Analysis of phosphofructokinase subunits and isozymes in ascites tumor cells and its original tissue, murine mammary gland

A positive feedback loop between PFKP and c-Myc drives head and neck squamous cell carcinoma progression

BACKGROUND

The aberrant expression of phosphofructokinase-platelet (PFKP) plays a crucial role in the development of various human cancers by modifying diverse biological functions. However, the precise molecular mechanisms underlying the role of PFKP in head and neck squamous cell carcinoma (HNSCC) are not fully elucidated.

METHODS

We assessed the expression levels of PFKP and c-Myc in tumor and adjacent normal tissues from 120 HNSCC patients. A series of in vitro and in vivo experiments were performed to explore the impact of the feedback loop between PFKP and c-Myc on HNSCC progression. Additionally, we explored the therapeutic effects of targeting PFKP and c-Myc in HNSCC using Patient-Derived Organoids (PDO), Cell Line-Derived Xenografts, and Patients-Derived Xenografts.

RESULTS

Our findings indicated that PFKP is frequently upregulated in HNSCC tissues and cell lines, correlating with poor prognosis. Our in vitro and in vivo experiments demonstrate that elevated PFKP facilitates cell proliferation, angiogenesis, and metastasis in HNSCC. Mechanistically, PFKP increases the ERK-mediated stability of c-Myc, thereby driving progression of HNSCC. Moreover, c-Myc stimulates PFKP expression at the transcriptional level, thus forming a positive feedback loop between PFKP and c-Myc. Additionally, our multiple models demonstrate that co-targeting PFKP and c-Myc triggers synergistic anti-tumor effects in HNSCC.

CONCLUSION

Our study demonstrates the critical role of the PFKP/c-Myc positive feedback loop in driving HNSCC progression and suggests that simultaneously targeting PFKP and c-Myc may be a novel and effective therapeutic strategy for HNSCC.

Acetyltransferase P300 Regulates Glucose Metabolic Reprogramming through Catalyzing Succinylation in Lung Cancer

Aberrant protein post-translational modification is a hallmark of malignant tumors. Lysine succinylation (Ksucc) plays a vital role in cell energy metabolism in various cancers. However, whether succinylation can be catalyzed by acetyltransferase p300 remains unclear. In this study, we unveiled that p300 is a "writer" for succinylation, and p300-mediated Ksucc promotes cell glycometabolism in lung adenocarcinoma (LUAD). Specifically, our succinylome data revealed that EP300 deficiency leads to the systemic reduction of Ksucc, and 79.55% of the p300-succinylated proteins were found in the cytoplasm, which were primarily enriched in the carbohydrate metabolism process. Interestingly, deleting EP300 led to a notable decrease in Ksucc levels on several glycolytic enzymes, especially Phosphoglycerate Kinase 1 (PGK1). Mutation of the succinylated site of PGK1 notably hindered cell glycolysis and lactic acid excretion. Metabolomics in vivo indicated that p300-caused metabolic reprogramming was mainly attributed to the altered carbohydrate metabolism. In addition, 89.35% of LUAD patients exhibited cytoplasmic localization of p300, with higher levels in tumor tissues than adjacent normal tissues. High levels of p300 correlated with advanced tumor stages and poor prognosis of LUAD patients. Briefly, we disclose the activity of p300 to catalyze succinylation, which contributes to cell glucose metabolic reprogramming and malignant progression of lung cancer.

PFKP: More than phosphofructokinase

Phosphofructokinase (PFK) is one of the key enzymes that functions in glycolysis. Studies show that PFKP regulates cell proliferation, apoptosis, autophagy, cell migration/metastasis, and stemness through glycolysis and glycolysis-independent functions. PFKP performs its function not only in the cytoplasm, but also at the cell membrane, on the mitochondria, at the lysosomal membrane, and in the nucleus. The functions of PFKP are extensively studied in cancer cells. PFKP is also highly expressed in certain immune cells; nevertheless, the study of the PFKP's role in immune cells is limited. In this review, we summarize how the expression and activity of PFKP are regulated in cancer cells. PFKP may be applied as a prognostic marker due to its overexpression and significant functions in cancer cells. As such, specifically targeting/inhibiting PFKP may be a critical and promising strategy for cancer therapy.

Interleukin -1β Promotes Lung Adenocarcinoma Growth and Invasion Through Promoting Glycolysis via p38 Pathway

Background

There is a close relationship among inflammation, glycolysis, and tumors. The IL-1 family includes important inflammatory cytokines, among which IL-1β has been widely studied. In this study, we focused on the effect of IL-1β on glycolysis of lung adenocarcinoma (LUAD) cells in vivo and in vitro and explored its possible mechanisms.

Methods

A bioinformatic database and quantitative real-time PCR were used to analyze the expression of glycolysis-related enzyme genes and their correlations with IL1β in human LUAD samples. The human LUAD cell line A549 and Lewis lung carcinoma LLC cell line were stimulated with IL-1β. In vitro treatment effects, including glycolysis level, migration, and invasion were evaluated with a glucose assay kit, lactate assay kit, Western blotting, wound healing, and the transwell method. We established a mouse model of subcutaneous tumors using LLC cells pretreated with IL-1β and analyzed in vivo treatment effects through positron-emission tomography-computed tomography and staining. Virtual screening and molecular dynamic simulation were used to screen potential inhibitors of IL-1β.

Results

Our results showed that IL1β was positively correlated with the expression of glycolysis-related enzyme genes in LUAD. Glycolysis, migration, and invasion significantly increased in A549 and LLC stimulated with IL-1β. In vivo, IL-1β increased growth, mean standard uptake value, and pulmonary tumor metastasis, which were inhibited by the glycolysis inhibitor 2-deoxy-D-glucose and p38-pathway inhibitors. Small molecular compound ZINC14610053 was suggested being a potential inhibitor of IL-1β.

Conclusion

IL-1β promotes glycolysis of LUAD cells through p38 signaling, further enhancing tumor-cell migration and invasion. These results show that IL-1β links inflammation to glycolysis in LUAD, and targeting IL-1β and the glycolysis pathway may be a potential therapeutic strategy for lung cancer.

