Insulin-like growth factor binding protein-4 proteolytic degradation in ovine preovulatory follicles: studies of underlying mechanisms.
The regulation of insulin-like growth factor binding protein (IGFBP)-4 proteolytic degradation by insulin-like growth factors (IGFs) has been largely studied in vitro, but not in vivo. The aim of this study was to investigate the involvement of IGFs, IGFBP-2, IGFBP-3, and IGFBP-3 proteolytic fragments in the regulation of IGFBP-4 proteolytic activity in ovine ovarian follicles. Follicular fluid from preovulatory follicles contains proteolytic activity degrading exogenous IGFBP-4. The addition of an excess of IGF-I enhanced IGFBP-4 proteolytic degradation, whereas addition of IGFBP-2 or -3 or monoclonal antibodies against IGF-I and -II dose dependently inhibited IGFBP-4 proteolytic degradation. IGF-I and IGF-II, but not LongR3-IGF-I, reversed this inhibition in a dose-dependent manner. C-terminal, but not N-terminal, proteolytic fragments derived from IGFBP-3 (aa 161-264), as well as heparin-binding domain-containing peptides derived from the C-terminal domain of IGFBP-3 and -5 also induced the inhibition of IGFBP-4 proteolytic degradation. Other heparin-binding domain-containing peptides derived from the connective tissue growth factor (CTGF) and from proteins not related to IGFBP, heparan/heparin interacting protein (HIP) and vitronectin, but not from p36 subunit of annexin II tetramer, inhibited IGFBP-4 degradation. Furthermore, IGFBP-3, mutated on its heparin-binding domain, was not able to inhibit IGFBP-4 proteolytic degradation. So, in ovine preovulatory follicles, IGFBP-4 proteolytic degradation both 1) depends on IGFs, and 2) is inhibited by IGFBP-3 via its C-terminal heparin-binding domain as well as by heparin-binding domain containing peptides. These data suggest that in early atretic follicles, the increase in IGFBP-2 participates in the decrease in IGFBP-4 degradation. In late atretic follicles, the increase in the levels of C-terminal IGFBP-3 proteolytic fragments, generated by IGFBP-3 degradation, as well as the increase in IGFBP-5 expression would strengthen the inhibition of IGFBP-4 degradation. This inhibition might be partly mediated by direct interaction of IGFBP-4 proteinase(s) and heparin-binding domain within the C-terminal region from IGFBP-3 and -5.
Mazerbourg
S
S
Station INRA de Physiologie de la Reproduction des Mammifères Domestiques, Nouzilly, France.
Zapf
J
J
Bar
R S
RS
Brigstock
D R
DR
Lalou
C
C
Binoux
M
M
Monget
P
P
D000818:Animals; D005260:Female; D005498:Follicular Phase / Q000502:physiology*; D006493:Heparin / Q000378:metabolism; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D009154:Mutation / Q000502:physiology; D006080:Ovarian Follicle / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism*; D010455:Peptides / Q000138:chemical synthesis / Q000494:pharmacology; D012756:Sheep; D013002:Somatomedins / Q000502:physiology
D018972:Insulin-Like Growth Factor Binding Protein 3; D018974:Insulin-Like Growth Factor Binding Protein 4; D010446:Peptide Fragments; D010455:Peptides; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D006493:Heparin; D010447:Peptide Hydrolases