| First Author | Song R | Year | 1995 |
| Journal | J Biol Chem | Volume | 270 |
| Issue | 43 | Pages | 25468-74 |
| PubMed ID | 7592715 | Mgi Jnum | J:29521 |
| Mgi Id | MGI:77053 | Doi | 10.1074/jbc.270.43.25468 |
| Citation | Song R, et al. (1995) Identification and characterization of a hepatoma cell-specific enhancer in the mouse multidrug resistance mdr1b promoter. J Biol Chem 270(43):25468-74 |
| abstractText | The expression of multidrug resistance/P-glycoprotein genes mdr1b(mdr1) and mdr1a(mdr3) is elevated during hepatocarcinogenesis. To investigate the regulation of mdr1b gene expression, we used transient transfection expression assays of reporter constructs containing various 5'-mdr1b flanking sequences in hepatoma and non-hepatoma cells. We found that nucleotides -233 to -116 preferentially enhanced the expression of reporter gene in mouse hepatoma cell lines in an orientation- and promoter context-independent manner. DNase I footprinting using nuclear extracts prepared from hepatoma and non-hepatoma cells identified four protein binding sites at nucleotides -205 to -186 (site A), -181 to -164 (site B), -153 to -135 (site C), and -128 to -120 (site D). Further analyses revealed that, while site B alone played a major part for the enhancer function, sites A and B combined conferred full enhancer activity. Site-directed mutagenesis results also supported these results. Gel retardation experiments using oligonucleotide competitors revealed that the site B contains a dominant binding protein. This is the first report demonstrating a cell type-specific enhancer in the mdr locus. The role of this enhancer in the activation of mdr1b gene during hepatocarcinogenesis is discussed. |
