Functional analysis of the polymorphism -211C>T in the regulatory region of the human ABCC3 gene.

The multidrug resistance protein 3 (MRP3/gene symbol: ABCC3) is an ATP-dependent efflux pump mediating the transport of endogenous glucuronides and conjugated drug metabolites across cell membranes. In humans the hepatic expression of ABCC3 mRNA seems to be influenced by the polymorphism C>T at the position -211 in the promoter of the ABCC3 gene. The aim of this study was to investigate the possible mechanisms of how this SNP influences the MRP3 expression. Promoter luciferase reporter gene constructs representing 0.5, 1.1, 4.4, and 8.1 kb upstream of the translational start site were cloned with cytosine or thymine at position -211 and transfected into HepG2, Caco-2, and LS174T cells. Reporter gene activity was dependent on the length of the promoter sequence but interestingly not on the nucleotide at position -211. Cotransfection with FTF cDNA (Fetoprotein Transcription Factor) binding to elements near the -211 polymorphism increased promoter activity in all constructs except the 0.5 kb fragment also independently of the -211 SNP. Taken together, we did not find any influence of the -211C>T ABCC3 promoter polymorphism on either the basal or the FTF induced reporter gene activity. Whether other tissue specific mechanisms reveal an impact of this SNP on the in vivo regulation of MRP3 remains to be determined.