Alterations in insulin binding accompanying differentiation of 3T3-L1 preadipocytes.

Abstract

Expression of the adipocyte phenotype by differentiating [mouse 3T3 fibroblast subline] 3T3-L1 preadipocytes occurs upon exposure of the cells to insulin. Differentiation-linked changes in 125I-labeled insulin binding to 3T3-L1 cells were monitored and compared with those in nondifferentiating 3T3-C2 controls treated similarly. Without chronic insulin treatment, 3T3-L1 cells failed to express the adipocyte phenotype but maintained a level of 25,000-35,000 insulin-binding sites/cell. Treatment of 3T3-L1 cells with insulin resulted in an initial suppression of insulin binding followed by a 12-fold increase that paralleled the appearance of differentiated cells. A maximum of 170,000 insulin-binding sites per cell was attained for a population in which > 75% of the cells had differentiated. The increase of insulin receptor level appears to be differentiation-dependent and is not a general response of cells to the culture conditions. 3T3-C2 cells maintained in the presence of insulin for 30 days exhibited the undifferentiated phenotype and suppressed levels of insulin binding (35,000 sites per cell). The binding capacity of 3T3-L1 cells for epidermal growth factor remained unchanged between 25,000 and 40,000 sites/cell and was independent of the state of differentiation. Induction by insulin of differentiation-linked expression in 3T3-L1 cells results in receptor-specific changes. Insulin receptors increase in number but epidermal growth factor receptors remain constant.