Increased concentrations of fructose 2,6-bisphosphate contribute to the Warburg effect in phosphatase and tensin homolog (PTEN)-deficient cells

Recent Advances in Drug Discovery for Triple-Negative Breast Cancer Treatment

Triple-negative breast cancer (TNBC) is one of the most heterogeneous and aggressive breast cancer subtypes with a high risk of death on recurrence. To date, TNBC is very difficult to treat due to the lack of an effective targeted therapy. However, recent advances in the molecular characterization of TNBC are encouraging the development of novel drugs and therapeutic combinations for its therapeutic management. In the present review, we will provide an overview of the currently available standard therapies and new emerging therapeutic strategies against TNBC, highlighting the promises that newly developed small molecules, repositioned drugs, and combination therapies have of improving treatment efficacy against these tumors.

HOXD9 contributes to the Warburg effect and tumor metastasis in non-small cell lung cancer via transcriptional activation of PFKFB3

Warburg effect is associated with the progression of various tumors, leading to the development of drugs targeting the phenomenon. PFKFB3 is an isoform of 6-phosphofructo-2-kinase (PFK2) that modulates the Warburg effect and has been implicated in most common types of cancer, including non-small cell lung cancer (NSCLC). However, the mechanisms underlying the upstream regulation of PFKFB3 in NSCLC remain poorly understood. This study reported that the transcription factor HOXD9 is upregulated in NSCLC patient samples relative to adjacent normal tissue. Elevated HOXD9 levels are primarily associated with poor prognosis in patients with NSCLC. Functionally, HOXD9 knockdown impaired the metastatic capacity of NSCLC cells, whereas its over-expression accelerated the metastasis and invasion of NSCLC cells in an orthotopic tumor mouse model. In addition, HOXD9 promoted metastasis by increasing cellular glycolysis. Further mechanistic studies revealed that HOXD9 directly binds to the promoter region of PFKFB3 to enhance its transcription. The recovery assay confirmed that the capability of HOXD9 to promote NSCLC cells metastasis was significantly weakened upon PFKFB3 inhibition. These data suggest that HOXD9 may exert as a novel biomarker in NSCLC, indicating that blocking the HOXD9/PFKFB3 axis may be a potential therapeutic strategy for NSCLC treatment.

Mutual connected IL-6, EGFR and LIN28/Let7-related mechanisms modulate PD-L1 and IGF upregulation in HNSCC using immunotherapy

The development of techniques and immunotherapies are widely applied in cancer treatment such as checkpoint inhibitors, adoptive cell therapy, and cancer vaccines apart from radiation therapy, surgery, and chemotherapy give enduring anti-tumor effects. Minority people utilize single-agent immunotherapy, and most people adopt multiple-agent immunotherapy. The difficulties are resolved by including the biomarkers to choose the non-responders' and responders' potentials. The possibility of the potential complications and side effects are examined to improve cancer therapy effects. The Head and Neck Squamous Cell Carcinoma (HNSCC) is analyzed with the help of programmed cell death ligand 1 (PD-L1) and Insulin-like growth factor (IGF). But how IGF and PD-L1 upregulation depends on IL-6, EGFR, and LIN28/Let7-related mechanisms are poorly understood. Briefly, IL-6 stimulates gene expressions of IGF-1/2, and IL-6 cross-activates IGF-1R signaling, NF-κB, and STAT3. NF-κB, up-regulating PD-L1 expressions. IL-6/JAK1 primes PD-L1 for STT3-mediated PD-L1 glycosylation, stabilizes PD-L1 and trafficks it to the cell surface. Moreover, ΔNp63 is predominantly overexpressed over TAp63 in HNSCC, elevates circulating IGF-1 levels by repressing IGFBP3, and activates insulin receptor substrate 1 (IRS1).TP63 and SOX2 form a complex with CCAT1 to promote EGFR expression. EGFR activation through EGF binding extends STAT3 activation, and EGFR and its downstream signaling prolong PD-L1 mRNA half-life. PLC-γ1 binding to a cytoplasmic motif of elevated PD-L1 improves EGF-induced activation of inositol 1,4,5-tri-phosphate (IP3), and diacylglycerol (DAG) subsequently elevates RAC1-GTP. RAC1-GTP was convincingly demonstrated to induce the autocrine production and action of IL-6/IL-6R, forming a feedback loop for IGF and PD-L1 upregulation. Furthermore, the LIN28-Let7 axis mediates the NF-κB-IL-6-STAT3 amplification loop, activated LIN28-Let7 axis up-regulates RAS, AKT, IL-6, IGF-1/2, IGF-1R, Myc, and PD-L1, plays pivotal roles in IGF-1R activation and Myc, NF-κB, STAT3 concomitant activation. Therefore, based on a detailed mechanisms review, our article firstly reveals that IL-6, EGFR, and LIN28/Let7-related mechanisms mediate PD-L1 and IGF upregulation in HNSCC, which comprehensively influences immunity, inflammation, metabolism, and metastasis in the tumor microenvironment, and might be fundamental for overcoming therapy resistance.

Canonical and Non-Canonical Roles of PFKFB3 in Brain Tumors

PFKFB3 is a bifunctional enzyme that modulates and maintains the intracellular concentrations of fructose-2,6-bisphosphate (F2,6-P2), essentially controlling the rate of glycolysis. PFKFB3 is a known activator of glycolytic rewiring in neoplastic cells, including central nervous system (CNS) neoplastic cells. The pathologic regulation of PFKFB3 is invoked via various microenvironmental stimuli and oncogenic signals. Hypoxia is a primary inducer of PFKFB3 transcription via HIF-1alpha. In addition, translational modifications of PFKFB3 are driven by various intracellular signaling pathways that allow PFKFB3 to respond to varying stimuli. PFKFB3 synthesizes F2,6P2 through the phosphorylation of F6P with a donated PO4 group from ATP and has the highest kinase activity of all PFKFB isoenzymes. The intracellular concentration of F2,6P2 in cancers is maintained primarily by PFKFB3 allowing cancer cells to evade glycolytic suppression. PFKFB3 is a primary enzyme responsible for glycolytic tumor metabolic reprogramming. PFKFB3 protein levels are significantly higher in high-grade glioma than in non-pathologic brain tissue or lower grade gliomas, but without relative upregulation of transcript levels. High PFKFB3 expression is linked to poor survival in brain tumors. Solitary or concomitant PFKFB3 inhibition has additionally shown great potential in restoring chemosensitivity and radiosensitivity in treatment-resistant brain tumors. An improved understanding of canonical and non-canonical functions of PFKFB3 could allow for the development of effective combinatorial targeted therapies for brain tumors.

