Inhibitors of transcription and translation act synergistically with tumor necrosis factor to cause the activation of phospholipase A2.

In this report we have examined the ability of tumor necrosis factor-alpha (TNF) to induce the activity of phospholipase A2 (PLA2) in the cell line C3HA, a murine 3T3-like cell line which is normally resistant to TNF-induced cytolysis but can be sensitized with inhibitors of transcription and translation. Our results show that TNF is normally unable to induce the activity of PLA2 in this cell, as measured by the release of [3H]arachidonic acid. We find, however, that in the presence of either actinomycin D (Act D) or cycloheximide (CHI), TNF is indeed able to induce phospholipase activity and that the TNF-induced activation of PLA2 occurs 2-4 h before the onset of 51Cr release. The release of [3H]arachidonic acid was inhibited by 40-50% by pretreatment with 1 microM dexamethasone. Treatment with dexamethasone also inhibited cytolysis by 40-50% indicating that the CHI-dependent, TNF-induced activation of PLA2 is a cause, not an effect of cytolysis. The ability of TNF to induce the activity of PLA2 was also tested in two other cell types which are resistant to TNF except in the presence of Act D or CHI: SK-MEL-28, a human melanoma-derived cell line, and pVBETK-1cl15.2, an SV40-transformed murine L cell line. Our results were the same, treatment with a combination of Act D and TNF or CHI and TNF was required to cause activation of PLA2.