Collett-Solberg P F, Nunn S E, Gibson T B, Cohen P
Division of Endocrinology and Diabetes, The Children's Hospital of Philadelphia, University of Pennsylvania 19104, USA.
J Clin Endocrinol Metab. 1998 Aug;83(8):2843-8. doi: 10.1210/jcem.83.8.5053.
The insulin-like growth factor (IGF)-binding proteins (IGFBPs) carry IGFs in serum and regulate their activity and bioavailability. The main IGFBP in serum, IGFBP-3, is known to form a 150-kDa complex with IGFs and the acid-labile subunit (ALS). We investigated the binding of IGFBP-3 to additional association proteins in human serum (IGFBP-3 APs). Ligand blots, column chromatography, and affinity cross-linking experiments revealed the specific binding of IGFBP-3 to at least three novel serum proteins. These techniques demonstrated the presence of proteins with molecular masses of 70, 100, and 150 kDa that bind IGFBP-3 with high affinity. Serum ALS migrated separately (at 88 kDa) from the novel IGFBP-3 APs (as evident by Western immunoblot), and bound IGFBP-3 weakly (by reverse ligand blots). We also demonstrated that large amounts of one of the IGFBP-3 APs and small amounts of ALS were coimmunoprecipitated with IGFBP-3 from human serum. Similar to ALS, these IGFBP-3 APs are acid labile and lose their IGFBP-3 binding capacity after exposure to low pH. We conclude that there are several serum proteins in addition to ALS and IGFs that bind IGFBP-3 with high affinity. These IGFBP-3 APs may serve as an additional reservoir of IGFBP-3 or modulate its functions.
胰岛素样生长因子（IGF）结合蛋白（IGFBPs）在血清中携带IGFs，并调节其活性和生物利用度。血清中的主要IGFBP，即IGFBP-3，已知可与IGFs和酸不稳定亚基（ALS）形成150 kDa的复合物。我们研究了IGFBP-3与人血清中其他结合蛋白（IGFBP-3 APs）的结合情况。配体印迹、柱色谱和亲和交联实验揭示了IGFBP-3与至少三种新型血清蛋白的特异性结合。这些技术证明存在分子量分别为70 kDa、100 kDa和150 kDa的蛋白质，它们以高亲和力结合IGFBP-3。血清中的ALS（88 kDa）与新型IGFBP-3 APs在免疫印迹中迁移情况不同，且与IGFBP-3的结合较弱（通过反向配体印迹显示）。我们还证明，从人血清中与IGFBP-3共免疫沉淀出大量的一种IGFBP-3 APs和少量的ALS。与ALS相似，这些IGFBP-3 APs对酸不稳定，在暴露于低pH后会失去其与IGFBP-3的结合能力。我们得出结论，除了ALS和IGFs外，还有几种血清蛋白以高亲和力结合IGFBP-3。这些IGFBP-3 APs可能作为IGFBP-3的额外储存库或调节其功能。
