Mazerbourg S, Zapf J, Bar R S, Brigstock D R, Lalou C, Binoux M, Monget P
Station INRA de Physiologie de la Reproduction des Mammifères Domestiques, Nouzilly, France.
Endocrinology. 1999 Sep;140(9):4175-84. doi: 10.1210/endo.140.9.6979.
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.
胰岛素样生长因子（IGF）对胰岛素样生长因子结合蛋白（IGFBP）-4蛋白水解降解的调节作用在体外已得到广泛研究，但在体内尚未见报道。本研究旨在探讨IGF、IGFBP-2、IGFBP-3和IGFBP-3蛋白水解片段在绵羊卵巢卵泡中对IGFBP-4蛋白水解活性调节中的作用。排卵前卵泡的卵泡液含有降解外源性IGFBP-4的蛋白水解活性。添加过量的IGF-I可增强IGFBP-4的蛋白水解降解，而添加IGFBP-2或-3或抗IGF-I和-II的单克隆抗体则剂量依赖性地抑制IGFBP-4的蛋白水解降解。IGF-I和IGF-II，但不是长R3-IGF-I，以剂量依赖性方式逆转这种抑制作用。来自IGFBP-3（第161-264位氨基酸）的C末端而非N末端蛋白水解片段，以及来自IGFBP-3和-5 C末端结构域的含肝素结合结构域的肽也可诱导对IGFBP-4蛋白水解降解的抑制。来自结缔组织生长因子（CTGF）以及与IGFBP无关的蛋白质、硫酸乙酰肝素/肝素相互作用蛋白（HIP）和玻连蛋白的其他含肝素结合结构域的肽，但不是来自膜联蛋白II四聚体p36亚基的肽，可抑制IGFBP-4的降解。此外，在其肝素结合结构域发生突变的IGFBP-3不能抑制IGFBP-4的蛋白水解降解。因此，在绵羊排卵前卵泡中，IGFBP-4的蛋白水解降解：1）依赖于IGF；2）被IGFBP-3通过其C末端肝素结合结构域以及含肝素结合结构域的肽所抑制。这些数据表明，在早期闭锁卵泡中，IGFBP-2的增加参与了IGFBP-4降解的减少。在晚期闭锁卵泡中，由IGFBP-3降解产生的C末端IGFBP-3蛋白水解片段水平的增加以及IGFBP-5表达的增加将加强对IGFBP-4降解的抑制。这种抑制可能部分是由IGFBP-4蛋白酶与IGFBP-3和-5 C末端区域内的肝素结合结构域的直接相互作用介导的。
