Acceleration of actin polymerization and rapid microfilament reorganization in cultured hepatocytes by cyclochlorotin, a hepatotoxic cyclic peptide

Cyclochlorotin (= chloropeptide, CC) is a hepatotoxic mycotoxin of Penicill ium islandicum Sopp. The effect of CC on actin polymerization was examined by the measurement of changes in fluorescence intensity using pyrene-labele d actin and high shear viscosity. In the presence of CC, the time course of actin polymerization was accelerated in a dose dependent manner (2.5 ng/ml -2.5 mu g/ml), without affecting the final level of viscosity. CC exerted a strong stabilizing effect on actin, enabling it to maintain its filamentou s form in the presence of members of actin-binding proteins, including thos e of the gelsolin family prepared from hepatocytes. Microscopic observation revealed that in cultured hepatocytes, 1.0 mu g/ml of CC induced bleb form ation and changes in the microfilament. These observations indicated that a fter contact of the hepatocyte with CC, the following events were probable. The toxin passed through the cell membrane by a transport system and immed iately reacted with the actin-actin binding proteins underlying the lipid b ilayer. Bleb formation and hepatotoxicity were thus induced. (C) 2000 Elsev ier Science Ltd, All rights reserved.