In 1923, Dr. Warburg had observed that tumors acidified the Ringer solution when 13 mM glucose was added, which was identi-fied as being due to lactate. When glucose is the only source of nutrient, ...it can serve for both biosynthesis and energy production. However, a series of studies revealed that the cancer cell consumes glucose for biosynthesis through fermentation, not for energy supply, under physiological conditions. Recently, a new observation was made that there is a metabolic symbiosis in which glycol-lytic and oxidative tumor cells mutually regulate their energy metabolism. Hypoxic cancer cells use glucose for glycolytic metabo-lism and release lactate which is used by oxygenated cancer cells. This study challenged the Warburg effect, because Warburg claimed that fermentation by irreversible damaging of mitochondria is a fundamental cause of cancer. However, recent studies revealed that mitochondria in cancer cell show active function of oxidative phosphorylation although TCA cycle is stalled. It was also shown that blocking cytosolic NADH production by aldehyde dehydrogenase inhibition, combined with oxidative phosphoryla-tion inhibition, resulted in up to 80% decrease of ATP production, which resulted in a significant regression of tumor growth in the NSCLC model. This suggests a new theory that NADH production in the cytosol plays a key role of ATP production through the mi-tochondrial electron transport chain in cancer cells, while NADH production is mostly occupied inside mitochondria in normal cells.
Several metabolic pathways for the supply of adenosine triphosphate (ATP) have been proposed; however, the major source of reducing power for ADP in cancer remains unclear. Although glycolysis is the ...source of ATP in tumors according to the Warburg effect, ATP levels do not differ between cancer cells grown in the presence and absence of glucose. Several theories have been proposed to explain the supply of ATP in cancer, including metabolic reprograming in the tumor microenvironment. However, these theories are based on the production of ATP by the TCA-OxPhos pathway, which is inconsistent with the Warburg effect. We found that blocking fatty acid oxidation (FAO) in the presence of glucose significantly decreased ATP production in various cancer cells. This suggests that cancer cells depend on fatty acids to produce ATP through FAO instead of glycolysis. We observed that cancer cell growth mainly relies on metabolic nutrients and oxygen systemically supplied through the bloodstream instead of metabolic reprogramming. In a spontaneous mouse tumor model (KrasG12D; Pdx1-cre), tumor growth was 2-fold higher in mice fed a high-fat diet (low-carbo diet) that caused obesity, whereas a calorie-balanced, low-fat diet (high-carbo diet) inhibited tumor growth by 3-fold compared with that in mice fed a control/normal diet. This 5-fold difference in tumor growth between mice fed low-fat and high-fat diets suggests that fat-induced obesity promotes cancer growth, and tumor growth depends on fatty acids as the primary source of energy.
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•All living cells produce ATP in mitochondria using the TCA cycle or fatty acid oxidation (FAO).•However, cancer cells do not use carbohydrates for the TCA cycle because of the Warburg effect.•Therefore, cancer cells must rely on OxPhos with the ETC using fatty acids supplied from blood vessels to produce ATP.
Dynamic regulation of glucose flux between aerobic glycolysis and the pentose phosphate pathway (PPP) during epithelial-mesenchymal transition (EMT) is not well-understood. Here we show that Snail ...(SNAI1), a key transcriptional repressor of EMT, regulates glucose flux toward PPP, allowing cancer cell survival under metabolic stress. Mechanistically, Snail regulates glycolytic activity via repression of phosphofructokinase, platelet (PFKP), a major isoform of cancer-specific phosphofructokinase-1 (PFK-1), an enzyme involving the first rate-limiting step of glycolysis. The suppression of PFKP switches the glucose flux towards PPP, generating NADPH with increased metabolites of oxidative PPP. Functionally, dynamic regulation of PFKP significantly potentiates cancer cell survival under metabolic stress and increases metastatic capacities in vivo. Further, knockdown of PFKP rescues metabolic reprogramming and cell death induced by loss of Snail. Thus, the Snail-PFKP axis plays an important role in cancer cell survival via regulation of glucose flux between glycolysis and PPP.