Wnt signaling promotes tumor development in part through phosphofructokinase 1 platelet isoform upregulation

The activation of Wnt signaling has been detected in various types of human cancer and has been shown to be associated with cancer development. In the present study, it was revealed that Wnt signaling induced the expression of phosphofructokinase 1 platelet isoform (PFKP), which has been reported to catalyze a rate‑limiting reaction in glycolysis and is important for the Warburg effect, proliferation, colony formation and cancer cell migration. Moreover, it was demonstrated that Wnt3A induced PFKP expression in a β‑catenin‑independent manner, resulting in increased PFK enzyme activity. Wnt3A‑induced epidermal growth factor receptor transactivation activated PI3K/AKT, which stabilized PFKP through PFKP S386 phosphorylation and subsequent PFKP upregulation. Wnt3A‑induced PFKP S386 phosphorylation increased PFKP expression and promoted the Warburg effect, cell proliferation, colony formation and the migratory ability of cancer cells. On the whole, the findings of the present study underscore the potential role of PFKP in Wnt signaling‑induced tumor development.

Selective activation of PFKL suppresses the phagocytic oxidative burst

In neutrophils, nicotinamide adenine dinucleotide phosphate (NADPH) generated via the pentose phosphate pathway fuels NADPH oxidase NOX2 to produce reactive oxygen species for killing invading pathogens. However, excessive NOX2 activity can exacerbate inflammation, as in acute respiratory distress syndrome (ARDS). Here, we use two unbiased chemical proteomic strategies to show that small-molecule LDC7559, or a more potent designed analog NA-11, inhibits the NOX2-dependent oxidative burst in neutrophils by activating the glycolytic enzyme phosphofructokinase-1 liver type (PFKL) and dampening flux through the pentose phosphate pathway. Accordingly, neutrophils treated with NA-11 had reduced NOX2-dependent outputs, including neutrophil cell death (NETosis) and tissue damage. A high-resolution structure of PFKL confirmed binding of NA-11 to the AMP/ADP allosteric activation site and explained why NA-11 failed to agonize phosphofructokinase-1 platelet type (PFKP) or muscle type (PFKM). Thus, NA-11 represents a tool for selective activation of PFKL, the main phosphofructokinase-1 isoform expressed in immune cells.

Nuclear PFKP promotes CXCR4-dependent infiltration by T cell acute lymphoblastic leukemia

PFKP (phosphofructokinase, platelet), the major isoform of PFK1 expressed in T cell acute lymphoblastic leukemia (T-ALL), is predominantly expressed in the cytoplasm to carry out its glycolytic function. Our study showed that PFKP is a nucleocytoplasmic shuttling protein with functional nuclear export and nuclear localization sequences (NLSs). Cyclin D3/CDK6 facilitated PFKP nuclear translocation by dimerization and by exposing the NLS of PFKP to induce the interaction between PFKP and importin 9. Nuclear PFKP stimulated the expression of C-X-C chemokine receptor type 4 (CXCR4), a chemokine receptor regulating leukemia homing/infiltration, to promote T-ALL cell invasion, which depended on the activity of c-Myc. In vivo experiments showed that nuclear PFKP promoted leukemia homing/infiltration into the bone marrow, spleen, and liver, which could be blocked with CXCR4 antagonists. Immunohistochemical staining of tissues from a clinically well-annotated cohort of T cell lymphoma/leukemia patients showed nuclear PFKP localization in invasive cancers, but not in nonmalignant T lymph node or reactive hyperplasia. The presence of nuclear PFKP in these specimens correlated with poor survival in patients with T cell malignancy, suggesting the potential utility of nuclear PFKP as a diagnostic marker.

R-2-hydroxyglutarate attenuates aerobic glycolysis in leukemia by targeting the FTO/m6A/PFKP/LDHB axis

R-2-hydroxyglutarate (R-2HG), a metabolite produced by mutant isocitrate dehydrogenases (IDHs), was recently reported to exhibit anti-tumor activity. However, its effect on cancer metabolism remains largely elusive. Here we show that R-2HG effectively attenuates aerobic glycolysis, a hallmark of cancer metabolism, in (R-2HG-sensitive) leukemia cells. Mechanistically, R-2HG abrogates fat-mass- and obesity-associated protein (FTO)/N6-methyladenosine (m6A)/YTH N6-methyladenosine RNA binding protein 2 (YTHDF2)-mediated post-transcriptional upregulation of phosphofructokinase platelet (PFKP) and lactate dehydrogenase B (LDHB) (two critical glycolytic genes) expression and thereby suppresses aerobic glycolysis. Knockdown of FTO, PFKP, or LDHB recapitulates R-2HG-induced glycolytic inhibition in (R-2HG-sensitive) leukemia cells, but not in normal CD34+ hematopoietic stem/progenitor cells, and inhibits leukemogenesis in vivo; conversely, their overexpression reverses R-2HG-induced effects. R-2HG also suppresses glycolysis and downregulates FTO/PFKP/LDHB expression in human primary IDH-wild-type acute myeloid leukemia (AML) cells, demonstrating the clinical relevance. Collectively, our study reveals previously unrecognized effects of R-2HG and RNA modification on aerobic glycolysis in leukemia, highlighting the therapeutic potential of targeting cancer epitranscriptomics and metabolism.

MiR-302 Regulates Glycolysis to Control Cell-Cycle during Neural Tube Closure

Neural tube closure is a critical early step in central nervous system development that requires precise control of metabolism to ensure proper cellular proliferation and differentiation. Dysregulation of glucose metabolism during pregnancy has been associated with neural tube closure defects (NTDs) in humans suggesting that the developing neuroepithelium is particularly sensitive to metabolic changes. However, it remains unclear how metabolic pathways are regulated during neurulation. Here, we used single-cell mRNA-sequencing to analyze expression of genes involved in metabolism of carbon, fats, vitamins, and antioxidants during neurulation in mice and identify a coupling of glycolysis and cellular proliferation to ensure proper neural tube closure. Using loss of miR-302 as a genetic model of cranial NTD, we identify misregulated metabolic pathways and find a significant upregulation of glycolysis genes in embryos with NTD. These findings were validated using mass spectrometry-based metabolite profiling, which identified increased glycolytic and decreased lipid metabolites, consistent with a rewiring of central carbon traffic following loss of miR-302. Predicted miR-302 targets Pfkp, Pfkfb3, and Hk1 are significantly upregulated upon NTD resulting in increased glycolytic flux, a shortened cell cycle, and increased proliferation. Our findings establish a critical role for miR-302 in coordinating the metabolic landscape of neural tube closure.

