Diacylglycerol kinase α suppresses tumor necrosis factor-α-induced apoptosis of human melanoma cells through NF-κB activation

We investigated the implication of diacylglycerol kinase (DGK) α (type I isoform) in melanoma cells because we found that this DGK isoform was expressed in several human melanoma cell lines but not in noncancerous melanocytes. Intriguingly, the overexpression of wild-type (WT) DGKα, but not of its kinase-dead (KD) mutant, markedly suppressed tumor necrosis factor (TNF)-α-induced apoptosis of AKI human melanoma cells. In the reverse experiment, siRNA-mediated knockdown of DGKα significantly enhanced the apoptosis. The overexpression of other type I isoforms (DGKβ and DGKγ) had, on the other hand, no detectable effects on the apoptosis. These results indicate that DGKα specifically suppresses the TNF-α-induced apoptosis through its catalytic action. We found that the overexpression of DGKα-WT, but not of DGKα-KD, further enhanced the TNF-α-stimulated transcriptional activity of an anti-apoptotic factor, NF-κB. Conversely, DGKα-knockdown considerably inhibited the NF-κB activity. Moreover, an NF-κB inhibitor blunted the anti-apoptotic effect of DGKα overexpression. Together, these results strongly suggest that DGKα is a novel positive regulator of NF-κB, which suppresses TNF-α-induced melanoma cell apoptosis.