Glycolytic enzymes from human neuroectodermal tumors of childhood

Evidence That Does Not Support Pyruvate Kinase M2 (PKM2)-catalyzed Reaction as a Rate-limiting Step in Cancer Cell Glycolysis

It has been recognized that the rate-limiting function of pyruvate kinase M2 (PKM2) in glycolysis plays an important role in distributing glycolytic intermediates for anabolic and catabolic purposes in cancer cells. However, after analysis of the catalytic capacity of PKM2 relative to other glycolytic enzymes, the regulation range of PKM2 activity, metabolic flux control, and thermodynamics, we suggest that the PKM2-catalyzed reaction is not a rate-limiting step in cancer cell glycolysis. Hexokinase and phosphofructokinase 1 (PFK1), the first and third enzyme along the pathway, are rate-limiting enzymes that limit the overall glycolytic rate, whereas PKM2 and lactate dehydrogenase, the last two enzymes in the pathway, are for the fast removal of upstream intermediates to prevent the obstruction of the pathway. The argument is in accordance with the catalytic capacity of glycolytic enzymes, regulation range of enzyme activities, metabolic flux control, and thermodynamics.

Differentiation of human neuroblastoma cells toward the osteogenic lineage by mTOR inhibitor

Current hypothesis suggest that tumors can originate from adult cells after a process of 'reprogramming' driven by genetic and epigenetic alterations. These cancer cells, called cancer stem cells (CSCs), are responsible for the tumor growth and metastases. To date, the research effort has been directed to the identification, isolation and manipulation of this cell population. Independently of whether tumors were triggered by a reprogramming of gene expression or seeded by stem cells, their energetic metabolism is altered compared with a normal cell, resulting in a high aerobic glycolytic 'Warburg' phenotype and dysregulation of mitochondrial activity. This metabolic alteration is intricately linked to cancer progression.The aim of this work has been to demonstrate the possibility of differentiating a neoplastic cell toward different germ layer lineages, by evaluating the morphological, metabolic and functional changes occurring in this process. The cellular differentiation reported in this study brings to different conclusions from those present in the current literature. We demonstrate that 'in vitro' neuroblastoma cancer cells (chosen as experimental model) are able to differentiate directly into osteoblastic (by rapamycin, an mTOR inhibitor) and hepatic lineage without an intermediate 'stem' cell step. This process seems owing to a synergy among few master molecules, metabolic changes and scaffold presence acting in a concerted way to control the cell fate.

Comparative analysis of some aspects of mitochondrial metabolism in differentiated and undifferentiated neuroblastoma cells

The aim of the present study is to clarify some aspects of the mechanisms of regulation of mitochondrial metabolism in neuroblastoma (NB) cells. Experiments were performed on murine Neuro-2a (N2a) cell line, and the same cells differentiated by all-trans-retinoic acid (dN2a) served as in vitro model of normal neurons. Oxygraphy and Metabolic Control Analysis (MCA) were applied to characterize the function of mitochondrial oxidative phosphorylation (OXPHOS) in NB cells. Flux control coefficients (FCCs) for components of the OXPHOS system were determined using titration studies with specific non-competitive inhibitors in the presence of exogenously added ADP. Respiration rates of undifferentiated Neuro-2a cells (uN2a) and the FCC of Complex-II in these cells were found to be considerably lower than those in dN2a cells. Our results show that NB is not an exclusively glycolytic tumor and could produce a considerable part of ATP via OXPHOS. Two important enzymes - hexokinase-2 and adenylate kinase-2 can play a role in the generation of ATP in NB cells. MCA has shown that in uN2a cells the key sites in the regulation of OXPHOS are complexes I, II and IV, whereas in dN2a cells complexes II and IV. Results obtained for the phosphate and adenine nucleotide carriers showed that in dN2a cells these carriers exerted lower control over the OXPHOS than in undifferentiated cells. The sum of FCCs for both types of NB cells was found to exceed significantly that for normal cells suggesting that in these cells the respiratory chain was somehow reorganized or assembled into large supercomplexes.

The expression of ketohexokinase is diminished in human clear cell type of renal cell carcinoma

For identification and targeting of tumor-associated marker proteins, the proteome of clear cell type of renal cell carcinoma (RCC) and normal kidney tissues was analyzed by 2-DE. Ketohexokinase (also called fructokinase), which catalyzes the phosphorylation of fructose to fructose 1-phosphate, was identified by MALDI-TOF MS and found to be expressed at low rates in the renal tumor tissues. We found a decreased amount of ketohexokinase mRNA in RCC compared to that observed in the normal kidney tissues by Northern blot. The activity of ketohexokinase in 20 clear cell RCC specimens and the 20 corresponding normal kidneys was investigated, and its activity was shown to be approximately 1.4-fold lower in the RCC specimens than in the normal kidney. Ketohexokinase activity in tumor stage pT3 RCC was 1.5-fold lower than in pT1 RCC. The level of ketohexokinase activity in histological grade 3 RCC was 1.8-fold lower than that in grade 1 cancer. In addition, using in situ hybridization, it was revealed that ketohexokinase in the normal kidney tissue was confined to the proximal tubular epithelial cells, while the expression of ketohexokinase in RCC tissues was extremely low. Our research results show that the expression of human ketohexokinase was diminished in clear cell RCC.