PFKFB3 Inhibition Impairs Erlotinib-Induced Autophagy in NSCLCs

Tyrosine kinase inhibitors (TKIs) targeting the kinase domain of the epidermal growth factor receptor (EGFR), such as erlotinib, have dramatically improved clinical outcomes of patients with EGFR-driven non-small cell lung carcinomas (NSCLCs). However, intrinsic or acquired resistance remains a clinical barrier to the success of FDA-approved EGFR TKIs. Multiple mechanisms of resistance have been identified, including the activation of prosurvival autophagy. We have previously shown that the expression and activity of PFKFB3—a known driver of glycolysis—is associated with resistance to erlotinib and that PFKFB3 inhibition improves the response of NSCLC cells to erlotinib. This study focuses on investigating the role of PFKFB3 in regulating erlotinib-driven autophagy to escape resistance to erlotinib. We evaluated the consequence of pharmacological inhibition of PFKFB3 on erlotinib-driven autophagy in NSCLC cells with different mutation statuses. Here, we identify PFKFB3 as a mediator of erlotinib-induced autophagy in NSCLCs. We demonstrate that PFKFB3 inhibition sensitizes NCSLCs to erlotinib via impairing autophagy flux. In summary, our studies uncovered a novel crosstalk between PFKFB3 and EGFR that regulates erlotinib-induced autophagy, thus contributing to erlotinib sensitivity in NSCLCs.

Role of PFKFB3 and PFKFB4 in Cancer: Genetic Basis, Impact on Disease Development/Progression, and Potential as Therapeutic Targets

Glycolysis is a crucial metabolic process in rapidly proliferating cells such as cancer cells. Phosphofructokinase-1 (PFK-1) is a key rate-limiting enzyme of glycolysis. Its efficiency is allosterically regulated by numerous substances occurring in the cytoplasm. However, the most potent regulator of PFK-1 is fructose-2,6-bisphosphate (F-2,6-BP), the level of which is strongly associated with 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase activity (PFK-2/FBPase-2, PFKFB). PFK-2/FBPase-2 is a bifunctional enzyme responsible for F-2,6-BP synthesis and degradation. Four isozymes of PFKFB (PFKFB1, PFKFB2, PFKFB3, and PFKFB4) have been identified. Alterations in the levels of all PFK-2/FBPase-2 isozymes have been reported in different diseases. However, most recent studies have focused on an increased expression of PFKFB3 and PFKFB4 in cancer tissues and their role in carcinogenesis. In this review, we summarize our current knowledge on all PFKFB genes and protein structures, and emphasize important differences between the isoenzymes, which likely affect their kinase/phosphatase activities. The main focus is on the latest reports in this field of cancer research, and in particular the impact of PFKFB3 and PFKFB4 on tumor progression, metastasis, angiogenesis, and autophagy. We also present the most recent achievements in the development of new drugs targeting these isozymes. Finally, we discuss potential combination therapies using PFKFB3 inhibitors, which may represent important future cancer treatment options.

Loss of PTEN expression is associated with PI3K pathway-dependent metabolic reprogramming in hepatocellular carcinoma

Background

Metabolic reprogramming, in which energetic metabolism changes from oxidative phosphorylation to glycolysis, is well-accepted as a hallmark of cancers including hepatocellular carcinoma (HCC). A growing body of evidence suggests the involvement of oncogenes and tumor suppressor genes in the control of metabolic reprogramming. In this study, we attempt to investigate whether loss of PTEN, a recognized tumor suppressor, drives metabolic reprogramming of HCC.

Methods

Cancerous liver tissues were surgically resected from 128 HCC patients, with 43 adjacent noncancerous liver tissues as control. Aerobic glycolysis (Warburg effect) was reflected by measurements of glucose uptake and lactate production, mitochondrial membrane potential collapse was observed by JC-1 staining, glycolytic rate and mitochondrial respiration were evaluated by determining glycolytic proton efflux rate (glycoPER) and oxygen consumption rate (OCR) in cultured human HHCC cells.

Results

Reciprocal expression of PTEN and PI3K was determined in cancer liver tissues. Overexpression of PTEN suppressed the Warburg effect, as evidenced by reductions in glucose uptake and lactate production, maintenance of mitochondrial function, and transformation of energetic metabolism from glycolysis to oxidative phosphorylation in cultured PTEN-negative HHCC cells. Importantly, 740 Y-P, a PI3K agonist that leads to activation of the PI3K pathway, partially abrogated the function of PTEN and reprogramed glucose metabolism in cultured HHCC cells.

Conclusions

The discovery that loss of PTEN allows the tumor metabolic program has been a major advance in understanding the carcinogenesis of HCC.

The Role of Pi, Glutamine and the Essential Amino Acids in Modulating the Metabolism in Diabetes and Cancer

Purpose

Re-examine the current metabolic models.

Methods

Review of literature and gene networks.

Results

Insulin activates Pi uptake, glutamine metabolism to stabilise lipid membranes. Tissue turnover maintains the metabolic health. Current model of intermediary metabolism (IM) suggests glucose is the source of energy, and anaplerotic entry of fatty acids and amino acids into mitochondria increases the oxidative capacity of the TCA cycle to produce the energy (ATP). The reduced cofactors, NADH and FADH2, have different roles in regulating the oxidation of nutrients, membrane potentials and biosynthesis. Trans-hydrogenation of NADH to NADPH activates the biosynthesis. FADH2 sustains the membrane potential during the cell transformations. Glycolytic enzymes assume the non-canonical moonlighting functions, enter the nucleus to remodel the genetic programmes to affect the tissue turnover for efficient use of nutrients. Glycosylation of the CD98 (4F2HC) stabilises the nutrient transporters and regulates the entry of cysteine, glutamine and BCAA into the cells. A reciprocal relationship between the leucine and glutamine entry into cells regulates the cholesterol and fatty acid synthesis and homeostasis in cells. Insulin promotes the Pi transport from the blood to tissues, activates the mitochondrial respiratory activity, and glutamine metabolism, which activates the synthesis of cholesterol and the de novo fatty acids for reorganising and stabilising the lipid membranes for nutrient transport and signal transduction in response to fluctuations in the microenvironmental cues. Fatty acids provide the lipid metabolites, activate the second messengers and protein kinases. Insulin resistance suppresses the lipid raft formation and the mitotic slippage activates the fibrosis and slow death pathways.

