Bafilomycin A1 activates HIF-dependent signalling in human colon cancer cells via mitochondrial uncoupling. Biosci Rep. 2012;32:587-595. [PMID: 22943412 PMCID: PMC3497721 DOI: 10.1042/bsr20120085]

Multi-omics revealed rumen microbiota metabolism and host immune regulation in Tibetan sheep of different ages

The rumen microbiota and metabolites play an important role in energy metabolism and immune regulation of the host. However, the regulatory mechanism of rumen microbiota and metabolite interactions with host on Tibetan sheep's plateau adaptability is still unclear. We analyzed the ruminal microbiome and metabolome, host transcriptome and serum metabolome characteristics of Tibetan sheep at different ages. Biomarkers Butyrivibrio, Lachnospiraceae_XPB1014_group, Prevotella, and Rikenellaceae_RC9_gut_group were found in 4 months, 1.5 years, 3.5 years, and 6 years Tibetan sheep, respectively. The rumen microbial metabolites were mainly enriched in galactose metabolism, unsaturated fatty acid biosynthesis and fatty acid degradation pathways, and had significant correlation with microbiota. These metabolites further interact with mRNA, and are co-enriched in arginine and proline metabolism, metabolism of xenobiotics by cytochrome P450, propanoate metabolism, starch and sucrose metabolism, gap junction pathway. Meanwhile, serum metabolites also have a similar function, such as chemical carcinogenesis - reactive oxygen species, limonene and pinene degradation, and cutin, suberine and wax biosynthesis, thus participating in the regulation of the body's immune and energy-related metabolic processes. This study systematically revealed that rumen microbiota, metabolites, mRNA and serum metabolites of Tibetan sheep were involved in the regulation of fermentation metabolic function and immune level of Tibetan sheep at different ages, which provided a new perspective for plateau adaptability research of Tibetan sheep at different ages.

Identification of Hypoxia-Associated Signature in Colon Cancer to Assess Tumor Immune Microenvironment and Predict Prognosis Based on 14 Hypoxia-Associated Genes

Purpose

Colon cancer is the main malignant tumor of the digestive tract. Hypoxia is highly related to the occurrence, progression and tumor immune microenvironment (TIME) of cancer. The aim of this study was to identify a hypoxia-associated signature with high accuracy for predicting the prognosis and TIME of colon cancer.

Methods

Download colon cancer data from the GEO and TCGA databases. A novel hypoxia risk model was identified to predict the prognosis of colon cancer patients. Subsequently, GSEA, TIME and mutation analysis were performed in the hypoxia high and low risk score groups. Finally, the signature gene ANKZF1 was selected for functional verification at the cellular level.

Results

A novel hypoxia risk model was identified. The risk score was significantly associated with poorer overall survival in colon cancer, and could be used as an independent prognostic factor for colon cancer. GSEA analysis found that the processes related to stimulate tumor proliferation and anti-apoptosis were significantly enriched in the hypoxia high risk score group. The expression of immunosuppressive cells and most immune checkpoints in the high risk score group was significantly higher than that in the low risk score group. In vitro cell experiments showed that knockdown the expression of ANKZF1 could inhibit the proliferation, migration and invasion of colon cancer cells.

Conclusion

Hypoxia plays an important role in evaluating the TIME and predicting the prognosis of colon cancer.

Activation of autophagy triggers mitochondrial loss and changes acetylation profile relevant for mechanotransduction in bladder cancer cells

Bladder cells are constantly exposed to multiple xenobiotics and bioactive metabolites. In addition to this challenging chemical environment, they are also exposed to shear stress originating from urine and interstitial fluids. Hence, physiological function of bladder cells relies on a high biochemical and biomechanical adaptive competence, which, in turn, is largely supported via autophagy-related mechanisms. As a negative side of this plasticity, bladder cancer cells are known to adapt readily to chemotherapeutic programs. At the molecular level, autophagy was described to support resistance against pharmacological treatments and to contribute to the maintenance of cell structure and metabolic competence. In this study, we enhanced autophagy with rapamycin (1-100 nM) and assessed its effects on the motility of bladder cells, as well as the capability to respond to shear stress. We observed that rapamycin reduced cell migration and the mechanical-induced translocation potential of Krüppel-like transcription factor 2 (KLF2). These effects were accompanied by a rearrangement of cytoskeletal elements and mitochondrial loss. In parallel, intracellular acetylation levels were decreased. Mechanistically, inhibition of the NAD + -dependent deacetylase sirtuin-1 (SIRT1) with nicotinamide (NAM; 0.1-5 mM) restored acetylation levels hampered by rapamycin and cell motility. Taken together, we described the effects of rapamycin on cytoskeletal elements crucial for mechanotransduction and the dependency of these changes on the mitochondrial turnover caused by autophagy activation. Additionally, we could show that targeted metabolic intervention could revert the outcome of autophagy activation, reinforcing the idea that bladder cells can easily adapt to multiple xenobiotics and circumvent in this way the effects of single chemicals.

