Effect of follicle stimulating hormone and insulin-like growth factors on proteolysis of insulin-like growth factor binding protein-4 in human granulosa cells.
Follicular fluid from dominant follicles, but not atretic follicles, contains insulin-like growth factor binding protein-4 (IGFBP-4) proteolytic activity. The effect of follicle stimulating hormone (FSH) and insulin-like growth factors (IGFs) on IGFBP-4 proteolytic activity was studied using granulosa cell cultures. Proteolytic activity was assessed by the incubation of [1251]-IGFBP-4 with medium and cleaved products which were analysed by autoradiography. The iodinated IGFBP-4 was cleaved into an 18 kDa fragment when cells were incubated with FSH or IGFs while IGFBP-4 remained intact in the control culture. Inhibition of IGFBP-4 degradation by several protease inhibitors suggests that IGFBP-4 degradation was induced by a metalloserine protease. The degradation of IGFBP-4 was not stimulated when cells were incubated with the IGF-I analogue, LR3-IGF-I, and insulin which binds to IGF-I receptor but has little or no affinity for IGFBPs. Addition of IGFs, but not FSH, to medium from untreated granulosa cell cultures stimulated proteolysis of [1251]-IGFBP-4. Similarly, exogenously added covalently cross-linked [125I]-IGF-II-IGFBP-4 complexes were proteolyzed; however, IGFs did not enhance the degradation of these complexes. These results suggest that human granulosa cells produce IGFBP-4 protease and that the increased susceptibility of IGFBP-4 to proteolysis is induced by the binding of IGFs to IGFBP-4. These novel mechanisms may be important in modulating IGF-mediated folliculogenesis in the ovary.
Iwashita
M
M
Department of Obstetrics and Gynecology, Tokyo Women's Medical College, Japan.
Kudo
Y
Y
Takeda
Y
Y
D001345:Autoradiography; D002478:Cells, Cultured; D003432:Cross-Linking Reagents / Q000494:pharmacology; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000378:metabolism*; D008666:Metalloendopeptidases / Q000378:metabolism*; D011266:Pregnancy-Associated Plasma Protein-A; D013002:Somatomedins / Q000494:pharmacology*
D003432:Cross-Linking Reagents; D018974:Insulin-Like Growth Factor Binding Protein 4; D013002:Somatomedins; D005640:Follicle Stimulating Hormone; D008666:Metalloendopeptidases; D011266:Pregnancy-Associated Plasma Protein-A