PFKFB2 regulates glycolysis and proliferation in pancreatic cancer cells

Tumor cells increase glucose metabolism through glycolysis and pentose phosphate pathways to meet the bioenergetic and biosynthetic demands of rapid cell proliferation. The family of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB1-4) are key regulators of glucose metabolism via their synthesis of fructose-2,6-bisphosphate (F2,6BP), a potent activator of glycolysis. Previous studies have reported the co-expression of PFKFB isozymes, as well as the mRNA splice variants of particular PFKFB isozymes, suggesting non-redundant functions. Majority of the evidence demonstrating a requirement for PFKFB activity in increased glycolysis and oncogenic properties in tumor cells comes from studies on PFKFB3 and PFKFB4 isozymes. In this study, we show that the PFKFB2 isozyme is expressed in tumor cell lines of various origin, overexpressed and localizes to the nucleus in pancreatic adenocarcinoma, relative to normal pancreatic tissue. We then demonstrate the differential intracellular localization of two PFKFB2 mRNA splice variants and that, when ectopically expressed, cytoplasmically localized mRNA splice variant causes a greater increase in F2,6BP which coincides with an increased glucose uptake, as compared with the mRNA splice variant localizing to the nucleus. We then show that PFKFB2 expression is required for steady-state F2,6BP levels, glycolytic activity, and proliferation of pancreatic adenocarcinoma cells. In conclusion, this study may provide a rationale for detailed investigation of PFKFB2's requirement for the glycolytic and oncogenic phenotype of pancreatic adenocarcinoma cells.

The immunological Warburg effect: Can a metabolic-tumor-stroma score (MeTS) guide cancer immunotherapy?

The "glycolytic switch" also known as the "Warburg effect" is a key feature of tumor cells and leads to the accumulation of lactate and protons in the tumor environment. Intriguingly, non-malignant lymphocytes or stromal cells such as tumor-associated macrophages and cancer-associated fibroblasts contribute to the lactate accumulation in the tumor environment, a phenomenon described as the "Reverse Warburg effect." Localized lactic acidosis has a strong immunosuppressive effect and mediates an immune escape of tumors. However, some tumors do not display the Warburg phenotype and either rely on respiration or appear as a mosaic of cells with different metabolic properties. Based on these findings and on the knowledge that T cell infiltration is predictive for patient outcome, we suggest a metabolic-tumor-stroma score to determine the likelihood of a successful anti-tumor immune response: (a) a respiring tumor with high T cell infiltration ("hot"); (b) a reverse Warburg type with respiring tumor cells but glycolytic stromal cells; (c) a mixed type with glycolytic and respiring compartments; and (d) a glycolytic (Warburg) tumor with low T cell infiltration ("cold"). Here, we provide evidence that these types can be independent of the organ of origin, prognostically relevant and might help select the appropriate immunotherapy approach.

Metformin attenuates hepatoma cell proliferation by decreasing glycolytic flux through the HIF-1α/PFKFB3/PFK1 pathway

AIMS

Enhanced aerobic glycolysis is an essential hallmark of malignant cancer. Blocking the glycolytic pathway has been suggested as a therapeutic strategy to impair the proliferation of tumor cells. Metformin, a widely used anti-diabetes drug, exhibits anti-tumor properties. However, the underlying molecular mechanism of its action linking glucose metabolism with the suppression of proliferation has not been fully clarified.

MAIN METHODS

Stable isotope tracing technology and gas chromatography-mass spectrometry method were utilized to analyze the effect of metformin on glycolytic flux in HCC cells. Western blot and immunohistochemistry were utilized to analyze the expression of phosphofructokinase-1 (PFK1) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) in HCC cells or xenograft tumor tissues. Lactate measurement and glucose uptake assay were used to analyze the level of lactate and glucose in the presence of frucose-2,6-diphosphate (F2,6BP) in HCC cells treated with metformin.

KEY FINDINGS

We found that metformin significantly impaired hepatoma cell proliferation by inhibiting the glycolytic flux via PFK1 blockade. Interestingly, activation of PFK1 by F2,6BP reverses the inhibitory effect of metformin on hepatoma cell proliferation and glycolysis. Mechanistically, PFKFB3，a potent allosteric activator of PFK1, was markedly suppressed through inhibiting hypoxia-induced factor 1 (HIF-1α) accumulation mediated by metformin.

SIGNIFICANCE

Taken together these data indicate that HIF-1α/PFKFB3/PFK1 regulatory axis is a vital determinant of glucose metabolic reprogramming in hepatocellular carcinoma, which gives new insights into the action of metformin in combatting liver cancer.

Autophagy inhibition elicits emergence from metastatic dormancy by inducing and stabilizing Pfkfb3 expression

Breast cancer stem cells (BCSCs) are unique in their ability to undergo unlimited self-renewal, an essential process in breast cancer recurrence following metastatic dormancy. Emergent metastatic lesions were subjected to microarray analysis, which identified 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (Pfkfb3) as a differentially expressed gene coupled to metastatic recurrence. Here, we report that elevated Pfkfb3 expression correlates with the appearance of aggressive breast cancers and reduces relapse-free survival, as well as enhances BCSC self-renewal and metastatic outgrowth. We observe an inverse relationship between Pfkfb3 expression and autophagy, which reduces Pfkfb3 expression and elicits cellular dormancy. Targeted depletion of Atg3, Atg7, or p62/sequestosome-1 to inactivate autophagy restores aberrant Pfkfb3 expression in dormant BCSCs, leading to their reactivation of proliferative programs and outgrowth. Moreover, Pfkfb3 interacts physically with autophagy machinery, specifically the UBA domain of p62/sequestosome-1. Importantly, disrupting autophagy and this event enables Pfkfb3 to drive dormant BCSCs and metastatic lesions to recur.

