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Phospholipase A₂ Activation and Autoinduction of Tumor Necrosis Factor Gene Expression by Tumor Necrosis Factor¹

Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115

Tumor necrosis factor (TNF) acts via a cell surface receptor to induce a variety of cellular events including cytolysis, differentiation, and mitogenesis. The mechanisms underlying the cell specific actions of TNF are not known. In the present study, postreceptor events associated with the autoinduction of TNF expression were examined in HL-60 cells. There was no detectable alteration in phospholipase C activity as measured by inositol phosphate generation or release of choline metabolites following TNF stimulation. However, TNF increased the release of arachidonic acid metabolites from HL-60 cells. This increase in arachidonic acid metabolism was associated with a 40% increase in phospholipase A₂ activity. Furthermore, the release of arachidonic acid metabolites was blocked by inhibitors of phospholipase A₂. Taken together, these findings indicated that TNF stimulates phospholipase A₂ and arachidonic acid metabolism in HL-60 cells. The results also demonstrate that TNF expression is induced 15–30 min after stimulation with TNF and that this effect is associated with an increase in the rate of TNF transcription. This autoinduction of TNF mRNA was blocked by inhibitors of phospholipase A₂. While the cyclooxygenase inhibitor indomethacin had no detectable effect, ketoconazole and nordihydroguaiaretic acid, inhibitors of lipoxygenase, also blocked the induction of TNF expression by TNF. These findings suggest that phospholipase A₂ and lipoxygenase activity are required for the transcriptional activation of TNF gene expression associated with TNF stimulation of HL-60 cells.

¹ This investigation was supported by USPHS Grants CA-47722 and CA-42802 awarded by the National Cancer Institute, Department of Health and Human Services, a grant from Asahi Chemical Industry America, Inc., and Burroughs Wellcome Clinical Pharmacology Award (D.W.K.).

² To whom requests for reprints should be addressed, at Department of Human Oncology, K4/634, 600 Highland Ave., Madison, WI 53792.

Received 2/26/90. Accepted 7/11/90.

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