Eukaryotes initiate autophagy to cope with the lack of external nutrients, which requires the activation of the nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase Sirtuin 1 (Sirt1). However, the mechanisms underlying the starvation-induced Sirt1 activation for autophagy initiation remain unclear. Here, we demonstrate that glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a conventional glycolytic enzyme, is a critical mediator of AMP-activated protein kinase (AMPK)-driven Sirt1 activation. Under glucose starvation, but not amino acid starvation, cytoplasmic GAPDH is phosphorylated on Ser122 by activated AMPK. This causes GAPDH to redistribute into the nucleus. Inside the nucleus, GAPDH interacts directly with Sirt1, displacing Sirt1's repressor and causing Sirt1 to become activated. Preventing this shift of GAPDH abolishes Sirt1 activation and autophagy, while enhancing it, through overexpression of nuclear-localized GAPDH, increases Sirt1 activation and autophagy. GAPDH is thus a pivotal and central regulator of autophagy under glucose deficiency, undergoing AMPK-dependent phosphorylation and nuclear translocation to activate Sirt1 deacetylase activity.

Background:The sphingolipid metabolite sphingosine 1-phosphate (S1P) is a potent angiogenic factor. Results: S1P content is 9-fold higher in glioblastomas compared with normal brain, and S1P production is necessary for glioblastoma cells to trigger endothelial cell angiogenesis. Conclusion: Excessive S1P synthesis is a major contributor to glioblastoma angiogenesis. Significance: Inhibiting S1P synthesis may be a valuable antiangiogenic approach in glioblastoma.

Because radiotherapy significantly increases median survival in patients with glioblastoma, the modulation of radiation resistance is of significant interest. High glycolytic states of tumor cells are known to correlate strongly with radioresistance; thus, the concept of metabolic targeting needs to be investigated in combination with radiotherapy. Metabolically, the elevated glycolysis in glioblastoma cells was observed postradiotherapy together with upregulated hypoxia-inducible factor (HIF)-1a and its target pyruvate dehydrogenase kinase 1 (PDK1). Dichloroacetate, a PDK inhibitor currently being used to treat lactic acidosis, can modify tumor metabolism by activating mitochondrial activity to force glycolytic tumor cells into oxidative phosphorylation. Dichloroacetate alone demonstrated modest antitumor effects in both in vitro and in vivo models of glioblastoma and has the ability to reverse the radiotherapy-induced glycolytic shift when given in combination. In vitro, an enhanced inhibition of clonogenicity of a panel of glioblastoma cells was observed when dichloroacetate was combined with radiotherapy. Further mechanistic investigation revealed that dichloroacetate sensitized glioblastoma cells to radiotherapy by inducing the cell-cycle arrest at the G 2 -M phase, reducing mitochondrial reserve capacity, and increasing the oxidative stress as well as DNA damage in glioblastoma cells together with radiotherapy. In vivo, the combinatorial treatment of dichloroacetate and radiotherapy improved the survival of orthotopic glioblastoma-bearing mice. In conclusion, this study provides the proof of concept that dichloroacetate can effectively sensitize glioblastoma cells to radiotherapy by modulating the metabolic state of tumor cells. These findings warrant further evaluation of the combination of dichloroacetate and radiotherapy in clinical trials.

Background: Palmitic acid is a saturated fatty acid known to cause lipotoxicity in cells. Results: Palmitic acid induces autophagy, which is independent of mTOR regulation. Conclusion: Palmitic acid-mediated autophagy is regulated via PKC-␣ and acts as a cell survival mechanism. Significance: Our data reveal a novel mechanism underlying free fatty acid-mediated autophagy and suggest the importance of autophagy in bioactivity of fatty acids.

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths worldwide. High mortality from HCC is mainly due to widespread prevalence and the lack of effective treatment, since systemic chemotherapy is ineffective, while the targeted agent Sorafenib extends median survival only briefly. The steroidal saponin 20(S)-ginsenoside Rg3 from Panax ginseng C.A. Meyer is proposed to chemosensitize to various therapeutic drugs through an unknown mechanism. Since autophagy often serves as cell survival mechanism in cancer cells exposed to chemotherapeutic agents, we examined the ability of Rg3 to inhibit autophagy and chemosensitize HCC cell lines to doxorubicin in vitro. We show that Rg3 inhibits late stage autophagy, possibly through changes in gene expression. Doxorubicin-induced autophagy plays a protective role in HCC cells, and therefore Rg3 treatment synergizes with doxorubicin to kill HCC cell lines, but the combination is relatively nontoxic in normal liver cells. In addition, Rg3 was well-tolerated in mice and synergized with doxorubicin to inhibit tumor growth in HCC xenografts in vivo. Since novel in vivo inhibitors of autophagy are desirable for clinical use, we propose that Rg3 is such a compound, and that combination therapy with classical chemotherapeutic drugs may represent an effective therapeutic strategy for HCC treatment.