Cytolysis by tumor necrosis factor is preceded by a rapid and specific dissolution of microfilaments

Tumor necrosis factor (TNF) is cytotoxic to certain transformed cells, whereas normal cells are resistant to its effects. The resistance of normal cells can often be overcome by treatment with inhibitors of transcription or translation such as actinomycin D or cycloheximide (CHI), suggesting that normal cells produce a protein(s) that protects them from TNF-induced cytolysis. In this report, we examine the mechanism of cytolysis in a 3T3-like mouse cell line, C3HA, which was sensitized to TNF by treatment with CHI. We found that an early change in TNF/CHI-treated cells was a significant loss of stress fibers in perinuclear areas of the cytoplasm. The disruption of microfilaments, which was observed within 15 min of treatment, was not seen in untreated cells or in cells treated with either TNF or CHI alone. The dissolution of microfilaments spread peripherally over time and preceded other TNF/CHI-induced effects such as cytoplasmic "boiling," decrease in cell volume, and lysis of the plasma membrane. The breakdown of stress fibers occurred without a change in microtubules or intermediate filaments. Cytochalasin E, which disrupts microfilaments, induced cytolysis of TNF-treated cells even in the absence of CHI; however, demecolcine, which depolymerizes microtubules, did not sensitize cells to TNF. We propose that the TNF-induced cytolysis of certain cell types is preceded by a selective disruption of the microfilament lattice.