Augmentation of TNF cytotoxicity by protein kinase C inhibitors: role of arachidonic acid and manganese superoxide dismutase.

The protein kinase C (PKC) inhibitors bisindolylmaleimide, calphostin C, H-7 and staurosporine were examined for their effect on tumour necrosis factor (TNF) cytotoxic activity. PKC inhibitors potentiated the cytotoxic activity of TNF in TNF-sensitive cell lines (CL8-1 melanoma and WEHI-164 fibrosarcoma), but had no effect on TNF cytolytic activity in TNF-resistant cells (BL6-8 melanoma and MCA-102 fibrosarcoma). The mechanism(s) of PKC inhibitor-mediated potentiation of the cytotoxic activity of TNF was investigated by analysing the effect of PKC inhibitors on TNF-induced arachidonic acid release in TNF-sensitive and -resistant cells. TNF induced the release of arachidonic acid in TNF-sensitive cells but had no effect in TNF-resistant cells. The combination of PKC inhibitor and TNF potentiated the release of arachidonic acid from TNF-sensitive cells, but failed to induce arachidonic acid release in TNF-resistant cells. Kinetic analysis of TNF-induced arachidonic acid release in CL8-1 melanoma cells revealed that it was an early event which preceded TNF tumour lytic activity. TNF was further shown to induce manganese superoxide dismutase (MnSOD) production in TNF-sensitive cells but failed to induce MnSOD activity in TNF-resistant BL6-8 and MCA 102 cells. MnSOD acts as a scaveneger of toxic superoxide radicals and its induction by TNF paralleled arachidonic acid release. Although the PKC-selective inhibitor bisindolylmaleimide potentiated TNF-induced release of arachidonic acid, it blocked TNF-mediated induction of MnSOD in CL8-1 melanoma and WEHI-164 fibrosarcoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)