calyculin-a and Carcinoma-256--Walker

The phosphatase inhibitor okadaic acid exerted a biphasic effect on the shape of spontaneously polarized Walker carcinosarcoma cells. At lower concentrations, the drug suppressed cell polarity (IC50 = 0.14 microM) and the cells reverted to a spherical shape. At higher concentrations (> 0.25 microM), cells developed large blebs (IC50 = 0.4 microM). Furthermore, 0.2 microM okadaic acid completely suppressed spontaneous cell locomotion. Two specific inhibitors of protein kinase C did not prevent the actions of okadaic acid on cell shape, showing that this enzyme is very likely not involved. Another phosphatase inhibitor, calyculin A, also suppressed polarity (IC50 = 60 nM) and produced blebbing cells (IC50 = 70 nM). 1 microM okadaic acid induced a 40- to 70-fold increase in phosphorylation of the intermediate filament protein vimentin in intact cells. Increased phosphorylation of this major phosphoprotein correlated with the generation of blebbing cells, rather than with inhibition of polarity and may thus be involved in generating the marked shape changes. We conclude that constitutive phosphatase activity is required for motility and control of shape in Walker carcinosarcoma cells.

Topics: Actins; Animals; Carcinoma 256, Walker; Cell Movement; Cell Size; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Immunoblotting; Marine Toxins; Okadaic Acid; Oxazoles; Phosphoprotein Phosphatases; Phosphorylation; Protein Kinase C; Staining and Labeling; Tumor Cells, Cultured; Vimentin