Insulin-like growth factor-I regulation of luteinizing hormone (LH) receptor messenger ribonucleic acid expression and LH-stimulated signal transduction in rat ovarian theca-interstitial cells.
Currently available evidence supports the hypothesis that insulin-like growth factor-I (IGF-I) secreted by small preantral follicles may be involved in stimulating the initial differentiation of the theca interna and, in particular, expression of the LH receptor in pre-theca cells. To test this hypothesis, we examined the effects of IGF-I on LH receptor mRNA expression in theca-interstitial cells (TIC) isolated from the ovaries of hypophysectomized immature rats by percoll gradient centrifugation. TIC (3.5 x 10(4) viable cells/well) were cultured up to 6 days with and without LH (0-10 ng/ml) and IGF-I (0-100 ng/ml). Androsterone in the medium was measured by RIA, and LH receptor mRNA was measured by specific reverse transcriptase-polymerase chain reaction assay. LH receptor mRNA was low in control (untreated) TIC. IGF-I stimulated a dose-related increase (2-fold) in LH receptor mRNA at 2 days (ED50 = 9.0 +/- 1.9 ng/ml) that remained constant at 4 days and then declined to basal levels at 6 days. LH stimulated a dose-related (ED50 = 17.6 +/- 1.0 pg/ml) increase in LH receptor mRNA that reached a maximum of 4-fold at 2 days. At 4 days, LH down-regulated LH receptor mRNA below basal levels, and it had no effect at 6 days. Addition of IGF-I (30 ng/ml) to LH-treated TIC abolished the stimulatory effect of LH throughout the culture period. LH receptor mRNA was highly sensitive to LH since the ED50 was approximately 2.5-fold lower than for stimulation of androsterone production (39.8 +/- 3.8 pg/ml). To understand the molecular mechanism of the synergistic stimulation of androgen production by IGF-I and LH, the effects of IGF-I on the cAMP/protein kinase A (PKA) signaling pathway were examined. When freshly isolated TIC were challenged with IGF-I alone (30 ng/ml), there was no effect on cAMP production or PKA activity, but IGF-I augmented LH stimulation of cAMP production slightly at high concentrations of LH and blocked stimulation of PKA activity by a saturating concentration of LH (3 ng/ml), suggesting that IGF-I increased LH down-regulation of PKA. We next examined the effects of IGF-I on LH receptor number. When TIC were placed into culture, LH/hCG binding sites decreased to approximately 35% of the initial number at 24 h and 25% at 2 days. This decrease was accompanied by a similar loss of cholera toxin- and hCG-stimulated cAMP production.(ABSTRACT TRUNCATED AT 400 WORDS)
Magoffin
D A
DA
Department of Obstetrics and Gynecology, Cedars-Sinai Research Institute, Cedars-Sinai Medical Center/UCLA School of Medicine 90048.
Weitsman
S R
SR
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D012194:RNA-Directed DNA Polymerase; D051381:Rats; D017207:Rats, Sprague-Dawley; D011974:Receptors, LH / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013799:Theca Cells / Q000187:drug effects / Q000378:metabolism*
D006063:Chorionic Gonadotropin; D012333:RNA, Messenger; D011974:Receptors, LH; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D012194:RNA-Directed DNA Polymerase