Bützow R, Fukushima D, Twardzik D R, Ruoslahti E
Cancer Research Center, La Jolla Cancer Research Foundation, La Jolla, California 92037.
J Cell Biol. 1993 Aug;122(3):721-7. doi: 10.1083/jcb.122.3.721.
The biological activity of many cytokines is regulated by binding proteins present at the cell surface, in extracellular matrices or in soluble phase. We describe here a TGF-beta binding protein that is both an extracellular matrix and a cell surface protein. When intact extracellular matrices of HEP-G2 cells were affinity cross-linked with 125I-TGF-beta 1, two major binding components were seen: a 250-kD, proteoglycan-like molecule, presumed to be betaglycan, and a 60-kD protein. The 60-kD TGF-beta-binding protein was also present at the cell surface. It could be released from the cell surface by treating cells with high salt, heparin, chondroitin sulfate, heparitinase, or chondroitinase, indicating that it is bound to heparan sulfate and chondroitin sulfate proteoglycans. The 60-kD protein bound TGF-beta 1 with an apparent dissociation constant of 1.6 nM, and there were 30,000 binding sites per cell at the cell surface. In addition to the HEP-G2 cells and another hepatoma cell line, the 60-kD protein was also found in a human colon carcinoma (HT-29) cell line but not in rat kidney (NRK-49F) or human fibroblast (HUT-12) cell lines. The 60-kD protein could be extracted from cells containing it and transferred to the surface of previously negative cells. The 60-kD protein may serve to regulate the binding of TGF-beta to its signal transducing receptors by targeting TGF-beta to appropriate locations in the microenvironment of cells.
许多细胞因子的生物活性受存在于细胞表面、细胞外基质或可溶性相中结合蛋白的调节。我们在此描述一种既是细胞外基质蛋白又是细胞表面蛋白的转化生长因子β（TGF-β）结合蛋白。当用125I-TGF-β1对HEP-G2细胞完整的细胞外基质进行亲和交联时，可见两个主要结合成分：一个250kD的蛋白聚糖样分子，推测为β聚糖，以及一个60kD的蛋白。60kD的TGF-β结合蛋白也存在于细胞表面。用高盐、肝素、硫酸软骨素、肝素酶或软骨素酶处理细胞可将其从细胞表面释放，这表明它与硫酸乙酰肝素和硫酸软骨素蛋白聚糖结合。60kD蛋白结合TGF-β1的表观解离常数为1.6 nM，细胞表面每个细胞有30000个结合位点。除HEP-G2细胞和另一种肝癌细胞系外，在人结肠癌细胞系（HT-29）中也发现了60kD蛋白，但在大鼠肾细胞系（NRK-49F）或人成纤维细胞系（HUT-12）中未发现。60kD蛋白可从含有它的细胞中提取并转移到先前阴性细胞的表面。60kD蛋白可能通过将TGF-β靶向细胞微环境中的适当位置来调节TGF-β与其信号转导受体的结合。
