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Regular Article |
a Department of Applied Dental Medicine, Southern Illinois University, School of Dental Medicine, Alton, Illinois 62002
Hepatocyte growth factor (HGF) down-modulates FSH-dependent estradiol-17ß (E2) production in ovarian granulosa cells in vitro. The mechanisms of action underlying the antiestrogenic effects of HGF are vague, although evidence indicates that HGF may affect cAMP signal transduction in rat granulosa cells. The present study investigated the effects of HGF on FSH-induced steroidogenesis in the presence and absence of insulin-like growth factor I (IGF-I), as well as the actions of HGF within cyclic nucleotide-dependent signal transduction cascades in granulosa cells. Immature rat granulosa cells were incubated with FSH, IGF-I, and HGF. HGF impaired the production of FSH-stimulated and FSH + IGF-I-stimulated E2 synthesis, as well as FSH + IGF-I-dependent estrone production. Progesterone synthesis was not altered by HGF. HGF suppressed FSH-dependent cAMP content at 24 h, but not at 36 h; cGMP content was stimulated by HGF with and without FSH at 24 h. In the presence of the cyclic nucleotide phosphodiesterase (PDE) inhibitor, 3-isobutyl-1-methylxanthine (IBMX), FSH-dependent cAMP accumulation was not affected by HGF. The suppressive effect of HGF on FSH-dependent E2 production was alleviated by IBMX, whereas the HGF-dependent block in FSH + IGF-I-supported E2 production was not prevented by IBMX. The effects of HGF on cyclic nucleotide PDE activities were manifested in a time-dependent and hormone-dependent manner. FSH-induced cAMP PDE was suppressed by HGF at 24 h but not at 36 h, whereas FSH-dependent cGMP PDE was impaired at 36 h, but not at 24 h. HGF prevented the IGF-I-dependent reduction in FSH-stimulated cAMP-PDE activity at 24 and 36 h, and lowered FSH + IGF-I-stimulated cGMP-PDE activity at 36 h, concomitant with an HGF-dependent increase in cGMP content at 24 h. These data indicate that HGF affects cAMP-directed and cGMP-directed signaling pathways at multiple sites in granulosa cells. These HGF-dependent effects may provide insight for mechanisms of action whereby HGF reduces E2 secretion by granulosa cells.
1 Supported by grant HD38277-01 from the National Institutes of Health and grants A1A 01-1 and A1A 02-1 from the Southern Illinois University School of Dental Medicine to R.J.Z.
2 Correspondence: Rob J. Zachow, Southern Illinois University, School of Dental Medicine, 2800 College Ave., Alton, IL 62002. FAX: 618 474 7124; rzachow{at}siue.edu
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