Knudtson K L, Boes M, Sandra A, Dake B L, Booth B A, Bar R S
Department of Internal Medicine, Diabetes and Endocrinology Research Center, Veterans Administration Medical Center, The University of Iowa, Iowa City, Iowa 52246, USA.
Endocrinology. 2001 Sep;142(9):3749-55. doi: 10.1210/endo.142.9.8353.
IGF binding proteins-3 and -4, whether given in the perfused rat heart or given iv in the intact animal, cross the microvascular endothelium of the heart and distribute in subendothelial tissues. IGF binding protein-3, like IGF-I/II, localizes in cardiac muscle, with lesser concentrations in CT elements. In contrast, IGFBP-4 preferentially localizes in CT. In this study, chimeric IGF binding proteins were prepared in which a basic 20-amino-acid C-terminal region of IGF binding protein-3 was switched with the homologous region of IGF binding protein-4, and vice-versa, to create IGF binding protein-3(4) and IGF binding protein-4(3). Perfused IGF binding protein-3(4) behaved like IGF binding protein-4, localizing in connective tissue elements, whereas IGF binding protein-4(3) now localized in cardiac muscle at concentrations identical to perfused IGF binding protein-3. To determine whether these small mutations altered the affinity of the chimera for cells, the ability of (125)I-IGF binding protein-3(4) and (125)I-IGF binding protein-4(3) to bind to microvascular endothelial cells was determined and compared with IGF binding protein-3. IGF binding protein-3(4) retained 15% of the binding capacity of IGF binding protein-3, whereas IGF binding protein-4(3) bound to microvessel endothelial cells with higher affinity and greater total binding than that of IGF binding protein-3. We conclude that small changes in the C-terminal basic domain of IGF binding protein-3 and the corresponding region of IGF binding protein-4 can alter their affinity for cultured cells and influence their tissue distribution in the rat heart.
胰岛素样生长因子结合蛋白-3和-4，无论是在灌注的大鼠心脏中给予还是在完整动物中静脉注射，都能穿过心脏的微血管内皮并分布于内皮下组织。胰岛素样生长因子结合蛋白-3与胰岛素样生长因子-I/II一样，定位于心肌，在结缔组织成分中的浓度较低。相比之下，胰岛素样生长因子结合蛋白-4优先定位于结缔组织。在本研究中，制备了嵌合胰岛素样生长因子结合蛋白，其中胰岛素样生长因子结合蛋白-3的20个氨基酸的碱性C末端区域与胰岛素样生长因子结合蛋白-4的同源区域进行了交换，反之亦然，以产生胰岛素样生长因子结合蛋白-3(4)和胰岛素样生长因子结合蛋白-4(3)。灌注的胰岛素样生长因子结合蛋白-3(4)的行为类似于胰岛素样生长因子结合蛋白-4，定位于结缔组织成分，而胰岛素样生长因子结合蛋白-4(3)现在定位于心肌，其浓度与灌注的胰岛素样生长因子结合蛋白-3相同。为了确定这些小突变是否改变了嵌合体对细胞的亲和力，测定了(125)I-胰岛素样生长因子结合蛋白-3(4)和(125)I-胰岛素样生长因子结合蛋白-4(3)与微血管内皮细胞结合的能力，并与胰岛素样生长因子结合蛋白-3进行了比较。胰岛素样生长因子结合蛋白-3(4)保留了胰岛素样生长因子结合蛋白-3结合能力的15%，而胰岛素样生长因子结合蛋白-4(3)与微血管内皮细胞结合的亲和力更高，总结合量比胰岛素样生长因子结合蛋白-3更大。我们得出结论，胰岛素样生长因子结合蛋白-3的C末端碱性结构域和胰岛素样生长因子结合蛋白-4的相应区域的微小变化可以改变它们对培养细胞的亲和力，并影响它们在大鼠心脏中的组织分布。
