ACUTE CHANGES IN LIVER GENE-EXPRESSION IN THE N-NITROSODIETHYLAMINE-TREATED RAT

We constructed a complementary DNA (cDNA) library from mRNAs of rat li ver induced by an initiating dose of a chemical carcinogen, N-nitrosod iethylamine (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 c loned. Colony hybridization and nucleotide sequencing demonstrated six independent cDNA clones. These were known genes encoding liver-specif ic proteins such as microsomal epoxide hydrolase (mEH; epoxide hydrola se, EC 3.3.2.3), albumin, transthyretin, CYP2B7, CYP1A2 (microsomal cy tochrome P450, EC 1.14.14.1) and argininosuccinate synthetase (EC 6.3. 4.5). Quantitative Northern blot hybridization was carried out to meas ure the mRNA content of DEN-initiated rat liver at various times after DEN injection. We also analyzed the expression of glutathione transfe rase P (GST-P; glutathione transferase, EC 2.5.1.18), c-jun and glycer aldehyde-3-phosphate dehydrogenase (GAPDH; glyceraldehyde-phosphate de hydrogenase, EC 1.2.1.12). A single injection of DEN increased the mRN A 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, alb umin and argininosuccinate synthetase. Transthyretin mRNA content was not changed, indicating that it was a false-positive clone picked up b y chance. These dramatic changes in liver gene expression after acute exposure to DEN are discussed in terms of acute reactions to the massi ve damage to the DNA and self-defense mechanisms against toxic xenobio tics.