Acute changes in liver gene expression in the N-nitrosodiethylamine-treated rat

We constructed a complementary DNA (cDNA) library from mRNAs of rat liver induced by an initiating dose of a chemical carcinogen, N-nitrosodiethylamine (DEN). Using a differential hybridization with cDNA probes prepared from mRNAs of control and DEN-treated rat liver, eight cDNAs of which expression was altered by an acute single dose of DEN were cloned. Colony hybridization and nucleotide sequencing demonstrated six independent cDNA clones. These were known genes encoding liver-specific proteins such as microsomal epoxide hydrolase (mEH; epoxide hydrolase, EC 3.3.2.3), albumin, transthyretin, CYP2B7, CYP1A2 (microsomal cytochrome P450, EC 1.14.14.1) and argininosuccinate synthetase (EC 6.3.4.5). Quantitative Northern blot hybridization was carried out to measure the mRNA content of DEN-initiated rat liver at various times after DEN injection. We also analyzed the expression of glutathione transferase P (GST-P; glutathione transferase, EC 2.5.1.18), c-jun and glyceraldehyde-3-phosphate dehydrogenase (GAPDH; glyceraldehyde-phosphate dehydrogenase, EC 1.2.1.12). A single injection of DEN increased the mRNA levels of mEH, beta-actin and c-jun markedly and those of GST-P and GAPDH moderately, but decreased the mRNA levels of CYP2B7, CYP1A2, albumin and argininosuccinate synthetase. Transthyretin mRNA content was not changed, indicating that it was a false-positive clone picked up by chance. These dramatic changes in liver gene expression after acute exposure to DEN are discussed in terms of acute reactions to the massive damage to the DNA and self-defense mechanisms against toxic xenobiotics.