HYPERPHOSPHORYLATION OF CALNEXIN, A CHAPERONE PROTEIN, INDUCED BY CLOSTRIDIUM-DIFFICILE CYTOTOXIN

Exposure of McCoy cultured cells to Clostridium difficile cytotoxin B or okadaic acid (OA), a potent phosphatase inhibitor, results in simil ar morphological changes. Using two-dimensional gel electrophoresis, w e have detected a protein of approximately 77 kDa, with a pI of 4.5 (t ermed pp77) which is hyperphosphorylated in both cases. The level of p hosphorylation of pp77 is increased by 293% and 35% after treatment wi th C. difficile cytotoxin B or OA, respectively. This protein was iden tified by microsequencing as calnexin, a protein which exhibits the ch aracteristics of an endoplasmic reticulum (ER) chaperone. (C) 1994 Aca demic Press, Inc.