Ligand-activated progesterone receptor isoform hPR-A is a stronger transactivator than hPR-B for the expression of IGFBP-1 (insulin-like growth factor binding protein-1) in human endometrial stromal cells

In human endometrium, the levels of progesterone receptor (PR) isoforms hPR -A and hPR-B are differentially regulated during the reproductive cycle. Pr ogesterone significantly increases the content of hPR-A, the predominant is oform in decidualized stromal cells (1). The purpose of this study was to d etermine the capacity of hPR-A and hPR-B to transactivate the progestin-dep endent target gene in human endometrial stromal cells. We examined the effe ct of cotransfection of hPR-A or hPR-B on the expression of the human insul in-like growth factor binding protein-1 (IGFBP-1) in endometrial stromal ce lls. The primary culture of human endometrial stromal cells was transfected with the hPR-A or hPR-B expression vector and the IGFBP-1 promoter constru ct p275CAT, which contains two functional progesterone response elements (P RE1 and PRE2) in decidualized stromal cells. Medroxyprogesterone acetate (M PA) increased the promoter activities ranging from 1.2- to 27-fold in cells cotransfected with hPR-A or hPR-B in eight endometrial specimens. The prom oter activity increased by the hPR-A was significantly higher than hPR-B (1 5 +/- 8 vs. 4 +/- 2, mean +/- SD; n = 8, P < 0.005). Site-specific mutation showed that the induced activity by hPR-A was mediated through the PRE1 an d PRE2 sites. Addition of hPR-B reduced the effect of hPR-A. The high trans activation capacity of hPR-A was also activated by other ligands, progester one, Org 2058, and norethindrone. These observations indicate that hPR-A is a stronger transactivator than hPR-B for the IGFBP-1 promoter in endometri al stromal cells. Previous studies have shown the progestin-dependent produ ction of IGFBP-1 correlates with its mRNA levels and transcription rate. Th us, we have determined the effect of hPR-A and hPR-B on the production of I GFBP-1 in stromal cells treated with MPA. The production rate in cells unif ormly infected with AdPRA (recombinant Ad5- directed PR expression system) was significantly higher (P < 0.001) than the rate in uninfected cells and in cells infected with AdPRB or AdCMV (the Ad5 viral expression vector). Th is result, in concert with the promoter analysis, provides evidence that hP R-A is a strong inducer for the chromosomal IGFBP-1 gene in endometrial str omal cells.