Dihydrotestosterone inhibits insulin-stimulated cyclin D2 messenger ribonucleic acid expression in rat ovarian granulosa cells by reducing the phosphorylation of insulin receptor substrate-1.
The effect of 5alpha-dihydrotestosterone (DHT) on insulin-stimulated granulosa cell proliferation was examined using cyclin D2 mRNA as a marker. Granulosa cells from 3-d estradiol-treated immature rats showed a concentration-dependent increase in cyclin D2 mRNA expression in response to insulin. Exposure to DHT reduced the insulin-stimulated cyclin D2 mRNA expression. Inhibition of the two insulin-signaling pathways, ERK and phosphatidylinositol 3 kinase (PI3 kinase), by using specific inhibitors, also reduced this insulin-stimulated response. These results suggest that both ERK and PI3 kinase signaling are involved in insulin stimulated granulosa cell proliferation. DHT exposure resulted in reduced insulin-stimulated ERK phosphorylation. DHT treatment also reduced the insulin mediated insulin receptor substrate-1 and Raf-1 phosphorylation, the upstream molecules of ERK in insulin signaling pathway. Additionally, inhibition of insulin stimulated PI3 kinase activation reduced ERK phosphorylation. The present study therefore shows that the inhibitory effect of DHT on insulin-stimulated granulosa cell proliferation occurs early in the signaling pathway at the level of insulin receptor substrate-1 phosphorylation, leading to reduced ERK phosphorylation and subsequent inhibition of cyclin D2 mRNA expression.
Kayampilly
Pradeep P
PP
Departments of Obstetrics and Gynecology and Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.
Menon
K M J
KM
D000818:Animals; D056742:Cyclin D2; D016213:Cyclins / Q000235:genetics*; D013196:Dihydrotestosterone / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D005260:Female; D006107:Granulosa Cells / Q000187:drug effects / Q000502:physiology*; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic
D056742:Cyclin D2; D016213:Cyclins; D013196:Dihydrotestosterone; D048049:Extracellular Signal-Regulated MAP Kinases; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D012333:RNA, Messenger; C486197:Ccnd2 protein, rat; C526296:Irs1 protein, rat