title: Modulation of multidrug resistance gene expression by dexamethasone in cultured hepatoma cells.
abstract: Considerable evidence has accumulated indicating that overexpression of P-glycoproteins encoded by the multidrug-resistance (mdr) genes is responsible for the development of collateral resistance to a number of structurally and functionally dissimilar cytotoxic compounds in animal cells. There are three mdr genes (mdr1, mdr2, and mdr3) in the mouse genome and two (MDR1 and MDR2) in the human genome; however, only two mouse genes (mdr1 and mdr3) and one human gene (MDR1) can confer multidrug resistance upon transfection into otherwise drug-sensitive cells. Using RNase protection assay we report here that the steady-state levels of mdr1 and mdr3 messenger RNA were elevated in mouse hepatoma cells treated with dexamethasone (Dex); whereas no induction of mdr2 gene was found. Western blot analyses using anti-mdr1 and anti-mdr3 antibodies revealed that the encoded proteins appeared to be increased, but at much reduced levels. The induction was time and Dex concentration dependent. Nuclear run-on experiments demonstrated that the induction was at least in part by transcriptional control. The induction apparently required new protein synthesis since no increases in mdr1 and mdr3 transcripts was found when cultured cells were simultaneously treated with Dex and cycloheximide. Neither mdr1 nor mdr3 gene was induced in the Dex-treated nonhepatoma cell lines, LMtk- and NIH3T3. Similarly, MDR1 messenger RNA levels were elevated in the Dex-treated human hepatoma line, HepG2, but not in the nonhepatoma, HeLa. This study demonstrated that the hormonal regulation of mdr gene expression is gene and cell type specific.
authors.affiliation: Department of Molecular Pathology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
authors.forename: J Y
authors.initials: JY
authors.lastname: Zhao
authors.forename: M
authors.initials: M
authors.lastname: Ikeguchi
authors.forename: T
authors.initials: T
authors.lastname: Eckersberg
authors.forename: M T
authors.initials: MT
authors.lastname: Kuo
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics*; D003513:Cycloheximide / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004351:Drug Resistance / Q000235:genetics*; D015870:Gene Expression / Q000187:drug effects*; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D015347:RNA Probes; D012333:RNA, Messenger / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D015347:RNA Probes; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D003513:Cycloheximide