Increased 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 activity in response to EGFR signaling contributes to non-small cell lung cancer cell survival

Constitutive activation of the epidermal growth factor receptor (EGFR) because of somatic mutations of the EGFR gene is commonly observed in tumors of non-small cell lung cancer (NSCLC) patients. Consequently, tyrosine kinase inhibitors (TKI) targeting the EGFR are among the most effective therapies for patients with sensitizing EGFR mutations. Clinical responses to the EGFR-targeting TKIs are evaluated through 2-[¹⁸F]fluoro-2-deoxy-glucose (¹⁸FDG)-PET uptake, which is decreased in patients responding favorably to therapy and is positively correlated with survival. Recent studies have reported that EGFR signaling drives glucose metabolism in NSCLC cells; however, the precise downstream effectors required for this EGFR-driven metabolic effect are largely unknown. 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3) is an essential glycolytic regulator that is consistently overexpressed in lung cancer. Here, we found that PFKFB3 is an essential target of EGFR signaling and that PFKFB3 activation is required for glycolysis stimulation upon EGFR activation. We demonstrate that exposing NSCLC cells harboring either WT or mutated EGFR to EGF rapidly increases PFKFB3 phosphorylation, expression, and activity and that PFKFB3 inhibition markedly reduces the EGF-mediated increase in glycolysis. Furthermore, we found that prolonged NSCLC cell exposure to the TKI erlotinib drives PFKFB3 expression and that chemical PFKFB3 inhibition synergizes with erlotinib in increasing erlotinib's anti-proliferative activity in NSCLC cells. We conclude that PFKFB3 has a key role in mediating glucose metabolism and survival of NSCLC cells in response to EGFR signaling. These results support the potential clinical utility of using PFKFB3 inhibitors in combination with EGFR-TKIs to manage NSCLC.

Effect of PTEN loss on metabolic reprogramming in prostate cancer cells

The tumor suppressor gene PTEN is one of the most often deleted genes in human prostate cancer. Loss of PTEN is an important event in prostate carcinogenesis. Metabolic reprogramming induced by PTEN loss fuels malignant growth and proliferation of prostate cancer cells. Targeted metabolomics analysis was used to investigate the effects of PTEN loss on intracellular metabolic pathways in prostate cancer cells. DU-145 cells were transfected with PTEN siRNAs (siRNA-1 and siRNA-2) for 48 h, and endogenous PTEN expression was monitored by western blotting. Changes in intracellular metabolites were determined by liquid chromatography-tandem mass chromatography (LC-MS/MS) and gas chromatography-mass spectrometry (GC-MS). Most intracellular metabolites involved in glycolysis and glutaminolysis were increased in PTEN knockdown prostate cancer cells. In addition, most intracellular metabolites involved in fatty acid de novo synthesis, fatty acid beta oxidation and branched chain amino acid catabolism were also increased in PTEN knockdown prostate cancer cells. These results revealed that PTEN loss induced the metabolic reprogramming of prostate cancer cells and promoted the malignant proliferation of prostate cancer cells. The present metabolomics analysis indicates that tumor suppressor gene PTEN mutation or deletion can induce metabolic reprogramming in prostate cancer cells and tumorigenesis by altering the metabolic flux of glycolysis, glutaminolysis, fatty acid metabolism and branched chain amino acid catabolism pathways. Metabolic reprogramming is one of the contributors to PTEN-loss driven prostate cancer.

An Apoptotic and Endosymbiotic Explanation of the Warburg and the Inverse Warburg Hypotheses

Otto Warburg, a Nobel prize winner, observed that cancer cells typically “switch” from aerobic to anaerobic respiration. He hypothesized that mitochondrial damage induces neoplastic transformation. In contrast, pathological aging is observed mainly in neuron cells in neurodegenerative diseases. Oxidative respiration is particularly active in neurons. There is inverse comorbidity between cancer and neurodegenerative diseases. This led to the creation of the “inverse Warburg hypothesis”, according to which excessive mitochondrial activity induces pathological aging. The findings of our studies suggest that both the Warburg effect and the “inverse Warburg hypothesis” can be elucidated by the activation or suppression of apoptosis through oxidative respiration. The key outcome of our phylogenetic studies was the discovery that apoptosis and apoptosis-like cell death evolved due to an evolutionary “arms race” conducted between “prey” protomitochondrion and “predator” primitive eukaryotes. The ancestral protomitochondrial machinery produces and releases toxic mitochondrial proteins. Extant apoptotic factors evolved from these toxins. Our experiments indicate that the mitochondrial machinery is directly involved in adaptation to aerobic conditions. Additionally, our hypothesis is supported by the fact that different apoptotic factors are directly involved in respiration.

Roles of PFKFB3 in cancer

The understanding of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFK-2/FBPase 3, PFKFB3) has advanced considerably since its initial identification in human macrophages in the mid-1990s. As a vital regulator of glycolysis, accumulating studies have suggested that PFKFB3 is associated with many aspects of cancer, including carcinogenesis, cancer cell proliferation, vessel aggressiveness, drug resistance and tumor microenvironment. In this review, we summarize current knowledge of PFKFB3 regulation by several signal pathways and its function in cancer development in different cell types in cancer tissues. Ubiquitous PFKFB3 has emerged as a potential target for anti-neoplastic therapy.

The molecular basis of targeting PFKFB3 as a therapeutic strategy against cancer

6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatases (PFKFBs) are bifunctional enzymes which regulate the transformation between fructose-2, 6-bisphosphate (F2, 6BP) and fructose-6-phosphate (F6P) in the process of glucose metabolism. Among the four isozymes (PFKFB1-4), PFKFB3 has stronger kinase activity than phosphatase activity, resulting in the synthesis of F2, 6BP and the promotion of glycolysis. Additionally, PFKFB3 plays a key role in cell cycle regulation. It has been confirmed that PFKFB3 is upregulated in a variety of tumor cells, and inhibition of it results in suppression of the growth of tumor cells by downregulating the glycolytic flux. It is expected to release drug resistance and prevent disease progression by PFKFB3 inhibition. Recent studies have also shown that the efficacy of PFKFB3 inhibition in tumor cells is not only related to glycolysis, but also autophagy. Here, we have reviewed the biological characteristics of PFKFB3, the regulation pathway of glucose metabolism manipulated by PFKFB3, and other regulatory mechanisms in hematologic and non-hematologic malignant tumor cells.

Role of Proton Pumps in Tumorigenesis

One of the differences between normal and cancer cells is lower pH of the extracellular space in tumors. Low pH in the extracellular space activates proteases and stimulates tumor invasion and metastasis. Tumor cells display higher level of the HIF1α transcription factor that promotes cell switch from mitochondrial respiration to glycolysis. The terminal product of glycolysis is lactate. Lactate formation from pyruvate is catalyzed by the specific HIF1α-dependent isoform of lactate dehydrogenase A. Because lactate accumulation is deleterious for the cell, it is actively exported by monocarboxylate transporters. Lactate is cotransported with proton, which acidifies the extracellular space. Another protein that contributes to proton concentration increase in the extracellular space is tumor-specific HIF1α-dependent carbonic anhydrase IX, which generates a proton in the reaction between carbon dioxide and water. The activity of Na+/H+ exchanger (another protein pump) is stimulated by stress factors (e.g. osmotic shock) and proliferation stimuli. This review describes the mechanisms of proton pump activation and reviews results of studies on effects of various proton pump inhibitors on tumor functioning and growth in cell culture and in vivo. The prospects of combined application of proton pump inhibitors and cytostatics in cancer therapy are discussed.