Prognostic and therapeutic relevance of phosphofructokinase platelet-type (PFKP) in breast cancer

In the present study, we have explored the prognostic value of the Phosphofructokinase Platelet-type (PFKP) expression and its therapeutic relevance in metastatic breast cancer. PFKP immunohistochemistry was performed on Invasive ductal carcinomas (IDCs; n = 87) of breast, and its association with clinicopathological parameters were evaluated. Using online meta-analysis tools, PFKP's prognostic value was investigated in overall breast cancer as well as in triple negative subtype (TNBCs). For in vitro analysis, MDA-MB-231 cells model was used in order to elucidate mechanisms behind PFKP regulated glycolysis and its impact on cancer cell physiology. Therapeutic relevance of PFKP was further evaluated using PFKP siRNA and Quercetin. PFKP protein expression was found to be positively associated with nodal invasion (p = 0.009), receptor (ER & PR) negative status (p = 0.005 & p = 0.028) and reduced overall survival in breast cancer patients (p = 0.014). In MDA-MB-231 cells, quercetin treatment impaired PFKP-LDHA signaling axis thereby inhibiting aerobic glycolysis mediated increased migration of cancer cells. Our present study demonstrates that elevated PFKP levels are associated with basal cells/TNBC subtypes and might serve as prognostic indicator for TNBC patients. Ability of quercetin to inhibit aerobic glycolysis, cell migration and clonogenic potential of malignant breast cancer cells advocates possibility of quercetin in aggressive breast cancer treatment.

SIRT5 deficiency enhances the proliferative and therapeutic capacities of adipose-derived mesenchymal stem cells via metabolic switching

BACKGROUND

Mesenchymal stem cells (MSCs) have therapeutic potential for multiple ischemic diseases. However, in vitro expansion of MSCs before clinical application leads to metabolic reprogramming from glycolysis to oxidative phosphorylation, drastically impairing their proliferative and therapeutic capacities. This study aimed to define the regulatory effects of Sirtuin 5 (SIRT5) on the proliferative and therapeutic functions of adipose-derived MSCs (ADMSCs) during in vitro expansion.

METHODS

ADMSCs were isolated from wild-type (WT) and Sirt5-knockout (Sirt5-/- ) mice. Cell counting assay was used to investigate the proliferative capacities of the ADMSCs. Dihydroethidium and senescence-associated β-galactosidase stainings were used to measure intracellular ROS and senescence levels. Mass spectrometry was used to analyze protein succinylation. Oxygen consumption rates and extra cellular acidification rates were measured as indicators of mitochondrial respiration and glycolysis. Metabolic-related genes expression were verified by quantitative PCR and western blot. Hind limb ischemia mouse model was used to evaluate the therapeutic potentials of WT and Sirt5-/- ADSMCs.

RESULTS

SIRT5 protein levels were upregulated in ADMCs during in vitro expansion. Sirt5-/- ADMSCs exhibited a higher proliferation rate, delayed senescence, and reduced ROS accumulation. Furthermore, elevated protein succinylation levels were observed in Sirt5-/- ADMSCs, leading to the reduced activity of tricarboxylic acid cycle-related enzymes and attenuated mitochondrial respiration. Glucose uptake, glycolysis, and pentose phosphate pathway were elevated in Sirt5-/- ADMSCs. Inhibition of succinylation by glycine or re-expression of Sirt5 reversed the metabolic alterations in Sirt5-/- ADMSCs, thus abolishing their enhanced proliferative capacities. In the hind limb ischemia mouse model, SIRT5-/- ADMSCs transplantation enhanced blood flow recovery and angiogenesis compared with WT ADMSCs.

CONCLUSIONS

Our results indicate that SIRT5 deficiency during ADMSC culture expansion leads to reversed metabolic pattern, enhanced proliferative capacities, and improved therapeutic outcomes. These data suggest SIRT5 as a potential target to enhance the functional properties of MSCs for clinical application.

PFKP is highly expressed in lung cancer and regulates glucose metabolism

PURPOSE

Although it has been reported that up-regulation of phosphofructokinase (PFK) expression is a major feature of malignant tumors, the role of platelet type PFK (PFKP) in tumor initiation and progression is as yet poorly understood. The objective of this study was to evaluate PFKP expression in lung cancer and its effect on glycolysis, and to explore correlations between PFKP expression levels and clinical lung cancer patient features.

METHODS

PFKP mRNA expression levels in cancer tissues and adjacent normal tissues were compared using The Cancer Genome Atlas (TCGA) database. PFKP mRNA and protein expression levels in fresh lung cancer tissues and cell lines were assessed using quantitative real-time PCR and Western blotting. Immunohistochemistry (IHC) was used to assess PFKP expression in 150 archival lung adenocarcinoma samples, after which follow-up data and their correlations with clinical features and patient prognosis were evaluated. A retroviral shRNA-mediated method was used to construct stable cell lines expressing low levels of PFKP. Glucose, lactate and adenosine triphosphate concentrations in the cell culture supernatants were determined using enzymatic, spectrophotometric and enzyme-linked immunosorbent (ELISA) assays, respectively. The effect of PFKP expression on the proliferation of lung cancer cells was assessed using colony forming, MTT and flow cytometry assays, respectively. Finally, data from tissue samples of 533 patients with lung adenocarcinoma and 502 patients with lung squamous cell carcinoma were downloaded from the TCGA database, after which pathway and gene correlation information was retrieved using gene set enrichment analyses.

RESULTS

We found that PFKP was highly expressed in lung cancer tissues and cell lines. Using IHC we found that PFKP was highly expressed in primary lung adenocarcinoma tissues and that a high expression was associated with a poor prognosis. Clinical data analysis revealed that the PFKP expression levels correlated with tumor size and patient survival. Lung cancer cell lines with decreased PFKP expression levels showed significant decreases in glucose uptake rates, lactate levels and adenosine triphosphate concentrations. They also exhibited significantly decreased proliferation rates, colony forming abilities and increased G2/M cell cycle phase percentages. Gene set enrichment analysis revealed that multiple pathways, including glycolytic pathways, may be involved in the regulation PFKP.

CONCLUSIONS

Our data indicate that PFKP is highly expressed in lung cancer tissues and cell lines and is associated with tumor size and patient prognosis. As such, PFKP may serve as a prognostic biomarker. We also found that PFKP regulates the level of glycolysis in lung cancer cells and is associated with lung cancer cell proliferation. These data may be instrumental for the design of new lung cancer treatment options.

