Structure of insulin/insulin-like growth factor-1 receptors on the insulinoma cell, RIN-m5F

The subunit structure of receptors for insulin and insulin-like growth factor-1 has been demonstrated on a rat insulinoma cell, RIN-m5F, grown in continuous culture. The specific binding of [125-I]-insulin-like growth factor-1 (2.9 +/- 0.42%; mean +/- SEM) to the RIN-m5F cell was significantly greater than of [125I]-insulin (0.7 +/- 0.2%). Immunoprecipitation of receptors from [125I]-surface labeled cells and analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis and autoradiography revealed reduced subunits of Mr 130,000 and 90,000, identical to those for both insulin and insulin-like growth factor-1 receptors on classic target tissues. An apparent abundance of insulin-like growth factor-1 over insulin receptors could be due to downregulation of the latter by secreted insulin. These findings support a role for insulin and insulin-like growth factor-1 receptors in regulating metabolic or growth functions in the beta cell.