Allosteric regulation of metabolism in cancer: endogenous mechanisms and considerations for drug design

Alterations in metabolic processes have been linked to various diseases, including cancer. Although gene expression can dictate long-term metabolic adaptation, many metabolic changes found in cancer are associated with altered allosteric properties of the underlying enzymes. Small molecule-protein interactions and intracellular signalling converge to orchestrate these allosteric mechanisms, which, emerging evidence suggests, constitute a promising therapeutic avenue. In this review we focus on glucose and energy metabolism to illustrate the role of allostery in cancer physiology and we discuss approaches to streamline the process of targeting aberrant allosteric pathways with small molecules.

The Glycolytic Enzyme PFKFB3 Is Involved in Estrogen-Mediated Angiogenesis via GPER1

The endogenous estrogen 17β-estradiol (E2) is a key factor in promoting endothelial healing and angiogenesis. Recently, proangiogenic signals including vascular endothelial growth factor and others have been shown to converge in endothelial cell metabolism. Because inhibition of the glycolytic enzyme activator phosphofructokinase-2/fructose-2,6-bisphosphatase 3 (PFKFB3) reduces pathologic angiogenesis and estrogen receptor (ER) signaling stimulates glucose uptake and glycolysis by inducing PFKFB3 in breast cancer, we hypothesized that E2 triggers angiogenesis in endothelial cells via rapid ER signaling that requires PFKFB3 as a downstream effector. We report that treatment with the selective G protein-coupled estrogen receptor (GPER1) agonist G-1 (10^-10 to 10^-7 M) mimicked the chemotactic and proangiogenic effect of E2 as measured in a number of short-term angiogenesis assays in human umbilical vein endothelial cells (HUVECs); in addition, E2 treatment upregulated PFKFB3 expression in a time- and concentration-dependent manner. Such an effect peaked at 3 hours and was also induced by G-1 and abolished by pretreatment with the GPER1 antagonist G-15 or GPER1 siRNA, consistent with engagement of membrane ER. Experiments with the PFKFB3 inhibitor 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one showed that PFKFB3 activity was required for estrogen-mediated HUVEC migration via GPER1. In conclusion, E2-induced angiogenesis was mediated at least in part by the membrane GPER1 and required upregulation of the glycolytic activator PFKFB3 in HUVECs. These findings unravel a previously unrecognized mechanism of estrogen-dependent endocrine-metabolic crosstalk in HUVECs and may have implications in angiogenesis occurring in ischemic or hypoxic tissues.

Cerebral Gluconeogenesis and Diseases

The gluconeogenesis pathway, which has been known to normally present in the liver, kidney, intestine, or muscle, has four irreversible steps catalyzed by the enzymes: pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase, and glucose 6-phosphatase. Studies have also demonstrated evidence that gluconeogenesis exists in brain astrocytes but no convincing data have yet been found in neurons. Astrocytes exhibit significant 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 activity, a key mechanism for regulating glycolysis and gluconeogenesis. Astrocytes are unique in that they use glycolysis to produce lactate, which is then shuttled into neurons and used as gluconeogenic precursors for reduction. This gluconeogenesis pathway found in astrocytes is becoming more recognized as an important alternative glucose source for neurons, specifically in ischemic stroke and brain tumor. Further studies are needed to discover how the gluconeogenesis pathway is controlled in the brain, which may lead to the development of therapeutic targets to control energy levels and cellular survival in ischemic stroke patients, or inhibit gluconeogenesis in brain tumors to promote malignant cell death and tumor regression. While there are extensive studies on the mechanisms of cerebral glycolysis in ischemic stroke and brain tumors, studies on cerebral gluconeogenesis are limited. Here, we review studies done to date regarding gluconeogenesis to evaluate whether this metabolic pathway is beneficial or detrimental to the brain under these pathological conditions.

Maf1, A New PTEN Target Linking RNA and Lipid Metabolism

PTEN is a critical tumor suppressor whose dysregulation leads to metabolic disease and cancer. How these diseases are linked at a molecular level is poorly understood. Maf1 is a novel PTEN target that connects PTEN's ability to repress intracellular lipid accumulation with its tumor suppressor function. Maf1 represses the expression of rRNAs and tRNAs to restrain biosynthetic capacity and oncogenic transformation. Recent studies demonstrate that Maf1 also controls intracellular lipid accumulation. In animal models, dysregulation of RNA polymerase I- and III-dependent transcription, and subsequent upregulation of rRNAs and tRNAs, leads to altered lipid metabolism and storage. Together these results identify unexpected connections between RNA and lipid metabolism that may help explain the strong epidemiological association between obesity and cancer.

Retinal regeneration mechanisms linked to multiple cancer molecules: A therapeutic conundrum

Over the last decade, a large number of research articles have been published demonstrating regeneration and/or neuroprotection of retinal ganglion cells following manipulation of specific genetic and molecular targets. Interestingly, of the targets that have been identified to promote repair following visual system damage, many are genes known to be mutated in different types of cancer. This review explores recent literature on the potential for modulating cancer genes as a therapeutic strategy for visual system repair and looks at the potential clinical challenges associated with implementing this type of therapy. We also discuss signalling mechanisms that have been implicated in cancer and consider how similar mechanisms may improve axonal regeneration in the optic nerve.

Type 2 Diabetes Dysregulates Glucose Metabolism in Cardiac Progenitor Cells

Type 2 diabetes is associated with increased mortality and progression to heart failure. Recent studies suggest that diabetes also impairs reparative responses after cell therapy. In this study, we examined potential mechanisms by which diabetes affects cardiac progenitor cells (CPCs). CPCs isolated from the diabetic heart showed diminished proliferation, a propensity for cell death, and a pro-adipogenic phenotype. The diabetic CPCs were insulin-resistant, and they showed higher energetic reliance on glycolysis, which was associated with up-regulation of the pro-glycolytic enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3). In WT CPCs, expression of a mutant form of PFKFB, which mimics PFKFB3 activity and increases glycolytic rate, was sufficient to phenocopy the mitochondrial and proliferative deficiencies found in diabetic cells. Consistent with activation of phosphofructokinase in diabetic cells, stable isotope carbon tracing in diabetic CPCs showed dysregulation of the pentose phosphate and glycero(phospho)lipid synthesis pathways. We describe diabetes-induced dysregulation of carbon partitioning using stable isotope metabolomics-based coupling quotients, which relate relative flux values between metabolic pathways. These findings suggest that diabetes causes an imbalance in glucose carbon allocation by uncoupling biosynthetic pathway activity, which could diminish the efficacy of CPCs for myocardial repair.

