Characterization of the rat mdr2 promoter and its regulation by the transcription factor Sp1.

The mdr2 gene encodes a P-glycoprotein that transports phospholipids across the canalicular membrane in hepatocytes. In this report we describe the isolation, sequencing and first functional characterization of the promoter of mdr2. Analysis of 1.6 kb of DNA upstream of the initiation of translation revealed that this sequence has a high GC content, lacks a TATA element and contains a number of putative transcription factor binding sites. We observed that transcription initiates at several sites between -290 and -463 and that this region was critical for promoter activity. Gel mobility shift assays indicated that Sp1 protein binds to a Sp1 consensus site located at -263. Co-expression of Sp1 protein with a reporter construct containing the -263 GC box demonstrated that Sp1 regulates transcription of this promoter. Expression of a non-functional Sp1 protein did not increase transcription from the mdr2 promoter. Mutation of the -263 GC box diminished the response of the promoter to Sp1 protein. Mutation of this site also decreased expression of this promoter in cells which normally express this gene. These data show that Spl has a role in the regulation of mdr2 expression.