GENE-EXPRESSION IN LIVER AFTER TOXIC INJURY - ANALYSIS OF HEAT-SHOCK RESPONSE AND OXIDATIVE STRESS-INDUCIBLE GENES

In the liver, CCl4 induces cell necrosis followed by regeneration. Cel l injury is caused by free radical damage and may be due, at least in part, to oxidative stress and the subsequent formation of reactive oxy gen intermediates (ROIs). In a rat model of acute CCl4-induced hepatic injury, we examined the expression of genes involved in cellular resp onse to different kinds of stress, including oxidative stress (hsp70 f amily, heme oxygenase), in free radical detoxification (Mn superoxide dismutase and Cu/Zn superoxide dismutase), in iron homeostasis (H and L ferritin subunits) and in the cell cycle (c-fos, c-jun, histone H3). As an experimental approach, we first analysed the pattern of protein synthesised by liver slices in vitro. Then we studied the mechanisms regulating the expression of different genes, by analysing both mRNA s teady state levels and transcription rates. Activation of the specific heat shock transcription factor (HSF) by CCl4 was also investigated. We observed that different members of the hsp70 family (hsp70, hsc73, grp78) are activated by different kinetics and are regulated mainly at the transcriptional level. Induction of the hsp70 gene occurs rapidly and transiently and is preceded by the activation of HSF DNA-binding activity. We demonstrated an increase in the steady-state levels of mR NAs for heme oxygenase, Mn and Cu/Zn superoxide dismutases and H and L ferritin subunits. However, different kinetics and regulatory mechani sms occurred with different genes. We showed that I induction of c-fos and c-jun protooncogenes is the earliest event after CCl4 administrat ion, whereas histone H3 expression peaked at 24-48 h. The results of t his study are interpreted as evidence that activation of specific stre ss response genes is primarily related to the defence against the rapi dly occurring cell damage, but may also be related to subsequent proce sses of tissue inflammation and cell proliferation.