Evidence for a Protein Synthesis-Dependent and -Independent TNFα Cytolytic Mechanism

Abstract

The analysis of the effect of the protein synthesis inhibitors emetine (EM) or actinomycin D (ACT-D) on the TNFα-mediated cytolysis of L929 target cells demonstrates a bipbasic, concentration (10 -12-10 -4 M )-dependent curve indicative of two cytolytic mechanisms operative in L929 cells. One TNFα cytolytic mechanism is dependent on protein synthesis in the target cells, while the other cytolytic mechanism is protein synthesis independent. Both TNFα cytolytic mechanisms cause apoptosis (fragmentation of DNA) as shown by the TNFα-mediated release of tritiated thymidine, Apoptag, and DAPI staining, in the presence or absence of EM or ACT-D. The two cytolytic mechanisms are also similar in their requirement for lipoxygenase enzymes as shown by the ability of nordihydroguaiaretic acid (10 -6-10 -5 M) and ketoconazole (4 × 10 -6-2 × 10 -5 M) to block TNFα-mediated lysis of the target cells. However, the two cytolytic mechanisms differ in their requirement for the production of oxygen free radicals. The oxygen free radical scavengers, dimethylsulphoxide (0.2-0.4 M) and glutathione (2 × 10 -6-10 -5 M) block the TNFα-mediated cytolysis of target cells in the absence of protein synthesis inhibitors, but not in the presence of EM or ACT-D.