Progesterone down-regulates insulin-like growth factor-I expression in cultured human uterine leiomyoma cells

BACKGROUND: Insulin-like growth factor-I (IGF-I) plays crucial roles in uterine leiomyoma cell growth through stimulating proliferation and inhibiting apoptosis. The present study was conducted to elucidate whether progesterone affects IGF-I and its receptor expression in cultured leiomyoma cells. METHODS: Isolated leiomyoma cells were subcultured in Phenol Red-free Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum for 120 h and then stepped down to serum-free conditions for an additional 48 h in the presence or absence of 17beta-estradiol (E(2)) (10 ng/ml) or progesterone (100 ng/ml). IGF-I and its receptor mRNA and immunoreactive IGF-I in the cultured cells were assessed by quantitative RT-PCR with Southern blot analysis and by radioimmunoassay with Seppak C18 chromatography, respectively. The presence of estrogen receptor (ER) and progesterone receptor (PR) in cultured leiomyoma cells was immunocytochemically examined. RESULTS: Both treatment with progesterone alone and treatment with E(2) and progesterone combined significantly decreased IGF-I mRNA and protein expression in cultured leiomyoma cells compared with that in untreated cultures, but treatment with E(2) alone did not. IGF-I receptor mRNA expression in those cells was not affected by treatment with either E(2) or progesterone. Immunocytochemical analysis revealed that PR protein expression in cultured leiomyoma cells maintained in a serum-free condition for 48 h whereas ER protein expression in the cells remarkably decreased after 24 h culture under the serum-free condition. CONCLUSIONS: The present study provided evidence for the first time that progesterone down-regulates IGF-I mRNA and protein expression in cultured leiomyoma cells without affecting IGF-I receptor mRNA expression.