Evidence for enhanced expression of c-fos, c-jun, and the Ca²⁺-activated neutral protease in rat liver following carbon tetrachloride administration

The effects of CCl₄ on hepatic c-fos and c-jun gene expression were examined, and the correspondence between intermediate-early gene expression and the expression of the Ca²⁺-activated neutral proteinase (μ and mCANP) characterized. Administration of CCl₄ to rats resulted in a pronounced dose- and time-dependent increase in c-jun and c-fos mRNA levels (∼8 to 17-fold) as detected by either Northern blot or RT-PCR analyses. The expression of μ and mCANP following CCl₄ treatment was monitored by Northern blot analysis and μ and mCANP mRNA levels were found to be elevated ˜5- to 15-fold over the time period of 18 to 24 h. Experiments were performed to determine whether the Fos-Jun heterodimeric AP-1 transcription factor complex bound the AP-1-like binding motif present in the mCANP gene. Gel retardation assays using hepatic nuclear extracts from CCl₄-treated animals revealed binding of a protein to the AP-1-like motif present in the mCANP gene and competition and supershift assays confirmed the specificity of AP-1 transcription factor binding. These results show that CANP gene expression is enhanced in response to oxidative cellular damage and that the AP-1 complex may be involved in the regulation of CANP gene expression.