Ghrelin rapidly elevates protein synthesis in vitro by employing the rpS6K-eEF2K-eEF2 signalling axis

Activated ghrelin receptor GHS-R1α triggers cell signalling pathways that modulate energy homeostasis and biosynthetic processes. However, the effects of ghrelin on mRNA translation are unknown. Using various reporter assays, here we demonstrate a rapid elevation of protein synthesis in cells within 15–30 min upon stimulation of GHS-R1α by ghrelin. We further show that ghrelin-induced activation of translation is mediated, at least in part, through the de-phosphorylation (de-suppression) of elongation factor 2 (eEF2). The levels of eEF2 phosphorylation at Thr56 decrease due to the reduced activity of eEF2 kinase, which is inhibited via Ser366 phosphorylation by rpS6 kinases. Being stress-susceptible, the ghrelin-mediated decrease in eEF2 phosphorylation can be abolished by glucose deprivation and mitochondrial uncoupling. We believe that the observed burst of translation benefits rapid restocking of neuropeptides, which are released upon GHS-R1α activation, and represents the most time- and energy-efficient way of prompt recharging the orexigenic neuronal circuitry.

Cell Energy Budget Platform for Multiparametric Assessment of Cell and Tissue Metabolism

Specific bioenergetic signature reports on the current metabolic state of the cell, which may be affected by metabolic rearrangement, dysfunction or dysregulation of relevant signaling pathways, altered physiological condition or energy stress. A combined analysis of respiration , glycolytic flux, Krebs cycle activity, ATP levels, and total biomass allows informative initial assessment. Such simple, high-throughput, multiparametric methodology, called cell energy budget (CEB ) platform, is presented here and demonstrated with particular cell and tissue models. The CEB uses a commercial fluorescent lanthanide probe pH-Xtra™ to measure extracellular acidification (ECA) associated with lactate (L-ECA) and combined lactate/CO₂ (T-ECA), a phosphorescent probe MitoXpress^®-Xtra to measure oxygen consumption rate (OCR), a bioluminescent ATP kit, and an absorbance-based total protein assay. All the assays are performed on a standard multi-label reader. Using the same readouts, the CEB approach can be extended to more detailed mechanistic studies, by targeting specific pathways in cell bioenergetics and measuring other cellular parameters, such as NAD(P)H, Ca²⁺, mitochondrial pH, membrane potential, redox state, with conventional fluorescent or luminescent probes.

Reduced Oxidative Phosphorylation and Increased Glycolysis in Human Glaucoma Lamina Cribrosa Cells

Purpose

The lamina cribrosa (LC) is a key site of damage in glaucomatous optic neuropathy. We previously found that glaucoma LC cells have an increased profibrotic gene expression, with mitochondrial dysfunction in the form of decreased mitochondrial membrane potential. Altered cell bioenergetics have recently been reported in organ fibrosis and in cancer. In this study, we carried out a systematic mitochondrial bioenergetic assessment and measured markers of alternative sources of cellular energy in normal and glaucoma LC cells.

Methods

LC cells from three glaucoma donors and three age-matched normal controls were assessed using VICTOR X4 Perkin Elmer (Waltham, MA) plate reader with different phosphorescent and luminescent probes. adenosine triphosphate levels, oxygen consumption rate, and extracellular acidification were measured and normalized to total protein content. RNA and protein expression levels of MCT1, MCT4, MTFHD2, and GLS2 were quantified using real-time RT-PCR and Western blotting.

Results

Glaucoma LC cells contain significantly less adenosine triphosphate (P < .05) when supplied with either glucose or galactose. They also showed significantly diminished oxygen consumption in both basal and maximal respiration with more lactic acid contribution in ECA. Both mRNA and protein expression levels of MCT1, MCT4, MTHFD2, and GLS2 were significantly increased in glaucoma LC cells.

Conclusions

We demonstrate evidence of metabolic reprogramming (The Warburg effect) in glaucoma LC cells. Expression of markers of glycolysis, glutamine, and one carbon metabolism are elevated in glaucoma cells at both the mRNA and protein levels. A better understanding of bioenergetics in glaucoma may help in the development of new therapeutics.

