Growth of differentiation: determination by FSH of the action of insulin-like growth factor-I in cultured rat granulosa cells.
Insulin-like growth factor-I (IGF-I) is a potent mitogen in many cell systems. In cultured rat granulosa cells, however, IGF-I is known to be an inducer of differentiation. The present study was conducted to identify the factor which determines the direction of IGF-I action: either DNA synthesis or LH receptor expression. When granulosa cells were incubated with IGF-I in the presence of various concentrations of follicle-stimulating hormone (FSH), DNA synthesis as assessed by [3H]thymidine incorporation was increased only in the presence of low doses of FSH. The stimulatory effect of FSH on DNA synthesis was observed in a very narrow range of FSH concentration between 2 and 10 ng/ml. At higher concentrations, FSH had little effect on DNA synthesis but instead induced expression of receptors for luteinizing hormone (LH), a marker of granulosa cell differentiation. At 5 ng/ml, FSH elicited maximal stimulation of DNA synthesis and simultaneously induced LH receptor expression to some extent. In these cells, DNA synthesis peaked at 36 h but expression of LH receptor occurred later than 36 h, peaking at 60 h. The ability of IGF-I to stimulate DNA synthesis was enhanced by the long term pretreatment with FSH: when FSH was added from the beginning and IGF-I was added after 36 h or later, IGF-I-mediated DNA synthesis was approximately twice as great, and was accompanied by a two-fold increase in the number of bromodeoxyuridine-labeled nuclei. Under these conditions, LH receptor expression was reduced to approximately 50%. Finally when cells were incubated for 12 h with or without FSH, washed extensively with the medium and then IGF-I was added, DNA synthesis was augmented only in FSH-primed cells. Forskolin, an activator of adenylate cyclase, reproduced the effect of FSH. These results indicate that, in the presence of FSH, IGF-I has the ability to induce both DNA synthesis and differentiation and that FSH determines the action of IGF-I on promotion of either growth or differentiation. Furthermore, priming with FSH renders granulosa cells responsive to IGF-I in terms of DNA synthesis.
Kanzaki
M
M
Department of Cell Biology, Gunma University, Maebashi, Japan.
Hattori
M
M
Kojima
I
I
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007700:Kinetics; D051381:Rats; D017208:Rats, Wistar; D011974:Receptors, LH / Q000096:biosynthesis
D011974:Receptors, LH; D005576:Colforsin; D007334:Insulin-Like Growth Factor I; D005640:Follicle Stimulating Hormone; D004247:DNA