Phosphorylation-dependent YAP translocation is a well-known intracellular mechanism of the Hippo pathway; however, the molecular effectors governing YAP cytoplasmic translocation remains undefined. ...Recent findings indicate that oncogenic YAP paradoxically suppresses Wnt activity. Here, we show that Wnt scaffolding protein Dishevelled (DVL) is responsible for cytosolic translocation of phosphorylated YAP. Mutational inactivation of the nuclear export signal embedded in DVL leads to nuclear YAP retention, with an increase in TEAD transcriptional activity. DVL is also required for YAP subcellular localization induced by E-cadherin, α-catenin, or AMPK activation. Importantly, the nuclear-cytoplasmic trafficking is dependent on the p53-Lats2 or LKB1-AMPK tumor suppressor axes, which determine YAP phosphorylation status. In vivo and clinical data support that the loss of p53 or LKB1 relieves DVL-linked reciprocal inhibition between the Wnt and nuclear YAP activity. Our observations provide mechanistic insights into controlled proliferation coupled with epithelial polarity during development and human cancer.
Oncogene-induced senescence (OIS) is a critical tumor-suppressor mechanism, which prevents hyper-proliferation and transformation of cells. c-Myc promotes OIS through the transcriptional activation ...of p14ARF followed by p53 activation. Although the oncogene-mediated transcriptional regulation of p14ARF has been well addressed, the post-translational modification of p14ARF regulated by oncogenic stress has yet to be investigated. Here, we found that c-Myc increased p14ARF protein stability by inducing the transcription of ubiquitin-specific protease 10 (USP10). USP10, in turn, mediated the deubiquitination of p14ARF, preventing its proteasome-dependent degradation. USP10-null mouse embryonic fibroblasts and human primary cells depleted of USP10 bypassed c-Myc-induced senescence via the destabilization of p14ARF, and these cells displayed accelerated hyper-proliferation and transformation. Clinically the c-Myc-USP10-p14ARF axis was disrupted in non-small cell lung cancer patients, resulting in significantly worse overall survival. Our studies indicate that USP10 induced by c-Myc has a crucial role in OIS by maintaining the stability of key tumor suppressor p14ARF.
Diabetic retinopathy is predominantly caused by vascular endothelial growth factor (VEGF)-induced vascular leakage; however, the underlying mechanism is unclear. Here we designed an in vivo ...transglutaminase (TGase) activity assay in mouse retina and demonstrated that hyperglycemia induced vascular leakage by activating TGase2 in diabetic retina. VEGF elevated TGase2 activity through sequential elevation of intracellular Ca(2+) and reactive oxygen species (ROS) concentrations in endothelial cells. The TGase inhibitors cystamine and monodansylcadaverin or TGase2 small interfering RNA (siRNA) prevented VEGF-induced stress fiber formation and vascular endothelial (VE)-cadherin disruption, which play a critical role in modulating endothelial permeability. Intravitreal injection of two TGase inhibitors or TGase2 siRNA successfully inhibited hyperglycemia-induced TGase activation and microvascular leakage in the retinas of diabetic mice. C-peptide or ROS scavengers also inhibited TGase activation in diabetic mouse retinas. The role of TGase2 in VEGF-induced vascular leakage was further supported using diabetic TGase2(-/-) mice. Thus, our findings suggest that ROS-mediated activation of TGase2 plays a key role in VEGF-induced vascular leakage by stimulating stress fiber formation and VE-cadherin disruption.
Anticancer drug resistance is a major challenge of cancer therapy. We found that irinotecan-resistant NSCLC cells showed increased mitochondrial oxidative phosphorylation compared to the drug ...sensitive NSCLC cells. Previously, we found that combined inhibition of aldehyde dehydrogenase using gossypol, and mitochondrial complex I using phenformin, effectively reduced oxidative phosphorylation in NSCLC. Here, we showed that targeting oxidative phosphorylation with gossypol and phenformin abrogated irinotecan resistance in NSCLC. Furthermore, irinotecan treatment by blocking oxidative phosphorylation induced synergistic anti-cancer effect in NSCLC. The pre-clinical xenograft model of human NSCLC also demonstrated a therapeutic response to the dual targeting treatment. Therefore, this combination of gossypol and phenformin increases irinotecan sensitivity as well as preventing irinotecan resistance.
