Susceptibility to TNF in the presence of inhibitors of transcription or translation is dependent on the activity of cytosolic phospholipase A2 in human melanoma tumor cells
Voelkel-Johnson, C.; Thorne, T.E.; Laster, S.M.
Journal of Immunology 156(1): 201-207
1996
ISSN/ISBN: 0022-1767 PMID: 8598463 Document Number: 463866
In this study, we have examined the relationship between the expression of the high molecular weight, cytosolic form of PLA-2 (cPLA-2) and ability of inhibitors of transcription or translation (ITT) to induce susceptibility to TNF. Susceptibility to lysis was assayed by 51Cr release, and the expression of cPLA-2 was assayed by activity assay and by Western blot. The panel of cells that we examined included two murine cell lines, six human melanoma-derived cell lines, two samples of freshly explanted melanoma tumor tissue, and a culture of normal epidermal melanocytes. Our experiments revealed a near perfect correlation between the activity of cPLA-2 per cell and susceptiblity to TNF in the presence of either cycloheximide (CHI) or actinomycin D (r = 0.97). These results suggest that the activity of cPLA-2 is both necessary and rate-limiting in this form of programmed cell death, conclusions that were confirmed in transfection experiments and in experiments with antisense oligonucleotides. Overexpression of cPLA-2 in two melanoma-derived cell lines, WM793 and SK-MEL-131, led to enhanced susceptibility to TNF and CHI. Conversely, suppression of cPLA-2 with antisense oligonucleotides dramatically decreased susceptibility to TNF and CHI in C3HA fibroblasts. These experiments also revealed a coupled, transformation-related change in the expression of cPLA-2 and susceptibility to lysis. Normal melanocytes contained the lowest levels of cPLA-2 and were completely resistant to sensitization with ITT. In contrast, all of the melanoma-derived cell lines and samples of melanoma tumor tissue we examined had higher levels of cPLA-2 and could be killed, to some extent, by treatment with TNF and ITT.