Protein kinase inhibitors modulate expression of alpha-ib adrenergic receptors in transfected chinese hamster ovary (cho) cells

Epinephrine (EPI) induced an unexpected up-regulation of [³H]prazosin binding to intact cells in a clone (H99) of CHO cells stably transfected to express high levels of the hamster alpha-1B adrenergic receptor. The protein kinase C inhibitor staurosporine (ST) also induced up-regulation. Exposure to 10 nM ST for 24 hr increased both the BnMX and KD values by approximately 2-fold, similar to the effects of EPI. Up-regulation occurred steadily over the 24 hr period, with half-maximal up-regulation at 1 nM ST. Neither the protein kinase C inhibitor GF109203X nor the tyrosine kinase inhibitor genistein induced up-regulation. However, genistein but not GF109203X inhibited EPI-induced upregulation; the less active genistein analog daidzein inhibited EPI up-regulation at higher concentrations. The protein synthesis inhibitor cycloheximide at low concentrations blocked ST-induced up-regulation and at higher concentrations revealed ST-induced down-regulation. In a sister clone (H88) in which EPI induced down-regulation, ST induced down-regulation as well. These results suggest multiple roles for protein kinases in regulation of transfected receptor expression.