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Transketolase counteracts oxidative stress to drive cancer development.

ABSTRACT: Cancer cells experience an increase in oxidative stress. The pentose phosphate pathway (PPP) is a major biochemical pathway that generates antioxidant NADPH. Here, we show that transketolase (TKT), an enzyme in the PPP, is required for cancer growth because of its ability to affect the production of NAPDH to counteract oxidative stress. We show that TKT expression is tightly regulated by the Nuclear Factor, Erythroid 2-Like 2 (NRF2)/Kelch-Like ECH-Associated Protein 1 (KEAP1)/BTB and CNC Homolog 1 (BACH1) oxidative stress sensor pathway in cancers. Disturbing the redox homeostasis of cancer cells by genetic knockdown or pharmacologic inhibition of TKT sensitizes cancer cells to existing targeted therapy (Sorafenib). Our study strengthens the notion that antioxidants are beneficial to cancer growth and highlights the therapeutic benefits of targeting pathways that generate antioxidants.

SUBMITTER: Xu IM

PROVIDER: S-EPMC4760787 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Transketolase counteracts oxidative stress to drive cancer development.

Xu Iris Ming-Jing IM Lai Robin Kit-Ho RK Lin Shu-Hai SH Tse Aki Pui-Wah AP Chiu David Kung-Chun DK Koh Hui-Yu HY Law Cheuk-Ting CT Wong Chun-Ming CM Cai Zongwei Z Wong Carmen Chak-Lui CC Ng Irene Oi-Lin IO

Proceedings of the National Academy of Sciences of the United States of America 20160125 6

Cancer cells experience an increase in oxidative stress. The pentose phosphate pathway (PPP) is a major biochemical pathway that generates antioxidant NADPH. Here, we show that transketolase (TKT), an enzyme in the PPP, is required for cancer growth because of its ability to affect the production of NAPDH to counteract oxidative stress. We show that TKT expression is tightly regulated by the Nuclear Factor, Erythroid 2-Like 2 (NRF2)/Kelch-Like ECH-Associated Protein 1 (KEAP1)/BTB and CNC Homolog ...[more]

PMID: 26811478

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Project description:INTRODUCTION:When confronted to stress or pathological conditions, the mitochondria overproduce reactive species that participate in the cellular dysfunction. These organelles are however difficult to target with antioxidants. A feature of mitochondria that can be used for this is the negatively charged compartments they form. Most of mitochondrion-targeting antioxidants are therefore cationic synthetic molecules. Our hypothesis is that such mitochondriotropic traits might also exists in natural molecules. AIM:We tested here whether sinapine, a natural phenolic antioxidant-bearing a permanent positive charge, can target mitochondria to modulate mitochondrial oxidative stress. METHODS:Experiments were performed in-vitro, in-cellulo, ex-vivo, and in-vivo, using cardiac tissue. The sinapic acid -lacking the positively-charged-choline-moiety present in sinapine-was used as a control. Sinapine entry into mitochondria was investigated in-vivo and in cardiomyocytes. We used fluorescent probes to detect cytosolic (H2DCFDA) and mitochondrial (DHR123) oxidative stress on cardiomyocytes induced with either hydrogen peroxide (H2O2) or antimycin A, respectively. Finally, ROS production was measured with DHE 10 min after ischemia-reperfusion (IR) on isolated heart, treated or not with sinapine, sinapic acid or with a known synthetic mitochondrion-targeted antioxidant (mitoTempo). RESULTS:We detected the presence of sinapine within mitochondria in-vitro, after incubation of isolated cardiomyocytes, and in-vivo, after oral treatment. The presence of sinapic acid was not detected in the mitochondria. Both the sinapine and the sinapic acid limited cytosolic oxidative stress in response to H2O2. Only sinapine was able to blunt oxidative stress resulting from antimycin A-induced mtROS. Both mitoTempo and sinapine improved cardiac functional recovery following IR. This was associated with lower ROS production within the cardiac tissue. CONCLUSION:Sinapine, a natural cationic hydrophilic phenol, commonly and substantially found in rapeseed species, effectively (i) enters within the mitochondria, (ii) selectively decreases the level of mitochondrial oxidative stress and, (iii) efficiently limits ROS production during cardiac ischemia-reperfusion.

Project description:Glucocorticoids (GCs) are currently used for the therapeutic management of cholestatic diseases, but their use and molecular mechanism remain controversial. The aims of this study were 1) to assess the therapeutic effect of a 2-week treatment with the GC dexamethasone on hepatic damage in bile duct-ligated rats; 2) to investigate its effect on the activation of the nuclear receptors (NRs) pregnane X receptor (PXR), constitutive androstane receptor (CAR) and GC receptor (GR), and NF-kB, as well as on oxidative stress and bile acid (BA) hepatic composition. Cholestasis was induced by ligation of bile duct (BDL animals) in 16 male Wistar-Kyoto rats, and eight of them were daily treated by oral gavage with 0.125 mg/ml/kg DEX for 14 days. Eight Sham-operated rats were used as controls. Severity of cholestasis was assessed histologically and on plasma biochemical parameters. The nuclear expression of NF-kB (p65), GR, PXR and CAR was measured in hepatic tissue by Western Blot. Oxidative stress was evaluated by measuring malondialdehyde, carbonylated proteins, GHS and ROS content in rat livers. LC-MS was used to measure the plasma and liver concentration of 7 BAs. Histological findings and a significant drop in several markers of inflammation (p65 nuclear translocation, mRNA expressions of TNF-α, IL-1β, IL-6) showed that DEX treatment reversed cholestasis-induced inflammation, and similar results have been obtained with oxidative stress markers. The nuclear expression of p65 and CAR were inversely correlated, with the latter increasing significantly after DEX treatment (p<0.01 vs vehicle). Hepatic BA levels tended to drop in the untreated cholestatic rats, whereas they were similar to those of healthy rats in DEX-treated animals. Plasma BAs decreased significantly in DEX-treated animals with respect to untreated cholestatic rats. In conclusion, DEX reduces inflammation and oxidative stress in BDL rats, and probably CAR is responsible for this effect. Therefore, this NR represents a promising pharmacological target for managing cholestatic and inflammatory liver diseases.

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Transketolase counteracts oxidative stress to drive cancer development.

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Transketolase counteracts oxidative stress to drive cancer development.

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