Guo Y S, Narayan S, Yallampalli C, Singh P
Department of Surgery, University of Texas Medical Branch, Galveston.
Gastroenterology. 1992 Apr;102(4 Pt 1):1101-8.
A possible role of insulinlike growth factor I (IGF-I) and IGF-I receptors in the proliferation of human colon cancer has, to the best of the authors' knowledge, not been examined as yet. To determine a role of IGF-I in colon cancer, several human colon cancer cell lines and colon cancers were screened for specific binding to 125I-IGF-I. Almost all the human colon cancer cells examined were variably positive for specifically binding 125I-IGF-I. Almost half the colon cancer cell lines examined showed significant growth response to 6.6 nmol/L IGF-I. Dose-dependent growth effects of exogenously added IGF-I (0.05-3.3 nmol/L) were shown in a representative human colon cancer cell line (Colo-205). To determine if IGF-I binding sites on colon cancer cells were similar or different from that described on other cells, the binding affinity, binding specificity, and molecular size of the IGF-I binding sites were characterized in representative human colon cancer cell lines (HCT-116 and Colo-205). The optimal binding assay conditions for measuring maximum number of 125I-IGF-I binding sites on the cells, in vitro, were determined and found to be similar to that described on other cells. Scatchard analysis of the specific binding data showed the presence of a single class of high-affinity binding sites [disassociation constant (Kd) = approximately 1.0-2.0 nmol/L], with a binding capacity of 1.0-2.0 x 10(5) sites per cell. The molecular weight of IGF-I receptors on cell membranes was determined by gel electrophoresis of the affinity cross-linked proteins, followed by autoradiography. A single band of binding proteins with a molecular mass of approximately 300 kilodaltons was evident under nonreducing conditions and separated out into two bands of approximately 240 and approximately 130 kilodaltons under reducing conditions. The 130-kilodalton band represents the alpha subunit of IGF-I receptors, and the 240-kilodalton band may represent aggregates of the receptor subunits that were not reduced completely. The widespread existence of high-affinity binding sites for IGF-I in established human colon cancer cell lines and freshly resected human colon cancers and the proliferative effect of IGF-I in several colon cancer cell lines, in vitro, reflect that IGF-I may be an important endocrine/paracrine/autocrine factor in the growth regulation of colon cancers in situ.
就作者所知，胰岛素样生长因子I（IGF-I）及其受体在人类结肠癌增殖过程中的潜在作用尚未得到研究。为了确定IGF-I在结肠癌中的作用，研究人员对几种人类结肠癌细胞系和结肠癌组织进行了筛选，以检测其与125I-IGF-I的特异性结合情况。几乎所有检测的人类结肠癌细胞对125I-IGF-I的特异性结合均呈不同程度的阳性。几乎一半的检测结肠癌细胞系对6.6 nmol/L的IGF-I表现出显著的生长反应。在一种代表性的人类结肠癌细胞系（Colo-205）中，显示出外源添加的IGF-I（0.05 - 3.3 nmol/L）具有剂量依赖性生长效应。为了确定结肠癌细胞上的IGF-I结合位点与其他细胞上所描述的位点是否相似或不同，研究人员在代表性的人类结肠癌细胞系（HCT-116和Colo-205）中对IGF-I结合位点的结合亲和力、结合特异性和分子大小进行了表征。确定了在体外测量细胞上125I-IGF-I结合位点最大数量的最佳结合测定条件，发现其与其他细胞上所描述的条件相似。对特异性结合数据的Scatchard分析表明存在一类单一的高亲和力结合位点[解离常数（Kd）=约1.0 - 2.0 nmol/L]，每个细胞的结合容量为1.0 - 2.0×10(5)个位点。通过对亲和交联蛋白进行凝胶电泳，然后进行放射自显影，测定了细胞膜上IGF-I受体的分子量。在非还原条件下，可见一条分子量约为300千道尔顿的单一结合蛋白条带，在还原条件下分离为两条分子量约为240千道尔顿和约130千道尔顿的条带。130千道尔顿的条带代表IGF-I受体的α亚基，240千道尔顿的条带可能代表未完全还原的受体亚基聚集体。在已建立的人类结肠癌细胞系和新鲜切除的人类结肠癌组织中广泛存在IGF-I的高亲和力结合位点，以及IGF-I在体外对几种结肠癌细胞系的增殖作用，表明IGF-I可能是原位结肠癌生长调节中的一种重要的内分泌/旁分泌/自分泌因子。
