Down-regulation of protein kinase C activity preferentially attenuates high K +-stimulated tyrosine hydroxylase activity in adrenal chromaffin cells cultured with insulin-like growth factor-I

Abstract

The purpose of this study was to determine whether the loss of protein kinase C (PKC) from adrenal chromaffin cells affected the enhancement of high K +- and forskolin-stimulated tyrosine hydroxylase (tyrosine 3-monooxygenase, EC 1.14.16.2) activity observed in cells treated with insulin-like growth factor-I (IGF-I). Forskolin-stimulated tyrosine hydroxylase activation was not affected by down-regulation of PKC. High K +-stimulated tyrosine hydroxylase activity decreased substantially after treating the cells for ∼18 h with active, but not inactive, phorbol ester (300 nM). After down-regulation of PKC, high K +-stimulated tyrosine hydroxylase activity in cells cultured with IGF-I decreased by 61 ± 5% ( n = 14) compared to 36 ± 8% ( n = 14) in cells cultured without IGF-I. These data suggest that PKC is required for the enhancement of high K +-stimulated tyrosine hydroxylase activity observed with IGF-I treatment.