Estradiol regulation of insulin-like growth factor-I expression in osteoblastic cells: evidence for transcriptional control.
Insulin-like growth factor-I (IGF-I) has anabolic effects on skeletal tissues, acting as both a systemic hormone and an autocrine/paracrine regulator of cellular function. We have previously reported that estradiol (E2) stimulation of rat osteoblast proliferation in vitro was inhibited by IGF-I antibodies. We show here that E2, similar to IGF-I, also increases alpha 1(I) procollagen mRNA levels in primary cultures of rat calvarial osteoblasts. The E2 effect on collagen mRNA lags behind that produced by recombinant IGF-I by about 12 h and was also abolished in the presence of cycloheximide or by the addition of antibodies against IGF-I. Furthermore, 17 beta E2 induced a 2- to 2.5-fold elevation of the level of IGF-I mRNA within 2-4 h, which persisted thereafter. The E2 stimulation of IGF-I mRNA was not blocked by cycloheximide, suggesting that de novo protein synthesis of an intermediate protein was not required. The IGF-I mRNA half-life, estimated by treating the cells with the RNA polymerase inhibitor 5,6-dichloro-1 beta-D-ribofuranosylbenzimidazole, was about 7 h and was not altered by E2 treatment. On the other hand, nuclear run-on assays indicated that E2 increased the transcriptional activity of the IGF-I gene, and this effect was further enhanced in cells overexpressing E2 receptors after transient transfection. These findings suggest that IGF-I may serve as a mediator for the anabolic effects of E2 on bone, and that E2 stimulates IGF-I gene expression at least in part through transcriptional control.
Ernst
M
M
Department of Bone Biology and Osteoporosis Research Merck, Sharp, and Dohme Research Laboratories, West Point, Pennsylvania 19486.
Rodan
G A
GA
D000818:Animals; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics; D003513:Cycloheximide / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D009693:Nucleic Acid Hybridization; D010006:Osteoblasts / Q000378:metabolism*; D011347:Procollagen / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D014162:Transfection
D011347:Procollagen; D012333:RNA, Messenger; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D003094:Collagen; D003513:Cycloheximide