The vascular smooth muscle type I angiotensin II receptor mRNA is destabilized by cyclic AMP-elevating agents.
Although processes involved in mRNA degradation play a significant role in dictating steady state mRNA levels, the influence of cell surface signaling on mRNA stability control is understood incompletely. In this study, the effects of cAMP-elevating agents on type I angiotensin II receptor (AT1-R) mRNA levels were assessed in cultured rat aortic vascular smooth muscle cells (VSMCs). AT1-R mRNA levels are rapidly reduced by forskolin treatment, in which the maximal effect yields an 80% reduction in AT1-R mRNA levels after 6 hr of treatment. The rate of AT1-R mRNA decay in response to forskolin is greater than its apparent intrinsic decay, as assessed in the presence of the transcriptional inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, suggesting forskolin treatment destabilizes the AT1-R mRNA. Nuclear run-on analysis indicates forskolin treatment does not affect transcription of the AT1-R gene in VSMCs, implying induced AT1-R mRNA destabilization accounts for the entire effect of forskolin in decreasing AT1-R mRNA levels. Dose-effect studies that assessed AT1-R mRNA levels and cAMP production were conducted using forskolin and the beta-adrenergic receptor agonist isoproterenol as agonists. Isoproterenol is almost 3 orders of magnitude more potent at eliciting the reduction in AT1-receptor mRNA levels than it is at stimulating cAMP production. Similarly, forskolin elicits reductions in AT1-R mRNA, which occur at concentrations that fail to elicit a detectable production of cAMP. However, protein kinase A activity is stimulated maximally by isoproterenol and forskolin concentrations that do not stimulate detectable cAMP production. These data provide evidence that the mechanism for down-regulation of AT1-R mRNA levels by cAMP-elevating agents in VSMCs occurs via a PKA-regulated mRNA destabilization pathway.
Wang
X
X
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Nickenig
G
G
Murphy
T J
TJ
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D007545:Isoproterenol / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D011945:Receptors, Angiotensin / Q000187:drug effects* / Q000235:genetics
D000318:Adrenergic beta-Agonists; D012333:RNA, Messenger; D011945:Receptors, Angiotensin; D005576:Colforsin; D000242:Cyclic AMP; D007545:Isoproterenol