Insulin-induced subcellular redistribution of insulin-like growth factor II receptors in the rat adipose cell. Counterregulatory effects of isoproterenol, adenosine, and cAMP analogues

Abstract

Insulin shifts the steady-state subcellular distribution of insulin-like growth factor II (IGF-II) receptors from a large intracellular pool to the plasma membrane in the rat adipose cell (Wardzala, L. J., Simpson, I. A., Rechler, M. M., and Cushman, S. W. (1984) J. Biol. Chem. 259, 8378-8383). In the present study, the counterregulatory effects of adrenergic stimulation, adenosine deaminase, and cAMP on this process were studied. Both isoproterenol (10(-6) M) and adenosine deaminase reduced insulin sensitivity and also rapidly (t1/2 approximately 1.5 min) decreased the effect of a maximal insulin concentration on the number of cell surface IGF-II receptors by 35-50%, and by 70% when added together. The marked reduction in binding was retained in isolated and solubilized plasma membranes. Both isoproterenol and adenosine deaminase alone increased the EC50 for insulin from 0.06 to 0.17 nM and, when combined, to 0.6 nM. N6-Monobutyryl-cAMP and 8-bromo-cAMP were equally potent in reducing IGF-II binding in the absence of insulin and inhibited maximal insulin-stimulated IGF-II binding by 60 and 30%, respectively. However, only the nonhydrolyzable cAMP analogue, N6-monobutyryl-cAMP, reduced the insulin sensitivity (EC50 0.7 nM). An important stimulatory role for Gi (guanine nucleotide-binding regulatory protein that inhibits adenylate cyclase) was indicated by the altered activities of cells from pertussis toxin-treated animals. The results suggest that beta-adrenergic stimulation through a cAMP-dependent mechanism markedly alters the insulin-stimulated redistribution of IGF-II receptors. This effect is additional to the potent antagonistic action of cAMP on insulin's signalling mechanism.