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1 Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical, Nashville, TN, USA
* To whom correspondence should be addressed. E-mail: jay.gainer{at}vanderbilt.edu.
Regulation of the constitutively expressed type 2 bradykinin (B2) receptor, which mediates the principal actions of bradykinin, occurs at multiple levels. The goal of the current study was to determine whether the human B2 3'- untranslated region (UTR) has effects on gene expression, with particular focus on the variable number of tandem repeats (B2-VNTR) polymorphic portion of the 3'-UTR and its flanking AU-rich elements (AREs). When inserted downstream of the luciferase coding region of the pGL3-Promoter vector, the B2-VNTR reduced reporter gene activity by 85% compared to pGL3-Promoter alone (promoter control; P<0.001), an effect that was not appreciably affected by mutation of the flanking AREs. The negative regulatory effects of the B2-VNTR region were position and orientation-dependent and strongly positively correlated with the number of tandem repeats in the B2-VNTR region (r=0.85, P<0.001). With respect to mechanism, quantitative RT-PCR revealed that the B2-VNTR mRNA level was 32% of that of promoter control (P=0.008); whereas, the number of polyadenylated transcripts was 4% (P=0.02). In contrast, the mRNA half-life of the B2-VNTR was increased (B2-VNTR: 14.9 vs. promoter control: 12.2 hours, P=0.009). Transient transfection of human kidney-derived tsA201 cells with the B2-VNTR construct increased transcription of the native B2 receptor mRNA by 43% (P<0.05) supporting an endogenous B2 receptor regulatory capacity of the B2-VNTR. In conclusion, these results identify novel pre-translational effects of the B2-VNTR region to act as a potent negative regulator of heterologous gene expression and support the notion that the bradykinin B2 3'-UTR may impact endogenous receptor regulation.
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