Identification of proteins differentially expressed in the conventional renal cell carcinoma by proteomic analysis

Renal cell carcinoma (RCC) is one of the most malignant tumors in urology, and due to its insidious onset patients frequently have advanced disease at the time of clinical presentation. Thus, early detection is crucial in management of RCC. To identify tumor specific proteins of RCC, we employed proteomic analysis. We prepared proteins from conventional RCC and the corresponding normal kidney tissues from seven patients with conventional RCC. The expression of proteins was determined by silver stain after two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). The overall protein expression patterns in the RCC and the normal kidney tissues were quite similar except some areas. Of 66 differentially expressed protein spots (p<0.05 by Student t-test), 8 different proteins from 11 spots were identified by MALDI-TOF-MS. The expression of the following proteins was repressed (p<0.05); aminoacylase-1, enoyl-CoA hydratase, aldehyde reductase, tropomyosin alpha-4 chain, agmatinase and ketohexokinase. Two proteins, vimentin and alpha-1 antitrypsin precursor, were dominantly expressed in RCC (p<0.05).

Kinetic characterization of hexokinase isoenzymes from glioma cells: implications for FDG imaging of human brain tumors

Quantitative imaging of glucose metabolism of human brain tumors with PET utilizes 2-[(18)F]-fluorodeoxy-D-glucose (FDG) and a conversion factor called the lumped constant (LC), which relates the metabolic rate of FDG to glucose. Since tumors have greater uptake of FDG than would be predicted by the metabolism of native glucose, the characteristic of tumors that governs the uptake of FDG must be part of the LC. The LC is chiefly determined by the phosphorylation ratio (PR), which is comprised of the kinetic parameters (Km and Vmax) of hexokinase (HK) for glucose as well as for FDG (LC proportional to (Km(glc) x Vmax(FDG))/(Km(FDG) x Vmax(glc)). The value of the LC has been estimated from imaging studies, but not validated in vitro from HK kinetic parameters. In this study we measured the kinetic constants of bovine and 36B-10 rat glioma HK I (predominant in normal brain) and 36B-10 glioma HK II (increased in brain tumors) for the hexose substrates glucose, 2-deoxy-D-glucose (2DG) and FDG. Our principal results show that the KmGlc < KmFDG << Km2DG and that PR2DG < PRFDG. The FDG LC calculated from our kinetic parameters for normal brain, possessing predominantly HK I, would be higher than the normal brain LC predicted from animal studies using 2DG or human PET studies using FDG or 2DG. These results also suggest that a shift from HK I to HK II, which has been observed to increase in brain tumors, would have little effect on the value of the tumor LC.

Expression of glucose transporter isoforms (GLUT1, GLUT2) and activities of hexokinase, pyruvate kinase, and malic enzyme in preneoplastic and neoplastic rat renal basophilic cell lesions

Sequential changes in the expression of two glucose transporter isoforms (GLUT1, GLUT2), and in the activities of hexokinase, pyruvate kinase and malic enzyme during the development of rat renal basophilic cell tumors were studied using histochemical techniques. Early basophilic cell tubules are similar to proximal convoluted tubules (PCT) in their overall histochemical pattern, particularly in the expression of glucose transporters, suggesting that basophilic cell tubules and tumors derived from them arise from PCT. In comparison with PCT, basophilic cell tubules show slightly increased activities of all the enzymes studied. In basophilic cell tumors, markedly elevated hexokinase and pyruvate kinase activities are accompanied by a considerable reduction in the expression of GLUT2. GLUT1 expression is not found in basophilic cell tubules or PCT. Small basophilic cell tumors also do not express GLUT1, but GLUT1 is regularly expressed in several cell layers surrounding necrotic areas within large basophilic cell tumors. Our results indicate that increased glycolytic activity and reduced GLUT2 expression take place during the development of renal basophilic cell tumors.

Deoxyglucose lumped constant estimated in a transplanted rat astrocytic glioma by the hexose utilization index

The lumped constant (LC) for calculating the regional glucose (glc) metabolic rate by the deoxyglucose (DG) method was estimated in a transplanted rat glioma and normal rat brain. First, the hexose utilization index (HUI) was measured at 1.5, 3.0, and 4.5 min in right hemisphere glioma implants and uninvolved contralateral hemisphere following bolus intravenous injections of [3H]DG and [14C]glucose. At these times, the glioma HUI values were 0.639, 0.732, and 0.712, respectively, and the coordinate left hemisphere values were 0.432, 0.449, and 0.418. Second, the volumes of distribution of DG and glucose were determined to be 0.436 and 0.235 in glioma implants and 0.402 and 0.237 in left hemisphere, respectively. Third, following simultaneous intracarotid injections of [3H]DG and [14C]glucose, the ratio K1/K1 was 1.1 in glioma grafts and 1.3 in left hemisphere. With these values for HUI, volume of distribution, and K1 ratio, the LC in this rat glioma was estimated to be 2.1 times higher than the left hemisphere LC (p less than 0.02). These results suggest that measurement of brain tumor CMRglc using a normal brain LC may significantly overestimate the true tumor CMRglc.