Jonas H A, Eckardt G S, Clark S
University of Melbourne Department of Medicine, Royal Melbourne Hospital, Parkville, Victoria, Australia.
Endocrinology. 1990 Sep;127(3):1301-9. doi: 10.1210/endo-127-3-1301.
Human placenta and IM-9 lymphocytes contain subpopulations of atypical insulin receptors which differ from classical insulin receptors in their higher binding affinity for insulin-like growth factors I and II (IGF-I and IGF-II). Both types of insulin receptors may be derived from different but related genes, or may represent alternative post-translational modifications of the same gene product. To test these possibilities, we have examined the IGF binding characteristics of the human insulin receptors expressed in Chinese hamster ovary (CHO) cells which had been stably transfected with cloned human insulin receptor cDNA (CHO-T cells). The parent CHO cells contained 3 x 10(3) rodent insulin receptors/cell, and the CHO-T cells, 2.0 x 10(6) human insulin receptors/cell. Competition binding studies showed that the binding of [125I]IGF-I and [125I]multiplication stimulating activity (MSA/rat IGF-II) to parent CHO cells was primarily to type I and II IGF receptors, which cross-react poorly or not at all with insulin. However, competition binding studies with CHO-T cells showed that [125I]IGF-I binding was displaced 60-70%, and [125I]MSA binding, 50-55%, by low concentrations of insulin (20 ng/ml) and no further by higher concentrations of insulin (500 ng/ml). The insulin-insensitive IGF binding sites corresponded to the rodent type I and II IGF receptors; the insulin-sensitive IGF binding sensitive sites resembled the human atypical insulin receptors in that they bound IGF-I and MSA with moderately high affinity and reacted with insulin, MSA, and IGF-I in that order of potency. Atypical insulin receptors were also demonstrated by insulin-sensitive [125I]IGF-I and [125I]MSA binding to solubilized CHO-T proteins adsorbed to microtiter wells coated with monoclonal antibodies specific for the human insulin receptor. These results suggest that atypical human insulin receptors are generated by differential post-translational processing of the same gene product as classical human insulin receptors.
人胎盘和IM - 9淋巴细胞含有非典型胰岛素受体亚群，这些亚群与经典胰岛素受体的不同之处在于，它们对胰岛素样生长因子I和II（IGF - I和IGF - II）具有更高的结合亲和力。这两种类型的胰岛素受体可能源自不同但相关的基因，或者可能代表同一基因产物的不同翻译后修饰。为了验证这些可能性，我们检测了在中国仓鼠卵巢（CHO）细胞中表达的人胰岛素受体的IGF结合特性，这些细胞已被稳定转染了克隆的人胰岛素受体cDNA（CHO - T细胞）。亲本CHO细胞每细胞含有3×10³个啮齿动物胰岛素受体，而CHO - T细胞每细胞含有2.0×10⁶个人胰岛素受体。竞争结合研究表明，[¹²⁵I]IGF - I和[¹²⁵I]增殖刺激活性（MSA /大鼠IGF - II）与亲本CHO细胞的结合主要是与I型和II型IGF受体结合，它们与胰岛素的交叉反应很差或根本不发生交叉反应。然而，对CHO - T细胞的竞争结合研究表明，低浓度胰岛素（20 ng/ml）可使[¹²⁵I]IGF - I结合被取代60 - 70%，[¹²⁵I]MSA结合被取代50 - 55%，而高浓度胰岛素（500 ng/ml）则不会进一步取代。对胰岛素不敏感的IGF结合位点对应于啮齿动物I型和II型IGF受体；对胰岛素敏感的IGF结合敏感位点类似于人非典型胰岛素受体，因为它们以中等高度亲和力结合IGF - I和MSA，并按效力顺序与胰岛素、MSA和IGF - I发生反应。通过对吸附在包被有针对人胰岛素受体的单克隆抗体的微量滴定孔上的可溶性CHO - T蛋白进行胰岛素敏感的[¹²⁵I]IGF - I和[¹²⁵I]MSA结合，也证明了非典型胰岛素受体的存在。这些结果表明，人非典型胰岛素受体是由与经典人胰岛素受体相同的基因产物的不同翻译后加工产生的。