Mapping O2 concentration in ex-vivo tissue samples on a fast PLIM macro-imager

O2 PLIM microscopy was employed in various studies, however current platforms have limitations in sensitivity, image acquisition speed, accuracy and general usability. We describe a new PLIM imager based on the Timepix3 camera (Tpx3cam) and its application for imaging of O2 concentration in various tissue samples stained with a nanoparticle based probe, NanO2-IR. Upon passive staining of mouse brain, lung or intestinal tissue surface with minute quantities of NanO2-IR or by microinjecting the probe into the lumen of small or large intestine fragments, robust phosphorescence intensity and lifetime signals were produced, which allow mapping of O2 in the tissue within 20 s. Inhibition of tissue respiration or limitation of O2 diffusion to tissue produced the anticipated increases or decreases in O2 levels, respectively. The difference in O2 concentration between the colonic lumen and air-exposed serosal surface was around 140 µM. Furthermore, subcutaneous injection of 5 µg of the probe in intact organs (a paw or tail of sacrificed mice) enabled efficient O2 imaging at tissue depths of up to 0.5 mm. Overall, the PLIM imager holds promise for metabolic imaging studies with various ex vivo models of animal tissue, and also for use in live animals.

V-ATPase blockade reduces renal gluconeogenesis and improves insulin secretion in type 2 diabetic rats

Vacuolar H⁺-adenosine triphosphatase (V-ATPase) stimulates vesicular acidification that may activate cytoplasmic enzymes, hormone secretion and membrane recycling of transporters. We investigated the effect of blockade of V-ATPase by bafilomycin B1 on renal gluconeogenesis, mitochondrial enzymes, and insulin secretion in type 2 diabetic rats. Spontaneous type 2 diabetic Torii rats were treated with intraperitoneal injection of bafilomycin B1 for 1 week, and the kidneys were examined after 24 h of starvation in metabolic cages. The renal expression and activity of V-ATPase were increased in the brush border membrane of the proximal tubules in diabetic rats. The blockade of V-ATPase by bafilomycin B1 reduced renal V-ATPase activity and urinary ammonium in diabetic rats. Treatment with bafilomycin suppressed the enhanced renal gluconeogenesis enzymes and mitochondrial electron transport enzymes in type 2 diabetic rats and reduced the renal cytoplasmic glucose levels. The insulin index and pancreatic insulin granules were decreased in diabetic rats with increased V-ATPase expression in islet cells, and treatment with bafilomycin B1 reversed these changes and increased the insulin secretion index. Hepatosteatosis in type 2 diabetic rats was ameliorated by bafilomycin treatment. As a consequence, treatment with bafilomycin B1 significantly decreased the plasma glucose level after 24 h of starvation in diabetic rats. In conclusion, a V-ATPase inhibitor improved plasma glucose levels in type 2 diabetes by inhibiting renal mitochondrial gluconeogenesis and improving insulin secretion.

Technical Feasibility and Physiological Relevance of Hypoxic Cell Culture Models

Hypoxia is characterized as insufficient oxygen delivery to tissues and cells in the body and is prevalent in many human physiology processes and diseases. Thus, it is an attractive state to experimentally study to understand its inner mechanisms as well as to develop and test therapies against pathological conditions related to hypoxia. Animal models in vivo fail to recapitulate some of the key hallmarks of human physiology, which leads to human cell cultures; however, they are prone to bias, namely when pericellular oxygen concentration (partial pressure) does not respect oxygen dynamics in vivo. A search of the current literature on the topic revealed this was the case for many original studies pertaining to experimental models of hypoxia in vitro. Therefore, in this review, we present evidence mandating for the close control of oxygen levels in cell culture models of hypoxia. First, we discuss the basic physical laws required for understanding the oxygen dynamics in vitro, most notably the limited diffusion through a liquid medium that hampers the oxygenation of cells in conventional cultures. We then summarize up-to-date knowledge of techniques that help standardize the culture environment in a replicable fashion by increasing oxygen delivery to the cells and measuring pericellular levels. We also discuss how these tools may be applied to model both constant and intermittent hypoxia in a physiologically relevant manner, considering known values of partial pressure of tissue normoxia and hypoxia in vivo, compared to conventional cultures incubated at rigid oxygen pressure. Attention is given to the potential influence of three-dimensional tissue cultures and hypercapnia management on these models. Finally, we discuss the implications of these concepts for cell cultures, which try to emulate tissue normoxia, and conclude that the maintenance of precise oxygen levels is important in any cell culture setting.

