Agonist-induced down-regulation of α_1B-adrenergic receptor in HEK293 cells transfected with α_1B cDNA

Abstract

HEK293 cells stably expressing hamster α_1B-adrenergic receptor (α_1B-AR) were used to observe the effect of nonepinephrine (NE) on α_1B-AR gene expression. Radioligand binding assys and RNase protection assays were used to determine α_1B-AR number and the mRNA level, respectively. Exposure (2–24 h) of HEK293 cella to NE (10 μmol) caused a decrease in α_1B-AR mRNA with maximum change found at the 4th hour. and in α_1B-AR density at the 24th hour. NE-induced decrease in α_1B-AR mRNA was inhibited by protein kinase C (PKC) inhibitor calphostin C (0.1. μmol) and mimicked by PKC activator PMA (1 μmol). Nuclear run-off transcription assay showed that treatment of the cells with NE (10 μmol) exerted no effect on the transcription rate of α_1B-AR, After the synthesis of new RNAs was inhibited by actinomycin D, NE muld not accelerate the degradation of α_1B-AR mRNA. The results suggested that in the HEK293 cells NE muld induce the down-regulation of α_1B-AR, and the effects were mediated by PKC pathway. NE could not alter the transcription rate of α_1B-AR mRNA, but it might induce the synthesis of some factors and indirectly accelerate the degradation.