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1.  Glutamine-driven oxidative phosphorylation is a major ATP source in transformed mammalian cells in both normoxia and hypoxia 
The impact of oncogene activation and hypoxia on energy metabolism is analyzed by integrating quantitative measurements into a redox-balanced metabolic flux model. Glutamine-driven oxidative phosphorylation is found to be a major ATP source even in oncogene-expressing or hypoxic cells.
The integration of oxygen uptake measurements and LC-MS-based isotope tracer analyses in a redox-balanced metabolic flux model enabled quantitative determination of energy generation pathways in cultured cells.In transformed mammalian cells, even in hypoxia (1% oxygen), oxidative phosphorylation produces the majority of ATP.The oncogene Ras simultaneously increases glycolysis and decreases oxidative phosphorylation, thus resulting in no net increase in ATP production.Glutamine is the major source of high-energy electrons for oxidative phosphorylation, especially upon Ras activation.
Mammalian cells can generate ATP via glycolysis or mitochondrial respiration. Oncogene activation and hypoxia promote glycolysis and lactate secretion. The significance of these metabolic changes to ATP production remains however ill defined. Here, we integrate LC-MS-based isotope tracer studies with oxygen uptake measurements in a quantitative redox-balanced metabolic flux model of mammalian cellular metabolism. We then apply this approach to assess the impact of Ras and Akt activation and hypoxia on energy metabolism. Both oncogene activation and hypoxia induce roughly a twofold increase in glycolytic flux. Ras activation and hypoxia also strongly decrease glucose oxidation. Oxidative phosphorylation, powered substantially by glutamine-driven TCA turning, however, persists and accounts for the majority of ATP production. Consistent with this, in all cases, pharmacological inhibition of oxidative phosphorylation markedly reduces energy charge, and glutamine but not glucose removal markedly lowers oxygen uptake. Thus, glutamine-driven oxidative phosphorylation is a major means of ATP production even in hypoxic cancer cells.
PMCID: PMC3882799  PMID: 24301801
cancer bioenergetics; isotope tracing; metabolic flux analysis
The Prostate  2012;72(12):10.1002/pros.22487.
Targeting multiple anti-apoptotic proteins is now possible with the small molecule BH3 domain mimetics such as ABT-737. Given recent studies demonstrating that autophagy is a resistance mechanism to multiple therapeutic agents in the setting of apoptotic inhibition, we hypothesized that hydroxychloroquine (HCQ), an anti-malarial drug that inhibits autophagy, will increase cytotoxicity of ABT-737.
Experimental Design
Cytotoxicity of ABT-737 and HCQ was assessed in vitro in PC-3 and LNCaP cells, and in vivo in a xenograft mouse model. The role of autophagy as a resistance mechanism was assessed by siRNA knockdown of the essential autophagy gene beclin1. ROS was measured by flow cytometry, and mitophagy assessed by the mCherry-Parkin reporter.
Induction of autophagy by ABT-737 was a mechanism of resistance in prostate cancer cell lines. Therapeutic inhibition of autophagy with HCQ increased cytotoxicity of ABT-737 both in vitro and in vivo. ABT-737 induced LC-3 and decreased p62 expression by immunoblot in cell lines and by immunohistochemistry in tumors in vivo. Assessment of ROS and mitochondria demonstrated that ROS production by ABT-737 and HCQ was a mechanism of cytotoxicity.
We demonstrated that autophagy inhibition with HCQ enhances ABT-737 cytotoxicity in vitro and in vivo, that LC-3 and p62 represent assessable markers in human tissue for future clinical trials, and that ROS induction is a mechanism of cytotoxicity. These results support a new paradigm of dual targeting of apoptosis and autophagy in future clinical studies.
PMCID: PMC3840901  PMID: 22241682
Prostate Cancer; Autophagy; Metabolism; Bcl-2; BH3; ABT-737; ABT-263
3.  Autophagy Suppresses RIP Kinase-Dependent Necrosis Enabling Survival to mTOR Inhibition 
PLoS ONE  2012;7(7):e41831.
mTOR inhibitors are used clinically to treat renal cancer but are not curative. Here we show that autophagy is a resistance mechanism of human renal cell carcinoma (RCC) cell lines to mTOR inhibitors. RCC cell lines have high basal autophagy that is required for survival to mTOR inhibition. In RCC4 cells, inhibition of mTOR with CCI-779 stimulates autophagy and eliminates RIP kinases (RIPKs) and this is blocked by autophagy inhibition, which induces RIPK- and ROS-dependent necroptosis in vitro and suppresses xenograft growth. Autophagy of mitochondria is required for cell survival since mTOR inhibition turns off Nrf2 antioxidant defense. Thus, coordinate mTOR and autophagy inhibition leads to an imbalance between ROS production and defense, causing necroptosis that may enhance cancer treatment efficacy.