Abstract
Background
Pancreatic cancer (PC) has a grim prognosis, and an early diagnostic biomarker has been highly desired. The molecular link between diabetes and PC has not been well established.
...Methods
Bioinformatics screening was performed for a serum PC marker. Experiments in cell lines (5 PC and 1 normal cell lines), mouse models, and human tissue staining (37 PC and 10 normal cases) were performed to test asprosin production from PC. Asprosin’s diagnostic performance was tested with serums from multi-center cohorts (347 PC, 209 normal, and 55 additional diabetic patients) and evaluated according to PC status, stages, and diabetic status, which was compared with that of CA19-9.
Results
Asprosin, a diabetes-related hormone, was found from the bioinformatics screening, and its production from PC was confirmed. Serum asprosin levels from multi-center cohorts yielded an age-adjusted diagnostic area under the curve (AUC) of 0.987 (95% confidence interval CI = 0.961 to 0.997), superior to that of CA19-9 (AUC = 0.876, 95% CI = 0.847 to 0.905), and a cut-off of 7.18 ng/mL, at which the validation set exhibited a sensitivity of 0.957 and a specificity of 0.924. Importantly, the performance was maintained in early-stage and non-metastatic PC, consistent with the tissue staining. A slightly lower performance against additional diabetic patients (n = 55) was restored by combining asprosin and CA19-9 (AUC = 0.985, 95% CI = 0.975 to 0.995).
Conclusions
Asprosin is presented as an early-stage PC serum marker that may provide clues for PC-induced diabetes. Larger prospective clinical studies are warranted to solidify its utility.
Necrosis is a hallmark of glioblastoma (GBM) and is responsible for poor prognosis and resistance to conventional therapies. However, the molecular mechanisms underlying necrotic ...microenvironment-induced malignancy of GBM have not been elucidated. Here, we report that transglutaminase 2 (TGM2) is upregulated in the perinecrotic region of GBM and triggered mesenchymal (MES) transdifferentiation of glioma stem cells (GSC) by regulating master transcription factors (TF), such as C/EBPβ, TAZ, and STAT3. TGM2 expression was induced by macrophages/microglia-derived cytokines via NF-κB activation and further degraded DNA damage-inducible transcript 3 (GADD153) to induce C/EBPβ expression, resulting in expression of the MES transcriptome. Downregulation of TGM2 decreased sphere-forming ability, tumor size, and radioresistance and survival in a xenograft mouse model through a loss of the MES signature. A TGM2-specific inhibitor GK921 blocked MES transdifferentiation and showed significant therapeutic efficacy in mouse models of GSC. Moreover, TGM2 expression was significantly increased in recurrent MES patients and inversely correlated with patient prognosis. Collectively, our results indicate that TGM2 is a key molecular switch of necrosis-induced MES transdifferentiation and an important therapeutic target for MES GBM.
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The major source of ATP in cancer cells remains unclear. Here, we examined energy metabolism in gastric cancer cells and found increased fatty acid oxidation and increased expression of ALDH3A1. ...Metabolic analysis showed that lipid peroxidation by reactive oxygen species led to spontaneous production of 4-hydroxynonenal, which was converted to fatty acids with NADH production by ALDH3A1, resulting in further fatty acid oxidation. Inhibition of ALDH3A1 by knock down using siRNA of ALDH3A1 resulted in significantly reduced ATP production by cancer cells, leading to apoptosis. Oxidative phosphorylation by mitochondria in gastric cancer cells was driven by NADH supplied via fatty acid oxidation. Therefore, blockade of ALDH3A1 together with mitochondrial complex I using gossypol and phenformin led to significant therapeutic effects in a preclinical gastric cancer model.
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