Insulin-like growth factor-I-mediated amplification of follicle-stimulating hormone-supported progesterone accumulation by cultured rat granulosa cells: enhancement of steroidogenic enzyme activity and expression.
A body of information now supports the existence of an ovarian intrafollicular insulin-like growth factor (IGF)-I system concerned with the amplification of FSH action at the level of the rat granulosa cell. In this study we examined the ability of IGF-I to modulate the basal and FSH-supported activity and expression of key steroidogenic enzymes concerned with progesterone generation and metabolism in cultured granulosa cells from immature rats. The provision of IGF-I stimulated FSH-supported (20 ng/ml) accumulation of progesterone in a dose-dependent manner, reaching a plateau at an IGF-I dose of 50 ng/ml. This dose of IGF-I substantially enhanced FSH action over a broad range of FSH concentrations, reaching a maximum at an FSH dose of 20 ng/ml. Pulse labeling of FSH-pretreated cells with [3H]pregnenolone revealed relatively rapid (< 5 h) transformation to [3H]progesterone and other distal products that was accelerated by the concurrent addition of IGF-I. These changes in progesterone metabolism were associated with IGF-I-mediated enhancement of the activities and expression of key steroidogenic enzymes. Specifically, treatment with IGF-I produced significant augmentation of the FSH-stimulated activities of cholesterol side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/ isomerase (3 beta-HSD) enzymes (2.4- and 1.8-fold, respectively). Similarly, P450scc and type I 3 beta-HSD transcripts were elevated by FSH in a dose-dependent manner, the concurrent addition of IGF-I further increasing expression (up to an additional 3-fold) in the range of 1-5 ng/ml (but not at the maximally stimulating dose of 20 ng/ml FSH). The addition of IGF-I also increased basal levels of type I 3 beta-HSD transcripts (3.8-fold). IGF-I enhanced FSH-stimulated 20 alpha-HSD activity and transcripts (2.3-fold and 1.8-fold, respectively) and increased the basal levels of 20 alpha-HSD transcripts (3-fold). Basal levels of 5 alpha-reductase were slightly elevated (1.3-fold) by IGF-I, but the FSH-attenuated activity was unchanged. Taken together, these findings suggest that IGF-I enhances the FSH-supported accumulation of progesterone in cultured granulosa cells through up-regulation of the expression and activity of key enzymes in the steroidogenic pathway. The acceleration of progesterone accumulation reflects a newly established steady state, favoring the activities of progesterone-forming over progesterone-metabolizing enzymes.
deMoura
M D
MD
Department of Obstetrics and Gynecology, University of Maryland School of Medicine, Baltimore 21201, USA.
Choi
D
D
Adashi
E Y
EY
Payne
D W
DW
D015096:3-Hydroxysteroid Dehydrogenases / Q000096:biosynthesis / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D002478:Cells, Cultured; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000096:biosynthesis / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D011284:Pregnenolone / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014158:Transcription, Genetic / Q000187:drug effects*
D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D011284:Pregnenolone; D005640:Follicle Stimulating Hormone; D015096:3-Hydroxysteroid Dehydrogenases; D002786:Cholesterol Side-Chain Cleavage Enzyme