EGFR-Phosphorylated Platelet Isoform of Phosphofructokinase 1 Promotes PI3K Activation

EGFR activates phosphatidylinositide 3-kinase (PI3K), but the mechanism underlying this activation is not completely understood. We demonstrated here that EGFR activation resulted in lysine acetyltransferase 5 (KAT5)-mediated K395 acetylation of the platelet isoform of phosphofructokinase 1 (PFKP) and subsequent translocation of PFKP to the plasma membrane, where the PFKP was phosphorylated at Y64 by EGFR. Phosphorylated PFKP binds to the N-terminal SH2 domain of p85α, which is distinct from binding of Gab1 to the C-terminal SH2 domain of p85α, and recruited p85α to the plasma membrane resulting in PI3K activation. PI3K-dependent AKT activation results in enhanced phosphofructokinase 2 (PFK2) phosphorylation and production of fructose-2,6-bisphosphate, which in turn promotes PFK1 activation. PFKP Y64 phosphorylation-enhanced PI3K/AKT-dependent PFK1 activation and GLUT1 expression promoted the Warburg effect, tumor cell proliferation, and brain tumorigenesis. These findings underscore the instrumental role of PFKP in PI3K activation and enhanced glycolysis through PI3K/AKT-dependent positive-feedback regulation.

The platelet isoform of phosphofructokinase contributes to metabolic reprogramming and maintains cell proliferation in clear cell renal cell carcinoma

Metabolic alterations underlying clear cell renal cell carcinoma (ccRCC) progression include aerobic glycolysis, increased pentose phosphate pathway activity and reduced oxidative phosphorylation. Phosphofructokinase (PFK), a key enzyme of the glycolytic pathway, has L, M, and P isoforms with different tissue distributions. The mRNA level of the platelet isoform of phosphofructokinase (PFKP) is reported to be up-regulated in ccRCC patients. However, it remains unclear whether PFKP plays an important role in promoting aerobic glycolysis and macromolecular biosynthesis to support cell proliferation in ccRCC. Here we found that the up-regulated PFKP became the predominant isoform of PFK in human ccRCC. Suppression of PFKP not only impaired cell proliferation by inducing cell cycle arrest and apoptosis, but also led to decreased glycolysis, pentose phosphate pathway and nucleotide biosynthesis, accompanied by activated tricarboxylic acid cycle in ccRCC cells. Moreover, we found that p53 activation contributed to cell proliferation and metabolic defects induced by PFKP knockdown in ccRCC cells. Furthermore, suppression of PFKP led to reduced ccRCC tumor growth in vivo. Our data indicate that PFKP not only is required for metabolic reprogramming and maintaining cell proliferation, but also may provide us with a valid target for anti-renal cancer pharmaceutical agents.

Stabilization of phosphofructokinase 1 platelet isoform by AKT promotes tumorigenesis

Phosphofructokinase 1 (PFK1) plays a critical role in glycolysis; however, its role and regulation in tumorigenesis are not well understood. Here, we demonstrate that PFK1 platelet isoform (PFKP) is the predominant PFK1 isoform in human glioblastoma cells and its expression correlates with total PFK activity. We show that PFKP is overexpressed in human glioblastoma specimens due to an increased stability, which is induced by AKT activation resulting from phosphatase and tensin homologue (PTEN) loss and EGFR-dependent PI3K activation. AKT binds to and phosphorylates PFKP at S386, and this phosphorylation inhibits the binding of TRIM21 E3 ligase to PFKP and the subsequent TRIM21-mediated polyubiquitylation and degradation of PFKP. PFKP S386 phosphorylation increases PFKP expression and promotes aerobic glycolysis, cell proliferation, and brain tumor growth. In addition, S386 phosphorylation in human glioblastoma specimens positively correlates with PFKP expression, AKT S473 phosphorylation, and poor prognosis. These findings underscore the potential role and regulation of PFKP in human glioblastoma development.Phosphofructokinase 1 (PFK1) plays a critical role in glycolysis. Here the authors show that PFK1 platelet isoform is upregulated in Glioblastoma and is required for tumor growth mechanistically, such upregulation is due to an increased stability induced by AKT activation via phosphorylation on residue S386.

Phosphofructokinase-P Modulates P44/42 MAPK Levels in HeLa Cells

It is known that interfering with glycolysis leads to profound modification of cancer cell proliferation. However, energy production is not the major reason for this correlation. Here, using HeLa cells as a model for cancer, we demonstrate that phosphofructokinase-P (PFK-P), which is overexpressed in diverse types of cancer including HeLa cells, modulates expression of P44/42 mitogen-activated protein kinase (MAPK). Silencing of PFK-P did not alter HeLa cell viability or energy production, including the glycolytic rate. On the other hand, silencing of PFK-P induced the downregulation of p44/42 MAPK, augmenting the sensitivity of HeLa cells to different drugs. Conversely, overexpression of PFK-P promotes the upregulation of p44/42 MAPK, making the cells more resistant to the drugs. These results indicate that overexpression of PFK-P by cancer cells is related to activation of survival pathways via upregulation of MAPK and suggest PFK-P as a promising target for cancer therapy. J. Cell. Biochem. 118: 1216-1226, 2017. © 2016 Wiley Periodicals, Inc.

A strategy for improving FDG accumulation for early detection of metastasis from primary pancreatic cancer: stimulation of the Warburg effect in AsPC-1 cells

INTRODUCTION

Early detection and/or prediction of metastasis provide more prognostic relevance than local recurrence. Direct spread into the peritoneum is frequently found in pancreatic cancer patients, but positron emission tomography (PET) with 2-deoxy-2-fluoro-d-glucose (FDG) is not useful for identifying such metastasis. We investigated a method to enhance FDG accumulation using AsPC-1 human ascites tumor cells.

METHODS

(14)C-FDG accumulation was assessed under the following conditions: 1) characteristics of (14)C-FDG transport were examined using phloridzin, a Na(+)-free buffer, and various hexoses, and 2) accumulation of (14)C-FDG was measured in cells that were pretreated with hexose for various time periods, and activity of 6-phosphofructo-1-kinase (PFK-1) was assayed.

RESULTS

(14)C-FDG transport into AsPC-1 cells was mediated primarily by a Na(+)-independent transport mechanism. Aldohexoses such as d-glucose, D-mannose, and D-galactose inhibited (14)C-FDG transport. Cells pretreated with d-glucose, D-mannose, or D-fructose exhibited augmented (14)C-FDG accumulation. Pretreatment with higher concentrations of D-glucose or D-fructose tended to increase PFK-1 activity.

CONCLUSIONS

Very little information has been published about the association between PFK-1 and FDG accumulation, and we confirmed the impacts of various hexoses on the activity of PFK-1 and FDG accumulation in AsPC-1 cells. Clarifying the relevance of PFK-1 in FDG accumulation will contribute to developing new features of FDG-PET, because PFK-1 is the main regulator of glycolysis.

