Molecular structure and transcriptional regulation by nuclear factor-κB of the mouse kinin B₁ receptor gene

Kinins are important mediators in cardiovascular homeostasis, inflammation, and nociception. Two kinin receptors have been described, B₁ and B₂. The B1 receptor is normally absent in healthy tissues, but is highly induced under pathological conditions. To understand the molecular mechanism of B₁ receptor up-regulation, we determined the mouse B₁ receptor gene structure, isolated and characterized the promoter region and studied its transcriptional regulation. The mouse B₁ receptor gene contains two exons (with the entire coding region located in the second exon) and a TATA-less promoter with multiple transcription start sites. A 7.7-kbp portion of the 5′-flanking region was examined for promoter activity in vascular smooth muscle cells (VSMCs). A minimal 92-bp fragment, located immediately upstream of the transcription start region, exerted basal and lipopolysaccharide (LPS)-inducible transcription activity in the sense and antisense orientation, and was thereby identified as an enhancer element. Nuclear extracts from VSMCs showed basal and LPS-inducible binding activity of nuclear factor (NF)-κB at this sequence. B₁ receptor transcription activation in response to LPS was abolished by cotransfection with IκBαΔN, an NF-κB repressor. In summary, our results reveal the structure of the mouse B₁ receptor gene and the involvement of NF-κB in the inducible mouse kinin B₁ receptor expression under pathological conditions.