Agonist- induced down- regulation of alpha_(1B)-adrenergic receptor in HEK293 cells transfected with alpha_(1B) cDNA

摘要

HEK293 cells stably expressing hamster alpha_(1B)-adrenergic receptor (alpha_(1B)-AR) were used to observe the effect of norepinephrine (NE) on alpha_(1B)-AR gene expression Radioligand binding assays and RNase protection assays were used to determinealpha_(1B)-AR number and the mRNA level, respectively. Exposure (2—24 h) of HEK393 cells to NE (10 mu mol) caused a decrease in alpha_(1B)-AR mRNA with maximum change found at the 4th hour and in alpha_(1B)-AR density at the 24th hour. NE-induced decrease in alpha_(1B)-AR mRNA was inhibited by protein kinase C (PKC) inhibitor calphostin C (0.1 mu mol) and mimicked by PKC activator PMA (1 mu mol). Nuclear run-off transcription assay showed that treatment of the cells with NE (10 mu mol) exerted no effect on the transcription rate of alpha_(1B)-AR. After the synthesis of new RNAs was inhibited by actinomycin D, NE could not accelerate the degradation of alpha_(1B)-AR mRNA. The results suggested that in the HEK293 cells NE could induce the down-regulation of alpha_(1B)-AR, and the effects were mediated by PKC pathway. NE could not alter the transcription rate of alpha_(1B)-AR mRNA, but it might induce the synthesis of some factors and indirectly accelerate the degradation.