Differential phosphofructokinase-1 isoenzyme patterns associated with glycolytic efficiency in human breast cancer and paracancer tissues

Cancers are characterized by an increasing glycolytic activity, which is called the Warburg effect. Although this phenomenon is well known, the mechanism of the enhanced rate of glycolysis in cancer has not yet been clearly recognized. The present study investigated the glycolytic rate, regulatory enzymatic activities and the expression of phosphofructokinase-1 (PFK-1) in human breast cancer and paracancer tissues. Human breast cancer tissues have an increased degree of glycolytic efficiency and regulatory enzymatic activities, which have been shown in previous studies. However, the present study identified a number of novel observations. The total PFK-1 levels were higher in human breast cancer tissues than in paracancer tissues, and further investigations revealed differential PFK-1 isoenzyme expression patterns between human breast cancer and paracancer tissues. The human breast cancer and paracancer tissues mainly expressed PFK-P and PFK-L isoforms, respectively. Linear-regression analysis showed that, depending on the pathological stage of breast cancer, the expression of PFK-P was significantly positively correlated with the activity of PFK-1. Thus, during the development of human breast cancer, the enhancement of glycolytic activity depends primarily on the conversion of the PFK-1, from PFK-L to PFK-P.

Emerging metabolic targets in the therapy of hematological malignancies

During the last decade, the development of anticancer therapies has focused on targeting neoplastic-related metabolism. Cancer cells display a variety of changes in their metabolism, which enable them to satisfy the high bioenergetic and biosynthetic demands for rapid cell division. One of the crucial alterations is referred to as the "Warburg effect", which involves a metabolic shift from oxidative phosphorylation towards the less efficient glycolysis, independent of the presence of oxygen. Although there are many examples of solid tumors having altered metabolism with high rates of glucose uptake and glycolysis, it was only recently reported that this phenomenon occurs in hematological malignancies. This review presents evidence that targeting the glycolytic pathway at different levels in hematological malignancies can inhibit cancer cell proliferation by restoring normal metabolic conditions. However, to achieve cancer regression, high concentrations of glycolytic inhibitors are used due to limited solubility and biodistribution, which may result in toxicity. Besides using these inhibitors as monotherapies, combinatorial approaches using standard chemotherapeutic agents could display enhanced efficacy at eradicating malignant cells. The identification of the metabolic enzymes critical for hematological cancer cell proliferation and survival appears to be an interesting new approach for the targeted therapy of hematological malignancies.

Estrogen-related receptor alpha modulates lactate dehydrogenase activity in thyroid tumors

Metabolic modifications of tumor cells are hallmarks of cancer. They exhibit an altered metabolism that allows them to sustain higher proliferation rates in hostile environment outside the cell. In thyroid tumors, the expression of the estrogen-related receptor α (ERRα), a major factor of metabolic adaptation, is closely related to the oxidative metabolism and the proliferative status of the cells. To elucidate the role played by ERRα in the glycolytic adaptation of tumor cells, we focused on the regulation of lactate dehydrogenases A and B (LDHA, LDHB) and the LDHA/LDHB ratio. Our study included tissue samples from 10 classical and 10 oncocytic variants of follicular thyroid tumors and 10 normal thyroid tissues, as well as samples from three human thyroid tumor cell lines: FTC-133, XTC.UC1 and RO82W-1. We identified multiple cis-acting promoter elements for ERRα, in both the LDHA and LDHB genes. The interaction between ERRα and LDH promoters was confirmed by chromatin immunoprecipitation assays and in vitro analysis for LDHB. Using knock-in and knock-out cellular models, we found an inverse correlation between ERRα expression and LDH activity. This suggests that thyroid tumor cells may reprogram their metabolic pathways through the up-regulation of ERRα by a process distinct from that proposed by the recently revisited Warburg hypothesis.

The pentose phosphate pathway: an antioxidant defense and a crossroad in tumor cell fate

The pentose phosphate pathway, one of the main antioxidant cellular defense systems, has been related for a long time almost exclusively to its role as a provider of reducing power and ribose phosphate to the cell. In addition to this "traditional" correlation, in the past years multiple roles have emerged for this metabolic cascade, involving the cell cycle, apoptosis, differentiation, motility, angiogenesis, and the response to anti-tumor therapy. These findings make the pentose phosphate pathway a very interesting target in tumor cells. This review summarizes the latest discoveries relating the activity of the pentose phosphate pathway to various aspects of tumor metabolism, such as cell proliferation and death, tissue invasion, angiogenesis, and resistance to therapy, and discusses the possibility that drugs modulating the pathway could be used as potential tools in tumor therapy.

Herpes simplex type 1 activates glycolysis through engagement of the enzyme 6-phosphofructo-1-kinase (PFK-1)

Viruses such as HIV, HCV, Mayaro and HCMV affect cellular metabolic pathways, including glycolysis. Although some studies have suggested that the inhibition of glycolysis affects HSV-1 replication and that HSV-1-infected eyes have increased lactate production, the mechanisms by which HSV-1 induces glycolysis have never been investigated in detail. In this study, we observed an increase in glucose uptake, lactate efflux and ATP content in HSV-1-infected cells. HSV-1 triggered a MOI-dependent increase in the activity of phosphofructokinase-1 (PFK-1), a key rate-limiting enzyme of the glycolytic pathway. After HSV-1 infection, we observed increased PFK-1 expression, which increased PFK-1 total activity, and the phosphorylation of this enzyme at serine residues. HSV-1-induced glycolysis was associated with increased ATP content, and these events were critical for viral replication. In summary, our results suggest that HSV-1 triggers glycolysis through a different mechanism than other herpesviruses, such as HCMV. Thus, this study contributes to a better understanding of HSV-1 pathogenesis and provides insights into novel targets for antiviral therapy.

HIGHLIGHTS

►HSV-1 activates glycolysis by PFK-1 activation. ►In HSV-1-infected cells PFK-1 synthesis is up-regulated and phosphorylated at serine residues. ►PFK-1 knockdown impairs HSV-1 replication. ►HSV-1-mediated glycolysis activation increases ATP content.

