Activation of distinct multidrug‐resistance (P‐glycoprotein) genes during rat liver regeneration and hepatocarcinogenesis

Abstract

The multidrug transporter P-glycoproteins are encoded by three multidrug-resistance (mdr) genes in rodents, designated mdr1a (mdr3), mdr1b (mdr1), and mdr2. Only the first two genes are functionally related to multidrug resistance. Activation of rodent mdr genes during liver regeneration and hepatocarcinogenesis has been reported. In mice, mdr1a is activated in hepatocellular carcinomas (HCCs) produced by various carcinogenic protocols, whereas both mdr1a and mdr2 are activated during liver regeneration. In this communication, we report isolating three gene-specific probes for the rat mdr homologues, which were used as probes in an RNase protection assay to demonstrate that mdr1b mRNA was expressed in HCCs induced by two different protocols. Furthermore, high levels of hepatic mdr1b mRNA but only moderate levels of mdr1a and mdr2 mRNA were seen in preneoplastic lesions in rats treated with 2-acetylaminofluorene. Likewise, highly elevated levels of hepatic mdr1b mRNA but only moderately increased levels of mdr1a and mdr2 mRNA were seen after partial hepatectomy. Nevertheless, the general patterns of tissue-specific expression of these three mdr genes were similar in rats and mice. These results reveal a complex hepatic gene expression pattern during hepatocarcinogenesis and hepatic proliferation for this conserved gene family in rodents.

Comparisons of P‐glycoprotein expression in isolated rat brain microvessels and in primary cultures of endothelial cells derived from microvasculature of rat brain, epididymal fat pad and from aorta

“…Single-strand cDNA was made from 1 pg of this RNA by reverse transcription using a random hexamer following which fragments specific to rat mdrla, mdrlb and mdr2 genes were amplified through 20 or 30 cycles of 94°C for 1 min, 55°C for 2 min and 72°C for 2 min using oligonucleotide primers appropriate to the particular isoform, i.e. sense sequence common to all three isoforms, ACAGA-AACAGAGGATCGC (bases 1599-1617) and antisense sequences for mdrla, CGTCTTGATCATGTGGCC (bases 2032 2015), for mdrlb, AGAGGCACCAGTGTCACT (bases 1951-1934) and for mdr2, ATGCGTGCTTTCCAGCCA (bases 1981 1964) [17]. As an internal control, a sample of each first-strand cDNA was also treated with primers able to amplify a 200 base-pair fragment of the rat flz-/d-globulingene [18].…”

The Role of Pregnane X Receptor in 2-Acetylaminofluorene-Mediated Induction of Drug Transport and -Metabolizing Enzymes in Mice

“…The hydroxylated metabolite of 2-AAF, produced predominantly by CYP1A2, has been shown to account for genotoxicity (Russell et al, 1994;Schrenk et al, 1994). Several studies have suggested that exposure to 2-AAF causes induction of the multidrug-resistant transporters MRP2 (Kauffmann et al, 1997) and MDR1 (Teeter et al, 1993;Schrenk et al, 1994), as well as the drug-metabolizing enzyme CYP3A23 (Sparfel et al, 2003).…”

2-Acetylaminofluorene Up-regulates Rat mdr1bExpression through Generating Reactive Oxygen Species That Activate NF-κB Pathway

“…Elevated expression of mdr gene transcripts and their encoded P-glycoprotein is also seen in rodent HCC (3,4). However, mechanisms of the elevation of MDR expression in HCC are largely unknown.…”