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.