Microtubule-dependent effect of phorbol ester on the contractility of cytoskeleton of cultured fibroblasts.

The effect of the tumor promoter phorbol 12-myristate 13-acetate (PMA) upon the contractility of permeabilized cell models (cytoskeletons) of mouse fibroblasts was examined. Contraction was induced by incubation of cell models in a solution containing ATP and was assessed quantitatively by measuring alterations of the area of cell model projection on the substrate. Immunofluorescence microscopy was used to assess alterations of cytoskeleton morphology in the course of permeabilization and contraction. It was found that contractility of cell models from PMA-treated fibroblasts was considerably diminished as compared with the models from control fibroblasts. ATP induced only local contraction of certain zones of actin cortex in models from PMA-treated fibroblasts; it did not induce general contraction, characteristic of control models. Normal high contractility was characteristic of the models from the cells preincubated with PMA in combination with Colcemid. PMA is a specific activator of protein kinase C, one of the key enzymes of the membrane signal-transduction pathway. It is suggested that protein kinase C regulates contractility of actin cortex and that the pathway of this regulation has a microtubule-dependent stage blocked by Colcemid.