Reeve J G, Morgan J, Schwander J, Bleehen N M
Medical Research Council Clinical Oncology and Radiotherapeutics Unit, Medical Research Council Centre, Cambridge, United Kingdom.
Cancer Res. 1993 Oct 1;53(19):4680-5.
The insulin-like growth factors (IGFs) have been implicated in the autocrine and/or paracrine growth of a number of tumor types, including lung tumors. Importantly, insulin-like growth factor-binding proteins (IGFBPs), which both enhance and inhibit the physiological and biological actions of the IGFs, have been shown to be secreted in vitro by a wide range of tumors. In particular, IGFBP-2 is frequently produced by human tumor cells, suggesting that this protein may be an important determinant of IGF action in tumors. In the present study, we investigated IGFBP-2 effects in lung tumor cells by examining the influence of IGFBP-2 on IGF-receptor interaction and the biological actions of IGF-I and IGF-II. Affinity cross-linking studies demonstrated expression of type-I and type-II IGF receptors on small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cells and the presence of abundant membrane-associated IGFBP in SCLC cells but not in NSCLC cells. An antiserum specific for IGFBP-2 was used in immunoprecipitation and immunoblotting studies which demonstrated that the membrane-associated IGFBP identified by affinity cross-linking in SCLC cells is IGFBP-2. In NSCLC cells, both IGF-I and IGF-II bound predominantly to IGF-I receptors, whereas in SCLC cells binding was principally to surface-associated IGFBP-2. SCLC cells failed to respond to IGF-I and -II stimulation in a DNA synthesis assay. For NSCLC cells, IGF-II was a more potent stimulator of DNA synthesis than IGF-I. Soluble IGFBP-2 inhibited the binding of radiolabeled IGF-I and -II to both SCLC and NSCLC cells in a concentration-dependent manner and inhibited IGF-stimulated DNA synthesis in NSCLC cells. These observations indicate that both soluble and membrane-associated IGFBP-2 compete with IGF receptors for ligand binding and, thus, are likely to be important determinants of IGF responsiveness. The findings of the present study also indicate that the type-I receptor on NSCLC cells contains a high-affinity binding site for IGF-II which presumably mediates the biological effects of IGF-II in these cells, thereby implicating IGF-II in the autocrine/paracrine growth of NSCLC.
胰岛素样生长因子（IGFs）与多种肿瘤类型（包括肺癌）的自分泌和/或旁分泌生长有关。重要的是，胰岛素样生长因子结合蛋白（IGFBPs）既能增强也能抑制IGFs的生理和生物学作用，已被证明在体外可由多种肿瘤分泌。特别是，IGFBP - 2经常由人类肿瘤细胞产生，这表明该蛋白可能是肿瘤中IGF作用的重要决定因素。在本研究中，我们通过检查IGFBP - 2对IGF受体相互作用以及IGF - I和IGF - II生物学作用的影响，来研究IGFBP - 2在肺癌细胞中的作用。亲和交联研究表明，I型和II型IGF受体在小细胞肺癌（SCLC）和非小细胞肺癌（NSCLC）细胞上表达，且SCLC细胞中存在大量与膜相关的IGFBP，而NSCLC细胞中则没有。一种针对IGFBP - 2的抗血清用于免疫沉淀和免疫印迹研究，结果表明在SCLC细胞中通过亲和交联鉴定出的与膜相关的IGFBP是IGFBP - 2。在NSCLC细胞中，IGF - I和IGF - II主要与IGF - I受体结合，而在SCLC细胞中，结合主要是与表面相关的IGFBP - 2。在DNA合成试验中，SCLC细胞对IGF - I和 - II刺激无反应。对于NSCLC细胞，IGF - II比IGF - I更能有效刺激DNA合成。可溶性IGFBP - 2以浓度依赖的方式抑制放射性标记的IGF - I和 - II与SCLC和NSCLC细胞的结合，并抑制NSCLC细胞中IGF刺激的DNA合成。这些观察结果表明，可溶性和与膜相关的IGFBP - 2都与IGF受体竞争配体结合，因此可能是IGF反应性的重要决定因素。本研究的结果还表明，NSCLC细胞上的I型受体含有一个对IGF - II的高亲和力结合位点，该位点可能介导IGF - II在这些细胞中的生物学效应，从而表明IGF - II参与NSCLC的自分泌/旁分泌生长。
