Tumor promoters induce changes in the chick embryo fibroblast cytoskeleton

We have examined the effect of the tumor promoter, 12-0-tetradecanoyl phorbol-13-acetate (TPA), on the actin-containing elements of the cytoskeleton of chick embryo fibroblasts (CEF). TPA at concentrations as low as 7.3 times 10-10M indices a reversible change in the cytoskeleton as visualized by indirect immunofluorescence using anti-actin antibodies. Cells incubated with TPA lose the ordered actin-containing structures found in normal cells and resemble Rous sarcoma virus-transformed cells in that the immunofluorescent actin pattern is diffuse. The TPA effects are both dose-and time-dependent. Analogs of TPA which are inactive as tumor promoters do not induce cytoskeletal changes at the concentrations tested, while a second tumor promoter, PDD, is also able to cause alterations in actin-containing structures. The action of TPA requires de novo synthesis of both RNA and protein. The direct cytoskeletal changes are neither plasmin-dependent nor subject to inhibition by incubating the cells with high levels of protease inhibitors during the exposure to TPA. However, plasminogen does increase the sensitivity of cells to TPA.