Characterization of 5'-flanking region of human MRP3

We previously cloned MRP3, which is responsible for the cellular extrusion of organic anions, as an inducible transporter in the liver under cholestatic conditions. In the present study, we investigated the mechanism for the expression of human MRP3. The cap site hunting method revealed that the transcription starts at -25 and -27 nt upstream of the initiation codon. Luciferase assay with a series of truncated 5'-flanking regions indicated that the region from -127 to -23 nt is important for MRP3 expression. Moreover, carrying out a gel shift assay indicated that Sp1 binds to the sequence between -92 and -58 nt. Collectively, it was demonstrated that human MRP3 is under the control of TATA-less promoter and Sp1 binding sites may be involved in the transcription.