Kleinman D, Karas M, Roberts C T, LeRoith D, Phillip M, Segev Y, Levy J, Sharoni Y
Clinical Biochemistry Department, Faculty of Health Sciences, Ben-Gurion University of the Negev, Soroka Medical Center of Kupat Holim, Beer-Sheva, Israel.
Endocrinology. 1995 Jun;136(6):2531-7. doi: 10.1210/endo.136.6.7750475.
Insulin-like growth factor I (IGF-I) receptors and membrane-associated IGF-binding proteins (IGFBPs) were examined in Ishikawa endometrial cancer cells. Our findings suggest that about 95% of [125I]IGF-I is bound to membrane-associated IGFBPs rather than to IGF-I receptors. Specifically, [125I]IGF-I binding to cell membranes could be completely displaced by cold IGF-I or IGF-II, but not by insulin, suggesting that binding was primarily due to IGFBPs. This was confirmed by using [125I]des-(1-3)IGF-I as the ligand. Des-(1-3) IGF-I binds with high affinity to IGF-I receptors, but with markedly lower affinity to IGFBPs. [125I]Des-(1-3)IGF-I bound to Ishikawa cells was displaced by IGF-I, IGF-II, and insulin. These results suggest that measuring IGF-I receptor levels using labeled IGF-I may be misleading. Accordingly, we evaluated the differential binding of [125I]IGF-I and [125I]des-(1-3)IGF-I to study the involvement of the IGF system in the stimulation of Ishikawa cell growth by estradiol. IGF-I stimulates Ishikawa cell proliferation, but at low concentrations, and this stimulation is largely dependent on the presence of estradiol. Estradiol caused a 2.5-fold increase in IGF-I receptor levels. Moreover, estradiol reduced soluble IGFBP levels, presumably increasing the availability of IGFs for their receptors. This elevation in IGF-I receptor levels and the decrease in IGFBP levels were accompanied by a 3.5-fold increase in IGF-I receptor messenger RNA and a 2.5-fold decrease in IGFBP messenger RNAs. These experiments suggest that estradiol sensitizes endometrial cancer cells to the effects of IGFs by simultaneously elevating receptor levels and decreasing (potentially inhibitory) IGFBP levels.
在石川子宫内膜癌细胞中检测了胰岛素样生长因子I（IGF-I）受体和膜相关胰岛素样生长因子结合蛋白（IGFBPs）。我们的研究结果表明，约95%的[125I]IGF-I与膜相关IGFBPs结合，而非与IGF-I受体结合。具体而言，[125I]IGF-I与细胞膜的结合可被冷IGF-I或IGF-II完全取代，但不能被胰岛素取代，这表明结合主要是由IGFBPs引起的。使用[125I]去（1-3）IGF-I作为配体证实了这一点。去（1-3）IGF-I与IGF-I受体具有高亲和力，但与IGFBPs的亲和力明显较低。与石川细胞结合的[125I]去（1-3）IGF-I可被IGF-I、IGF-II和胰岛素取代。这些结果表明，使用标记的IGF-I测量IGF-I受体水平可能会产生误导。因此，我们评估了[125I]IGF-I和[125I]去（1-3）IGF-I的差异结合，以研究IGF系统在雌二醇刺激石川细胞生长中的作用。IGF-I刺激石川细胞增殖，但仅在低浓度时，且这种刺激很大程度上依赖于雌二醇的存在。雌二醇使IGF-I受体水平增加了2.5倍。此外，雌二醇降低了可溶性IGFBP水平，推测这增加了IGF与其受体结合的可用性。IGF-I受体水平的升高和IGFBP水平的降低伴随着IGF-I受体信使RNA增加3.5倍和IGFBP信使RNA减少2.5倍。这些实验表明，雌二醇通过同时提高受体水平和降低（潜在抑制性的）IGFBP水平，使子宫内膜癌细胞对IGF的作用敏感。
