[The role of intermediate filaments in forming cellular processes induced in fibroblasts by the tumor promoter TPA].

A tumor promoter phorbol 12-myristate 13-acetate (PMA) induces characteristic reversible changes in the cell shape in certain fibroblastic lines. This reaction to PMA may be regarded as a prototype of reorganizations involving formation of stable cytoplasmic processes. Two specific drugs, Taxol and Colcemid, were used to study the role of microtubules and vimentin-containing intermediate filaments (IF) in the development of PMA-induced reorganizations. A short (I h) exposure to PMA induced formation of processes in the control cells rather than in the Colcemid treated cells having depolymerized microtubules and the IF that collapsed around the nucleus. A longer (3-4 h) exposure to PMA of the colcemid-treated cells induced a partial reversal of the IF collapse; those parts of peripheral lamellae that contained IF were transformed into narrow noncontractile processes. It is suggested that the local interaction of the IF with the actin system is an essential step in the formation of processes from lamellae.