Krüppel-like factor 4 (KLF4) activates the transcription of the gene for the platelet isoform of phosphofructokinase (PFKP) in breast cancer

Krüppel-like factor 4 (KLF4) is a transcription factor that plays an important role in cell differentiation, proliferation, and survival, especially in the context of cancers. This study revealed that KLF4 activates glycolytic metabolism in breast cancer cells by up-regulating the platelet isoform of phosphofructokinase (PFKP). KLF4 activated the transcription of the PFKP gene by directly binding to the PFKP promoter. Whereas glucose uptake and lactate production were inhibited by the knockdown of KLF4, they were activated by the overexpression of KLF4. Unlike PFKP, the expressions of the other isoforms of phosphofructokinase and glycolytic genes were unaffected by KLF4. The human breast cancer tissues showed a close correlation between KLF4 and PFKP expression. This study also showed that PFKP plays a critical role in cell proliferation in breast cancer cells. In conclusion, it is suggested that KLF4 plays a role in maintenance of high glycolytic metabolism by transcriptional activation of the PFKP gene in breast cancer cells.

The bioenergetics of cancer: is glycolysis the main ATP supplier in all tumor cells?

The molecular mechanisms by which tumor cells achieve an enhanced glycolytic flux and, presumably, a decreased oxidative phosphorylation are analyzed. As the O(2) concentration in hypoxic regions of tumors seems not limiting for oxidative phosphorylation, the role of this mitochondrial pathway in the ATP supply is re-evaluated. Drugs that inhibit glycoysis and oxidative phosphorylation are analyzed for their specificity toward tumor cells and effect on proliferation. The energy metabolism mechanisms involved in the use of positron emission tomography are revised and updated. It is proposed that energy metabolism may be an alternative therapeutic target for both hypoxic (glycolytic) and oxidative tumors. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.

The molecular determinants of de novo nucleotide biosynthesis in cancer cells

Tumor cells increase the use of anabolic pathways to satisfy the metabolic requirements associated with a high growth rate. Transformed cells take up and metabolize nutrients such as glucose and glutamine at high levels that support anabolic growth. Oncogenic signaling through the PI3K/Akt and Myc pathways directly control glucose and glutamine uptake, respectively. In order to achieve elevated rates of nucleotide biosynthesis, neoplastic cells must divert carbon from PI3K/Akt-induced glycolytic flux into the nonoxidative branch of the pentose phosphate pathway to generate ribose-5-phosphate. This redirection of glucose catabolism appears to be regulated by cytoplasmic tyrosine kinases. Myc-induced glutamine metabolism also increases the abundance and activity of different rate-limiting enzymes that produce the molecular precursors required for de novo nucleotide synthesis. In this review, we will focus on recent progress in understanding how glucose and glutamine metabolism is redirected by oncogenes in order to support de novo nucleotide biosynthesis during proliferation and how metabolic reprogramming can be potentially exploited in the development of new cancer therapies.

Regulation of glucose metabolism by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases in cancer

A high rate of glycolytic flux, even in the presence of oxygen, is a central metabolic hallmark of neoplastic tumors. Cancer cells preferentially utilize glycolysis in order to satisfy their increased energetic and biosynthetic requirements. This metabolic phenotype has been confirmed in human studies using positron emission tomography (PET) with (18)F-2-fluoro-deoxy-glucose which have demonstrated that tumors take up 10-fold more glucose than adjacent normal tissues in vivo. The high glucose metabolism of cancer cells is caused by a combination of hypoxia-responsive transcription factors, activation of oncogenic proteins and the loss of tumor suppressor function. Over-expression of HIF-1alpha and myc, activation of ras and loss of p53 function each have been found to stimulate glycolysis in part by activating a family of regulatory bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB). The PFKFB enzymes synthesize fructose-2,6-bisphosphate (F2,6BP) which allosterically activates 6-phosphofructo-1-kinase (PFK-1), a rate-limiting enzyme and essential control point in the glycolytic pathway. PFK-1 is inhibited by ATP when energy stores are abundant and F2,6BP can override this inhibition and enhance glucose uptake and glycolytic flux. It is therefore not surprising that F2,6BP synthesis is stimulated by several oncogenic alterations which simultaneously cause both enhanced consumption of glucose and growth. Importantly, these studies suggest that selective depletion of intracellular F2,6BP in cancer cells may suppress glycolytic flux and decrease their survival, growth and invasiveness. This review will summarize the requirement of the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases for the regulation of glycolysis in tumor cells and their potential utility as targets for the development of antineoplastic agents.

Energy metabolism in tumor cells

In early studies on energy metabolism of tumor cells, it was proposed that the enhanced glycolysis was induced by a decreased oxidative phosphorylation. Since then it has been indiscriminately applied to all types of tumor cells that the ATP supply is mainly or only provided by glycolysis, without an appropriate experimental evaluation. In this review, the different genetic and biochemical mechanisms by which tumor cells achieve an enhanced glycolytic flux are analyzed. Furthermore, the proposed mechanisms that arguably lead to a decreased oxidative phosphorylation in tumor cells are discussed. As the O(2) concentration in hypoxic regions of tumors seems not to be limiting for the functioning of oxidative phosphorylation, this pathway is re-evaluated regarding oxidizable substrate utilization and its contribution to ATP supply versus glycolysis. In the tumor cell lines where the oxidative metabolism prevails over the glycolytic metabolism for ATP supply, the flux control distribution of both pathways is described. The effect of glycolytic and mitochondrial drugs on tumor energy metabolism and cellular proliferation is described and discussed. Similarly, the energy metabolic changes associated with inherent and acquired resistance to radiotherapy and chemotherapy of tumor cells, and those determined by positron emission tomography, are revised. It is proposed that energy metabolism may be an alternative therapeutic target for both hypoxic (glycolytic) and oxidative tumors.

Chimeric phosphofructokinases involving exchange of the N- and C-terminal halves of mammalian isozymes: implications for ligand binding sites

Two phosphofructokinase (PFK) chimeras were constructed by exchanging the N- and C-terminal halves of the mammalian M- and C-type isozymes, to investigate the contribution of each terminus to the catalytic site and the fructose-2,6-P(2)/fructose-1,6-P(2) allosteric site. The homogeneously-purified chimeric enzymes organized into tetramers, and exhibited kinetic properties for fructose-6-P and MgATP similar to those of the native enzyme that furnished the N-terminal domain in each case, whereas their fructose-2,6-P(2) activatory characteristics coincided with those of the isozyme that provided the C-terminal half. This reflected the role of each domain in the formation of the corresponding binding site. Grafting the N-terminus of PFK-M onto the C-terminus of the fructose-1,6-P(2) insensitive PFK-C restored transduction of this signal to the catalytic site, which significance is also discussed.