Ammonia mediates mitochondrial uncoupling and promotes glycolysis via HIF-1 activation in human breast cancer MDA-MB-231 cells

It has been reported that ammonia produced by glutaminolysis activates the HIF-1 pathway in several types of cancer cells, but the underlying mechanisms remain unclear. In this study, the effects of ammonia on the activation of HIF-1 pathway and glycolysis in MDA-MB-231 breast cancer cells were investigated and the underlying mechanisms involved were elucidated. The results showed that NH₄Cl concentration-dependently increased the protein level of HIF-1α and enhanced the transactivation activity of HIF-1 in MDA-MB-231 cells. In addition, NH₄Cl increased the expression of GluT1 and LDHA and promoted aerobic glycolysis by activating the HIF-1 pathway. Further study revealed that NH₄Cl increased the mitochondrial ROS level and decreased the cellular Fe²⁺ level in MDA-MB-231 cells. Activation of the HIF-1 pathway induced by NH₄Cl was inhibited by addition of the antioxidant NAC or the NADPH oxidase (NOX) inhibitor apocynin, indicating the involvement of the NOX-induced ROS generation. When MDA-MB-231 cells were treated with NH₄Cl, the oxygen consumption of cells increased, followed by the decreased mitochondrial membrane potential and cellular ATP level, indicating the uncoupling of mitochondria. In conclusion, NH₄Cl activated the HIF-1 signaling pathway and promoted aerobic glycolysis in MDA-MB-231 cells, likely through the promotion of mitochondrial ROS release and mitochondrial uncoupling.

V-ATPase-dependent repression of androgen receptor in prostate cancer cells

Prostate Cancer (PCa) is the most commonly diagnosed cancer and the third leading cause of death for men in the United States. Suppression of androgen receptor (AR) expression is a desirable mechanism to manage PCa. Our studies showed that AR expression was reduced in LAPC4 and LNCaP PCa cell lines treated with nanomolar concentrations of the V-ATPase inhibitor concanamycin A (CCA). This treatment decreased PSA mRNA levels, indicative of reduced AR activity. V-ATPase-dependent repression of AR expression was linked to defective endo-lysosomal pH regulation and reduced AR expression at the transcriptional level. CCA treatment increased the protein level and nuclear localization of the alpha subunit of the transcription factor HIF-1 (HIF-1α) in PCa cells via decreased hydroxylation and degradation of HIF-1α. The addition of iron (III) citrate restored HIF-1α hydroxylation and decreased total HIF-1α levels in PCa cells treated with CCA. Moreover, iron treatment partially rescued CCA-mediated AR repression. Dimethyloxalylglycine (DMOG), which prevents HIF-1α degradation independently of V-ATPase, also decreased AR levels, supporting our hypothesis that HIF-1α serves as a downstream mediator in the V-ATPase-AR axis. We propose a new V-ATPase-dependent mechanism to inhibit androgen receptor expression in prostate cancer cells involving defective endosomal trafficking of iron and the inhibition of HIF-1 α-subunit turnover.

KRAS/BRAF基因与结肠癌糖代谢研究现状

正电子发射断层成像术(positron emission tomography, PET)/计算机断层扫描(computed tomography, CT)显像可用于结肠癌的诊断、监测疗效和预后评估. ¹⁸F标记葡萄糖(2-fluorine-18-fluoro-2-deeoxy-D-glucose, ¹⁸F-FDG)是PET/CT常用显像剂, 可以反映结肠癌活体组织葡萄糖代谢. KRAS/BRAF基因检测常用于结肠癌靶向治疗方案的选择及评估其治疗效果. 文献报道¹⁸F-FDG-PET/CT显像可预测结肠癌KRAS/BRAF基因状态, 能以无创的方式预测结肠癌抗表皮生长因子受体靶向治疗效果. 目前国内有关KRAS/BRAF基因与结肠癌糖代谢的研究相对较少, 本文结合近期的相关文献进行概述.

Mild mitochondrial uncoupling induces HSL/ATGL-independent lipolysis relying on a form of autophagy in 3T3-L1 adipocytes

Obesity is characterized by an excessive triacylglycerol accumulation in white adipocytes. Various mechanisms allowing the tight regulation of triacylglycerol storage and mobilization by lipid droplet-associated proteins as well as lipolytic enzymes have been identified. Increasing energy expenditure by inducing a mild uncoupling of mitochondria in adipocytes might represent a putative interesting anti-obesity strategy as it reduces the adipose tissue triacylglycerol content (limiting alterations caused by cell hypertrophy) by stimulating lipolysis through yet unknown mechanisms, limiting the adverse effects of adipocyte hypertrophy. Herein, the molecular mechanisms involved in lipolysis induced by a mild uncoupling of mitochondria in white 3T3-L1 adipocytes were characterized. Mitochondrial uncoupling-induced lipolysis was found to be independent from canonical pathways that involve lipolytic enzymes such as HSL and ATGL. Finally, enhanced lipolysis in response to mitochondrial uncoupling relies on a form of autophagy as lipid droplets are captured by endolysosomal vesicles. This new mechanism of triacylglycerol breakdown in adipocytes exposed to mild uncoupling provides new insights on the biology of adipocytes dealing with mitochondria forced to dissipate energy.

Low energy costs of F1Fo ATP synthase reversal in colon carcinoma cells deficient in mitochondrial complex IV

Mitochondrial polarisation is paramount for a variety of cellular functions. Under ischemia, mitochondrial membrane potential (ΔΨm) and proton gradient (ΔpH) are maintained via a reversal of mitochondrial F1Fo ATP synthase (mATPase), which can rapidly deplete ATP and drive cells into energy crisis. We found that under normal conditions in cells with disassembled cytochrome c oxidase complex (COX-deficient HCT116), mATPase maintains ΔΨm at levels only 15-20% lower than in WT cells, and for this utilises relatively little ATP. For a small energy expenditure, mATPase enables mitochondrial ΔpH, protein import, Ca²⁺ turnover, and supports free radical detoxication machinery enlarged to protect the cells from oxidative damage. Whereas in COX-deficient cells the main source of ATP is glycolysis, the ΔΨm is still maintained upon inhibition of the adenine nucleotide translocators with bongkrekic acid and carboxyatractyloside, indicating that the role of ANTs is redundant, and matrix substrate level phosphorylation alone or in cooperation with ATP-Mg/P_i carriers can continuously support the mATPase activity. Intriguingly, we found that mitochondrial complex III is active, and it contributes not only to free radical production, but also to ΔΨm maintenance and energy budget of COX-deficient cells. Overall, this study demonstrates that F1Fo ATP synthase can support general mitochondrial and cellular functions, working in extremely efficient 'energy saving' reverse mode and flexibly recruiting free radical detoxication and ATP producing / transporting pathways.

The vacuolar-ATPase complex and assembly factors, TMEM199 and CCDC115, control HIF1α prolyl hydroxylation by regulating cellular iron levels

Hypoxia Inducible transcription Factors (HIFs) are principally regulated by the 2-oxoglutarate and Iron(II) prolyl hydroxylase (PHD) enzymes, which hydroxylate the HIFα subunit, facilitating its proteasome-mediated degradation. Observations that HIFα hydroxylation can be impaired even when oxygen is sufficient emphasise the importance of understanding the complex nature of PHD regulation. Here, we use an unbiased genome-wide genetic screen in near-haploid human cells to uncover cellular processes that regulate HIF1α. We identify that genetic disruption of the Vacuolar H+ ATPase (V-ATPase), the key proton pump for endo-lysosomal acidification, and two previously uncharacterised V-ATPase assembly factors, TMEM199 and CCDC115, stabilise HIF1α in aerobic conditions. Rather than preventing the lysosomal degradation of HIF1α, disrupting the V-ATPase results in intracellular iron depletion, thereby impairing PHD activity and leading to HIF activation. Iron supplementation directly restores PHD catalytic activity following V-ATPase inhibition, revealing important links between the V-ATPase, iron metabolism and HIFs.

Bafilomycin A1 induces caspase-independent cell death in hepatocellular carcinoma cells via targeting of autophagy and MAPK pathways

Hepatocellular carcinoma (HCC) is refractory to chemotherapies, necessitating novel effective agents. The lysosome inhibitor Bafilomycin A1 (BafA1) at high concentrations displays cytotoxicity in a variety of cancers. Here we show that BafA1 at nanomolar concentrations suppresses HCC cell growth in both 2 dimensional (2D) and 3D cultures. BafA1 induced cell cycle arrest in the G1 phase and triggered Cyclin D1 turnover in HCC cells in a dual-specificity tyrosine phosphorylation-regulated kinase 1B (DYRK1B) dependent manner. Notably, BafA1 induced caspase-independent cell death in HCC cells by impairing autophagy flux as demonstrated by elevated LC3 conversion and p62/SQSTM1 levels. Moreover, genetic ablation of LC3 significantly attenuated BafA1-induced cytotoxicity of HCC cells. We further demonstrate that pharmacological down-regulation or genetic depletion of p38 MAPK decreased BafA1-induced cell death via abolishment of BafA1-induced upregulation of Puma. Notably, knockdown of Puma impaired BafA1-induced HCC cell death, and overexpression of Puma enhanced BafA1-mediated HCC cell death, suggesting a role for Puma in BafA1-mediated cytotoxicity. Interestingly, pharmacological inhibition of JNK with SP600125 enhanced BafA1-mediated cytotoxicity both in vitro and in xenografts derived from HCC cells. Taken together, our data suggest that BafA1 may offer potential as an effective therapy for HCC.

The Ca2+/Mn2+-transporting SPCA2 pump is regulated by oxygen and cell density in colon cancer cells

The mammalian SPCA1 and SPCA2 ATPases localize in membranes of the secretory pathway and transport ions of Ca(2+) and Mn(2+) The role of tissue-specific SPCA2 isoform, highly expressed in lungs, mammary gland and gastrointestinal tract, is poorly understood. To elucidate the function of SPCA2, we studied human colon cancer HCT116 cells, grown under ambient and decreased O2 levels. We found that in contrast with other Ca(2+)-ATPase isoforms the expression of SPCA2 was up-regulated under hypoxia (3% O2), in both adherent (2D) and spheroid (3D) cultures. In spheroids, experiencing lowest O2 levels (30-50 μM, measured by phosphorescence lifetime imaging microscopy), we observed lower staining with reactive oxygen species (ROS)-specific fluorescent probe, which correlated with increased SPCA2. However, SPCA2 expression was up-regulated in cells exposed to reactive oxygen and nitrogen species donors, and when grown at higher density. We noticed that the culture exposed to hypoxia showed overall increase in S phase-positive cells and hypothesized that SPCA2 up-regulation under hypoxia can be linked to Mn(2+)-dependent cell cycle arrest. Consequently, we found that SPCA2-transfected cells display a higher number of cells entering S phase. Altogether, our results point at the important role of SPCA2 in regulation of cell cycle in cancer cells.

miR-526b-3p functions as a tumor suppressor in colon cancer by regulating HIF-1α

HIF-1α is an important transcriptional factor, which plays roles in cancer development and progression. But its regulation by miRNAs is not clear. Here, to investigate the regulation of HIF-1α by miRNAs, miRNAs were predicted and miR-526b-3p was verified as a regulator of HIF-1α in colon cancer cells. Using TaqMan RT-PCR analysis, we analyzed the expression of miR-526b-3p in tumor tissues and cell lines and found that miR-526b-3p was consistently under-expressed in cancer tissues and cell lines compared with their normal controls. When miR-526b-3p was induced into the colon cancer cells, cell proliferation, metastasis and glycolysis of colon cancer cells were suppressed. We also found that miR-526b-3p was down-regulated in metastatic colon cancer tissues and negatively with HIF-1α mRNA in colon cancer tissues. In a summary, miR-526b-3p plays as a tumor suppressor by down-regulation of HIF-1α expression in colon cancer and may be a new diagnosis or therapeutic target.

Expression of glucose transporter protein 1 and p63 in serous ovarian tumor

AIM

It has been shown that glycolytic metabolism is increased in malignant cells. Cancer cell growth is an energy-related process supported by an increased glucose metabolism. In addition, p63, a known homolog of p53, is expressed predominantly in basal cell and squamous cell carcinomas. The purpose of this study was to evaluate the expression of glucose transporter protein 1 (GLUT1) and p63 in patients with serous ovarian tumor (benign, borderline and malignant) and study their close relationship with the malignant transformation of serous ovarian tumors.

METHODS

Two hundred formalin-fixed, paraffin-embedded sections were immunostained with rabbit anti-GLUT1 polyclonal antibody and mouse anti-p63 monoclonal antibody using the streptavidin-biotin method. The samples were as follows: 40 normal ovarian tissues, 40 serous cystadenomas, 40 borderline serous cystadenomas and 80 serous cystadenocarcinomas were stained.

RESULT

Normal ovarian tissues showed completely negative staining for GLUT1 and p63. However, from benign serious cystadenomas, borderline cystadenomas to cystadenocarcinomas, the expression of GLUT1 and p63 grew stronger (P < 0.05). Moreover, the intensity staining of GLUT1 maintained a significant association with the expression of p63 (P < 0.05). In χ²-test analysis, expression of borderline cystadenomas and cystadenocarcinomas, intraperitoneal implants, ascites, lymph node status and International Federation of Gynecology and Obstetrics (FIGO) stage and GLUT1 expression levels have an appalling significance (P < 0.05), while FIGO stage, intraperitoneal implants and lymph node status except patient age and ascites have a statistical significance with the expression of p63 levels (P < 0.05).

CONCLUSION

Our findings show a progressive increase in the expression of GLUT1 and p63 from the benign serous cystadenomas, borderline cystadenomas to cystadenocarcinomas. Overexpression of GLUT1 and p63 are associated with the histology FIGO stage and metastasis of the tumors. These data suggested that the expression of GLUT1 and p63 may be closely related to the malignant transformation of serous ovarian tumors. However, the relative importance of GLUT1 and p63 in ovarian serous tumor development and tumorigenesis remains mostly unclear and awaits further investigation.

Cell energy budget platform for assessment of cell metabolism

Changes in bioenergetic parameters report on metabolic rearrangement, dysfunction of major pathways, and regulatory processes within the cell, adaptation to energy stress, or new physiological condition. A combined measurement of oxidative phosphorylation, glycolytic flux, the Krebs cycle activity, ATP levels, and total biomass allows detailed metabolic assessment. We describe a simple methodology for high-throughput multiparametric assessment of cell bioenergetics, called cell energy budget (CEB) platform, and demonstrate its practical use with cell models. The CEB relies on a standard multi-label reader with time-resolved fluorescence capabilities, the lanthanide probe pH-Xtra™ to measure extracellular acidification (ECA) associated with lactate (L-ECA) and combined lactate/CO2 (T-ECA) extrusion, the phosphorescent probe MitoXpress®-Xtra to measure oxygen consumption rate (OCR), the bioluminescent total ATP assay, and absorbance-based total protein assay. This approach can be further extended with the measurement of other cellular parameters, such as NAD(P)H, Ca(2+), mitochondrial pH, membrane potential, and redox state, using the corresponding fluorescent or luminescent probes.

Differential contribution of key metabolic substrates and cellular oxygen in HIF signalling

Changes in availability and utilisation of O2 and metabolic substrates are common in ischemia and cancer. We examined effects of substrate deprivation on HIF signalling in PC12 cells exposed to different atmospheric O2. Upon 2-4h moderate hypoxia, HIF-α protein levels were dictated by the availability of glutamine and glucose, essential for deep cell deoxygenation and glycolytic ATP flux. Nuclear accumulation of HIF-1α dramatically decreased upon inhibition of glutaminolysis or glutamine deprivation. Elevation of HIF-2α levels was transcription-independent and associated with the activation of Akt and Erk1/2. Upon 2h anoxia, HIF-2α levels strongly correlated with cellular ATP, produced exclusively via glycolysis. Without glucose, HIF signalling was suppressed, giving way to other regulators of cell adaptation to energy crisis, e.g. AMPK. Consequently, viability of cells deprived of O2 and glucose decreased upon inhibition of AMPK with dorsomorphin. The capacity of cells to accumulate HIF-2α decreased after 24h glucose deprivation. This effect, associated with increased AMPKα phosphorylation, was sensitive to dorsomorphin. In chronically hypoxic cells, glutamine played no major role in HIF-2α accumulation, which became mainly glucose-dependent. Overall, the availability of O2 and metabolic substrates intricately regulates HIF signalling by affecting cell oxygenation, ATP levels and pathways involved in production of HIF-α.

HRES-1/Rab4 promotes the formation of LC3(+) autophagosomes and the accumulation of mitochondria during autophagy

HRES-1/Rab4 is a small GTPase that regulates endocytic recycling. It has been colocalized to mitochondria and the mechanistic target of rapamycin (mTOR), a suppressor of autophagy. Since the autophagosomal membrane component microtubule-associated protein light chain 3 (LC3) is derived from mitochondria, we investigated the impact of HRES-1/Rab4 on the formation of LC3(+) autophagosomes, their colocalization with HRES-1/Rab4 and mitochondria, and the retention of mitochondria during autophagy induced by starvation and rapamycin. HRES-1/Rab4 exhibited minimal baseline colocalization with LC3, which was enhanced 22-fold upon starvation or 6-fold upon rapamycin treatment. Colocalization of HRES-1/Rab4 with mitochondria was increased >2-fold by starvation or rapamycin. HRES-1/Rab4 overexpression promoted the colocalization of mitochondria with LC3 upon starvation or rapamycin treatment. A dominant-negative mutant, HRES-1/Rab4(S27N) had reduced colocalization with LC3 and mitochondria upon starvation but not rapamycin treatment. A constitutively active mutant, HRES-1/Rab4(Q72L) showed diminished colocalization with LC3 but promoted the partitioning of mitochondria with LC3 upon starvation or rapamycin treatment. Phosphorylation-resistant mutant HRES-1/Rab4(S204Q) showed diminished colocalization with LC3 but increased partitioning to mitochondria. A newly discovered C-terminally truncated native isoform, HRES-1/Rab4(1-121), showed enhanced localization to LC3 and mitochondria without starvation or rapamycin treatment. HRES-1/Rab4(1-121) increased the formation of LC3(+) autophagosomes in resting cells, while other isoforms promoted autophagosome formation upon starvation. HRES-1/Rab4, HRES-1/Rab4(1-121), HRES-1/Rab4(Q72L) and HRES-1/Rab4(S204Q) promoted the accumulation of mitochondria during starvation. The specificity of HRES-1/Rab4-mediated mitochondrial accumulation is indicated by its abrogation by dominant-negative HRES-1/Rab4(S27N) mutation. The formation of interconnected mitochondrial tubular networks was markedly enhanced by HRES-1/Rab4(Q72L) upon starvation, which may contribute to the retention of mitochondria during autophagy. The present study thus indicates that HRES-1/Rab4 regulates autophagy through promoting the formation of LC3(+) autophagosomes and the preservation of mitochondria.

Availability of the key metabolic substrates dictates the respiratory response of cancer cells to the mitochondrial uncoupling

Active glycolysis and glutaminolysis provide bioenergetic stability of cancer cells in physiological conditions. Under hypoxia, metabolic and mitochondrial disorders, or pharmacological treatment, a deficit of key metabolic substrates may become life-threatening to cancer cells. We analysed the effects of mitochondrial uncoupling by FCCP on the respiration of cells fed by different combinations of Glc, Gal, Gln and Pyr. In cancer PC12 and HCT116 cells, a large increase in O2 consumption rate (OCR) upon uncoupling was only seen when Gln was combined with either Glc or Pyr. Inhibition of glutaminolysis with BPTES abolished this effect. Despite the key role of Gln, addition of FCCP inhibited respiration and induced apoptosis in cells supplied with Gln alone or Gal/Gln. For all substrate combinations, amplitude of respiratory responses to FCCP did not correlate with Akt, Erk and AMPK phosphorylation, cellular ATP, and resting OCR, mitochondrial Ca(2+) or membrane potential. However, we propose that proton motive force could modulate respiratory response to FCCP by regulating mitochondrial transport of Gln and Pyr, which decreases upon mitochondrial depolarisation. As a result, an increase in respiration upon uncoupling is abolished in cells, deprived of Gln or Pyr (Glc). Unlike PC12 or HCT116 cells, mouse embryonic fibroblasts were capable of generating pronounced response to FCCP when deprived of Gln, thus exhibiting lower dependence on glutaminolysis. Overall, the differential regulation of the respiratory response to FCCP by metabolic environment suggests that mitochondrial uncoupling has a potential for substrate-specific inhibition of cell function, and can be explored for selective cancer treatment.

ADAM17 mediates hypoxia-induced drug resistance in hepatocellular carcinoma cells through activation of EGFR/PI3K/Akt pathway

A disintegrin and metalloproteinase-17 (ADAM17) is a member of the metalloproteinase superfamily and involved in the cleavage of ectodomain of many transmembrane proteins. ADAM17 is overexpressed in a variety of human tumors, which is associated with tumor development and progression. In the present study, we sought to investigate the expression and function of ADAM17 in hypoxia-treated hepatocellular carcinoma (HCC) cells. Western blot analysis was used to measure the expression of ADAM17 in HCC cell lines (Hep3B and HepG2 cells). Annexin V/PI double staining was performed to analyze the effects of ADAM17 on hypoxia-mediated cisplatin resistance. ADAM17 expression was upregulated by hypoxia treatment in HCC cells at both mRNA and protein levels. Overexpression of ADAM17 reduced cisplatin-induced apoptosis in HCC cells, accompanies by less cleavage of caspase-3 and poly (ADP-ribose) polymerase (PARP). Forced expression of ADAM17 enhanced the phosphorylation of epidermal growth factor receptor (EGFR) and Akt without affecting the expression of total EGFR and Akt. Pretreatment with EGFR inhibitor AG1478 or phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 rescued ADAM17-mediated cisplatin resistance of HCC cells. ADAM17 silencing attenuated hypoxia-induced cisplatin resistance and enhanced the accumulation of cleaved caspase-3 and PARP. Western blot analysis showed that overexpression of hypoxia-inducible factor-1α (HIF-1α), a transcription factor, upregulated the expression of ADAM17 and HIF-1α silencing downregulated the expression of ADAM17 in hypoxia-treated HCC cells, indicating the regulation of ADAM17 by HIF-1α. Taken together, our results indicated that ADAM17 is upregulated by hypoxia and contributes to hypoxia-induced cisplatin resistance via EGFR/PI3K/Akt pathway.