Post-translational reduction of cell surface expression of insulin receptors by cyclosporin A, FK506 and rapamycin in bovine adrenal chromaffin cells

Long-term (greater than or equal to3 h) treatment of cultured bovine adrenal chromaffin cells with cyclosporin A (CsA) decreased cell surface I-125-insulin binding by 62% in a concentration (IC50 = 18 muM)- and time (t(1/2) = 16 h)-dependent manner, but did not change the Kd value. FK506 (1 muM) or rapamycin (3 muM) treatment reduced I-125-insulin binding. Western blot analysis showed that CsA treatment decreased insulin receptor (IR) P-subunit level (t(1/2) = 15 h) in membrane fraction, but did not alter total cellular levels of IR precursor and IR P-subunit. Internalization rate of cell surface IR measured by using brefeldin A, an inhibitor of vesicular exit from the trans-Golgi network, was comparable between non-treated and CsA-treated cells. Thus, CsA, FK506 and rapamycin inhibit peptidyl prolyl cis-trans isomerase activities of cyclophilin and FK506-binding protein, and down-regulate IR presumably by reducing cell surface externalization of IR. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.