PTEN stabilizes TOP2A and regulates the DNA decatenation

PTEN is a powerful tumor suppressor that antagonizes the cytoplasmic PI3K-AKT pathway and suppresses cellular proliferation. PTEN also plays a role in the maintenance of genomic stability in the nucleus. Here we report that PTEN facilitates DNA decatenation and controls a decatenation checkpoint. Catenations of DNA formed during replication are decatenated by DNA topoisomerase II (TOP2), and this process is actively monitored by a decatenation checkpoint in G2 phase. We found that PTEN deficient cells form ultra-fine bridges (UFBs) during anaphase and these bridges are generated as a result of insufficient decatenation. We show that PTEN is physically associated with a decatenation enzyme TOP2A and that PTEN influences its stability through OTUD3 deubiquitinase. In the presence of PTEN, ubiquitination of TOP2A is inhibited by OTUD3. Deletion or deficiency of PTEN leads to down regulation of TOP2A, dysfunction of the decatenation checkpoint and incomplete DNA decatenation in G2 and M phases. We propose that PTEN controls DNA decatenation to maintain genomic stability and integrity.

PFKFB3-mediated glycolysis is involved in reactive astrocyte proliferation after oxygen-glucose deprivation/reperfusion and is regulated by Cdh1

Reactive astrocyte proliferation is involved in many central degenerative diseases. The enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase isoform 3 (PFKFB3), an allosteric activator of 6-phosphofructo-1-kinase (PFK1), controls glycolytic flux. Furthermore, APC/C-Cdh1 plays a crucial role in brain metabolism by regulating PFKFB3 expression. Previous studies have defined the roles of PFKFB3-mediated glycolysis in pathological angiogenesis, cell autophagy, and amyloid plaque deposition in proliferating cells. However, the role of PFKFB3 in reactive astrocyte proliferation after cerebral ischemia is unknown. In this study, we cultured rat primary cortical astrocytes and established an oxygen-glucose deprivation/reperfusion (OGD/R) model to mimic cerebral ischemia in vivo. Astrocyte proliferation was measured by western blotting for proliferating cell nuclear antigen (PCNA) and by EdU incorporation. We found that OGD/R up-regulated PFKFB3 and PFK1 expression, which was accompanied by reactive astrocyte proliferation. Knockdown of PFKFB3 by siRNA transfection significantly inhibited reactive astrocyte proliferation and lactate release, an indicator of glycolysis. We found that PFKFB3 and PFK1 expression were down-regulated and lactate release was decreased when OGD/R-induced astrocyte proliferation was inhibited by a Cdh1-expressing lentivirus. Thus, reactive astrocyte proliferation can be effectively suppressed by down-regulation of PFKFB3 through control of glycolytic flux, which is downstream of APC/C-Cdh1.

Resonance light scattering detection of fructose bisphosphates using uranyl-salophen complex-modified gold nanoparticles as optical probe

In this paper, we report a resonance light scattering (RLS) method for the determination of fructose bisphosphates (FBPs) in water solution using fructose 1,6-bisphosphate (F-1,6-BP) as a model analyte without the procedure of extracting target analyte. The method used a type of modified gold nanoparticles (GNPs) as optical probe. The modified GNPs are uranyl-salophen-cysteamine-GNPs (U-Sal-Cy-GNPs) which are obtained through the acylation reaction of carboxylated salophen with cysteamine-capped GNPs (Cy-GNPs) to form Sal-Cy-GNPs and then the chelation reaction of uranyl with tetradentate ligand salophen in the Sal-Cy-GNPs. A FBP molecule is used easily to connect two U-Sal-Cy-GNPs to cause the aggregation of the GNPs by utilizing the specific affinity of uranyl-salophen complex to phosphate group, resulting in the production of strong RLS signal from the system. The amount of FBPs can be determined through detecting the RLS intensity change of the system. A linear range was found to be 2.5 to 75 nmol/L with a detection limit of 0.91 nmol/L under optimal conditions. The method has been successfully used to determine FBPs in real samples with the recoveries of 96.5-103.5 %.

Kinome Screen Identifies PFKFB3 and Glucose Metabolism as Important Regulators of the Insulin/Insulin-like Growth Factor (IGF)-1 Signaling Pathway

The insulin/insulin-like growth factor (IGF)-1 signaling pathway (ISP) plays a fundamental role in long term health in a range of organisms. Protein kinases including Akt and ERK are intimately involved in the ISP. To identify other kinases that may participate in this pathway or intersect with it in a regulatory manner, we performed a whole kinome (779 kinases) siRNA screen for positive or negative regulators of the ISP, using GLUT4 translocation to the cell surface as an output for pathway activity. We identified PFKFB3, a positive regulator of glycolysis that is highly expressed in cancer cells and adipocytes, as a positive ISP regulator. Pharmacological inhibition of PFKFB3 suppressed insulin-stimulated glucose uptake, GLUT4 translocation, and Akt signaling in 3T3-L1 adipocytes. In contrast, overexpression of PFKFB3 in HEK293 cells potentiated insulin-dependent phosphorylation of Akt and Akt substrates. Furthermore, pharmacological modulation of glycolysis in 3T3-L1 adipocytes affected Akt phosphorylation. These data add to an emerging body of evidence that metabolism plays a central role in regulating numerous biological processes including the ISP. Our findings have important implications for diseases such as type 2 diabetes and cancer that are characterized by marked disruption of both metabolism and growth factor signaling.