PMCID: PMC3406086  PMID: 22848625
4.  Autophagy in Tumorigenesis and Energy Metabolism: Friend by Day, Foe by Night 
Autophagy is the mechanism by which cells consume parts of themselves to survive starvation and stress. This self-cannibalization limits cell death and tissue inflammation, recycles energy and biosynthetic substrates and removes damaged proteins and organelles, accumulation of which is toxic. In normal tissues, autophagy-mediated damage mitigation may suppress tumorigenesis, while in advanced tumors macromolecular recycling may support survival by buffering metabolic demand under stress. As a result, autophagy-activation in normal cells may suppress tumorigenesis, while autophagy inhibition may be beneficial for therapy of established tumors. The mechanisms by which autophagy supports cancer cell metabolism are slowly emerging. As cancer is being increasingly recognized as a metabolic disease, how autophagy-mediated catabolism impacts cellular and mammalian metabolism and tumor growth is of great interest. Most cancer therapeutics induce autophagy, either directly by modulating signaling pathways that control autophagy in the case of many targeted therapies, or indirectly in the case of cytotoxic therapy. However, the functional consequence of autophagy induction in the context of cancer therapy is not yet clear. A better understanding of how autophagy modulates cell metabolism under various cellular stresses and the consequences of this on tumorigenesis will help develop better therapeutic strategies against cancer prevention and treatment.
PMCID: PMC3039840  PMID: 21255998
autophagy; p62; inflammation; cancer; energy; metabolism; mitochondria
5.  Autophagy Suppresses Tumorigenesis Through Elimination of p62 
Cell  2009;137(6):1062-1075.
Allelic loss of the essential autophagy gene beclin1 occurs in human cancers and renders mice tumor-prone suggesting that autophagy is a tumor-suppression mechanism. While tumor cells utilize autophagy to survive metabolic stress, autophagy also mitigates the resulting cellular damage that may limit tumorigenesis. In response to stress, autophagy-defective tumor cells preferentially accumulate p62/SQSTM1 (p62), endoplasmic reticulum (ER) chaperones, damaged mitochondria, reactive oxygen species (ROS), and genome damage. Moreover, suppressing ROS or p62 accumulation prevented damage resulting from autophagy defects indicating that failure to regulate p62 caused oxidative stress. Importantly, sustained p62 expression resulting from autophagy defects was sufficient to alter NF-κB regulation and gene expression and to promote tumorigenesis. Thus defective autophagy is a mechanism for p62 upregulation commonly observed in human tumors that contributes directly to tumorigenesis likely by perturbing the signal transduction adaptor function of p62 controlling pathways critical for oncogenesis.
PMCID: PMC2802318  PMID: 19524509
autophagy; beclin1; atg5; genomic instability; p62; NF- κB; DNA damage; cancer
6.  Induction of Apoptosis by Diterpenes from the Soft Coral Xenia elongata 
Journal of natural products  2007;70(10):1551-1557.
Four new diterpenes (1–4) were isolated from the soft coral Xenia elongata using a novel cell-based screen for apoptosis-inducing, potential anticancer compounds. The molecular structures of the diterpenes were determined using a combination of NMR and mass spectrometry. The bioactivities were confirmed using a specific apoptosis induction assay based on genetically engineered mammalian lines with differential, defined capacities for apoptosis. The diterpenes induce apoptosis in micromolar concentrations. This is the first report of apoptosis induction by marine diterpenes in xenicane skeletons.
PMCID: PMC2866001  PMID: 17900165
7.  Role of autophagy in cancer 
Nature reviews. Cancer  2007;7(12):961-967.
Autophagy is a cellular degradation pathway for the clearance of damaged or superfluous proteins and organelles. The recycling of these intracellular constituents also serves as an alternative energy source during periods of metabolic stress to maintain homeostasis and viability. In tumour cells with defects in apoptosis, autophagy allows prolonged survival. Paradoxically, autophagy defects are associated with increased tumorigenesis, but the mechanism behind this has not been determined. Recent evidence suggests that autophagy provides a protective function to limit tumour necrosis and inflammation, and to mitigate genome damage in tumour cells in response to metabolic stress.
PMCID: PMC2866167  PMID: 17972889
8.  Why Sick Cells Produce Tumors 
Autophagy  2007;3(5):502-505.
