Human monocyte-released cytotoxic factor: effect on various cellular functions, and dependency of cytolysis on...

The ability of the human monocyte-released cytotoxic protein factor(s) (CF) to mediate cytolysis when various metabolic processes in target cells were inhibited, and its effect on various cell functions have been studied. Cytolysis was reduced when target cells were exposed to either chloroquine or colchicine, indicating that lysosome function and the formation of microtubule are of importance with respect to the interaction between CF and target cells, possibly by effecting internalization and processing CF and its receptor. A decrease in the energy charge of the target cells did not affect the ability of CF to mediate cytolysis, since the 60-70% reduction of the cellular ATP content by uncoupling oxidative phosphorylation had little effect on CF-induced lysis. It was unnecessary for target cells to be actively growing and dividing for CF to induce lysis because inhibition of cellular protein, RNA, and DNA synthesis potentiated the cytolytic effect of CF. CF-induced cell lysis of Walter and Eliza Hall Institute (WEHI) 164 target cells was first detected between 3.0 and 4.5 hr after addition of CF. Target cell DNA synthesis nearly terminated within 3-4 hr, about the time of first cell lysis detection. Compared to the effect on DNA synthesis, the CF effect on protein synthesis was negligible and only a slight reduction was detected in the RNA synthesis and in the cellular ATP content. The results indicated that the DNA-synthesizing machinery may either be a primary target site of CF or a rapid influence of CF action on its primary target site; however, neither the protein- or RNA-synthesizing machinery nor the cellular ATP generating systems are likely to be primary target sites.