Sonic hedgehog stimulates glycolysis and proliferation of breast cancer cells: Modulation of PFKFB3 activation

Sonic hesgehog (Shh) signaling has been reported to play an essential role in cancer progression. The mechanism of Shh involved in breast cancer carcinogenesis remains unclear. The present study sought to explore whether Shh signaling could regulate the glycolytic metabolism in breast cancers. Overexpression of the smoothed (Smo) and Gli-1 was found in human primary breast cancers. The expressions of Shh and Gli-1 correlated significantly with tumor size and tumor stage. In vitro, human recombinant Shh (rShh) triggered Smo and Gli-1 expression, promoted glucose utilization and lactate production, and accelerated cell proliferation in MCF-7 and MDA-MB-231 cells. Notably, rShh did not alter 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) expression but augmented PFKFB3 phosphorylation on ser(461), along with elevated fructose-2,6-bisphosphate (F2,6BP) generation by MCF-7 and MDA-MB-231 cells. This effect could be dampened by Smo siRNA but not by Gli-1 siRNA. In addition, our data showed the upregulated expressions of MAPK by rShh and elevatory PFKFB3 phosphorylation by p38/MAPK activated kinase (MK2). In conclusion, our study characterized a novel role of Shh in promoting glycolysis and proliferation of breast cancer cells via PFKFB3 phosphorylation, which was mediated by Smo and p38/MK2.

Fructose-2,6-bisphosphate synthesis by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 (PFKFB4) is required for the glycolytic response to hypoxia and tumor growth

Fructose-2,6-bisphosphate (F2,6BP) is a shunt product of glycolysis that allosterically activates 6-phosphofructo-1-kinase (PFK-1) resulting in increased glucose uptake and glycolytic flux to lactate. The F2,6BP concentration is dictated by four bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB1-4) with distinct kinase:phosphatase activities. PFKFB4 is over-expressed in human cancers, induced by hypoxia and required for survival and growth of several cancer cell lines. Although PFKFB4 appears to be a rational target for anti-neoplastic drug development, it is not clear whether its kinase or phosphatase activity is required for cancer cell survival. In this study, we demonstrate that recombinant human PFKFB4 kinase activity is 4.3-fold greater than its phosphatase activity, siRNA and genomic deletion of PFKFB4 decrease F2,6BP, PFKFB4 over-expression increases F2,6BP and selective PFKFB4 inhibition in vivo markedly reduces F2,6BP, glucose uptake and ATP. Last, we find that PFKFB4 is required for cancer cell survival during the metabolic response to hypoxia, presumably to enable glycolytic production of ATP when the electron transport chain is not fully operational. Taken together, our data indicate that the PFKFB4 expressed in multiple transformed cells and tumors functions to synthesize F2,6BP. We predict that pharmacological disruption of the PFKFB4 kinase domain may have clinical utility for the treatment of human cancers.

Tissue invasion and metastasis: Molecular, biological and clinical perspectives

Cancer is a key health issue across the world, causing substantial patient morbidity and mortality. Patient prognosis is tightly linked with metastatic dissemination of the disease to distant sites, with metastatic diseases accounting for a vast percentage of cancer patient mortality. While advances in this area have been made, the process of cancer metastasis and the factors governing cancer spread and establishment at secondary locations is still poorly understood. The current article summarizes recent progress in this area of research, both in the understanding of the underlying biological processes and in the therapeutic strategies for the management of metastasis. This review lists the disruption of E-cadherin and tight junctions, key signaling pathways, including urokinase type plasminogen activator (uPA), phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene (PI3K/AKT), focal adhesion kinase (FAK), β-catenin/zinc finger E-box binding homeobox 1 (ZEB-1) and transforming growth factor beta (TGF-β), together with inactivation of activator protein-1 (AP-1) and suppression of matrix metalloproteinase-9 (MMP-9) activity as key targets and the use of phytochemicals, or natural products, such as those from Agaricus blazei, Albatrellus confluens, Cordyceps militaris, Ganoderma lucidum, Poria cocos and Silybum marianum, together with diet derived fatty acids gamma linolenic acid (GLA) and eicosapentanoic acid (EPA) and inhibitory compounds as useful approaches to target tissue invasion and metastasis as well as other hallmark areas of cancer. Together, these strategies could represent new, inexpensive, low toxicity strategies to aid in the management of cancer metastasis as well as having holistic effects against other cancer hallmarks.

PS48 can replace bovine serum albumin in pig embryo culture medium, and improve in vitro embryo development by phosphorylating AKT

The application of embryo-related technology is dependent on in vitro culture systems. Unfortunately, most culture media are suboptimal and result in developmentally compromised embryos. Since embryo development is partially dependent upon Warburg Effect-like metabolism, our goal was to test the response of embryos treated with compounds that are known to stimulate or enhance this Effect. One such compound is 5-(4-chloro-phenyl)-3-phenyl-pent-2-enoic acid (PS48). When added during oocyte maturation, the quality of the resultant embryos was compromised, whereas when added to the culture medium after fertilization, PS48 improved both the percentage of embryos that reach the blastocyst stage and the number of nuclei in those blastocysts. Embryonic PS48 treatment resulted in more phosphorylated v-akt murine thymoma viral oncogene homolog (AKT) in blastocyst-stage embryos as compared to the controls. Further, PS48 could replace bovine serum albumin in embryo culture medium, as demonstrated by high-quality embryos that were developmentally competent. The action of PS48 appears to be via stimulation of phosphoinositide-3 kinase and phosphorylation of AKT, which is consistent with stimulation of the Warburg Effect.

Evasion of anti-growth signaling: A key step in tumorigenesis and potential target for treatment and prophylaxis by natural compounds

The evasion of anti-growth signaling is an important characteristic of cancer cells. In order to continue to proliferate, cancer cells must somehow uncouple themselves from the many signals that exist to slow down cell growth. Here, we define the anti-growth signaling process, and review several important pathways involved in growth signaling: p53, phosphatase and tensin homolog (PTEN), retinoblastoma protein (Rb), Hippo, growth differentiation factor 15 (GDF15), AT-rich interactive domain 1A (ARID1A), Notch, insulin-like growth factor (IGF), and Krüppel-like factor 5 (KLF5) pathways. Aberrations in these processes in cancer cells involve mutations and thus the suppression of genes that prevent growth, as well as mutation and activation of genes involved in driving cell growth. Using these pathways as examples, we prioritize molecular targets that might be leveraged to promote anti-growth signaling in cancer cells. Interestingly, naturally occurring phytochemicals found in human diets (either singly or as mixtures) may promote anti-growth signaling, and do so without the potentially adverse effects associated with synthetic chemicals. We review examples of naturally occurring phytochemicals that may be applied to prevent cancer by antagonizing growth signaling, and propose one phytochemical for each pathway. These are: epigallocatechin-3-gallate (EGCG) for the Rb pathway, luteolin for p53, curcumin for PTEN, porphyrins for Hippo, genistein for GDF15, resveratrol for ARID1A, withaferin A for Notch and diguelin for the IGF1-receptor pathway. The coordination of anti-growth signaling and natural compound studies will provide insight into the future application of these compounds in the clinical setting.

