A critical review of the role of M2PYK in the Warburg effect

LncRNA SH3BP5-AS1 promotes hepatocellular carcinoma progression by sponging miR-6838-5p and activation of PTPN4

BACKGROUND

Long noncoding RNAs (LncRNAs) have been demonstrated to have significant roles in the carcinogenesis of hepatocellular carcinoma (HCC). In this work, we sought to determine LncRNA SH3BP5-AS1's function and mechanism in the emergence of HCC.

RESULTS

First, we discovered that the advanced tumor stage was strongly correlated with high levels of LncRNA SH3BP5-AS1 expression in HCC. MiR-6838-5p expression was down-regulated and inversely correlated with SH3BP5-AS1 expression. Additionally, overexpression of SH3BP5-AS1 boosted cell invasion, migration, and proliferation. The oncogenic effects of the inhibitor of miR-6838-5p were eliminated when PTPN4 was suppressed, following the identification of PTPN4 as a direct target of miR-6838-5p. In addition, SH3BP5-AS1 promoted cellular glycolysis via miR-6838-5p sponging and PTPN4 activation. Lastly, by directly interacting to the promoter of SH3BP5-AS1, HIF-1α could control the transcription of the gene.

CONCLUSIONS

Our research suggests that SH3BP5-AS1 controls miR-6838-5p/PTPN4 in order to act as a new carcinogenic LncRNA during the growth of HCC cells.

METHODS

The expression levels of SH3BP5-AS1, miR-6838-5p and PTPN4 were detected by qRT-PCR and Western blot. The effects of LncRNA SH3BP5-AS1/miR-6838-5p/PTPN4 on the proliferation, metastasis and glycolysis of HCC cells were clarified by experimental cellular functionality assays, cell derived xenograft and Glycolysis assay.

What is allosteric regulation? Exploring the exceptions that prove the rule!

"Allosteric" was first introduced to mean the other site (i.e., a site distinct from the active or orthosteric site), an adjective for "regulation" to imply a regulatory outcome resulting from ligand binding at another site. That original idea outlines a system with two ligand-binding events at two distinct locations on a macromolecule (originally a protein system), which defines a four-state energy cycle. An allosteric energy cycle provides a quantifiable allosteric coupling constant and focuses our attention on the unique properties of the four equilibrated protein complexes that constitute the energy cycle. Because many observed phenomena have been referenced as "allosteric regulation" in the literature, the goal of this work is to use literature examples to explore which systems are and are not consistent with the two-ligand thermodynamic energy cycle-based definition of allosteric regulation. We emphasize the need for consistent language so comparisons can be made among the ever-increasing number of allosteric systems. Building on the mutually exclusive natures of an energy cycle definition of allosteric regulation versus classic two-state models, we conclude our discussion by outlining how the often-proposed Rube-Goldberg-like mechanisms are likely inconsistent with an energy cycle definition of allosteric regulation.

The 2.4 Å structure of Zymomonas mobilis pyruvate kinase: Implications for stability and regulation

Human liver pyruvate kinase (hlPYK) catalyzes the final step in glycolysis, the formation of pyruvate (PYR) and ATP from phosphoenolpyruvate (PEP) and ADP. Fructose 1,6-bisphosphate (FBP), a pathway intermediate of glycolysis, serves as an allosteric activator of hlPYK. Zymomonas mobilis pyruvate kinase (ZmPYK) performs the final step of the Entner-Doudoroff pathway, which is similar to glycolysis in that energy is harvested from glucose and pyruvate is generated. The Entner-Doudoroff pathway does not have FBP as a pathway intermediate, and ZmPYK is not allosterically activated. In this work, we solved the 2.4 Å X-ray crystallographic structure of ZmPYK. The protein is dimeric in solution as determined by gel filtration chromatography, but crystallizes as a tetramer. The buried surface area of the ZmPYK tetramerization interface is significantly smaller than that of hlPYK, and yet tetramerization using the standard interfaces from higher organisms provides an accessible low energy crystallization pathway. Interestingly, the ZmPYK structure showed a phosphate ion in the analogous location to the 6-phosphate binding site of FBP in hlPYK. Circular Dichroism (CD) was used to measure melting temperatures of hlPYK and ZmPYK in the absence and presence of substrates and effectors. The only significant difference was an additional phase of small amplitude for the ZmPYK melting curves. We conclude that the phosphate ion plays neither a structural or allosteric role in ZmPYK under the conditions tested. We hypothesize that ZmPYK does not have sufficient protein stability for activity to be tuned by allosteric effectors as described for rheostat positions in the allosteric homologues.