6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase and tumor cell glycolysis

PURPOSE OF REVIEW

Neoplastic cells metabolize abundant glucose relative to normal cells in order to satisfy the increased energetic and anabolic needs of the transformed state. This review will summarize the requirement of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases for the regulation of glycolysis in cancer cells and their potential utility as targets for the development of antineoplastic agents.

RECENT FINDINGS

The steady-state concentration of fructose-2,6-bisphosphate controls the overall rate of glycolysis by allosterically activating a rate-limiting enzyme, 6-phosphofructo-1-kinase. The intracellular concentration of fructose-2,6-bisphosphate is controlled by a family of bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases that are encoded by four independent genes (PFKFB1-4). The 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase encoded by the PFKFB3 gene has the highest kinase:phosphatase activity ratio of the four enzymes and thus contributes significantly to the synthesis of fructose-2,6-bisphosphate. PFKFB3 is activated by mitogenic, inflammatory and hypoxic stimuli, and was recently found to be constitutively expressed by several human leukemias and solid tumor cells. By setting the intracellular fructose-2,6-bisphosphate concentration, PFKFB3 controls glycolytic flux to lactate and the nonoxidative pentose shunt, and is selectively required for the tumorigenic growth of ras-transformed cells.

SUMMARY

These findings demonstrate a key role for the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases in neoplastic transformation and provide rationale for the development of agents that selectively inhibit the PFKFB3 enzyme as antineoplastic agents.

Determining and understanding the control of glycolysis in fast-growth tumor cells. Flux control by an over-expressed but strongly product-inhibited hexokinase

Control analysis of the glycolytic flux was carried out in two fast-growth tumor cell types of human and rodent origin (HeLa and AS-30D, respectively). Determination of the maximal velocity (V(max)) of the 10 glycolytic enzymes from hexokinase to lactate dehydrogenase revealed that hexokinase (153-306 times) and phosphofructokinase-1 (PFK-1) (22-56 times) had higher over-expression in rat AS-30D hepatoma cells than in normal freshly isolated rat hepatocytes. Moreover, the steady-state concentrations of the glycolytic metabolites, particularly those of the products of hexokinase and PFK-1, were increased compared with hepatocytes. In HeLa cells, V(max) values and metabolite concentrations for the 10 glycolytic enzyme were also significantly increased, but to a much lesser extent (6-9 times for both hexokinase and PFK-1). Elasticity-based analysis of the glycolytic flux in AS-30D cells showed that the block of enzymes producing Fru(1,6)P2 (i.e. glucose transporter, hexokinase, hexosephosphate isomerase, PFK-1, and the Glc6P branches) exerted most of the flux control (70-75%), whereas the consuming block (from aldolase to lactate dehydrogenase) exhibited the remaining control. The Glc6P-producing block (glucose transporter and hexokinase) also showed high flux control (70%), which indicated low flux control by PFK-1. Kinetic analysis of PFK-1 showed low sensitivity towards its allosteric inhibitors citrate and ATP, at physiological concentrations of the activator Fru(2,6)P2. On the other hand, hexokinase activity was strongly inhibited by high, but physiological, concentrations of Glc6P. Therefore, the enhanced glycolytic flux in fast-growth tumor cells was still controlled by an over-produced, but Glc6P-inhibited hexokinase.

Mayaro virus infection alters glucose metabolism in cultured cells through activation of the enzyme 6-phosphofructo 1-kinase

Although it is well established that cellular transformation with tumor virus leads to changes on glucose metabolism, the effects of cell infection by non-transforming virus are far to be completely elucidated. In this study, we report the first evidence that cultured Vero cells infected with the alphavirus Mayaro show several alterations on glucose metabolism. Infected cells presented a two fold increase on glucose consumption, accompanied by an increment in lactate production. This increase in glycolytic flux was also demonstrated by a significant increase on the activity of 6-phosphofructo 1-kinase, one of the regulatory enzymes of glycolysis. Analysis of the kinetic parameters revealed that the regulation of 6-phosphofructo 1-kinase is altered in infected cells, presenting an increase in Vmax along with a decrease in Km for fructose-6-phosphate. Another fact contributing to an increase in enzyme activity was the decrease in ATP levels observed in infected cells. Additionally, the levels of fructose 2,6-bisphosphate, a potent activator of this enzyme, was significantly reduced in infected cells. These observations suggest that the increase in PFK activity may be a compensatory cellular response to the viral-induced metabolic alterations that could lead to an impairment of the glycolytic flux and energy production.

Identification of C-terminal motifs responsible for transmission of inhibition by ATP of mammalian phosphofructokinase, and their contribution to other allosteric effects

Systematic deletions and point mutations in the C-terminal extension of mammalian PFK (phosphofructokinase) led us to identify Leu-767 and Glu-768 of the M-type isoform (PFK-M) as the motifs responsible for the role of this region in inhibition by MgATP. These amino acids are the only residues of the C-terminus that are conserved in all mammalian isoforms, and were found to have a similar function in the C-type isoenzyme. Both residues in PFK-C and Leu-767 in PFK-M were also observed to be critical for inhibition by citrate, which is synergistic with that by MgATP. Binding studies utilizing titration of intrinsic protein fluorescence indicated that the C-terminal part of the enzyme participates in the signal transduction route from the MgATP inhibitory site to the catalytic site, but does not contribute to the binding of this inhibitor, whereas it is essential for the binding of citrate. Mutations of the identified structural motifs did not alter either the action of other allosteric effectors that also interact with MgATP, such as the inhibitor phosphoenolpyruvate and the strong activator fructose 2,6-bisphosphate, or the co-operative effect of fructose 6-phosphate. The latter data provide evidence that activation by fructose 2,6-bisphosphate and fructose 6-phosphate co-operativity are not linked to the same allosteric transition as that mediating inhibition by MgATP.

Cellular distribution of phosphofructokinase activity and implications to metabolic regulation in human breast cancer

Neoplastic cells generally present profound changes in glucose metabolism. The mechanisms underlying such process are numerous and all may involve altered cellular hormonal responses. Here we report the first evidence that cellular location of phosphofructokinase activity in human breast cancer tissues is different from the one observed in control tissues and that this phenomenon may be involved in the increased glycolytic flux observed in those cells. Through co-sedimentation techniques, we observed that 60% of phosphofructokinase activity in neoplastic tissues is located in an actin-enriched fraction, against 36% in control tissues. Additionally, metastatic tumor tissues presented a two fold increase in this particulate activity when compared to non-metastatic tumor samples. We propose that the alteration in cellular distribution of phosphofructokinase activity in human breast cancer tissues is a mechanism associated to the process of cell transformation and may be a consequence of the altered hormonal milieu observed in several types of cancer.

