Effect of Cholera Toxin and Pertussis Toxin on the Growth of A431 Cells: Kinetics of Cyclic AMP and Inositol Trisphosphate in Toxin-Treated Cells

Abstract

Cholera toxin and pertussis toxin were inhibitory to the incorporation of thymidine into A431 cells in serum-free culture. Cholera toxin enhanced the growth inhibitory effect of epidermal growth factor (EGF) on A431 cells, whereas pertussis toxin attenuated the effect. Cholera toxin increased the concentration of intracellular cyclic AMP (cAMP) to three-times the initial concentration at 120 minutes and it increased the concentration of intracellular inositol trisphosphate (IP₃) rapidly but transiently. Pertussis toxin reduced the concentration of IP₃ both in EGF treated and untreated A431 cells at 10 minutes. cAMP was not involved in pertussis toxin-mediated effects. In conclusion, the intracellular cAMP and IP₃ concentrations in CT-treated A431 cells are compatible with previous reports regarding the growth inhibitory effects on A431 cells. The inhibitory effect of PTX on the EGF-induced increase of intracellular IP₃ is thought to be compatible with the finding that PTX attenuated the EGF-induced growth inhibition.