Progesterone receptor regulates Bcl-2 gene expression through direct binding to its promoter region in uterine leiomyoma cells

Context: Uterine leiomyomas are smooth muscle cell tumors that cause irregular uterine bleeding and pregnancy loss in many reproductive-age women. Progesterone stimulates their growth, whereas treatment with progesterone receptor ( PR) antagonists or selective progesterone receptor modulators shrinks these tumors. Molecular mechanisms underlying these observations are unknown. Objective: Bcl- 2 is a key protein that inhibits apoptosis. It was proposed that growth enhancement of leiomyoma cells by progesterone was mediated via bcl- 2 induction. Here we test the hypothesis that PR regulates the bcl- 2 gene by directly binding to its promoter. Results: The pure progesterone agonist R5020 increased the total number of viable primary human leiomyoma smooth muscle ( LSM) cells in culture. Progesterone or R5020 ( 10(-6) M) significantly increased bcl- 2 mRNA levels after 2 and 4 h by 9.2- and 3.4- fold, respectively, in LSM cells. Transient transfection with deletion mutants of bcl- 2 promoter showed that the - 1281/ - 258- bp region conferred responsiveness to progesterone induction in the presence of PR- A. We identified a palindromic progesterone response element ( PRE) at - 553/ - 539 bp. EMSA showed that PR in nuclear extracts from LSM cells bound specifically to this PRE. Chromatin immunoprecipitation-PCR confirmed in situ recruitment of PR to the - 629/ - 388- bp region bearing the PRE. In vivo, bcl- 2 mRNA levels correlated significantly with total PR mRNA levels in leiomyoma tissues. Conclusion: Taken together, progesterone via PR interacts with the bcl- 2 promoter to induce its expression in leiomyoma tissue. This may explain, in part, the progesterone- dependent enhancement of growth in uterine leiomyoma.