Trifunctional chemical probes for the consolidated detection and identification of enzyme activities from complex proteomes

Chemical probes that covalently modify the active sites of enzymes in complex proteomes are useful tools for identifying enzyme activities associated with discrete (patho) physiological states. Researchers in proteomics typically use two types of activity-based probes to fulfill complementary objectives: fluorescent probes for rapid and sensitive target detection and biotinylated probes for target purification and identification. Accordingly we hypothesized that a strategy in which the target detection and target isolation steps of activity-based proteomic experiments were merged might accelerate the characterization of differentially expressed protein activities. Here we report the synthesis and application of trifunctional chemical proteomic probes in which elements for both target detection (e.g. rhodamine) and isolation (e.g. biotin) are appended to a sulfonate ester reactive group, permitting the consolidated visualization and affinity purification of labeled proteins by a combination of in-gel fluorescence and avidin chromatography procedures. A trifunctional phenyl sulfonate probe was used to identify several technically challenging protein targets, including the integral membrane enzyme 3beta-hydroxysteroid dehydrogenase/Delta5-isomerase and the cofactor-dependent enzymes platelet-type phosphofructokinase and type II tissue transglutaminase. The latter two enzyme activities were significantly up-regulated in the invasive estrogen receptor-negative (ER(-)) human breast cancer cell line MDA-MB-231 relative to the non-invasive ER(+) breast cancer lines MCF7 and T-47D. Collectively these studies demonstrate that chemical proteomic probes incorporating elements for both target detection and target isolation fortify the important link between the visualization of differentially expressed enzyme activities and their subsequent molecular identification, thereby augmenting the information content achieved in activity-based profiling experiments.

Phosphofructokinase C isozyme from ascites tumor cells: cloning, expression, and properties

The phosphofructokinase C isozyme (PFK-C) from ascites tumor cells has been cloned and characterized to investigate the particular properties of PFK activity in this type of cells. The isolated cDNA encodes a protein of 784 amino acids and 85.5 kDa, whose expression was constant along tumor growth and markedly decreased when cell proliferation stops. The enzyme was functionally expressed in a PFK-deficient strain of Saccharomyces cerevisiae and purified to homogeneity. Recombinant PFK-C exhibited the same subunit size as the tumor wild-type isozyme and its steady-state kinetic parameters were similar to those of the form present in normal cells. The regulatory properties of the C isozyme accounted for the lack of fructose-1,6-P(2) activation and the P-enolpyruvate inhibition of PFK activity observed in ascites tumor preparations containing the various isozyme types. Nevertheless, PFK-C binds fructose-1,6-P(2) to an allosteric site as suggested by protection against thermal denaturation. Our results indicate that glucose metabolism in tumor cells is not regulated by a mutant form of PFK-C but by a high level expression of the normal C isozyme.

Phosphofructokinase from Dictyostelium discoideum is a potent inhibitor of tubulin polymerization

We identified the nonallosteric phosphofructokinase from the slime mold Dictyostelium discoideum as a potent protein factor that inhibits the rate of polymerization of tubulin at a molar ratio of 1 molecule to about 300 tubulin dimers for half-maximal action (IC50 = 32 nM). This effect was (i) assessed by turbidity measurements, pelleting of microtubules, and electron microscopy, (ii) observed when tubulin assembly was induced by taxol as well as by GTP in the presence of microtubule-associated proteins or glutamate, and (iii) specific as it was not produced by the phosphofructokinase from rabbit muscle. Also in contrast to the latter, neither tubulin nor microtubules modified the catalytic activity of the slime mold isozyme. Immunoelectron microscopy provided further evidence that D. discoideumphosphofructokinase physically interacts with tubulin, leading to the formation of aggregates. The process seems to be reversible since microtubules eventually formed in the presence of the inhibitor with concomitant reduction of tubulin aggregates. Limited proteolysis by subtilisin showed that the hypervariable C-termini of tubulin is not involved in the interaction with the enzyme. The possible physiological relevance of this novel function of D. discoideum phosphofructokinase different from its glycolytic action is discussed.

Reciprocal subtraction differential RNA display: an efficient and rapid procedure for isolating differentially expressed gene sequences

A reciprocal subtraction differential RNA display (RSDD) approach has been developed that permits the rapid and efficient identification and cloning of both abundant and rare differentially expressed genes. RSDD comprises reciprocal subtraction of cDNA libraries followed by differential RNA display. The RSDD strategy was applied to analyze the gene expression alterations resulting during cancer progression as adenovirus-transformed rodent cells developed an aggressive transformed state, as documented by elevated anchorage-independence and enhanced in vivo oncogenesis in nude mice. This approach resulted in the identification and cloning of both known and a high proportion (>65%) of unknown sequences, including cDNAs displaying elevated expression as a function of progression (progression-elevated gene) and cDNAs displaying suppressed expression as a function of progression (progression-suppressed gene). Sixteen differentially expressed genes, including five unknown progression-elevated genes and six unknown progression-suppressed genes, have been characterized. The RSDD scheme should find wide application for the effective detection and isolation of differentially expressed genes.

Subcellular localization of enzyme activities in chemostat-grown murine myeloma cells

As part of the development of structured models for the metabolism of myeloma cells in suspension culture, a study was made of the subcellular localization of key enzymes of glucose and glutamine metabolism. Steady state chemostat cultures of the mouse myeloma SP2/0-Ag14 were used as a reproducible source of biomass. Homogenates of the cells, obtained via mechanical disruption, were separated into a mitochondrial and a cytosolic fraction via differential centrifugation. The following conclusions are drawn: (1) approximately one fifth of the hexokinase activity of cell-free homogenates is associated with the mitochondria; (2) a malate-aspartate shuttle may operate for oxidation of cytosolic NADH, as indicated by high levels of malate dehydrogenase and aspartate aminotransferase in both particulate and soluble fractions; (3) the pentose phosphate pathway and isocitrate dehydrogenase may contribute to the provision of cytosolic NADPH; (4) phosphoenolpyruvate carboxykinase and pyruvate kinase, which are present in high activities, are exclusively cytosolic and probably play a key role in glutamine metabolism; (5) oxidation of glutamine via these enzymes leads to the formation of pyruvate that enters the same pool as pyruvate generated by glycolysis. As a result, lactate and alanine formation can occur from both glucose and glutamine.