Bonner J C, Osornio-Vargas A R
Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
J Biol Chem. 1995 Jul 7;270(27):16236-42. doi: 10.1074/jbc.270.27.16236.
Alpha 2-Macroglobulin (alpha 2M) is a multifunctional secreted glycoprotein that serves as a ubiquitous proteinase inhibitor and as a binding protein for platelet-derived growth factor (PDGF) BB and homologues of PDGF-BB secreted in culture by macrophages. The interaction of alpha 2M with PDGF-A chain molecules has not been addressed. This is a potentially important issue because fibroblasts and smooth muscle cells produce PDGF-AA, whereas macrophages produce mainly PDGF-BB. Recombinant human 125I-PDGF-B chain molecules (AB and BB) bound to plasma-derived, native human, or bovine alpha 2M and trypsin-activated alpha 2M on Superose 6 fast protein liquid chromatography gel filtration and on nondenaturing polyacrylamide gel electrophoresis, whereas 125I-PDGF-AA did not. Similar results were obtained with 125I-PDGF isoforms binding to immobilized bovine alpha 2M and alpha 2M-methylamine. The same differential pattern of unlabeled PDGF isoforms binding to alpha 2M was observed by Western blotting of PDGF. Human lung fibroblasts secreted alpha 2M as measured by Western blotting, and fibroblast-derived alpha 2M possessed the same differential binding pattern for PDGF isoforms as did plasma-derived alpha 2M. The specific binding of PDGF-AB and -BB to these fibroblasts was inhibited by native bovine alpha 2M, although PDGF-AA binding was not affected. Native alpha 2M preferentially blocked fibroblast chemotaxis to the PDGF-B chain dimers. These data suggest that only PDGF-B chain dimers, such as those produced by macrophages or released from platelets, are regulated by alpha 2M and that PDGF-AA produced by fibroblasts and smooth muscle cells is not controlled by this cytokine-binding protein.
α2-巨球蛋白（α2M）是一种多功能分泌糖蛋白，作为一种普遍存在的蛋白酶抑制剂，以及血小板衍生生长因子（PDGF）BB和巨噬细胞在培养物中分泌的PDGF-BB同源物的结合蛋白。α2M与PDGF-A链分子之间的相互作用尚未得到研究。这是一个潜在的重要问题，因为成纤维细胞和平滑肌细胞产生PDGF-AA，而巨噬细胞主要产生PDGF-BB。在Superose 6快速蛋白质液相色谱凝胶过滤和非变性聚丙烯酰胺凝胶电泳中，重组人125I-PDGF-B链分子（AB和BB）与血浆来源的、天然人源或牛源α2M以及胰蛋白酶激活的α2M结合，而125I-PDGF-AA则不结合。用125I-PDGF同工型与固定化牛α2M和α2M-甲胺结合也得到了类似结果。通过PDGF的蛋白质印迹法观察到未标记的PDGF同工型与α2M结合的相同差异模式。通过蛋白质印迹法测定，人肺成纤维细胞分泌α2M，且成纤维细胞来源的α2M对PDGF同工型的差异结合模式与血浆来源的α2M相同。天然牛α2M抑制PDGF-AB和-BB与这些成纤维细胞的特异性结合，而PDGF-AA的结合不受影响。天然α2M优先阻断成纤维细胞对PDGF-B链二聚体的趋化作用。这些数据表明，只有巨噬细胞产生的或从血小板释放的PDGF-B链二聚体受α2M调节，而成纤维细胞和平滑肌细胞产生的PDGF-AA不受这种细胞因子结合蛋白的控制。
