Original Article

Effects of 12 beticolins, Cercospora beticola toxins, on proliferation of ras-transformed adrenocortical cell

Authors: Guo-Qing Ding, Gabrielle Maume, Hanan Osman, Martine Padieu, Marie-Louise Milat, Claude Humbert, Jean-Pierre Blein, Bernard F Maume

Abstract

Aim: To explore different effects of 12 beticolins, Cercospora beticola toxins, on ras-transformed adrenocortical cell growth inhibition and their functional mechanism.
Methods: Beticolin-induced inhibition was measured with survival cell number determined by an automated photocolorimetric method. The penetration of beticolin was examined by confocal microscopy. Ras protein determined by Lowry method were separated by 14 % SDS-PAGE and electroblotted to Immobilon-P transfer membrane and detected with pan-Ras (Ab-3) monoclonal antibody. The Ca2+ chelation by beticolin was investigated using a calcium ionophore.
Results: Cell growth inhibition was found dose- and time-dependently at submicromolar level for beticolin-1, -2, and -13 (IC50 = 250 nmol/L) and for beticolin-0, 6, and -11 (400 nmol/L < IC50 = 500 nmol/L). The inhibition by beticolin-1 was immediate, independent of cell culture step and not reversible for 3-day treatment. Beticolin-3 and -4 were slightly active (1 micromol/L < IC50 = 2 micromol/L) and beticolin-7, -9, -12, and -5 were inactive at micromolar level. The beticolin-induced cell growth inhibition was correlated with the hydrophobicity of these compounds. Beticolin-1 fluorescence in RTAC cells was detected by confocal microscopy whereas beticolin-3 and -12 were not even after a 24 h incubation period. Beticolin-1-induced cell growth inhibition was partially reverted by calcium ionophore suggesting a role of intracellular Ca2+ chelation by beticolin-1 on cell growth inhibition. Furthermore, beticolin-1 blocked up Ras p21 translocation to membrane and induced accumulation of Ras in the cytosol as an inactive form by different ways.
Conclusion: Beticolins with high hydrophobicity inhibit tumorigenic cell proliferation by different ways.
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