Cells exploit autophagy for survival to metabolic stress in vitro as well as in tumors where it localizes to regions of metabolic stress suggesting its role as a survival pathway. Consistent with this survival function, deficiency in autophagy impairs cell survival, but also promotes tumor growth, creating a paradox that the loss of a survival pathway leads to tumorigenesis. There is evidence that autophagy is a homeostatic process functioning to limit the accumulation of poly-ubiquitinated proteins and mutant protein aggregates associated with neuronal degeneration.2,3 Interestingly, we found that deficiency in autophagy caused by monoallelic loss of beclin1 or deletion of atg5 leads to accelerated DNA damage and chromosomal instability demonstrating a mutator phenotype.4 These cells also exhibit enhanced chromosomal gains or losses suggesting that autophagy functions as a tumor suppressor by limiting chromosomal instability. Thus the impairment of survival to metabolic stress due to deficiency in autophagy may be compensated by an enhanced mutation rate thereby promoting tumorigenesis. The protective role of autophagy may be exploited in developing novel autophagy modulators as rational chemotherapeutic as well as chemopreventive agents.
PMCID: PMC2866178  PMID: 17611387
autophagy; metabolism; beclin1; atg5; DNA damage; chromosomal instability; cancer
9.  Assessing Metabolic Stress and Autophagy Status in Epithelial Tumors 
Methods in enzymology  2009;453:53-81.
Autophagy is a survival mechanism activated in response to metabolic stress. In normal tissues autophagy plays a major role in energy homeostasis through catabolic self-digestion of damaged proteins and organelles. Contrary to its survival function, autophagy defects are implicated in tumorigenesis suggesting that autophagy is a tumor suppression mechanism. Although the exact mechanism of this tumor suppressor function is not known, it likely involves mitigation of cellular damage leading to chromosomal instability. The complex role of functional autophagy in tumors calls for model systems that allow the assessment of autophagy status, stress management and the impact on oncogenesis both in vitro as well as in vivo. We developed model systems that involve generation of genetically defined, isogenic and immortal epithelial cells from different tissue types that are applicable to both wild-type and mutant mice. This permits the study of tissue- as well as gene-specific tumor promoting functions. We successfully employed this strategy to generate isogenic, immortal epithelial cell lines from wild-type and mutant mice deficient in essential autophagy genes such as beclin 1 (beclin 1+/-) and atg5 (atg 5-/-). As these cell lines are amenable to further genetic manipulation, they allowed us to generate cell lines with apoptosis defects and stable expression of the autophagy marker EGFP-LC3 that facilitate in vitro and in vivo assessment of stress-mediated autophagy induction. We applied this model system to directly monitor autophagy in cells and 3D-morphogenesis in vitro as well as in tumor allografts in vivo. Using this model system we demonstrated that autophagy is a survival response in solid tumors that co-localizes with hypoxic regions, allowing tolerance to metabolic stress. Furthermore, our studies have established that autophagy also protects tumor cells from genome damage and limits cell death and inflammation as possible means to tumor suppression. Additionally these cell lines provide an efficient way to perform biochemical analyses, and high throughput screening for modulators of autophagy for potential use in cancer therapy and prevention.
PMCID: PMC2857509  PMID: 19216902
10.  Autophagy promotes tumor cell survival and restricts necrosis, inflammation, and tumorigenesis 
Cancer cell  2006;10(1):51-64.
Defective apoptosis renders immortalized epithelial cells highly tumorigenic, but how this is impacted by other common tumor mutations is not known. In apoptosis-defective cells, inhibition of autophagy by AKT activation or by allelic disruption of beclin1 confers sensitivity to metabolic stress by inhibiting an autophagy-dependent survival pathway. While autophagy acts to buffer metabolic stress, the combined impairment of apoptosis and autophagy promotes necrotic cell death in vitro and in vivo. Thus, inhibiting autophagy under conditions of nutrient limitation can restore cell death to apoptosis-refractory tumors, but this necrosis is associated with inflammation and accelerated tumor growth. Thus, autophagy may function in tumor suppression by mitigating metabolic stress and, in concert with apoptosis, by preventing death by necrosis.
PMCID: PMC2857533  PMID: 16843265
11.  Metabolic catastrophe as a means to cancer cell death 
Journal of cell science  2007;120(Pt 3):379-383.
During tumorigenesis, normal growth mechanisms are deregulated and safeguards that eliminate abnormal cells by apoptosis are disabled. Tumor cells must also increase nutrient uptake and angiogenesis to support the upregulation of metabolism necessary for unrestricted growth. In addition, they have to rely on inefficient energy production by glycolysis. This glycolytic state can result from mutations that promote cell proliferation, the hypoxic tumor microenvironment and perhaps mitochondrial malfunction. Moreover, the very signals that enable unrestricted cell proliferation inhibit autophagy, which normally sustains cells during nutrient limitation. In tumors, inactivation of the autophagy pathway may enhance necrosis and inflammation and promote genomic instability, which can further enhance tumor growth. Thus, tumor cells cannot adapt efficiently to metabolic stress and could be induced to die by metabolic catastrophe, in which high energy demand is contrasted by insufficient energy production. Efforts to exploit this unique metabolic state clinically previously focused mainly on detecting tissue displaying increased glycolytic metabolism. The challenge now is to induce metabolic catastrophe therapeutically as an approach to killing the unkillable cells.
