Lawrence J B, Oxvig C, Overgaard M T, Sottrup-Jensen L, Gleich G J, Hays L G, Yates J R, Conover C A
Endocrine Research Unit, Mayo Clinic and Mayo Foundation, Rochester, MN 55905, USA.
Proc Natl Acad Sci U S A. 1999 Mar 16;96(6):3149-53. doi: 10.1073/pnas.96.6.3149.
Proteolytic cleavage of the six known insulin-like growth factor binding proteins (IGFBPs) is a powerful means of rapid structure and function modification of these important growth-regulatory proteins. Intact IGFBP-4 is a potent inhibitor of IGF action in vitro, and cleavage of IGFBP-4 has been shown to abolish its ability to inhibit IGF stimulatory effects in a variety of systems, suggesting that IGFBP-4 proteolysis acts as a positive regulator of IGF bioavailability. Here we report the isolation of an IGF-dependent IGFBP-4-specific protease from human fibroblast-conditioned media and its identification by mass spectrometry microsequencing as pregnancy-associated plasma protein-A (PAPP-A), a protein of unknown function found in high concentrations in the maternal circulation during pregnancy. Antibodies raised against PAPP-A both inhibited and immunodepleted IGFBP-4 protease activity in human fibroblast-conditioned media. Moreover, PAPP-A purified from pregnancy sera had IGF-dependent IGFBP-4 protease activity. PAPP-A mRNA was expressed by the human fibroblasts and osteoblasts, and PAPP-A protein was secreted into the culture medium. In conclusion, we have identified an IGF-dependent IGFBP protease and at the same time assigned a function to PAPP-A. This represents an unanticipated union of two areas of research that were not linked in any way before this report.
对六种已知的胰岛素样生长因子结合蛋白（IGFBPs）进行蛋白水解切割，是快速改变这些重要生长调节蛋白结构与功能的有力手段。完整的IGFBP-4在体外是IGF作用的强效抑制剂，并且在多种系统中，IGFBP-4的切割已被证明会消除其抑制IGF刺激作用的能力，这表明IGFBP-4蛋白水解是IGF生物利用度的正向调节因子。在此，我们报告了从人成纤维细胞条件培养基中分离出一种IGF依赖性IGFBP-4特异性蛋白酶，并通过质谱微测序将其鉴定为妊娠相关血浆蛋白-A（PAPP-A），这是一种在孕期母体循环中高浓度存在但功能未知的蛋白。针对PAPP-A产生的抗体既能抑制人成纤维细胞条件培养基中的IGFBP-4蛋白酶活性，也能使其免疫耗竭。此外，从妊娠血清中纯化的PAPP-A具有IGF依赖性IGFBP-4蛋白酶活性。人成纤维细胞和成骨细胞表达PAPP-A mRNA，并且PAPP-A蛋白分泌到培养基中。总之，我们鉴定出了一种IGF依赖性IGFBP蛋白酶，同时赋予了PAPP-A一种功能。这代表了两个此前毫无关联的研究领域意外的结合。
