable PGR proteins. When FOXO1A expression was silenced using small interference RNA, IGFBP1 expression decreased in both HuF and HEC-1B cells. Using the chromatin immunoprecipitation technique, we demonstrated that liganded PGR was recruited to the IGFBP1 promoter region (-358 to -49). In addition, immunoprecipitation of HuF nuclear proteins with a PGR antibody followed by immunoblotting with anti-FOXO1A revealed that these two proteins interact in these cells. Reporter studies demonstrated that while liganded PGRA or PGRB increased a progesterone response element linked-reporter construct, pPRE/GRE.E1b.Luc, co-expression of FOXO1A inhibited the PGRB response in HuF and synergistically increased PGRA and PGRB response in HEC-1B. Furthermore, in HEC-1B cells, FOXO1A increased IGFBP1 promoter activity and co-expression of PGRA or PGRB further increased the promoter activity in a cooperative manner. In HuF, the response to FOXO1A and PGR was not additive but lower than the sum of individual responses. Thus, FOXO1A and PGR associate with one another and influence each other's transactivating potential. The cell type dependent responses strongly implicate the involvement of other cofactors.

Key words: Female Reproductive Tract • Decidua • Implantation • Progesterone receptor • Uterus

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