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Vol. 54, Issue 3, 514-524, September 1998
Department of Pharmacology, Emory University School of Medicine,
and Program in Molecular Therapeutics and Toxicology, Graduate Division
of Biological and Biomedical Sciences, Emory University, Atlanta,
Georgia 30322
Expression of the angiotensin II type 1 receptor (AT1-R)
mRNA in vascular smooth muscle cells (VSMC) is down-regulated by a
variety of agonists, including growth factors, agonists of
G
q protein-coupled receptors, and activators of adenylyl
cyclase. To determine whether cAMP-dependent protein kinases (PKA)
participates in AT1-R mRNA down-regulation controlled by
multiple classes of receptors, a PKA inhibitor peptide (PKI
) was
developed and expressed in rat VSMC as a fusion with the enhanced green
fluorescent protein (eGFP). PKA activity elicited both by forskolin and
angiotensin II is suppressed in cells expressing this fusion protein
(PKI
-eGFP), but platelet-derived growth factor-BB does not stimulate
PKA activity in this preparation. PKI
-eGFP expression fully inhibits
the forskolin-stimulated down-regulation of AT1-R mRNA
levels and blocks 50% of the effect elicited by angiotensin II. This
indicates that PKA plays a substantial role in angiotensin
II-stimulated AT1-R mRNA down-regulation. However,
inhibition of PKA has no effect on AT1-R mRNA
down-regulation caused by platelet-derived growth factor-BB. These
findings show how agonists such as angiotensin II that are not normally
considered as activators of PKA can use PKA-dependent processes to
modulate gene expression. These findings also provide definitive
evidence that PKA-dependent pathways are involved in modulation of
AT1-R mRNA levels in VSMC.
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