Mitochondrial transfer in PC-3 cells fingerprinted in ferroptosis sensitivity: a brand new approach targeting cancer metabolism

Despite recent therapeutic advancements, cancer remains one of the leading causes of death worldwide, with mitochondrial dysfunction being associated with cancer initiation and progression, along with chemotherapeutic resistance and ferroptotic cell death failure; however, the significance of mitochondria in various cancer types remains a matter of debate for the moment. The aim of this study is to ascertain the outcome of transferring healthy mitochondria into the aggressive and rapidly proliferating prostate cancer (PC-3) cells and afterwards evaluate the efficacy of combination therapy with or without the ferroptosis inducer erastin. In this sense, normal mitochondria were first isolated from human umbilical cord-derived mesenchymal stem cells, human umbilical vein endothelial cells, and human embryonic kidney cells and were later transferred into PC-3 cells and rhodamine 6G-treated PC-3 cells exhibiting mitochondrial dysfunction. Next, cell proliferation and sensitivity to cisplatin were measured using Cell Counting Kit-8 and the Malondialdehyde Assay Lipid Peroxidation Kit, respectively, along with ferroptotic damage. Transferring the healthy mitochondria into PC-3 cells was observed to increase cell proliferation and rescue the cisplatin-induced cell death, but not the erastin-induced ferroptosis, as in mitochondrial transfer effectively enhanced erastin-mediated ferroptosis in PC-3 cells. Hence, the introduction of healthy mitochondria into the highly aggressive and proliferating cancer cells would be deemed a brand new therapeutic strategy for a variety of cancers.

Nitric oxide regulates metabolism in murine stress erythroid progenitors to promote recovery during inflammatory anemia

Inflammation skews bone marrow hematopoiesis increasing the production of myeloid effector cells at the expense of steady-state erythropoiesis. A compensatory stress erythropoiesis response is induced to maintain homeostasis until inflammation is resolved. In contrast to steady-state erythroid progenitors, stress erythroid progenitors (SEPs) utilize signals induced by inflammatory stimuli. However, the mechanistic basis for this is not clear. Here we reveal a nitric oxide (NO)-dependent regulatory network underlying two stages of stress erythropoiesis, namely proliferation, and the transition to differentiation. In the proliferative stage, immature SEPs and cells in the niche increased expression of inducible nitric oxide synthase ( Nos2 or iNOS ) to generate NO. Increased NO rewires SEP metabolism to increase anabolic pathways, which drive the biosynthesis of nucleotides, amino acids and other intermediates needed for cell division. This NO-dependent metabolism promotes cell proliferation while also inhibiting erythroid differentiation leading to the amplification of a large population of non-committed progenitors. The transition of these progenitors to differentiation is mediated by the activation of nuclear factor erythroid 2-related factor 2 (Nfe2l2 or Nrf2). Nrf2 acts as an anti-inflammatory regulator that decreases NO production, which removes the NO-dependent erythroid inhibition and allows for differentiation. These data provide a paradigm for how alterations in metabolism allow inflammatory signals to amplify immature progenitors prior to differentiation.

Key points

Nitric-oxide (NO) dependent signaling favors an anabolic metabolism that promotes proliferation and inhibits differentiation.Activation of Nfe2l2 (Nrf2) decreases NO production allowing erythroid differentiation.

Potential biomarkers in endometrial cancer: a narrative review

CONTEXT

Every year, approximately 0.4 million women suffer from endometrial cancer (EC) worldwide and it has become the most common gynecological malignancy. Almost 66% of EC cases are diagnosed at an early stage and can be cured by performing surgery while those at an advanced stage turns out to be fatal. Biomarkers of endometrial cancer would be very valuable for screening of women who are at high risk and in detecting the chance of recurrence of disease.

