Haplotype-Oriented Genetic Analysis and Functional Assessment of Promoter Variants in theMDR1(ABCB1) Gene

Abstract

Recently, a number of nucleotide variants have been described in the multidrug resistance 1 (MDR1/ABCB1) gene; however, most studies have focused on the coding region. In the present study, we identified promoter variants of the MDR1 gene and evaluated their phenotypic consequences using a reporter gene assay and the real-time polymerase chain reaction method. Ten allelic variants were detected in the promoter region (approximately 2 kilobases), seven of which were newly identified. Certain mutations occurred simultaneously, and a total of 10 haplotypes were observed. These promoter polymorphisms were found more frequently in Japanese than Caucasians. Some haplotypes were associated with changes in luciferase activity and placental and hepatic mRNA levels. We also determined DNA methylation status in the proximal promoter region of the MDR1 gene. The promoter region around potential binding sites for transcription factors was found to be hypomethylated and thus likely to be independent of the gene expression. Nucleotide and/or haplotype variants not only in the coding region but also in the promoter region of the MDR1 gene may be important for interindividual differences of P-glycoprotein expression.

The Promoter Region of theMDR1Gene Is Largely Invariant, but Different Single Nucleotide Polymorphism Haplotypes Affect MDR1 Promoter Activity Differently in Different Cell Lines

“…Sequencing of the core promoter region in another European population was reported to identify only SNP e1/-129TϾC where the minor C-allele only occurs at a frequency of 5.9% (Hoffmeyer et al, 2000). In the Japanese population, various groups using either sequencing or single strand conformation polymorphism also identified SNPs i1/ -41(A/G), e1/-129(T/C), and sometimes SNPe1/-145(C/G) at the MDR1 promoter region Tanabe et al, 2001;Saito et al, 2002;Taniguchi et al, 2003;Takane et al, 2004). The minor allele frequency of these SNPs in the Japanese population was reported to be Յ10% (Table 2; Lee et al, 2004a).…”

“…MDR1 SNPs, particularly exonic SNPs, have also been associated with susceptibility to renal epithelial tumor (Siegsmund et al, 2002); ulcerative colitis and Crohn's disease (Schwab et al, 2003); Parkinson's disease (Furuno et al, 2002;Drozdzik et al, 2003;Lee et al, 2004b;Tan et al, 2004Tan et al, , 2005; human immunodeficiency virus-1 infection (Ifergan et al, 2002); and other diseases (Marzolini et al, 2004). SNPs within the MDR1 promoter region, which may play an important role in the regulation of MDR1 gene expression, have thus far been examined only in two reports (Taniguchi et al, 2003;Takane et al, 2004).…”

“…Because the MDR1 transporter potentially protects the individual against environmental stress and is a significant determinant of the success of cancer chemotherapy or other drug therapy, SNPs at its promoter may influence its gene expression and account for differences in response to drug therapy or susceptibility to various diseases between individuals. There are two reports examining SNPs and haplotype of SNPs at the MDR1 promoter locus in the Japanese population (Taniguchi et al, 2003;Takane et al, 2004). Both studies examined SNP haplotypes in slightly different 2-kb region of the MDR1 promoter and identified different relatively low- Fig.…”

“…frequency polymorphisms with slight allelic differences in promoter activity (Taniguchi et al, 2003;Takane et al, 2004). In this study, we scanned for polymorphisms in a 1.5-kb region of the MDR1 promoter in five different populations and characterized the effect of SNP haplotypes on MDR1 promoter activity.…”

ABCB1 Genotype of the Donor but Not of the Recipient Is a Major Risk Factor for Cyclosporine-Related Nephrotoxicity after Renal Transplantation

“…Confounding factors such as differences in study populations, particularly in sample size, ethnicities, or disease states, and differences in diet and environmental chemicals seem to be most important. Moreover, because commonly only the variants at positions 2677 and 3435 were tested without genotyping for additional intronic and exonic SNP including newly identified promoter mutations (41,42), it cannot be excluded with certainty that specific complex haplotypes may be more predictive.…”