Augmentation of cytotoxic effect of tumor necrosis factor on human immunodeficiency virus-infected cells by staurosporine, a potent protein kinase C inhibitor.

We have examined the effect of the protein kinase C (PKC) inhibitor, staurosporine, on tumor necrosis factor (TNF)-induced cytotoxic action and augmentation of human immunodeficiency virus (HIV) expression on the chronically HIV-infected T-cell line, MOLT-4/HIV (HTLV-IIIB strain). Staurosporine enhanced the decrease in the number of viable cells caused by TNF treatment for 3 days (1 ng/ml of TNF, 43% decrease; 1 ng/ml of TNF + 20 nM staurosporine, 94%), whereas the cytotoxic action on that cell line induced by 10 ng/ml of 12-O-tetradecanoylphorbol-13-acetate (TPA), which was known to be an activator of PKC, was partially inhibited by staurosporine. In addition, staurosporine augmented the TNF cytotoxic activity against other cell lines including HIV-uninfected U937 cells(100 ng/ml of TNF, 53% decrease in the number of viable cells; 100 ng/ml of TNF + 5 nM staurosporine, 86%). However, staurosporine did not change the sensitivity of cells to TNF; thus, those insensitive to TNF were not changed to TNF sensitive by staurosporine. Furthermore, staurosporine did not affect the augmentative effect of TNF on HIV expression evaluated by levels of p24 antigen. Moreover, HIV long terminal repeat (LTR)-directed chloramphenicol acetyltransferase assay showed that staurosporine strongly inhibited the TPA-induced activation of HIV LTR, while that caused by TNF was little affected (10 ng/ml of TPA, 98.4% conversion; 10 ng/ml of TPA + 40 nM staurosporine, 22.2%, 1 ng/ml of TNF, 98.5%; 10 ng/ml of TNF + 40 nM staurosporine, 93.9%). These results suggest that TPA and TNF facilitate HIV replication by different pathways and that staurosporine augments TNF cytotoxicity by possible suppression of PKC activity in both HIV-infected and uninfected cells.