Regulation of steroidogenic genes by insulin-like growth factor-1 and follicle-stimulating hormone: differential responses of cytochrome P450 side-chain cleavage, steroidogenic acute regulatory protein, and 3beta-hydroxysteroid dehydrogenase/isomerase in rat granulosa cells.
The present study sought to characterize the concerted action of FSH and insulin-like growth factor-1 (IGF-1) on functional differentiation of prepubertal rat ovarian granulosa cells in culture. To this end, we examined the regulation of three key genes encoding pivotal proteins required for progesterone biosynthesis, namely, side-chain cleavage cytochrome P450 (P450(scc)), steroidogenic acute regulatory (StAR) protein, and 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD). Time-dependent expression profiles showed that P450(scc), StAR, and 3beta-HSD gene products accumulate in chronic, acute, and constitutive patterns, respectively. Each of these genes responded to FSH and/or IGF-1 in a characteristic manner: A synergistic action of IGF-1 was indispensable for FSH induction of P450(scc) mRNA and protein; IGF-1 did not affect FSH-mediated upregulation of StAR products; and IGF-1 alone was enough to promote expression of 3beta-HSD. The responsiveness of the genes to IGF-1 correlated well with their apparent susceptibility to the inhibitory impact of tyrphostin AG18, a potent inhibitor of protein tyrosine kinase receptors. Thus, IGF-1-dependent P450(scc) and 3beta-HSD expression was completely arrested in the presence of AG18, whereas StAR expression was unaffected in the presence of tyrphostin. These findings suggest that FSH/cAMP signaling and IGF-1/tyrosine phosphorylation events are interwoven in rat ovarian cells undergoing functional differentiation. We also sought the mechanism of IGF-1 synergy with FSH. In this regard, our studies were unable to demonstrate a stabilizing effect of IGF-1 on P450(scc) mRNA, nor could IGF-1 augment FSH-induced transcription examined using a proximal region of the P450(scc) promoter (-379/+6). Thus, the mechanism of IGF-1 and FSH synergy remains enigmatic and provides a major challenge for future studies.
Eimerl
Sarah
S
Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Orly
Joseph
J
D000818:Animals; D002478:Cells, Cultured; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000032:analysis / Q000235:genetics*; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006107:Granulosa Cells / Q000737:chemistry / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D016253:Microscopy, Immunoelectron; D009097:Multienzyme Complexes / Q000032:analysis / Q000235:genetics*; D010750:Phosphoproteins / Q000032:analysis / Q000235:genetics*; D011375:Progesterone Reductase / Q000032:analysis / Q000235:genetics*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013251:Steroid Isomerases / Q000032:analysis / Q000235:genetics*; D020032:Tyrphostins / Q000494:pharmacology; D000098682:Steroidogenic Acute Regulatory Protein
C021425:3 beta-hydroxysteroid oxidoreductase-delta(5) 3-ketosteroid isomerase; D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D010750:Phosphoproteins; D012333:RNA, Messenger; D020032:Tyrphostins; D000098682:Steroidogenic Acute Regulatory Protein; D007334:Insulin-Like Growth Factor I; D005640:Follicle Stimulating Hormone; D011375:Progesterone Reductase; D002786:Cholesterol Side-Chain Cleavage Enzyme; D011505:Protein-Tyrosine Kinases; D013251:Steroid Isomerases; C060641:tyrphostin A23