PMCID: PMC2857576  PMID: 17251378
Autophagy; Apoptosis; AKT; mTOR; BCL-2; Beclin1; Cancer
12.  Role of autophagy in suppression of inflammation and cancer 
Current opinion in cell biology  2010;22(2):212-217.
Autophagy is a crucial component of the cellular stress adaptation response that maintains mammalian homeostasis. Autophagy protects against neurodegenerative and inflammatory conditions, aging, and cancer. This is accomplished by the degradation and intracellular recycling of cellular components to maintain energy metabolism and by damage mitigation through the elimination of damaged proteins and organelles. How autophagy modulates oncogenesis is gradually emerging. Tumor cells induce autophagy in response to metabolic stress to promote survival, suggesting deployment of therapeutic strategies to block autophagy for cancer therapy. By contrast, defects in autophagy lead to cell death, chronic inflammation, and genetic instability. Thus, stimulating autophagy may be a powerful approach for chemoprevention. Analogous to infection or toxins that create persistent tissue damage and chronic inflammation that increases the incidence of cancer, defective autophagy represents a cell-intrinsic mechanism to create the damaging, inflammatory environment that predisposes to cancer. Thus, cellular damage mitigation through autophagy is a novel mechanism of tumor suppression.
PMCID: PMC2857707  PMID: 20056400
13.  Therapeutic Starvation and Autophagy in Prostate Cancer: A New Paradigm for Targeting Metabolism in Cancer Therapy 
The Prostate  2008;68(16):1743-1752.
Autophagy is a starvation induced cellular process of self-digestion that allows cells to degrade cytoplasmic contents. The understanding of autophagy, as either a mechanism of resistance to therapies that induce metabolic stress, or as a means to cell death, is rapidly expanding and supportive of a new paradigm of therapeutic starvation.
To determine the effect of therapeutic starvation in prostate cancer, we studied the effect of the prototypical inhibitor of metabolism, 2-deoxy-D-glucose (2DG), in multiple cellular models including a transfected pEGFP-LC3 autophagy reporter construct in PC-3 and LNCaP cells.
We found that 2DG induced cytotoxicity in PC-3 and LNCaP cells in a dose dependent fashion. We also found that 2DG modulated checkpoint proteins cdk4, and cdk6. Using the transfected pEGFP-LC3 autophagy reporter construct, we found that 2DG induced LC3 membrane translocation, characteristic of autophagy. Furthermore, knockdown of beclin1, an essential regulator of autophagy, abrogated 2DG induced autophagy. Using Western analysis for LC3 protein, we also found increased LC3-II expression in 2DG treated cells, again consistent with autophagy. In an effort to develop markers that may be predictive of autophagy, for assessment in clinical trials, we stained human prostate tumors for Beclin1 by immunohistochemistry (IHC). Additionally, we used a digitized imaging algorithm to quantify Beclin1 staining assessment.
These data demonstrate the induction of autophagy in prostate cancer by therapeutic starvation with 2DG, and support the feasibility of assessment of markers predictive of autophagy such as Beclin1 that can be utilized in clinical trials.
PMCID: PMC2855052  PMID: 18767033
prostate cancer; deoxyglucose; beclin1; autophagy; glycolysis; metabolism
14.  Role of the Polarity Determinant Crumbs in Suppressing Mammalian Epithelial Tumor Progression 
Cancer research  2008;68(11):4105-4115.
Most tumors are epithelial-derived, and although disruption of polarity and aberrant cellular junction formation is a poor prognosticator in human cancer, the role of polarity determinants in oncogenesis is poorly understood. Using in vivo selection, we identified a mammalian orthologue of the Drosophila polarity regulator crumbs as a gene whose loss of expression promotes tumor progression. Immortal baby mouse kidney epithelial (iBMK) cells selected in vivo to acquire tumorigenicity displayed dramatic repression of crumbs3 (crb3) expression associated with disruption of tight junction formation, apicobasal polarity, and contact-inhibited growth. Restoration of crb3 expression restored junctions, polarity and contact inhibition, while suppressing migration and metastasis. These findings suggest a role for mammalian polarity determinants in suppressing tumorigenesis that may be analogous to the well-studied polarity tumor suppressor mechanisms in Drosophila.
PMCID: PMC2696887  PMID: 18519669
Crumbs; crb3; tight junctions; polarity; metastasis; cancer

Results 1-14 (14)