title: Alternative transcription of sodium/bicarbonate transporter SLC4A7 gene enhanced by single nucleotide polymorphisms.
abstract: Genome-wide association studies have identified the single nucleotide polymorphism (SNP) rs3278 in the humanSLC4A7gene as one of the marker loci for addiction vulnerability. This marker is located in an intron of the gene, and its genomic role has been unknown. In this study, we examined rs3278 and three adjacent SNPs prevalent in alcoholics for their effects on an alternative promoter that would lead to the production of the NH2-terminally truncated protein NBCn1ΔN450, missing the first 450 amino acids. Analysis of the transcription start site database and a promoter prediction algorithm identified a cluster of three promoters in intron 7 and two short CpG-rich sites in intron 6. The promoter closest to rs3278 showed strong transcription activity in luciferase reporter gene assays. Major-to-minor allele substitution at rs3278 resulted in increased transcription activity. Equivalent substitutions at adjacent rs3772723 (intron 7) and rs13077400 (exon 8) had negligible effect; however, the substitution at nonsynonymous rs3755652 (exon 8) increased the activity by more than twofold. The concomitant substitution at rs3278/rs3755652 produced an additive effect. The rs3755652 had more profound effects on the promoter than the upstream regulatory CpG sites. The amino acid change E326K caused by rs3755652 had negligible effect on transporter function. In HEK 293 cells, NBCn1ΔN450 was expressed in plasma membranes, but at significantly lower levels than the nontruncated NBCn1-E. The pH change mediated by NBCn1ΔN450 was also low. We conclude that rs3278 and rs3755652 stimulate an alternative transcription of theSLC4A7gene, increasing the production of a defective transporter.
authors.affiliation: Department of Pharmacology, Kyung Hee University School of Medicine, Seoul, South Korea; and.
authors.forename: Hae Jeong
authors.initials: HJ
authors.lastname: Park
authors.affiliation: Department of Physiology, Emory University School of Medicine, Atlanta, Georgia.
authors.forename: Soojung
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Physiology, Emory University School of Medicine, Atlanta, Georgia.
authors.forename: Eunji
authors.initials: E
authors.lastname: Ju
authors.affiliation: Department of Physiology, Emory University School of Medicine, Atlanta, Georgia.
authors.forename: Jayre A
authors.initials: JA
authors.lastname: Jones
authors.affiliation: Department of Physiology, Emory University School of Medicine, Atlanta, Georgia ichoi@emory.edu.
authors.forename: Inyeong
authors.initials: I
authors.lastname: Choi
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D018899:CpG Islands / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007438:Introns / Q000235:genetics; D050505:Mutant Proteins / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic; D027982:Sodium-Bicarbonate Symporters / Q000235:genetics* / Q000378:metabolism; D024363:Transcription Initiation Site; D014158:Transcription, Genetic; D014981:Xenopus
chemical_list: D050505:Mutant Proteins; C422022:SLC4A7 protein, human; D027982:Sodium-Bicarbonate Symporters
keywords: NBCn1; SLC4A7; bicarbonate transporter; rs3278