Insulin receptor in cells of two transplanted tumors of mouse mammary gland.

Highly specific insulin receptors have been identified in the cells of two transplanted tumors of mammary gland in mice. The two tumors used for transplantation had morphological characteristics of an undifferentiated adenocarcinoma with a different growth rate. The specific binding was proportional to the number of tumor cells in the incubation mixture. Saturation of insulin binding sites was observed when the concentration of 125I-insulin increased over 5 X 10(-9) moles/l. The specificity of insulin binding to tumor cells was examined by means of competition with insulin derivatives: des-octapeptide insulin, tert-butyloxycarbonyl3-insulin (BOC3) and its des-octapeptide derivative were without any detectable activity in the concentration range used, i.e. from 5.5 X 10(-11) to 5.5 X 10(-5) moles/l. The data obtained from Scatchard's analysis of the binding were not linear and the affinity constants were similar for the cells of the two tumors. The total number of insulin receptor sites per cell, estimated by linear regression analysis, were higher for the cells isolated from the slow-growing tumor as compared to that of cells isolated from the fast-growing tumor and a lactating mammary gland. These results point to the possibility that the growth of mammary tumors could be under insulin regulation via insulin receptors.