Basal expression of the rat, but not of the human, multidrug resistance protein 2 (MRP2) gene is mediated by CBF/NF-Y and Sp1 promoter-binding sites

The most important biliary efflux transporter known so far is the multidrug resistance protein 2 (MRP2). Previously, we isolated and characterized the 5 ' -flanking region of the rat mrp2 gene. In the present study, we perfor med site-directed mutagenesis experiments indicating that both a Y-Box and a GC-Box in the rat mrp2 promoter are essential for the full basal expressi on of the gene, but have no significant relevance for its inducibility by t he chemical carcinogen 2-acetylaminofluorene. Gel mobility shift experiment s demonstrated the binding of the transcription factor CBF/NF-Y, but not of EFIA/YB-1, to the Y-Box. Site-directed mutations in the Y-Box decreasing r eporter gene activity of a promoter construct prevented the binding of NF-Y . Consequently, NF-Y contributes substantially to the basal expression of t he gene. A site-directed mutation in the GC-Box also reduced basal expressi on and resulted in a reduced complex formation with the transcription facto r Spl. The corresponding region of the human MRP2 promoter comprises no Spl site, but a Y-Box-like element binding YB-1 but not NF-Y, which, however, does not contribute to basal expression. In conclusion, NF-Y and Spl bindin g sites play a decisive role in the basal expression of the rat mrp2 gene, while the human MRP2 gene is regulated differently. (C) 2001 Elsevier Scien ce Ireland Ltd. All rights reserved.