Targeting the glucose-regulated protein-78 abrogates Pten-null driven AKT activation and endometrioid tumorigenesis

Rates of the most common gynecologic cancer, endometrioid adenocarcinoma (EAC), continue to rise, mirroring the global epidemic of obesity, a well-known EAC risk factor. Thus, identifying novel molecular targets to prevent and/or mitigate EAC is imperative. The prevalent Type 1 EAC commonly harbors loss of the tumor suppressor, Pten, leading to AKT activation. The major endoplasmic reticulum (ER) chaperone, GRP78, is a potent pro-survival protein to maintain ER homeostasis, and as a cell surface protein, is known to regulate the PI3K/AKT pathway. To determine whether targeting GRP78 could suppress EAC development, we created a conditional knockout mouse model utilizing progesterone receptor (PR)-Cre-recombinase to achieve Pten and Grp78 (cPten^f/fGrp78^f/f) deletion in the endometrial epithelium. Mice with a single Pten (cPten^f/f) deletion developed well-differentiated EAC by 4 weeks. In contrast, no cPten^f/fGrp78^f/f mice developed EAC, even after more than 8 months of observation. Histologic examination of uteri from cPten^f/fGrp78^f/f mice also revealed no complex atypical hyperplasia (CAH), a well-established EAC precursor. These histologic observations among the cPten^f/fGrp78^f/f murine uteri also corresponded to abrogation of AKT activation within the endometrium. We further observed that GRP78 co-localized with activated AKT on the surface of EAC thus providing an opportunity for therapeutic targeting. Consistent with previous findings that cell surface GRP78 is an upstream regulator of PI3K/AKT signaling, we show here that in vivo short-term systemic treatment with a highly specific monoclonal antibody against GRP78 suppressed AKT activation and increased apoptosis in the cPten^f/f tumors. Collectively, these findings present GRP78-targeting therapy as an efficacious therapeutic option for EAC.

Mechanisms of regulation of PFKFB expression in pancreatic and gastric cancer cells

Enzymes 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 and -4 (PFKFB-3 and PFKFB-4) play a significant role in the regulation of glycolysis in cancer cells as well as its proliferation and survival. The expression of these mRNAs is increased in malignant tumors and strongly induced in different cancer cell lines by hypoxia inducible factor (HIF) through active HIF binding sites in promoter region of PFKFB-4 and PFKFB-3 genes. Moreover, the expression and hypoxia responsibility of PFKFB-4 and PFKFB-3 was also shown for pancreatic (Panc1, PSN-1, and MIA PaCa-2) as well as gastric (MKN45 and NUGC3) cancer cells. At the same time, their basal expression level and hypoxia responsiveness vary in the different cells studied: the highest level of PFKFB-4 protein expression was found in NUGC3 gastric cancer cell line and lowest in Panc1 cells, with a stronger response to hypoxia in the pancreatic cancer cell line. Overexpression of different PFKFB in pancreatic and gastric cancer cells under hypoxic condition is correlated with enhanced expression of vascular endothelial growth factor (VEGF) and Glut1 mRNA as well as with increased level of HIF-1α protein. Increased expression of different PFKFB genes was also demonstrated in gastric, lung, breast, and colon cancers as compared to corresponding non-malignant tissue counterparts from the same patients, being more robust in the breast and lung tumors. Moreover, induction of PFKFB-4 mRNA expression in the breast and lung cancers is stronger than PFKFB-3 mRNA. The levels of both PFKFB-4 and PFKFB-3 proteins in non-malignant gastric and colon tissues were more pronounced than in the non-malignant breast and lung tissues. It is interesting to note that Panc1 and PSN-1 cells transfected with dominant/negative PFKFB-3 (dnPFKFB-3) showed a lower level of endogenous PFKFB-3, PFKFB-4, and VEGF mRNA expressions as well as a decreased proliferation rate of these cells. Moreover, a similar effect had dnPFKFB-4. In conclusion, there is strong evidence that PFKFB-4 and PFKFB-3 isoenzymes are induced under hypoxia in pancreatic and other cancer cell lines, are overexpressed in gastric, colon, lung, and breast malignant tumors and undergo changes in their metabolism that contribute to the proliferation and survival of cancer cells. Thus, targeting these PFKFB may therefore present new therapeutic opportunities.

6-Phosphofructo-2-kinase (PFKFB3) promotes cell cycle progression and suppresses apoptosis via Cdk1-mediated phosphorylation of p27

The control of glucose metabolism and the cell cycle must be coordinated in order to guarantee sufficient ATP and anabolic substrates at distinct phases of the cell cycle. The family of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB1-4) are well established regulators of glucose metabolism via their synthesis of fructose-2,6-bisphosphate (F2,6BP), a potent allosteric activator of 6-phosphofructo-1-kinase (Pfk-1). PFKFB3 is overexpressed in human cancers, regulated by HIF-1α, Akt and PTEN, and required for the survival and growth of multiple cancer types. Although most functional studies of the role of PFKFB3 in cancer progression have invoked its well-recognized function in the regulation of glycolysis, recent observations have established that PFKFB3 also traffics to the nucleus and that its product, F2,6BP, activates cyclin-dependent kinases (Cdks). In particular, F2,6BP stimulates the Cdk-mediated phosphorylation of the Cip/Kip protein p27 (threonine 187), which in turn results in p27's ubiquitination and proteasomal degradation. As p27 is a potent suppressor of the G1/S transition and activator of apoptosis, we hypothesized that the known requirement of PFKFB3 for cell cycle progression and prevention of apoptosis may be partly due to the ability of F2,6BP to activate Cdks. In this study, we demonstrate that siRNA silencing of endogenous PFKFB3 inhibits Cdk1 activity, which in turn stabilizes p27 protein levels causing cell cycle arrest at G1/S and increased apoptosis in HeLa cells. Importantly, we demonstrate that the increase in apoptosis and suppression of the G1/S transition caused by siRNA silencing of PFKFB3 expression is reversed by co-siRNA silencing of p27. Taken together with prior publications, these observations support a model whereby PFKFB3 and F2,6BP function not only as regulators of Pfk-1 but also of Cdk1 activity, and therefore serve to couple glucose metabolism with cell proliferation and survival in transformed cells.