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1-Adrenergic Receptor
Gene Identifies Sequences Involved in Basal Expression
Department of Pharmacology, College of Medicine, The University of
Tennessee, Memphis, Tennessee 38163 (S.W.B., X.C., M.J.B., E.A.P.),
Department of Oral Biochemistry, Nippon Dental University, Niigata,
Japan (H.S.), and
Inovir Inc., New York, New York 10021 (S.T.G.)
The
1-adrenergic receptor (
1-AR) mediates
several functions of catecholamines in the heart, including the
stimulation of heart rate and contractility. The expression of the rat
1-AR gene was assessed by transiently transfecting
chimeric genes containing the
1-AR promoter, driving the
luciferase reporter gene into various cell lines.
1-AR/luciferase vectors containing 3 kb of the
5
-flanking region and extending to
126 relative to the start site of
translation were expressed at high levels in ventricular myocytes,
SK-N-MC cells, and HepG2 cells. The addition of 26 nucleotides from
125 to
100 to the
3311
1-AR/luciferase chimeric
gene reduced expression in myocytes and SK-N-MC cells while eliminating expression in HepG2 cells. This element is located 125 base-pairs 3
to
the transcriptional start site. The mutation of four nucleotides between
121 and
118 diminished the inhibitory effect of this element. The inhibitory activity of the
125 to
100 sequence was
completely dependent on promoter context and positioning. In addition
to this 3
element, sequences between
3311 and
2740 in the
5
-flanking region of the
1-AR gene were required for the full transcriptional suppression. Using DNase I footprinting and
gel mobility assays, it was determined that within the 26-bp region,
rat heart nuclear proteins bound to two sites between nucleotides
123
and
112 and
106 and
100. Therefore, appropriate basal expression
of the
1-AR gene involves widely separated sequences 3
and 5
to the transcriptional start site.
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