Regulation of mdr1b gene expression in Fischer, Wistar and Sprague-Dawley rats in vivo and in vitro.
Administration of 2-acetylaminofluorene (2-AAF) to rats increased mdr1b expression in Fischer, Wistar and Sprague-Dawley rat livers; however, the response was much smaller in Sprague-Dawley livers. To investigate the basis of this difference we further examined the regulation of the mdr1b gene in hepatocytes isolated from Fischer, Sprague-Dawley and Wistar rats. A time-dependent increase in basal expression of mdr1b but not mdr2 was observed in hepatocytes isolated from all three strains of rats. After 4 days in culture, a larger increase in mdr1b mRNA levels was observed in Fischer and Wistar rat hepatocytes (3.5- and 4.6-fold respectively) than Sprague-Dawley hepatocytes (2-fold). Treatment of primary hepatocytes with 2-AAF caused an induction of mdr1b expression that varied among the three strains. Notably, Sprague-Dawley hepatocytes were not responsive to 2-AAF. In contrast to the parent compound, the electrophilic metabolites N-hydroxy-2-acetylaminofluorene and N-acetoxy-2-acetylaminofluorene caused a dose-dependent induction of mdr1b expression in both Fischer and Sprague-Dawley hepatocytes, indicating that differences in the metabolic activation of 2-AAF between the strains may account for the differences in mdr1b by 2-AAF. Hepatocytes isolated from all three strains of rats showed an equivalent induction of mdr1b after treatment with cycloheximide. Nuclear run-on assays demonstrated that the increases in mdr1b expression with time in culture and after xenobiotic treatment were due to increased transcription.
Hill
B A
BA
Laboratory of Experimental Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Brown
P C
PC
Preisegger
K H
KH
Silverman
J A
JA
D015073:2-Acetylaminofluorene / Q000633:toxicity; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002273:Carcinogens; D003513:Cycloheximide / Q000633:toxicity; D018432:Drug Resistance, Multiple / Q000235:genetics*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011500:Protein Synthesis Inhibitors / Q000633:toxicity; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013045:Species Specificity; D013997:Time Factors
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002273:Carcinogens; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D003513:Cycloheximide; D015073:2-Acetylaminofluorene; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases