Molecular and cellular regulation of glucose transporter (GLUT) proteins in cancer

Targeting hypoxia in cancer therapy

Hypoxia is a feature of most tumours, albeit with variable incidence and severity within a given patient population. It is a negative prognostic and predictive factor owing to its multiple contributions to chemoresistance, radioresistance, angiogenesis, vasculogenesis, invasiveness, metastasis, resistance to cell death, altered metabolism and genomic instability. Given its central role in tumour progression and resistance to therapy, tumour hypoxia might well be considered the best validated target that has yet to be exploited in oncology. However, despite an explosion of information on hypoxia, there are still major questions to be addressed if the long-standing goal of exploiting tumour hypoxia is to be realized. Here, we review the two main approaches, namely bioreductive prodrugs and inhibitors of molecular targets upon which hypoxic cell survival depends. We address the particular challenges and opportunities these overlapping strategies present, and discuss the central importance of emerging diagnostic tools for patient stratification in targeting hypoxia.

Experimental study on the therapeutic effect of positron emission tomography agent [¹⁸F]-labeled 2-deoxy-2-fluoro-d-glucose in a colon cancer mouse model

The purpose of this study was to assess the therapeutic effect of positron emission tomography agent [¹⁸F]-labeled 2-deoxy-2-fluoro-d-glucose (¹⁸F-FDG) in a colorectal cancer mouse model. Three (3) tumor-bearing mice groups were treated with different doses of ¹⁸F-FDG. Mice were imaged by positron emission tomography with ¹⁸F-FDG before and after treatment weekly and the tumor growth rate was calculated. Tumor, brain, heart, and kidney of mice were analyzed for expression of glucose transporters and vascular endothelial growth factor (VEGF) by immunofluorescent staining, and the presence of apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) method. All 3 treated groups showed significant ¹⁸F-FDG reduction compared with the control group (p < 0.05). With higher treatment dose, better treatment response was observed. The tumor growth rate of all 3 treated groups was also significantly decreased after treatment (p < 0.05). Immunohistochemistry showed that tumors expressed more glucose transporters than in brain, heart, and kidney. The ¹⁸F-FDG treatment of mice resulted in apoptotic cell death in all 3 treated groups, which showed significant higher apoptotic cells than the control group (p < 0.05). The study suggests that ¹⁸F-FDG has a therapeutic effect in colonic cancer animal model, which indicates the potential for the development of positron therapy for colonic cancer and other cancers.

Metabolic tumor imaging using magnetic resonance spectroscopy

The adaptability and the genomic plasticity of cancer cells, and the interaction between the tumor microenvironment and co-opted stromal cells, coupled with the ability of cancer cells to colonize distant organs, contribute to the frequent intractability of cancer. It is becoming increasingly evident that personalized molecular targeting is necessary for the successful treatment of this multifaceted and complex disease. Noninvasive imaging modalities such as magnetic resonance (MR), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) are filling several important niches in this era of targeted molecular medicine, in applications that span from bench to bedside. In this review we focus on noninvasive magnetic resonance spectroscopy (MRS) and spectroscopic imaging (MRSI) and their roles in future personalized medicine in cancer. Diagnosis, the identification of the most effective treatment, monitoring treatment delivery, and response to treatment are some of the broad areas into which MRS techniques can be integrated to improve treatment outcomes. The development of novel probes for molecular imaging--in combination with a slew of functional imaging capabilities--makes MRS techniques, especially in combination with other imaging modalities, valuable in cancer drug discovery and basic cancer research.

Glucose transporter-1 as a new therapeutic target in laryngeal carcinoma

Treatment options for laryngeal carcinoma, one of the most common head and neck malignancies, consist of radiotherapy, surgery, chemotherapy or a combination thereof. The functional treatment of laryngeal carcinoma poses a considerable challenge because of its resistance to chemotherapy and radiotherapy, and its tendency for local recurrence. Finding ways to inhibit the energy supply of malignant tumours is becoming an increasingly attractive proposition. Glucose transporter-1 (Glut-1; encoded by the SLC2A1 gene in humans) is the main transporter of glucose in solid carcinomas and has become a focus of cancer research. Recently, it was shown that the increased expression of SLC2A1 in head and neck carcinomas is correlated with lymph node metastasis, poor survival and clinical stage, and revealed that the suppression of SLC2A1 expression by antisense oligodeoxynucleotides decreased glucose uptake and inhibited the proliferation of Hep-2 cells. Thus, the authors propose the suppression of SLC2A1 expression as a new therapeutic target for laryngeal carcinoma.

Glucose metabolism disorders and the risk of cancer

Diabetes and cancer are diseases which take the size of an epidemic spread across the globe. Those diseases are influenced by many factors, both genetic and environmental. Precise knowledge of the complex relationships and interactions between these two conditions is of great importance for their prevention and treatment. Many epidemiological studies have shown that certain types of cancer, especially gastrointestinal cancers (pancreas, liver, colon) and also the urinary and reproductive system cancers in women are more common in patients with diabetes or related metabolic disorders. There are also studies showing the inverse relationship between diabetes and cancer, or the lack of it, but they are less numerous and relate mainly to prostate cancer or squamous cell carcinoma of the esophagus. Epidemiological studies, however, do not say anything about the mechanisms of these dependencies. For this purpose, molecular research is needed on the metabolism of cells (including tumor cells) and on metabolic dysfunctions that arise due to changes in the cell environment taking place in the sick, as well as in the intensely treated human organism.

Oncogene activation induces metabolic transformation resulting in insulin-independence in human breast cancer cells

Normal breast epithelial cells require insulin and EGF for growth in serum-free media. We previously demonstrated that over expression of breast cancer oncogenes transforms MCF10A cells to an insulin-independent phenotype. Additionally, most breast cancer cell lines are insulin-independent for growth. In this study, we investigated the mechanism by which oncogene over expression transforms MCF10A cells to an insulin-independent phenotype. Analysis of the effects of various concentrations of insulin and/or IGF-I on proliferation of MCF10A cells demonstrated that some of the effects of insulin were independent from those of IGF-I, suggesting that oncogene over expression drives a true insulin-independent proliferative phenotype. To test this hypothesis, we examined metabolic functions of insulin signaling in insulin-dependent and insulin-independent cells. HER2 over expression in MCF10A cells resulted in glucose uptake in the absence of insulin at a rate equal to insulin-induced glucose uptake in non-transduced cells. We found that a diverse set of oncogenes induced the same result. To gain insight into how HER2 oncogene signaling affected increased insulin-independent glucose uptake we compared HER2-regulated gene expression signatures in MCF10A and HER2 over expressing MCF10A cells by differential analysis of time series gene expression data from cells treated with a HER2 inhibitor. This analysis identified genes specifically regulated by the HER2 oncogene, including VAMP8 and PHGDH, which have known functions in glucose uptake and processing of glycolytic intermediates, respectively. Moreover, these genes specifically implicated in HER2 oncogene-driven transformation are commonly altered in human breast cancer cells. These results highlight the diversity of oncogene effects on cell regulatory pathways and the importance of oncogene-driven metabolic transformation in breast cancer.

Xenobiotic metabolism and disposition in human lung: transcript profiling in non-tumoral and tumoral tissues

The lung is directly exposed to a wide variety of inhaled toxicants and carcinogens. In order to improve our knowledge of the cellular processing of these compounds in the respiratory tract, we investigated the mRNA expression level of 380 genes encoding xenobiotic-metabolizing enzymes (XME), transporters, nuclear receptors and transcription factors, in pulmonary parenchyma (PP), bronchial mucosa (BM) and tumoral lung tissues from 12 patients with non-small cell lung cancer (NSCLC). Using a high throughput quantitative real-time RT-PCR method, we found that ADH1B, CYP4B1, CES1 and GSTP1 are the major XME genes expressed both in BM and PP. Our results also documented the predominant role played by the xenosensor AhR in human lung. The gene expression profiles were different for BM and PP, with a tendency toward increased mRNA levels of phase I and phase II XME genes in BM, suggesting major differences in the initial stages of xenobiotic metabolism. Some of the significantly overexpressed genes in BM (i.e. CYP2F1, CYP2A13, CYP2W1, NQO1…) encode proteins involved in the bioactivation of procarcinogens, pointing out distinct susceptibility to xenobiotics and their toxic effects between these two tissue types. Additionally, interindividual differences in transcript levels observed for some genes may be of genetic origin and may contribute to the variability in response to environmental exposure and, consequently, in the risk of developing lung diseases. A global decrease in gene expression was observed in tumoral specimens. Some of the proteins are involved in the metabolism or transport of anti-cancer drugs and their influence in the response of tumors to chemotherapy should be considered. In conclusion, the present study provides an overview of the cellular response to toxicants and drugs in healthy and cancerous human lung tissues, and thus improves our understanding of the mechanisms of chemical carcinogenesis as well as cellular resistance to chemotherapy.

GLUT-1 expression in pancreatic neoplasia: implications in pathogenesis, diagnosis, and prognosis

OBJECTIVES

GLUT-1 has been found to have an important role in the upregulation of various cellular pathways and implicated in neoplastic transformation correlating with biological behavior in malignancies. However, literature regarding the significance of GLUT-1 expression in pancreatic neoplasia has been limited and controversial.

METHODS

Immunohistochemical expression of GLUT-1 was tested in a variety of pancreatic neoplasia including ductal adenocarcinomas (DAs), pancreatic intraepithelial neoplasms (PanINs), intraductal papillary mucinous neoplasms (IPMNs), and serous cystadenomas.

RESULTS

There was a progressive increase in the expression of GLUT-1 from low- to higher-grade dysplastic lesions: All higher-grade PanINs/IPMNs (the ones with moderate/high-grade dysplasia) revealed noticeable GLUT-1 expression. Among the 94 DAs analyzed, there were minimal/moderate expression in 46 and significant expression in 24 DAs. However, all 4 clear-cell variants of DAs revealed significant GLUT-1 immunolabeling, as did areas of clear-cell change seen in other DAs. Moreover, all 12 serous cystadenomas expressed significant GLUT-1. GLUT-1 expression was also directly correlated with DA histological grade (P = 0.016) and tumor size (P = 0.03).

CONCLUSIONS

GLUT-1 may give rise to the distinctive clear-cell appearance of these tumors by inducing the accumulation of glycogen in the cytoplasm. Additionally, because GLUT-1 expression was related to histological grade and tumor size of DA, further studies are warranted to investigate the association of GLUT-1 with prognosis and tumor progression.

Metabolic correlates of tumour hypoxia in malignant canine mammary carcinoma

Given its importance in human and canine tumour biology, a profound understanding of tumour hypoxia is of paramount importance. Therefore, the aim of this work was to investigate the relationship between tumour hypoxia and the expression of a number of hypoxia-induced proteins that play a role in tumour metabolism. The hypoxia marker pimonidazole was administered to dogs affected by spontaneous mammary carcinoma and compared with immunohistochemical staining for GLUT1 and 3, HK 2 and CA IX. A statistically significant correlation was found between pimonidazole staining and GLUT1-expression (R=0.607; p=0.001). These results indicate a strong interaction between tumour hypoxia and tumour metabolism by the induction of proteins essential to maintain a stable tumour microenvironment.

Radiopharmacological evaluation of 6-deoxy-6-[18F]fluoro-D-fructose as a radiotracer for PET imaging of GLUT5 in breast cancer

INTRODUCTION

Several clinical studies have shown low or no expression of GLUT1 in breast cancer patients, which may account for the low clinical specificity and sensitivity of 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) used in positron emission tomography (PET). Therefore, it has been proposed that other tumor characteristics such as the high expression of GLUT2 and GLUT5 in many breast tumors could be used to develop alternative strategies to detect breast cancer. Here we have studied the in vitro and in vivo radiopharmacological profile of 6-deoxy-6-[(18)F]fluoro-D-fructose (6-[(18)F]FDF) as a potential PET radiotracer to image GLUT5 expression in breast cancers.

METHODS

Uptake of 6-[(18)F]FDF was studied in murine EMT-6 and human MCF-7 breast cancer cells over 60 min and compared to [(18)F]FDG. Biodistribution of 6-[(18)F]FDF was determined in BALB/c mice. Tumor uptake was studied with dynamic small animal PET in EMT-6 tumor-bearing BALB/c mice and human xenograft MCF-7 tumor-bearing NIH-III mice in comparison to [(18)F]FDG. 6-[(18)F]FDF metabolism was investigated in mouse blood and urine.

RESULTS

6-[(18)F]FDF is taken up by EMT-6 and MCF-7 breast tumor cells independent of extracellular glucose levels but dependent on the extracellular concentration of fructose. After 60 min, 30±4% (n=9) and 12±1% (n=7) ID/mg protein 6-[(18)F]FDF was found in EMT-6 and MCF-7 cells, respectively. 6-deoxy-6-fluoro-d-fructose had a 10-fold higher potency than fructose to inhibit 6-[(18)F]FDF uptake into EMT-6 cells. Biodistribution in normal mice revealed radioactivity uptake in bone and brain. Radioactivity was accumulated in EMT-6 tumors reaching 3.65±0.30% ID/g (n=3) at 5 min post injection and decreasing to 1.75±0.03% ID/g (n=3) at 120 min post injection. Dynamic small animal PET showed significantly lower radioactivity uptake after 15 min post injection in MCF-7 tumors [standard uptake value (SUV)=0.76±0.05; n=3] compared to EMT-6 tumors (SUV=1.23±0.09; n=3). Interestingly, [(18)F]FDG uptake was significantly different in MCF-7 tumors (SUV(15 min) 0.74±0.12 to SUV(120 min) 0.80±0.15; n=3) versus EMT-6 tumors (SUV(15 min) 1.01±0.33 to SUV(120 min) 1.80±0.25; n=3). 6-[(18)F]FDF was shown to be a substrate for recombinant human ketohexokinase, and it was metabolized rapidly in vivo.

CONCLUSION

Based on the GLUT5 specific transport and phosphorylation by ketohexokinase, 6-[(18)F]FDF may represent a novel radiotracer for PET imaging of GLUT5 and ketohexokinase-expressing tumors.

4F2hc stabilizes GLUT1 protein and increases glucose transport activity

Glucose transporter 1 (GLUT1) is widely distributed throughout various tissues and contributes to insulin-independent basal glucose uptake. Using a split-ubiquitin membrane yeast two-hybrid system, we newly identified 4F2 heavy chain (4F2hc) as a membrane protein interacting with GLUT1. Though 4F2hc reportedly forms heterodimeric complexes between amino acid transporters, such as LAT1 and LAT2, and regulates amino acid uptake, we investigated the effects of 4F2hc on GLUT1 expression and the associated glucose uptake. First, FLAG-tagged 4F2hc and hemagglutinin-tagged GLUT1 were overexpressed in human embryonic kidney 293 cells and their association was confirmed by coimmunoprecipitation. The green fluorescent protein-tagged 4F2hc and DsRed-tagged GLUT1 showed significant, but incomplete, colocalization at the plasma membrane. In addition, an endogenous association between GLUT1 and 4F2hc was demonstrated using mouse brain tissue and HeLa cells. Interestingly, overexpression of 4F2hc increased the amount of GLUT1 protein in HeLa and HepG2 cells with increased glucose uptake. In contrast, small interfering RNA (siRNA)-mediated 4F2hc gene suppression markedly reduced GLUT1 protein in both cell types, with reduced glucose uptake. While GLUT1 mRNA levels were not affected by overexpression or gene silencing of 4F2hc, GLUT1 degradation after the addition of cycloheximide was significantly suppressed by 4F2hc overexpression and increased by 4F2hc siRNA treatment. Taken together, these observations indicate that 4F2hc is likely to be involved in GLUT1 stabilization and to contribute to the regulation of not only amino acid but also glucose metabolism.

A novel cross-talk between endothelin-1 and cyclic AMP signaling pathways in the regulation of GLUT1 transcription in 3T3-L1 adipocytes

We showed previously that chronic exposure to both endothelin-1 (ET-1) and cAMP resulted in a synergistic increase in Glut1 transcription in 3T3-L1 adipocytes via a protein kinase C (PKC)-dependent mechanism. In the present study, we further examined the molecular mechanism involved. Employing transient transfections with Glut1 promoter/enhancer -luciferase reporter and several dominant negative or constitutively active PKC mutants, we identified PKCε as the responsible PKC. Investigation with deletion and mutation mutants of the promoter/enhancer reporter suggested that Sp1, CREB and AP-1 responsive elements on enhancer 2 were involved. Furthermore, chromatin immunoprecipitation and co-immunoprecipitation analysis were applied to characterize the interactions between these transcription factors and their bindings to enhancer 2 in vivo. The results indicate that there are both negative and positive interactions between ET-1 and cAMP signaling pathways. On the one hand, cAMP inhibits ET-1 induced NF-κB activation required for ET-1-stimulated Glut1 transcription; on the other hand, cAMP, via sustained CREB phosphorylation, may activate AP-1 and cooperate with ET-1-activated PKCε to enhance Sp1 expression and consequently to generate a stable enhancer 2-bound Sp1/pCREB/AP-1 complex, which can strongly facilitate Glut1 transcription more than the additive effect of ET-1 and cAMP alone.

Metabolic imaging allows early prediction of response to vandetanib

The RET (rearranged-during-transfection protein) protooncogene triggers multiple intracellular signaling cascades regulating cell cycle progression and cellular metabolism. We therefore hypothesized that metabolic imaging could allow noninvasive detection of response to the RET inhibitor vandetanib in vivo.

METHODS

The effects of vandetanib treatment on the full-genome expression and the metabolic profile were analyzed in the human medullary thyroid cancer cell line TT. In vitro, transcriptional changes of pathways regulating cell cycle progression and glucose, dopa, and thymidine metabolism were correlated to the results of cell cycle analysis and the uptake of (3)H-deoxyglucose, (3)H-3,4-dihydroxy-L-phenylalanine, and (3)H-thymidine under vandetanib treatment. In vivo, the tumor metabolism under vandetanib was monitored by small-animal PET of tumor-bearing mice.

RESULTS

Vandetanib treatment resulted in the transcriptional downregulation of various effector pathways with consecutive downregulation of cyclin expression and a G(0)/G(1) arrest. In vitro, vandetanib treatment resulted in the decreased expression of genes regulating glucose, 3,4-dihydroxy-L-phenylalanine, and thymidine metabolism, with a subsequent reduction in the functional activity of the corresponding pathways. In vivo, metabolic imaging with PET was able to assess changes in the tumoral glucose metabolism profile as early as 3 d after initiation of vandetanib treatment.

CONCLUSION

We describe a metabolic imaging approach for the noninvasive detection of successful vandetanib treatment. Our results suggest that PET may be useful for identifying patients who respond to vandetanib early in the course of treatment.

Long-term in vitro treatment of human glioblastoma cells with temozolomide increases resistance in vivo through up-regulation of GLUT transporter and aldo-keto reductase enzyme AKR1C expression

Glioblastoma (GBM) is the most frequent malignant glioma. Treatment of GBM patients is multimodal with maximum surgical resection, followed by concurrent radiation and chemotherapy with the alkylating drug temozolomide (TMZ). The present study aims to identify genes implicated in the acquired resistance of two human GBM cells of astrocytic origin, T98G and U373, to TMZ. Resistance to TMZ was induced by culturing these cells in vitro for months with incremental TMZ concentrations up to 1 mM. Only partial resistance to TMZ has been achieved and was demonstrated in vivo in immunocompromised mice bearing orthotopic U373 and T98G xenografts. Our data show that long-term treatment of human astroglioma cells with TMZ induces increased expression of facilitative glucose transporter/solute carrier GLUT/SLC2A family members, mainly GLUT-3, and of the AKR1C family of proteins. The latter proteins are phase 1 drug-metabolizing enzymes involved in the maintenance of steroid homeostasis, prostaglandin metabolism, and metabolic activation of polycyclic aromatic hydrocarbons. GLUT-3 has been previously suggested to exert roles in GBM neovascularization processes, and TMZ was found to exert antiangiogenic effects in experimental gliomas. AKR1C1 was previously shown to be associated with oncogenic potential, with proproliferative effects similar to AKR1C3 in the latter case. Both AKR1C1 and AKR1C2 proteins are involved in cancer pro-proliferative cell chemoresistance. Selective targeting of GLUT-3 in GBM and/or AKR1C proteins (by means of jasmonates, for example) could thus delay the acquisition of resistance to TMZ of astroglioma cells in the context of prolonged treatment with this drug.

Prostate cancer

Prostate cancer is biologically and clinically a heterogeneous disease and its imaging evaluation will need to be tailored to the specific phases of the disease in a patient-specific, risk-adapted manner. We first present a brief overview of the natural history of prostate cancer before discussing the role of various imaging tools, including opportunities and challenges, for different clinical phases of this common disease in men. We then review the preclinical and clinical evidence on the potential and emerging role of positron emission tomography with various radiotracers in the imaging evaluation of men with prostate cancer.

GLUT1 expression in malignant tumors and its use as an immunodiagnostic marker

OBJECTIVE

To analyze glucose transporter 1 expression patterns in malignant tumors of various cell types and evaluate their diagnostic value by immunohistochemistry.

INTRODUCTION

Glucose is the major source of energy for cells, and glucose transporter 1 is the most common glucose transporter in humans. Glucose transporter 1 is aberrantly expressed in several tumor types. Studies have implicated glucose transporter 1 expression as a prognostic and diagnostic marker in tumors, primarily in conjunction with positron emission tomography scan data.

METHODS

Immunohistochemistry for glucose transporter 1 was performed in tissue microarray slides, comprising 1955 samples of malignant neoplasm from different cell types.

RESULTS

Sarcomas, lymphomas, melanomas and hepatoblastomas did not express glucose transporter 1. Forty-seven per cent of prostate adenocarcinomas were positive, as were 29% of thyroid, 10% of gastric and 5% of breast adenocarcinomas. Thirty-six per cent of squamous cell carcinomas of the head and neck were positive, as were 42% of uterine cervix squamous cell carcinomas. Glioblastomas and retinoblastomas showed membranous glucose transporter 1 staining in 18.6% and 9.4% of all cases, respectively. Squamous cell carcinomas displayed membranous expression, whereas adenocarcinomas showed cytoplasmic glucose transporter 1 expression.

CONCLUSION

Glucose transporter 1 showed variable expression in various tumor types. Its absence in sarcomas, melanomas, hepatoblastomas and lymphomas suggests that other glucose transporters mediate the glycolytic pathway in these tumors. The data suggest that glucose transporter 1 is a valuable immunohistochemical marker that can be used to identify patients for evaluation by positron emission tomography scan. The function of cytoplasmic glucose transporter 1 in adenocarcinomas must be further examined.

The control of the metabolic switch in cancers by oncogenes and tumor suppressor genes

Cells from some tumors use an altered metabolic pattern compared with that of normal differentiated adult cells in the body. Tumor cells take up much more glucose and mainly process it through aerobic glycolysis, producing large quantities of secreted lactate with a lower use of oxidative phosphorylation that would generate more adenosine triphosphate (ATP), water, and carbon dioxide. This is the Warburg effect, which provides substrates for cell growth and division and free energy (ATP) from enhanced glucose use. This metabolic switch places the emphasis on producing intermediates for cell growth and division, and it is regulated by both oncogenes and tumor suppressor genes in a number of key cancer-producing pathways. Blocking these metabolic pathways or restoring these altered pathways could lead to a new approach in cancer treatments.

Prostate cancer: PET with 18F-FDG, 18F- or 11C-acetate, and 18F- or 11C-choline

Prostate cancer is biologically and clinically a heterogeneous disease that makes imaging evaluation challenging. The role of imaging in prostate cancer should include diagnosis, localization, and characterization (indolent vs. lethal) of the primary tumor, determination of extracapsular spread, guidance and evaluation of local therapy in organ-confined disease, staging of locoregional lymph nodes, detection of locally recurrent and metastatic disease in biochemical relapse, planning of radiation treatment, prediction and assessment of tumor response to salvage and systemic therapy, monitoring of active surveillance and definition of a trigger for definitive therapy, and prognostication of time to hormone refractoriness in castrate disease and overall survival. To address these tasks effectively, imaging needs to be tailored to the specific phases of the disease in a patient-specific, risk-adjusted manner. In this article, I review the preclinical and clinical evidence on the potential and emerging role of PET with the 3 most commonly studied radiotracers in prostate cancer, namely 18F-FDG, 18F- or 11C-acetate, and 18F- or 11C-choline.

Regulation of Na(+)-coupled glucose carrier SGLT1 by human papillomavirus 18 E6 protein

Tumor cells utilize preferably glucose for energy production. They accomplish cellular glucose uptake in part through Na(+)-coupled glucose transport mediated by SGLT1 (SLC5A1). This study explored the possibility that the human papillomavirus 18 E6 protein HPV18 E6 (E6) participates in the stimulation of SGLT1 activity. E6 is one of the two major oncoproteins of high-risk human papillomaviruses, which are the causative agent for cervical carcinoma. According to Western blotting, SGLT1 is expressed in the HPV18-positive cervical carcinoma cell line HeLa. To explore whether E6 affects SGLT1 activity, SGLT1 was expressed in Xenopus oocytes with and without E6 and electrogenic glucose transport determined by dual electrode voltage clamp. In SGLT1-expressing oocytes, but not in oocytes injected with water or expressing E6 alone, glucose triggered a current (I(g)). I(g) was significantly increased by coexpression of E6 but not by coexpression of E2. According to chemiluminescence and confocal microscopy, coexpression of E6 significantly increased the SGLT1 protein abundance in the cell membrane. The decay of I(g) following inhibition of carrier insertion by Brefeldine A (5 μM) was not significantly affected E6 coexpression. Accrodingly, E6 was not effective by increasing carrier protein stability in the membrane. In conclusion, HPV18 E6 oncoprotein participates in the upregulation of SGLT1.

Acidic stress promotes a glioma stem cell phenotype

Malignant gliomas are lethal cancers that display cellular hierarchies with cancer stem cells at the apex. Glioma stem cells (GSCs) are not uniformly distributed, but rather located in specialized niches, suggesting that the cancer stem cell phenotype is regulated by the tumor microenvironment. Indeed, recent studies show that hypoxia and its molecular responses regulate cancer stem cell maintenance. We now demonstrate that acidic conditions, independent of restricted oxygen, promote the expression of GSC markers, self-renewal and tumor growth. GSCs exert paracrine effects on tumor growth through elaboration of angiogenic factors, and low pH conditions augment this expression associated with induction of hypoxia inducible factor 2α (HIF2α), a GSC-specific regulator. Induction of HIF2α and other GSC markers by acidic stress can be reverted by elevating pH in vitro, suggesting that raising intratumoral pH may be beneficial for targeting the GSC phenotype. Together, our results suggest that exposure to low pH promotes malignancy through the induction of a cancer stem cell phenotype, and that culturing cancer cells at lower pH reflective of endogenous tumor conditions may better retain the cellular heterogeneity found in tumors.

Expression of genes related to apoptosis, cell cycle and signaling pathways are independent of TP53 status in urinary bladder cancer cells

Urinary bladder cancer is the fourth most common malignancy in the Western world. Transitional cell carcinoma (TCC) is the most common subtype, accounting for about 90% of all bladder cancers. The TP53 gene plays an essential role in the regulation of the cell cycle and apoptosis and therefore contributes to cellular transformation and malignancy; however, little is known about the differential gene expression patterns in human tumors that present with the wild-type or mutated TP53 gene. Therefore, because gene profiling can provide new insights into the molecular biology of bladder cancer, the present study aimed to compare the molecular profiles of bladder cancer cell lines with different TP53 alleles, including the wild type (RT4) and two mutants (5637, with mutations in codons 280 and 72; and T24, a TP53 allele encoding an in-frame deletion of tyrosine 126). Unsupervised hierarchical clustering and gene networks were constructed based on data generated by cDNA microarrays using mRNA from the three cell lines. Differentially expressed genes related to the cell cycle, cell division, cell death, and cell proliferation were observed in the three cell lines. However, the cDNA microarray data did not cluster cell lines based on their TP53 allele. The gene profiles of the RT4 cells were more similar to those of T24 than to those of the 5637 cells. While the deregulation of both the cell cycle and the apoptotic pathways was particularly related to TCC, these alterations were not associated with the TP53 status.

[F]fluoro-2-deoxy-d-glucose incorporation by mcf-7 breast tumour cells in vitro is modulated by treatment with tamoxifen, Doxorubicin, and docetaxel: relationship to chemotherapy-induced changes in ATP content, hexokinase activity, and glucose transport

Breast tumours responding to chemotherapy exhibit decreased [¹⁸F]fluoro-2-deoxy-D-glucose ([¹⁸F]FDG) incorporation. Underlying mechanisms of these changes is poorly understood. Here, in MCF-7 cells, responding to chemotherapy drugs commonly utilised in the treatment of breast cancer, [¹⁸F]FDG incorporation and several pivotal factors associated with [¹⁸F]FDG incorporation investigated. Methods. IC50 and subclinical doxorubicin, docetaxel, and tamoxifen doses determined using MTT assay. [¹⁸F]FDG incorporation by cells treated with IC50 drug doses for 48 hours and 72 hours were determined and FDG dephosphorylation estimated by measuring loss of 18F from [¹⁸F]FDG-preincubated cells (pulse-chase). Glucose transport determined by measuring initial uptake rate of non-metabolised glucose analogue omethylglucose; hexokinase activity and ATP content measured in cell homogenates; Cell cycle distribution determined using flow cytometry of propidium iodide stained nuclei. Results. [¹⁸F]FDG incorporation and ATP content decreased in cells after 72 hours treatment with IC50 doses of tamoxifen, doxorubicin, and docetaxel compared with untreated controls. Decreased glucose transport and/or hexokinase activity accompanied decreased [¹⁸F]FDG incorporation by MCF-7 cells treated with tamoxifen or doxorubicin but not docetaxel. Conclusions. Tumour cell [¹⁸F]FDG incorporation along with ATP content decreased by treatment with tamoxifen, doxorubicin and docetaxel paralleling clinical observations for solid tumours. Effect of each treatment on glucose transport and hexokinase activity was chemotherapy-drug dependent.

Assessment of chemoselective neoglycosylation methods using chlorambucil as a model

To systematically assess the impact of glycosylation and the corresponding chemoselective linker upon the anticancer activity/selectivity of the drug chlorambucil, herein we report the synthesis and anticancer activities of a 63-member library of chlorambucil-based neoglycosides. A comparison of N-alkoxyamine-, N-acylhydrazine-, and N-hydroxyamine-based chemoselective glycosylation of chlorambucil revealed sugar- and linker-dependent partitioning among open- and closed-ring neoglycosides and corresponding sugar-dependent variant biological activity. Cumulatively, this study represents the first neoglycorandomization of a synthetic drug and expands our understanding of the impact of sugar structure upon product distribution/equilibria in the context of N-alkoxyamino-, N-hydroxyamino-, and N-acylhydrazine-based chemoselective glycosylation. This study also revealed several analogues with increased in vitro anticancer activity, most notably D-threoside 60 (NSC 748747), which displayed much broader tumor specificity and notably increased potency over the parent drug.

NAD(P)H oxidase isoform Nox2 plays a prosurvival role in human leukaemia cells

The mechanism involved in the prosurvival effect of interleukin-3 on the human acute myeloid leukaemia cell line M07e is investigated. A decrease in intracellular reactive oxygen species (ROS) content, glucose transport activity and cell survival was observed in the presence of inhibitors of plasma membrane ROS sources, such as diphenylene iodonium and apocynin, and by small interference RNA for Nox2. Moreover, IL-3 incubation stimulated the synthesis of Nox2 cytosolic sub-unit p47phox and glucose transporter Glut1. Thus, the inhibition of ROS generation by Nox inhibitors stimulated apoptosis showing that ROS production, induced by IL-3 via Nox2, protects leukaemic cells from cell death. Also incubation with receptor tyrosine kinase inhibitors, such as anti-leukaemic drugs blocking the stem cell factor receptor (c-kit), showed similar effects, hinting that IL-3 transmodulates c-kit phosphorylation. These mechanisms may play an important role in acute myeloid leukaemia treatment, representing a novel therapeutic target.

Protein kinase WNK1 promotes cell surface expression of glucose transporter GLUT1 by regulating a Tre-2/USP6-BUB2-Cdc16 domain family member 4 (TBC1D4)-Rab8A complex

One mechanism by which mammalian cells regulate the uptake of glucose is the number of glucose transporter proteins (GLUT) present at the plasma membrane. In insulin-responsive cells types, GLUT4 is released from intracellular stores through inactivation of the Rab GTPase activating protein Tre-2/USP6-BUB2-Cdc16 domain family member 4 (TBC1D4) (also known as AS160). Here we describe that TBC1D4 forms a protein complex with protein kinase WNK1 in human embryonic kidney (HEK293) cells. We show that WNK1 phosphorylates TBC1D4 in vitro and that the expression levels of WNK1 in these cells regulate surface expression of the constitutive glucose transporter GLUT1. WNK1 was found to increase the binding of TBC1D4 to regulatory 14-3-3 proteins while reducing its interaction with the exocytic small GTPase Rab8A. These effects were dependent on the catalytic activity because expression of a kinase-dead WNK1 mutant had no effect on binding of 14-3-3 and Rab8A, or on surface GLUT1 levels. Together, the data describe a pathway regulating constitutive glucose uptake via GLUT1, the expression level of which is related to several human diseases.

Hemoglobin level predicts outcome for vulvar cancer patients independent of GLUT-1 and CA-IX expression in tumor tissue

Intratumoral hypoxia has been associated with poor prognosis in several solid tumors. The aim of this study was to determine whether the hypoxia-associated markers glucose transporter (GLUT)-1 and carbonic anhydrase (CA)-IX expression and preoperative hemoglobin (Hb) levels correlate with presence of inguinofemoral or distant metastases, and disease-free survival (DSS) in vulvar squamous cell carcinoma (SCC) patients. Vulvar SCC (n = 103) were reviewed for histopathological characteristics by an expert gynecopathologist and stained for GLUT-1 and CA-IX. Clinical data and preoperative Hb levels were obtained from medical records. No significant correlations were observed between GLUT-1 or CA-IX expression patterns and preoperative Hb levels, presence of inguinofemoral or distant metastases and DSS. However, anemic patients (Hb < 11.2 g/dL) had significantly more inguinofemoral metastases and lower Hb level was an independent prognostic factor for a worse DSS (p < 0.001). The number of comorbidic conditions was inversely correlated with preoperative Hb level. Preoperative Hb levels are associated with poor DSS for vulvar SCC patients, whereas tumor hypoxia reflected by GLUT-1 and CA-IX expression does not have a predictive value. Because preoperative Hb levels inversely correlated with the number of comorbidic conditions and not with GLUT-1 or CA-IX expression, it is most likely that preoperative Hb levels represent overall physical condition.

Studies of insulin resistance in patients with clinical and subclinical hyperthyroidism

OBJECTIVE

Although clinical hyperthyroidism (HR) is associated with insulin resistance, the information on insulin action in subclinical hyperthyroidism (SHR) is limited.

DESIGN AND METHODS

To investigate this, we assessed the sensitivity of glucose metabolism to insulin in vivo (by an oral glucose tolerance test) and in vitro (by measuring insulin-stimulated rates of glucose transport in isolated monocytes) in 12 euthyroid subjects (EU), 16 patients with HR, and 10 patients with SHR.

RESULTS

HR and SHR patients displayed higher postprandial glucose levels (area under the curve, AUC(0)(-)(300) 32,190±1067 and 31,497±716,mg/dl min respectively) versus EU (27,119±1156 mg/dl min, P<0.05). HR but not SHR patients displayed higher postprandial insulin levels (AUC(0)(-)(300) 11,020±985 and 9565±904 mU/l min respectively) compared with EU subjects (AUC(0)(-)(300) 7588±743 mU/l min, P<0.05). Homeostasis model assessment index was increased in HR and SHR patients (2.81±0.3 and 2.43±0.38 respectively) compared with EU subjects (1.27±0.16, P<0.05), while Matsuda and Belfiore indices were decreased in HR (4.21±0.41 and 0.77±0.05 respectively, P<0.001) and SHR patients (4.47±0.33 and 0.85±0.05 respectively, P<0.05 versus EU (7.76±0.87 and 1 respectively). At 100 μU/ml insulin, i) GLUT3 levels on the monocyte plasma membrane were increased in HR (468.8±7 mean fluorescence intensity (MFI)) and SHR patients (522.2±25 MFI) compared with EU subjects (407±18 MFI, P<0.01 and P<0.05 respectively), ii) glucose transport rates in monocytes (increases from baseline) were decreased in HR patients (37.8±5%) versus EU subjects (61.26±10%, P<0.05).

CONCLUSIONS

Insulin-stimulated glucose transport in isolated monocytes of patients with HR was decreased compared with EU subjects. Insulin resistance was comparable in patients with both HR and SHR.

Early reduction of glucose uptake after cisplatin treatment is a marker of cisplatin sensitivity in ovarian cancer

Cisplatin is an effective chemotherapeutic agent for ovarian cancer, but the sensitivity of cancers differs in individual cases. Because cisplatin is reported to suppress glucose uptake, we investigated the correlation between glucose uptake and sensitivity to the drug. A fluorescent derivative of D-glucose, 2-NBDG (2-[N-(7-nitrobenz-2-oxa-1,3-diaxol-4-yl) amino]-2-deoxyglucose), was used to evaluate glucose uptake. Two ovarian cancer cell lines, SKOV-3 as a relatively resistant line and OVCAR-3 as a relatively sensitive line, were analyzed. Both cell lines had a decreased number of cells accompanied by cell death 24 h after cisplatin treatment, but not at 3 h. In contrast, glucose uptake was decreased 3 h after high-dose cisplatin treatment, which correlated with the sensitivity to the drug at 24 h. The protein levels of glucose transporter 1 (GLUT1) did not change with cisplatin treatment. In contrast, the membrane localization of GLUT1 disappeared after cisplatin treatment. Other cisplatin-resistant cell lines did not show an early decrease in glucose uptake after cisplatin treatment. The early decrease in glucose uptake and later cell death also correlated in cultured cancer cells from ovarian cancer patients. Thus, the decrease in glucose uptake at an early time point after high dose cisplatin treatment reflected cisplatin chemosensitivity in ovarian cancer cells. Measuring glucose uptake might be useful as a rapid evaluation of cisplatin chemosensitivity in ovarian cancer patients.

DNA damage-induced modulation of GLUT3 expression is mediated through p53-independent extracellular signal-regulated kinase signaling in HeLa cells

Many cancer cells exhibit increased rates of uptake and metabolism of glucose compared with normal cells. Glucose uptake in mammalian cells is mediated by the glucose transporter (GLUT) family. Here, we report that DNA-damaging anticancer agents such as Adriamycin and etoposide suppressed the expression of GLUT3, but not GLUT1, in HeLa cells and a tumorigenic HeLa cell hybrid. Suppression of GLUT3 expression determined by the real-time PCR was also evident with another DNA-damaging agent, camptothecin, which reduced the promoter's activity as determined with a luciferase-linked assay. The suppression by these agents seemed to be induced independently of p53, and it was evident when wild-type p53 was overproduced in these cells. In contrast, the mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) kinase (MEK) inhibitor U0126 (but not the phosphoinositide 3-kinase inhibitor LY294002) prevented the drug-induced suppression as determined by reverse transcription-PCR and promoter assays. Furthermore, overexpression of GLUT3 in HeLa cell hybrids increased resistance to these drugs, whereas depletion of the gene by small interfering RNA rendered the cells more sensitive to the drugs, decreasing glucose consumption. The results suggest that DNA-damaging agents reduce GLUT3 expression in cancer cells through activation of the MEK-ERK pathway independently of p53, leading to cell death or apoptosis. The findings may contribute to the development of new chemotherapeutic drugs based on the GLUT3-dependent metabolism of glucose.

Proliferating cell nuclear antigen in the cytoplasm interacts with components of glycolysis and cancer

Proliferating cell nuclear antigen (PCNA) is involved in a wide range of functions in the nucleus. However, a substantial amount of PCNA is also present in the cytoplasm, although their function is unknown. Here we show, through Far-Western blotting and mass spectrometry, that PCNA is associated with several cytoplasmic oncoproteins, including elongation factor, malate dehydrogenase, and peptidyl-prolyl isomerase. Surprisingly, PCNA is also associated with six glycolytic enzymes that are involved in the regulation of steps 4-9 in the glycolysis pathway.

The XbaI G>T polymorphism of the glucose transporter 1 gene modulates 18F-FDG uptake and tumor aggressiveness in breast cancer

We investigated the relevance of single-nucleotide polymorphisms (SNPs) in the glucose transporter 1 (GLUT1) gene to the uptake of (18)F-FDG and tumor aggressiveness in breast cancer.

METHODS

In 52 individuals with breast cancer, a diagnostic PET/CT scan was obtained, and the standardized uptake value was determined as a measure of (18)F-FDG uptake using a region-of-interest technique. Three GLUT1 SNPs (XbaI G>T, HpyCH4V A>T, and HaeIII T>C) were investigated in genomic DNA that was isolated from the paraffin-embedded specimens of all patients. Tumors were typed and graded according to the World Health Organization classifications.

RESULTS

The GG genotype of the XbaI G>T SNP was associated with increased tumor uptake of (18)F-FDG, with a mean standardized uptake value of 11.7 (TT/GT genotypes, 5.9; P = 0.03). Furthermore, the GG genotype was positively related to enhanced tumor proliferation (mitotic count, P = 0.01). In line with this finding, the GG genotype was absent in grade 1 carcinomas and increasingly prevalent in tumors with higher malignancy (grade 2, 28.0%; grade 3, 50%; P = 0.04).

CONCLUSION

This study found that the XbaI G>T SNP of the GLUT1 gene is associated with an increased (18)F-FDG uptake and a more advanced tumor grade or growth in breast cancer. Thus, this genetic variant might favor aggressive phenotypes by modulating the efficiency of cancer cells to recruit glucose and escalate growth rate, suggesting the XbaI G>T SNP as a proliferation-related prognostic factor.

Variable 18F-fluorodeoxyglucose uptake in gastric cancer is associated with different levels of GLUT-1 expression

OBJECTIVES

Detection rates of gastric cancer in F-fluorodeoxyglucose (FDG)-PET depend on the histopathological characteristics of the primary tumor. To clarify this observation, FDG uptake in gastric carcinoma was analyzed by focusing on histopathology and on the expression of the glucose transporter (GLUT-1) in the primary tumor.

METHODS

Thirty-five patients with the diagnosis of gastric cancer underwent FDG-PET with visual image analysis and measurement of maximum standardized uptake value (SUV(max)) before surgical treatment. Resected tumor samples were categorized according to Union internationale contre le cancer, WHO, and Laurén classification and tumor differentiation. GLUT-1 expression was graded semiquantitatively by immunohistochemistry. Statistical analysis was done for the correlation of histology, different classifications, and tumor grading with SUV(max) and GLUT-1 expression.

RESULTS

SUV(max) significantly correlated with histopathological classifications according to the WHO (P=0.009) and Laurén classification (P=0.034). Signet-ring cell carcinoma had a median SUV(max) of only 3.0 (range, 1.0-11.5). Median SUV(max) for papillary and tubular carcinoma was 7.8 (range, 1.8-14.4). In 21 (60%) cases, GLUT-1 expression in the primary tumor was positive. GLUT-1 expression correlated significantly with tumor differentiation (P=0.018) and the classification according to Laurén (P=0.023) and WHO (P<0.001). Thirteen (76%) of 17 signet-ring cell carcinoma cases did not show any GLUT-1 expression. SUV(max) in relation to GLUT-1 expression showed a significant correlation (P=0.002). For cases with detectable GLUT-1 expression the median SUV(max) was 6.9 (range, 2.3-14.1) versus a median of 3.1 (range, 1-8.8) for cases without GLUT-1 expression.

CONCLUSION

FDG uptake in gastric cancer depends on GLUT-1 expression. One major reason for low FDG uptake in signet-ring cell carcinoma is the low GLUT-1 expression in this histological subtype of gastric cancer.

Para-hydrogenated glucose derivatives as potential 13C-hyperpolarized probes for magnetic resonance imaging

A set of molecules in which a glucose moiety is bound to a hydrogenable synthon has been synthesized and evaluated for hydrogenation reactions and for the corresponding para-hydrogen-induced polarization (PHIP) effects, in order to select suitable candidates for an in vivo magnetic resonance imaging (MRI) method for the assessment of glucose cellular uptake. It has been found that amidic derivatives do not yield any polarization enhancement, probably due to singlet-triplet state mixing along the reaction pathway. In contrast, ester derivatives are hydrogenated in high yield and afford enhanced (1)H and (13)C NMR spectra after para-hydrogenation. The obtained PHIP patterns are discussed and explained on the basis of the calculated spin level populations in the para-hydrogenated products. These molecules may find interesting applications in (13)C MRI as hyperpolarized probes for assessing the activity of glucose transporters in cells.

Ifosfamide metabolite chloroacetaldehyde inhibits cell proliferation and glucose metabolism without decreasing cellular ATP content in human breast cancer cells MCF-7

Chloroacetaldehyde (CAA), a product of hepatic metabolism of the widely used anticancer drug ifosfamide (IFO), has been reported to decrease cancer cell proliferation. The basis of this effect is not completely known but has been attributed to a drop of cellular ATP content. Given the importance of glucose metabolism and of the 'Warburg effect' in cancer cells, we examined in the present study the ability of CAA to inhibit cancer cell proliferation by altering the glycolytic pathway. Cell proliferation, ATP content, glucose transport and metabolism as well as the activities of the main enzymes of glycolysis were determined in human breast cancer cells MCF-7 in the presence of various CAA concentrations (5-50 microm). Our results show that low CAA concentrations inhibited cell proliferation in a concentration-dependent manner. This inhibition was explained by a decrease in glucose utilization. Cellular ATP content was not reduced but even increased with 25 microm CAA. The inhibition of glucose metabolism was mainly explained by the decrease in glucose transport and hexokinase activity. The activity of glyceraldehyde-3-phosphate dehydrogenase, but not that of phosphofructokinase, was also inhibited. Glycolysis inhibition by CAA was effective in decreasing the proliferation of MCF-7 cells. Interestingly, this decrease was not due to ATP depletion; rather, it was linked to a drop of biosynthetic precursors from glycolytic intermediates. This CAA-induced inhibition of cell proliferation suggests that it might play a role in the antitumor activity of IFO.

Small compound inhibitors of basal glucose transport inhibit cell proliferation and induce apoptosis in cancer cells via glucose-deprivation-like mechanisms

Cancer cells depend heavily on glucose as both energy and biosynthesis sources and are found to upregulate glucose transport and switch their main energy supply pathway from oxidative phosphorylation to glycolysis. These molecular and metabolic changes also provide targets for cancer treatment. Here we report that novel small molecules inhibited basal glucose transport and cell proliferation, and induced apoptosis in lung and breast cancer cells without affecting much their normal cell counterparts. Cancer cells survived the compound treatment lost their capability to proliferate. Mechanistic study indicates that the cancer cell inhibition by the test compounds has a component of apoptosis and the induced apoptosis was p53-independent and caspase 3-dependent, similar to those resulted from glucose deprivation. Compound treatment also led to cell cycle arrest in G1/S phase. The inhibition of cancer cell growth was partially relieved when additional glucose was supplied to cells, suggesting that the inhibition was due to, at least in part, the inhibition of basal glucose transport. When used in combination, the test compounds demonstrated synergistic effects with anticancer drugs cisplatin or paclitaxel in inhibition of cancer cell growth. All these results suggest that these glucose transport inhibitors mimic glucose deprivation and work through inhibiting basal glucose transport. These inhibitors have the potential to complement and replace traditional glucose deprivation, which cannot be used in animals, as new tools to study the effects of glucose transport and metabolism on cancer and normal cells.

The human cancer and stem cell marker podocalyxin interacts with the glucose-3-transporter in malignant pluripotent stem cells

Podocalyxin, an integral plasma membrane cell-adhesion glycoprotein, is a marker of human pluripotent and multipotent stem cells. Podocalyxin is also a marker of many types of cancers and its expression correlates with an aggressive and poor-prognosis tumor phenotype. The function of podocalyxin in stem cells and malignant cells is unknown. Protein sequence data obtained from purified podocalyxin protein isolated from embryonal carcinoma cancer stem cells reveals peptide sequence data for the glucose-3-transporter. Protein-precipitation experiments of embryonal carcinoma protein extracts identify a podocalyxin/glucose-3-transporter protein complex. Cell imaging studies demonstrate co-localization of podocalyxin and glucose-3-transporter and confirm the interaction in vivo. Finally, siRNA podocalyxin-knockdown experiments show decreased expression levels of the glucose-3-transporter. These findings suggest a novel interaction of the glucose-3-transporter and the cell-adhesion protein podocalyxin. In pluripotent stem cells and in human cancer disease, podocalyxin may function in part to regulate and maintain the cell surface expression of the glucose-3-transporter.

Cellular pathways for transport and efflux of ascorbate and dehydroascorbate

The mechanisms allowing the cellular transport of ascorbic acid represent a primary aspect for the understanding of the roles played by this vitamin in pathophysiology. Considerable research effort has been spent in the field, on several animal models and different cell types. Several mechanisms have been described to date, mediating the movements of different redox forms of ascorbic acid across cell membranes. Vitamin C can enter cells both in its reduced and oxidized form, ascorbic acid (AA) and dehydroascorbate (DHA), utilizing respectively sodium-dependent transporters (SVCT) or glucose transporters (GLUT). Modulation of SVCT expression and function has been described by cytokines, steroids and post-translational protein modification. Cellular uptake of DHA is followed by its intracellular reduction to AA by several enzymatic and non-enzymatic systems. Efflux of vitamin C has been also described in a number of cell types and different pathophysiological functions were proposed for this phenomenon, in dependence of the cell model studied. Cellular efflux of AA is mediated through volume-sensitive (VSOAC) and Ca(2+)-dependent anion channels, gap-junction hemichannels, exocytosis of secretory vesicles and possibly through homo- and hetero-exchange systems at the plasma membrane level. Altogether, available data suggest that cellular efflux of ascorbic acid - besides its uptake - should be taken into account when evaluating the cellular homeostasis and functions of this important vitamin.

Evolutionary ancestry and novel functions of the mammalian glucose transporter (GLUT) family

Background

In general, sugar porters function by proton-coupled symport or facilitative transport modes. Symporters, coupled to electrochemical energy, transport nutrients against a substrate gradient. Facilitative carriers transport sugars along a concentration gradient, thus transport is dependent upon extracellular nutrient levels. Across bacteria, fungi, unicellular non-vertebrates and plants, proton-coupled hexose symport is a crucial process supplying energy under conditions of nutrient flux. In mammals it has been assumed that evolution of whole body regulatory mechanisms would eliminate this need. To determine whether any isoforms bearing this function might be conserved in mammals, we investigated the relationship between the transporters of animals and the proton-coupled hexose symporters found in other species.

Results

We took a comparative genomic approach and have performed the first comprehensive and statistically supported phylogenetic analysis of all mammalian glucose transporter (GLUT) isoforms. Our data reveals the mammalian GLUT proteins segregate into five distinct classes. This evolutionary ancestry gives insight to structure, function and transport mechanisms within the groups. Combined with biological assays, we present novel evidence that, in response to changing nutrient availability and environmental pH, proton-coupled, active glucose symport function is maintained in mammalian cells.

Conclusions

The analyses show the ancestry, evolutionary conservation and biological importance of the GLUT classes. These findings significantly extend our understanding of the evolution of mammalian glucose transport systems. They also reveal that mammals may have conserved an adaptive response to nutrient demand that would have important physiological implications to cell survival and growth.

Optical redox ratio differentiates breast cancer cell lines based on estrogen receptor status

Autofluorescence spectroscopy is a powerful imaging technique that exploits endogenous fluorophores. The endogenous fluorophores NADH and flavin adenine dinucleotide (FAD) are two of the principal electron donors and acceptors in cellular metabolism, respectively. The optical oxidation-reduction (redox) ratio is a measure of cellular metabolism and can be determined by the ratio of NADH/FAD. We hypothesized that there would be a significant difference in the optical redox ratio of normal mammary epithelial cells compared with breast tumor cell lines and that estrogen receptor (ER)-positive cells would have a higher redox ratio than ER-negative cells. To test our hypothesis, the optical redox ratio was determined by collecting the fluorescence emission for NADH and FAD via confocal microscopy. We observed a statistically significant increase in the optical redox ratio of cancer compared with normal cell lines (P < 0.05). Additionally, we observed a statistically significant increase in the optical redox ratio of ER(+) breast cancer cell lines. The level of ESR1 expression, determined by real-time PCR, directly correlated with the optical redox ratio (Pearson's correlation coefficient = 0.8122, P = 0.0024). Furthermore, treatment with tamoxifen and ICI 182,870 statistically decreased the optical redox ratio of only ER(+) breast cancer cell lines. The results of this study raise the important possibility that fluorescence spectroscopy can be used to identify subtypes of breast cancer based on receptor status, monitor response to therapy, or potentially predict response to therapy. This source of optical contrast could be a potentially useful tool for drug screening in preclinical models.

Metronomic administration of the drug GMX1777, a cellular NAD synthesis inhibitor, results in neuroblastoma regression and vessel maturation without inducing drug resistance

High-risk neuroblastoma is a rapidly growing tumor with a survival rate below 50%. A new treatment strategy is to administer chemotherapeutic drugs metronomically, i.e., at lower doses and frequent intervals. The aim of the study was to investigate the effects of GMX1777, a chemotherapeutic drug affecting cellular energy metabolism, in a mouse model for high-risk neuroblastoma. Female SCID mice were injected s.c. with MYCN-amplified human neuroblastoma cells and randomized to either treatment with GMX1777 or vehicle. In some animals, treatment was discontinued allowing tumor relapse. Treatment response was evaluated using the pediatric preclinical testing program (PPTP). Immunohistochemistry and qRT-PCR was performed on tumor cryosections to investigate the microscopic and molecular changes in tumors in response to GMX1777. Despite an increase in vessel density, tumor regression and a high group response score according to PPTP criteria was induced by GMX1777 without inducing drug resistance. Treatment resulted in inhibition of tumor cell proliferation, vessel maturation, reduced hypoxia, increased infiltration of MHC class II negative macrophages and expansion of the nonvascular stromal compartment. Decreased stromal VEGF-A and PDGF-B mRNA in response to treatment together with the structural data suggest a "deactivation" or "silencing" of the tumor stroma as a paracrine entity. In conclusion, GMX1777 was highly efficient against high-risk neuroblastoma xenografts through modulation of both the tumor cell and stromal compartment.

Research resource: expression profiling reveals unexpected targets and functions of the human steroid receptor RNA activator (SRA) gene

The human steroid receptor RNA activator (SRA) gene encodes both noncoding RNAs (ncRNAs) and protein-generating isoforms. In reporter assays, SRA ncRNA enhances nuclear receptor and myogenic differentiation 1 (MyoD)-mediated transcription but also participates in specific corepressor complexes, serving as a distinct scaffold. That SRA RNA levels might affect some biological functions, such as proliferation, apoptosis, steroidogenesis, and myogenesis, has been reported. However, the breadth of endogenous target genes that might be regulated by SRA RNAs remains largely unknown. To address this, we depleted SRA RNA in two human cancer cell lines with small interfering RNAs and then assayed for changes in gene expression by microarray analyses. The majority of significantly changed genes were reduced upon SRA knockdown, implicating SRA RNAs as endogenous coactivators. Unexpectedly, only a small subset of direct estrogen receptor-alpha target genes was affected in estradiol-treated MCF-7 cells. Eight bona fide SRA downstream target genes were identified (SLC2A3, SLC2A12, CCL20, TGFB2, DIO2, TMEM65, TBL1X, and TMPRSS2), representing entirely novel SRA targets, except for TMPRSS2. These data suggest unanticipated roles for SRA in glucose uptake, cellular signaling, T(3) hormone generation, and invasion/metastasis. SRA depletion in MDA-MB-231 cells reduced invasiveness and expression of some genes critical for this process. Consistent with the knockdown data, overexpressed SRA ncRNA coactivates certain target promoters and may enhance the activity of some coregulatory proteins. This study is a valuable resource because it represents the first genome-wide analysis of a mammalian RNA coregulator.

Dynamic alteration of protein expression profiles during neoplastic transformation of rat hepatic oval-like cells

To explore the molecular basis of neoplastic transformation of hepatic oval cells, a proteomic strategy was utilized to examine the global protein expression alterations during neoplastic transformation of rat hepatic oval-like cells. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-initiated WB-F344 cells were treated with H(2)O(2) for neoplastic transformation. The transformed cells were identified by soft agar assay and MTT assay. The subsequent proteomic separation and identification were performed with 2-DE followed by MALDI-TOF-MS/MS analysis. Of the 148 differentially displayed protein spots analyzed, 121 spots representing 79 distinct proteins were finally identified. The expression levels of interested proteins were validated by western blotting including 40 S ribosomal protein A (RPSA) and cytokeratin 8. Bioinformatics annotations indicated that these identified proteins were enriched with oxidoreduction and stress response; transcription, translation, and protein processing; and energy/metabolism functions. Interestingly, 17 of the identified proteins were also found to be involved in early hepatic differentiation of mouse embryonic stem (ES) cells in our previous study. Twenty-six proteins had been reported as being dysregulated in hepatocellular carcinoma and other cancers. It suggested that these changed proteins may be implicated in neoplastic transformation of WB-F344 cells. The results may provide some clues for understanding the molecular mechanisms of hepatocarcinogenesis as viewed from dysregulation of differentiation.