Differential effects of cholera toxin and pertussis toxin on the c-fos andc-jun mRNA expression in rat C6 glioma cells

Cholera toxin (CTX) increased c-fos mRNA level whereas it down-regulated th e c-jun mRNA level in rat C6 glioma cells. In contrast to the action of CTX , pertussis toxin (PTX) did not affect either c-fos or c-jun mRNA level. Th e elevated c-fos mRNA level induced by CTX was significantly inhibited by t he co-treatment with dexamethasone (DEX), However, DEX did not affect CTX-i nduced down-regulation of c-jun mRNA level. Cycloheximide (CHX) increased c -fos and c-jun mRNA levels. CHX caused a super-induction of CTX-induced c-f os mRNA level. Our results suggest that CTX-, but not PTX-, sensitive G-pro teins may play an important role for c-fos mRNA up-regulation and c-jun mRN A down-regulation. In addition, DEX appears to have a selective inhibitory action against c-fos mRNA expression regulated by CTX, Ongoing protein synt hesis inhibition is required for the superinduction of c-fos, but not c-jun , mRNA induced by CTX.