title: Promoter polymorphisms and allelic imbalance in ABCB1 expression.
abstract: OBJECTIVE
  The ABCB1 (MDR1) gene, encoding the transporter P-glycoprotein, is known to act on a broad range of prescription medicines. For this reason a large number of studies have assessed the functional consequences of variation in this gene. Particular attention has focused on the ABCB1_3435C>T polymorphism, an exonic variant resulting in a synonymous change. This variant has been associated with mRNA, protein and serum levels, and with responses to a number of medicines. The results of association studies have, however, been variable and it is not currently clear whether this polymorphism is functional or is in linkage disequilibrium with functionally distinct alleles.
  
  
  RESULTS
  To identify functional variation in the ABCB1 gene we assessed allelic imbalance by pyrosequencing cDNA from 80 lymphoblastoid B cell lines from the Centre d'Etude du Polymorphisme Humain (CEPH) collection, including 74 individuals heterozygous for 3435C>T. We found that the degree of ABCB1 allelic imbalance differed among B-cell lines. In an effort to fine-map variants that influence the proportion of the two allelic mRNA species we genotyped representative common variations near the 3435C>T polymorphism by using a tagging single nucleotide polymorphism (SNP) approach. In one approach, we assessed in segregating families the impact of cis-acting variants on mRNA levels by using allelic imbalance as the phenotype in a regression analysis that distinguishes the coupling arrangements (phase) among alleles. In a second approach, we assessed allelic imbalance levels in lymphoblastoid B-cell lines from unrelated HapMap individuals, and performed an association using tagSNPs in a 5-Mb region surrounding the gene. Two potential cis-acting variants, a promoter rs28656907/rs28373093 dinucleotide polymorphism (P=0.007) and the rs10245483 SNP (P=0.0003) located 2 Mb upstream from the gene, were predictors of ABCB1 expression.
  
  
  CONCLUSIONS
  The study outlines a general experimental approach for fine mapping gene variants that influence mRNA expression by using cultured cell lines.
authors: Institute of Microbiology, University Hospital, Lausanne, Switzerland.
authors: Corinne
authors: C
authors: Loeuillet
authors: Michael
authors: M
authors: Weale
authors: Samuel
authors: S
authors: Deutsch
authors: Margalida
authors: M
authors: Rotger
authors: Nicole
authors: N
authors: Soranzo
authors: Josiane
authors: J
authors: Wyniger
authors: Guillaume
authors: G
authors: Lettre
authors: Yann
authors: Y
authors: Dupré
authors: Delphine
authors: D
authors: Thuillard
authors: Jacques S
authors: JS
authors: Beckmann
authors: Stylianos E
authors: SE
authors: Antonarakis
authors: David B
authors: DB
authors: Goldstein
authors: Amalio
authors: A
authors: Telenti
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D022981:Allelic Imbalance; D001402:B-Lymphocytes / Q000378:metabolism; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D015331:Cohort Studies; D005190:Family; D005260:Female; D005838:Genotype; D017320:HIV Protease Inhibitors / Q000097:blood / Q000493:pharmacokinetics; D006801:Humans; D008297:Male; D019888:Nelfinavir / Q000097:blood / Q000493:pharmacokinetics; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D017320:HIV Protease Inhibitors; D012333:RNA, Messenger; D019888:Nelfinavir