Activation of two distinct anti-proliferative pathways, apoptosis and p38 MAP kinase-dependent cell cycle arrest, by tumor necrosis factor in human melanoma cell line A375.
The proliferation of human melanoma cell line A375-6 cells is inhibited by several cytokines, including interleukin-1 (IL-1). A375-R8 cells, a subclone of A375-6, are resistant to IL-1-induced growth inhibition. The proliferation of both cell lines is inhibitable by tumor necrosis factor (TNF). In this study, we characterized the mechanisms of TNF-induced growth inhibition. TNF-induced growth inhibition in both cell lines was partially suppressed by a selective p38 mitogen-activated protein kinase (MAPK) inhibitor (SB203580), whereas a combination of SB203580 and Z-VAD-fmk, an inhibitor for a wide range of caspases, completely blocked TNF-induced growth inhibition, indicating that TNF-induced growth inhibition is mediated by both p38 MAPK and caspases. However, Z-VAD-fmk alone suppressed TNF-induced growth inhibition in A375-R8, but not A375-6, cells, suggesting that there may exist a TNF-induced anti-apoptotic mechanism in A375-6 cells which is lost or mutated in A375-R8 cells. Evidence in support of this notion includes (1) TNF-induced apoptosis only in A375-R8, but not A375-6 cells; (2) cycloheximide enabled TNF to induce apoptosis even in A375-6 cells; and (3) somatic hybrid cells between A375-6 and A375-R8 cells are resistant to TNF-induced apoptosis. Since TNF-induced NF-kappa B activation, cell cycle arrest, RB dephosphorylation, and E2F downregulation are indistinguishable in both cell lines, none of these factors is likely to be involved in the TNF-induced anti-apoptotic mechanism in A375-6 cells. Our results indicate that TNF activates two distinct anti-proliferative pathways including p38 MAPK-dependent cell cycle arrest and caspase-mediated apoptosis, as well as an anti-apoptotic mechanism in melanoma cells.
Hattori
T
T
Department of Hygienic Chemistry, Faculty of Pharmaceutical Sciences, Nagoya City University, Mizuho, Nagoya 467-8603, Japan.
Hayashi
H
H
Chiba
T
T
Onozaki
K
K
D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division / Q000502:physiology*; D004789:Enzyme Activation; D006801:Humans; D008545:Melanoma / Q000201:enzymology / Q000473:pathology*; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D016328:NF-kappa B / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases
D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases