Protein synthesis is required for cholera toxin-induced stimulation of arachidonic acid metabolism

The molecular events in the mechanism of action of cholera toxin were analyzed using Chinese hamster ovary (CHO) cells. Cholera toxin stimulated both 3′,5′-cyclic adenosine monophosphate (cAMP) synthesis and arachidonic acid metabolism in these cells. The turnover of phospholipid by cholera toxin-induced stimulation of phospholipase activity evoked the synthesis of PGE₂ and other prostaglandins. Cholera toxin-induced release of both [³H]arachidonic acid and PGE₂ was blocked by addition of either cycloheximide or actinomycin D. In contrast, accumulation of cAMP in cholera toxin-treated CHO cells was unaffected by adding these drugs. Further, dibutyryl cAMP or forskolin caused [³H]arachidonic acid release, which also was blocked by cycloheximide and actinomycin D. We concluded that the sequence of molecular events in cholera toxin-treated CHO cells first involved activation of adenylate cyclase, which caused an increase in cAMP. In turn, cAMP promoted transcription of mRNA that encoded either a specific phospholipase or a phospholipase-activating protein. The emerging arachadonic acid metabolites (e.g., PGE₂ and PGF_2α) might be important mediators of cholera toxin's stimulatory effects on vascular permeability and smooth muscle contraction in the intestine during cholera.