Resveratrol enhances perforin expression and NK cell cytotoxicity through NKG2D-dependent pathways

In a previous report, we showed that the in vivo cytotoxic activity of the natural killer (NK) cells isolated from resveratrol-pretreated rats is significantly enhanced compared with that of the non-pretreated rats; however, the underlying mechanism remains unclear. In the present study, we use cultured NK92 cell line to examine the possible signaling pathways underlying the resveratrol-induced activation. Using cultured K562, HepG2, and A549 cells as targets, we show that resveratrol pretreatment increases NK cell cytotoxicity in a dose-dependent manner. The enhanced cytotoxic effect is accompanied by increases in JNK and ERK-1/2 MAP kinase activity and perforin expression. Moreover, the expression of NKG2D, an upstream signaling molecule of the MAP kinases pathway, is also enhanced. Resveratrol-enhanced perforin expression and cytotoxic activity are effectively inhibited by pretreatment with the inhibitors of JNK (SP600125), ERK-1/2 (PD98059), or by siRNAs against JNK-1 and ERK-2. However, the inhibitors or siRNA to p38 exhibits no effect. Since IL-2 has been shown to induce NKG2D expression and perforin release, we therefore, examined whether IL-2 and resveratrol act in parallel. We show that IL-2 also stimulates perforin expression, however, when treated together with resveratrol, they exhibit no additive effect. The results suggest that in NK92 cells, resveratrol may act via a similar or overlapping pathway as that of IL-2, to enhance perforin expression and cytotoxic activity. Data presented strongly indicate that resveratrol act via NKG2D-dependent JNK and ERK-1/2 pathways.