Abstract
MRP2 is a member of the ATP binding cassette superfamily (ABC) of efflux transporters and mediates the ATP‐dependent efflux of glucuronide and glutathione conjugates from liver, kidney and intestinal cells. The MRP2 5′UTR was investigated for its regulation of downstream gene expression. Both transient gene expression in HepG2 cells and in vitro translation assays of MRP2 5′UTR‐luciferase constructs showed that a 35 nt RNA motif in the MRP2 5′UTR stimulates downstream open reading frame (ORF) translation. One, 2, 3 and 5 copies of the 35 nt motif were inserted between renilla and firefly luciferase ORFs in bicistronic constructs and transfected into HepG2 cells, where analysis of gene expression showed that the 35 nt motif enhanced translation of the 3′ cistron without affecting its mRNA expression. In vitro translation assays of the bicistronic transcripts showed that the 35 nt motif increased translation of the 3′ cistron, consistent with potential Internal Ribosome Entry Site (IRES) activity of the 35 nt RNA motif. Using RNA EMSA, affinity purification and Mass Spectrometry, IGF2BP1 was identified as a protein that bound to the 35 nt RNA motif, while over‐expression of IGF2BP1 in HepG2 cells increased MRP2 translation. Thus, IGF2BP1 stimulates cap‐dependent and cap‐independent translation initiation through binding to the MRP2 5′UTR 35 nt motif.