Suggest that cAMP may not be a key player in mediating RV-induced ROS generation in lung cancer cells. The NADPH oxidases (Noxs) are a get Avasimibe family of transmembrane enzymes that generate superoxide and other ROS [41]. To better understand how RV induces ROS generation in cancer cells, we investigated if RV treatment has any impact on the expression of Nox1, Nox2, Nox3, Nox4 and Nox5 in NSCLC cells. Real-time RT-PCR results indicate that Nox1, 2 and 5 are abundantly expressed in both A549 and H460 cells, whereas Nox 3 and 4 are barely detectable in lung cancer cells (Figure S2). Surprisingly, our data reveal that RV treatment selectively increases Nox5 expression in both A549 and H460 cells (Figs. 6A and 6C),suggesting that RV-induced ROS generation in cancer cells is likely attributable to increased Nox5 expression. Given the important roles of antioxidant enzymes such as mitochondrial superoxide dismutase (SOD) and thioredoxin (TXN) in modulating intracellular ROS balance [42], we decided to determine if RV treatment affects the expression of SOD and TXN in lung cancer cells. The real-time PCR data demonstrate that RV treatment only causes a modest increase (less than 2-fold) in SOD2 expression in A549 cells, but has no effect on the expression of SOD1, SOD2 and TXN mRNAs in H460 cells (Figs. 6B and 6D). Together, these data suggest that RV may induce ROS generation in cancer cells through up-regulating Nox5 expression.Resveratrol-Induced Senescence in Cancer CellsFigure 3. RV induces premature senescence in NSCLC cells. (A) SA-b-gal staining increased with RV doses in both A549 cells (upper panel) and H460 cells (lower panel). (B) The percentage of SA-b-gal positive senescent cells in RV-treated and control A549 cells is presented as mean 6 SEM. (C) The percentage of SA-b-gal positive senescent cells in RV-treated and control H460 cells is presented as mean 6 SEM. (D) Western blot assays were performed to determine the expression of p53, p21 and EF1A in A549 cells. Actin was used as a loading control. (E) Western blot assays were performed to determine the expression of p53, p21 and EF1A in H460 cells. Actin was used as a loading control. *, p,0.05 vs. control; **, p,0.001 vs. control. doi:10.1371/journal.pone.0060065.gDiscussionCellular senescence is a state of permanent cell cycle arrest that can be triggered by a variety of stresses including DNA damage, telomere shortening and oxidative stress. Senescence limits the life span and proliferative capacity of cells, therefore the induction of senescence is regarded as an important mechanism of cancer prevention [20?2]. More importantly, growing evidence has SIS3 cost demonstrated that therapy-induced senescence is a critical mechanism of action for many chemotherapeutic agents and radiation treatment [11,12,15,17,23]. However, the contribution of senescence induction to RV’s anticancer and 
chemopreventive effects has not been well elucidated. Here we provide experimental data demonstrating that low dose RV treatment inhibits the growth of lung cancer cells via an apoptosis-independent mechanism. The results reveal that RV may exert its anticancerand chemopreventive activities via the induction of senescence in cancer cells. Consistent with our observations, Rusin et al. also reported that RV treatment induces senescence-like phenotype in cancer cells [43]. This is a significant finding because the induction of senescence, as opposed to apoptosis, requires much lower concentration of RV, suggesting R.Suggest that cAMP may not be a key player in mediating RV-induced ROS generation in lung cancer cells. The NADPH oxidases (Noxs) are a family of transmembrane enzymes that generate superoxide and other ROS [41]. To better understand how RV induces ROS generation in cancer cells, we investigated if RV treatment has any impact on the expression of Nox1, Nox2, Nox3, Nox4 and Nox5 in NSCLC cells. Real-time RT-PCR results indicate that Nox1, 2 and 5 are abundantly expressed in both A549 and H460 cells, whereas Nox 3 and 4 are barely detectable in lung cancer cells (Figure S2). Surprisingly, our data reveal that RV treatment selectively increases Nox5 expression in both A549 and H460 cells (Figs. 6A and 6C),suggesting that RV-induced ROS generation in cancer cells is likely attributable to increased Nox5 expression. Given the important roles of antioxidant enzymes such as mitochondrial superoxide dismutase (SOD) and thioredoxin (TXN) in modulating intracellular ROS balance [42], we decided to determine if RV treatment affects the expression of SOD and TXN in lung cancer cells. The real-time PCR data demonstrate that RV treatment only causes a modest increase (less than 2-fold) in SOD2 expression in A549 cells, but has no effect on the expression of SOD1, SOD2 and TXN mRNAs in H460 cells (Figs. 6B and 6D). Together, these data suggest that RV may induce ROS generation in cancer cells through up-regulating Nox5 expression.Resveratrol-Induced Senescence in Cancer CellsFigure 3. RV induces premature senescence in NSCLC cells. (A) SA-b-gal staining increased with RV doses in both A549 cells (upper panel) and H460 cells (lower panel). (B) The percentage of SA-b-gal positive senescent cells in RV-treated and control A549 cells is presented as mean 6 SEM. (C) The percentage of SA-b-gal positive senescent cells in RV-treated and control H460 cells is presented as mean 6 SEM. (D) Western blot assays were performed to determine the expression of p53, p21 and EF1A in A549 cells. Actin was used as a loading control. (E) Western blot assays were performed to determine the expression of p53, p21 and EF1A in H460 cells. Actin was used as a loading control. *, p,0.05 vs. control; **, p,0.001 vs. control. doi:10.1371/journal.pone.0060065.gDiscussionCellular senescence is a state of permanent cell cycle 
arrest that can be triggered by a variety of stresses including DNA damage, telomere shortening and oxidative stress. Senescence limits the life span and proliferative capacity of cells, therefore the induction of senescence is regarded as an important mechanism of cancer prevention [20?2]. More importantly, growing evidence has demonstrated that therapy-induced senescence is a critical mechanism of action for many chemotherapeutic agents and radiation treatment [11,12,15,17,23]. However, the contribution of senescence induction to RV’s anticancer and chemopreventive effects has not been well elucidated. Here we provide experimental data demonstrating that low dose RV treatment inhibits the growth of lung cancer cells via an apoptosis-independent mechanism. The results reveal that RV may exert its anticancerand chemopreventive activities via the induction of senescence in cancer cells. Consistent with our observations, Rusin et al. also reported that RV treatment induces senescence-like phenotype in cancer cells [43]. This is a significant finding because the induction of senescence, as opposed to apoptosis, requires much lower concentration of RV, suggesting R.
