Identification and characterization of novel polymorphisms in the basal promoter of the human transporter, MATE1

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Abstract
Human multidrug and toxin extrusion member 1, MATE1 (SLC47A1), plays an important role in the renal and biliary excretion of endogenous and exogenous organic cations including many therapeutic drugs. In this study, we characterized the transcriptional effects of five polymorphic variants and six common haplotypes in the basal promoter region of MATE1 that were identified in 272 DNA samples from ethnically diverse US populations. We measured luciferase activities of the six common promoter haplotypes of MATE1 using in-vitro and in-vivo reporter assays. Haplotypes that contain the most common variant (mean allele frequency in four ethnic groups: 0.322), g.–66T>C, showed a significant decrease in reporter activities compared to the reference. Two transcription factors, activating protein-1 (AP-1) and activating protein-2 repressor (AP-2rep), were predicted to bind to the promoter in the region of g.–66T>C. Results from electrophoretic mobility shift assays showed that the g.–66T allele, exhibited greater binding to AP-1 than the g.–66C allele. AP-2rep inhibited the binding of AP-1 to the MATE1 basal promoter region, and the effect was considerably greater for the g.–66T>C. These data suggest that the reduced transcriptional activity of g.–66T>C results from a reduction in the binding potency of the transcriptional activator, AP-1, and an enhanced binding potency of the repressor, AP-2rep to the MATE1 basal promoter region. Consistent with the reporter assays, MATE1 mRNA expression levels were significantly lower in kidney samples from individuals who were homozygous or heterozygous for g.–66T>C in comparison with samples from individuals who were homozygous for the g.–66T allele. Our study suggests that the rate of transcription of MATE1 is regulated by AP-1 and AP-2rep and that a common promoter variant, g.–66T>C may affect the expression level of MATE1 in human kidney, and ultimately result in variation in drug disposition and response.

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