[Show abstract][Hide abstract] ABSTRACT: Although luteolin is identified as a potential cancer therapeutic and preventive agent because of its potent cancer cell-killing activity, the molecular mechanisms by which its cancer cell cytotoxicity is achieved have not been well elucidated. In this report, luteolin-induced cellular signaling was systematically investigated, and a novel pathway for luteolin's lung cancer killing was identified. The results show that induction of superoxide is an early and crucial step for luteolin-induced apoptotic and nonapoptotic death in lung cancer cells. The c-Jun N-terminal kinase (JNK) was potently activated after superoxide accumulation. Suppression of superoxide completely blocked luteolin-induced JNK activation, which was well correlated to alleviation of luteolin's cytotoxicity. Although luteolin slightly stimulated the JNK-activating kinase mitogen-activated protein kinase kinase 7, the latter was not dependent on superoxide. We further found that luteolin triggers a superoxide-dependent rapid degradation of the JNK-inactivating phosphatase mitogen-activated protein kinase phosphatase-1 (MKP-1). Introduction of a degradation-resistant MKP-1 mutant effectively attenuated luteolin-induced JNK activation and cytotoxicity, suggesting that inhibition of the JNK suppressor MKP-1 plays a major role in luteolin-induced lung cancer cell death. Taken together, our results unveil a novel pathway consisting of superoxide, MKP-1, and JNK for luteolin's cytotoxicity in lung cancer cells, and manipulation of this pathway could be a useful approach for applying luteolin for lung cancer prevention and therapy.
[Show abstract][Hide abstract] ABSTRACT: Smac mimetics are potential anticancer therapeutics selectively killing cancer cells through autocrine tumor necrosis factor (TNF)-mediated apoptosis pathway. Our recent study reveal that the Smac mimetic compound 3 (SMC3)-activated NF-kappaB protects cancer cells against apoptosis, thus blunting SMC3's anticancer activity. Based on our previous observations that the nutrient flavonoid luteolin potently blocks TNF-induced NF-kappaB activation in cancer cells, we investigated if the combination of SMC3 and luteolin would achieve a synergistic anticancer activity. The results show that luteolin had no effect on autocrine TNF but it effectively blocked SMC3-induced nuclear factor kappa B (NF-kappaB) activation and expression of anti-apoptotic NF-kappaB targets. When SMC3 and luteolin were combined in treating cancer cells derived from lung and liver tumors, the activation of TNF-dependent apoptosis was markedly sensitized and a synergistic cytotoxic effect was achieved. In addition, the SMC3 and luteolin co-treatment had marginal effect on immortalized normal human bronchial epithelial cells. The results suggest that combination of SMC3 and luteolin is an effective approach for improving the anticancer value of SMC3, which has implications in cancer prevention and therapy.
[Show abstract][Hide abstract] ABSTRACT: Nuclear factor kappaB (NF-kappaB) activated by tumor necrosis factor (TNF) attenuates the TNF-induced apoptosis pathway. Therefore, blockage of NF-kappaB should improve the anticancer activity of TNF. Luteolin, a naturally occurring polyphenol flavonoid, has been reported to sensitize colorectal cancer cells to TNF-induced apoptosis through suppression of NF-kappaB; however, the mechanisms of this effect have not been well elucidated. In this article, we provide evidence showing a critical role of reactive oxygen species (ROS) accumulation induced by luteolin in modulating TNF-activated pathways in lung cancer cells. Luteolin effectively suppressed NF-kappaB, whereas it potentiated the c-Jun N-terminal kinase (JNK) to increase apoptosis induced by TNF in lung cancer cells. Our results further demonstrate that luteolin induced an early phase ROS accumulation via suppression of the cellular superoxide dismutase activity. It is noteworthy that suppression of ROS accumulation by ROS scavengers butylated hydroxyanisole, and N-acetyl-L-cysteine prevented the luteolin-induced suppression of NF-kappaB and potentiation of JNK and significantly suppressed the synergistic cytotoxicity seen with cotreatment of luteolin and TNF. Taken together, these results suggest that the accumulation of ROS induced by luteolin plays a pivotal role in suppression of NF-kappaB and potentiation of JNK to sensitize lung cancer cells to undergo TNF-induced apoptosis.
[Show abstract][Hide abstract] ABSTRACT: Nuclear factor-kappaB (NF-kappaB), a survival signal induced by tumor necrosis factor (TNF), contributes substantially to the resistance to TNF-induced cell death. Previous studies suggest that heat shock protein 90 (Hsp90) regulates the stability and function of receptor-interaction proteins (RIP) and IkappaB kinase beta (IKKbeta), the key components of the TNF-induced NF-kappaB activation pathway. In this study, we showed that the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG) was synergistic with TNF to induce apoptotic cell death in a panel of lung tumor-derived cell lines. Treatment with 17AAG caused degradation of RIP and IKKbeta that, in turn, blocked TNF-induced NF-kappaB activation and antiapoptotic gene expression. The synergistic cytotoxicity was detected only when TNF treatment followed 17AAG preexposure. Importantly, the potentiation of cell death was abolished in NF-kappaB-disabled cells that express a nondegradable IkappaBalpha mutant (IkappaBalphaAA). These results suggest that the cytotoxicity seen with 17AAG and TNF treatment results from blocking TNF-induced NF-kappaB activation. The other components of the TNF receptor I signaling cascade were not altered, whereas TNF-induced c-Jun NH(2)-terminal kinase activation and apoptosis were potentiated. A similar synergism for inducing apoptosis was also observed in 17AAG-treated and TNF-related apoptosis-inducing ligand (TRAIL)-treated cancer cells. Our results suggest that NF-kappaB plays a key role in the resistance of lung cancer cells to TNF and TRAIL and that disabling this survival signal with 17AAG followed by TNF or TRAIL treatment could be an effective new therapeutic strategy for lung cancer.
Cancer Research 02/2006; 66(2):1089-95. DOI:10.1158/0008-5472.CAN-05-2698 · 9.33 Impact Factor