Characterization of the α_1B-adrenergic receptor gene promoter region and hypoxia regulatory elements in vascular smooth muscle

Abstract

We previously demonstrated that α_1B-adrenergic receptor (AR) gene transcription, mRNA, and functionally coupled receptors increase during 3% O₂ exposure in aorta, but not in vena cava smooth muscle cells (SMC). We report here that α_1BAR mRNA also increases during hypoxia in liver and lung, but not heart and kidney. A single 2.7-kb α_1BAR mRNA was detected in aorta and vena cava during normoxia and hypoxia. The α_1BAR 5′ flanking region was sequenced to −2,460 (relative to ATG +1). Transient transfection experiments identify the minimal promoter region between −270 and −143 and sequence between −270 and −248 that are required for transcription of the α_1BAR gene in aorta and vena cava SMC during normoxia and hypoxia. An ATTAAA motif within this sequence specifically binds aorta, vena cava, and DDT₁MF-2 nuclear proteins, and transcription primarily initiates downstream of this motif at approximately −160 in aorta SMC. Sequence between −837 and −273 conferred strong hypoxic induction of transcription in aorta, but not in vena cava SMC, whereas the cis-element for the transcription factor, hypoxia-inducible factor 1, conferred hypoxia-induced transcription in both aorta and vena cava SMC. These data identify sequence required for transcription of the α_1BAR gene in vascular SMC and suggest the atypical TATA-box, ATTAAA, may mediate this transcription. Hypoxia-sensitive regions of the α_1BAR gene also were identified that may confer the differential hypoxic increase in α_1BAR gene transcription in aorta, but not in vena cava SMC.