The p53-induced glycolysis and apoptosis regulator (TIGAR) inhibits glycolysis, resulting in higher intracellular NADPH, lower reactive oxygen species (ROS) and autophagy activity. In this study, we investigated whether TIGAR might exert dual impacts on cancer cell survival based on its ability to inhibit both apoptosis and autophagy. In liver or lung cancer cells treated with the anticancer drug epirubicin, TIGAR levels increased in a dose-and time-dependent manner. TIGAR silencing enhanced epirubicin-induced elevations in ROS levels and apoptosis rates, in a manner that was blocked by ectopic addition of NADPH or N-acetyl cysteine. These findings were correlated with reduced tumorigenicity and increased chemosensitivity in mouse xenograft tumor assays. In parallel, TIGAR silencing also enhanced the epirubicin-induced activation of autophagy, in a manner that was also blocked by ectopic addition of NADPH. Notably, TIGAR silencing also licensed epirubicin-mediated inactivation of the mTOR pathway, suggesting TIGAR also exerted a negative impact on autophagy. However, genetic or pharmacologic inhibition of autophagy increased epirubicin-induced apoptosis in TIGAR-silenced cells. Overall, our results revealed that TIGAR inhibits both apoptosis and autophagy, resulting in a dual impact on tumor cell survival in response to tumor chemotherapy. Cancer Res; 74(18); 5127-38. Ó2014 AACR.

Previous study revealed that the protective effect of TIGAR in cell survival is mediated through the increase in PPP (pentose phosphate pathway) flux. However, it remains unexplored if TIGAR plays an important role in DNA damage and repair. This study investigated the role of TIGAR in DNA damage response (DDR) induced by genotoxic drugs and hypoxia in tumor cells. Results showed that TIGAR was increased and relocated to the nucleus after epirubicin or hypoxia treatment in cancer cells. Knockdown of TIGAR exacerbated DNA damage and the effects were partly reversed by the supplementation of PPP products NADPH, ribose, or the ROS scavenger NAC. Further studies with pharmacological and genetic approaches revealed that TIGAR regulated the phosphorylation of ATM, a key protein in DDR, through Cdk5. The Cdk5-AMT signal pathway involved in regulation of DDR by TIGAR defines a new role of TIGAR in cancer cell survival and it suggests that TIGAR may be a therapeutic target for cancers.

Previous studies reported the oral administration of Naja naja atra venom (NNAV) reduced adriamycin-induced chronic kidney damage. This study investigated the effects of intragastric administrated cardiotoxin from Naja naja atra venom on chronic kidney disease in rats. Wistar rats were injected with adriamycin (ADR; 6 mg/kg body weight) via the tail vein to induce chronic kidney disease. The cardiotoxin was administrated daily by intragastric injection at doses of 45, 90, and 180 μg/kg body weight until the end of the protocol. The rats were placed in metabolic cages for 24 hours to collect urine, for determination of proteinuria, once a week. After 6 weeks, the rats were sacrificed to determine serum profiles relevant to chronic kidney disease, including albumin, total cholesterol, phosphorus, blood urea nitrogen, and serum creatinine. Kidney histology was examined with hematoxylin and eosin, periodic acid-Schiff, and Masson's trichrome staining. The levels of kidney podocin were analyzed by Western blot analysis and immunofluorescence. We found that cardiotoxin reduced proteinuria and can improve biological parameters in the adriamycin-induced kidney disease model. Cardiotoxin also reduced adriamycin-induced kidney pathology, suggesting that cardiotoxin is an active component of NNAV for ameliorating adriamycin-induced kidney damage and may have a potential therapeutic value on chronic kidney disease.

Hepatocellular carcinoma is the primary malignancy of the liver and is the third leading cause of cancer-related death worldwide. Despite its severity, the treatment methods for hepatocellular carcinoma are limited due to poor prognosis. This study identified the short hairpin RNA-mediated silencing of myosin VI as a potential approach for the treatment of hepatocellular carcinoma. Firstly, the expression of myosin VI was analyzed in 57 hepatocellular carcinoma samples and 10 non-neoplastic samples by immunohistochemistry. The results demonstrated that myosin VI expression was much stronger in hepatocellular carcinoma tissues than in adjacent normal tissues. Myosin VI short hairpin RNA was then transduced into HepG2 and SMMC-7721 hepatocellular carcinoma cell lines, respectively, using a lentivirus delivery system. Knockdown of myosin VI led to a significant reduction in cell proliferation and colony-forming capacity, as well as a blockade of cell cycle progression. Moreover, an obvious decrease in PRAS40 phosphorylation and a concomitant increase in p38 phosphorylation were observed in myosin VI knockdown cells, which suggest that myosin VI silencing inhibits hepatocellular carcinoma cell growth in vitro probably via inactivation of PRAS40 and activation of p38 mitogen-activated protein kinase-dependent signaling pathway. This study highlights the potential of myosin VI to be developed as a target for hepatocellular carcinoma therapy.

<p>Supplemental Figure S4. Knockdown of TIGAR enhanced epirubicin-induced activation of caspase 3 and apoptosis.</p>