OBJECTIVE

The current article has reviewed studies published on expression of biomarkers and susceptibility to EC.

METHODS

Google Scholar and PubMed were used as searching platforms and we have majorly considered the literature from last 10 years.

RESULTS

Potential biomarkers of EC identified from various studies were summarised.

The roles of metabolic profiles and intracellular signaling pathways of tumor microenvironment cells in angiogenesis of solid tumors

Innate and adaptive immune cells patrol and survey throughout the human body and sometimes reside in the tumor microenvironment (TME) with a variety of cell types and nutrients that may differ from those in which they developed. The metabolic pathways and metabolites of immune cells are rooted in cell physiology, and not only provide nutrients and energy for cell growth and survival but also influencing cell differentiation and effector functions. Nowadays, there is a growing awareness that metabolic processes occurring in cancer cells can affect immune cell function and lead to tumor immune evasion and angiogenesis. In order to safely treat cancer patients and prevent immune checkpoint blockade-induced toxicities and autoimmunity, we suggest using anti-angiogenic drugs solely or combined with Immune checkpoint blockers (ICBs) to boost the safety and effectiveness of cancer therapy. As a consequence, there is significant and escalating attention to discovering techniques that target metabolism as a new method of cancer therapy. In this review, a summary of immune-metabolic processes and their potential role in the stimulation of intracellular signaling in TME cells that lead to tumor angiogenesis, and therapeutic applications is provided. Video abstract.

Reciprocal abrogation of PKM isoforms: contradictory outcomes and differing impact of splicing signal on CRISPR /Cas9 mediates gene editing in keratinocytes

The healing of wounded skin is a highly organized process involving a massive cell in- and outflux, proliferation and tissue remodelling. It is well accepted that metabolic constraints such as diabetes mellitus, overweight or anorexia impairs wound healing. Indeed, wound inflammation involves a boost of overall metabolic changes. As wound healing converges inflammatory processes that are also common to transformation, we investigate the functional role of the pro-neoplastic factor pyruvate kinase (PK) M2 and its metabolic active splice variant PKM1 in keratinocytes. Particularly, we challenge the impact of reciprocal ablation of PKM1 or two expression. Here, CRISPR/Cas9 genome editing of the PKM gene in HaCaT reveals an unexpected mutational bias at the 3'SS of exon 9, whereas no preference for any particular kind of mutation at exon 10 3' splice, despite the close vicinity (400 nucleotides apart) and sequence similarity between the two sites. Furthermore, as opposed to transient silencing of PKM2, exclusion splicing of PKM2 via genome editing mutually increases PKM1 mRNA and protein expression and compensates for the absence of PKM2, whereas the reciprocal elimination of PKM1 splicing reduces PKM2 expression and impedes cell proliferation, thus unveiling an essential role for PKM1 in growth and metabolic balance of HaCaT keratinocytes.

Noncoding RNAs in the Glycolysis of Ovarian Cancer

Energy metabolism reprogramming is the characteristic feature of tumors. The tumorigenesis, metastasis, and drug resistance of ovarian cancer (OC) is dependent on energy metabolism. Even under adequate oxygen conditions, OC cells tend to convert glucose to lactate, and glycolysis can rapidly produce ATP to meet their metabolic energy needs. Non-coding RNAs (ncRNAs) interact directly with DNA, RNA, and proteins to function as an essential regulatory in gene expression and tumor pathology. Studies have shown that ncRNAs regulate the process of glycolysis by interacting with the predominant glycolysis enzyme and cellular signaling pathway, participating in tumorigenesis and progression. This review summarizes the mechanism of ncRNAs regulation in glycolysis in OC and investigates potential therapeutic targets.

PKM2 Modulation in Head and Neck Squamous Cell Carcinoma

The enzyme pyruvate kinase M2 (PKM2) plays a major role in the switch of tumor cells from oxidative phosphorylation to aerobic glycolysis, one of the hallmarks of cancer. Different allosteric inhibitors or activators and several posttranslational modifications regulate its activity. Head and neck squamous cell carcinoma (HNSCC) is a common disease with a high rate of recurrence. To find out more about PKM2 and its modulation in HNSCC, we examined a panel of HNSCC cells using real-time cell metabolic analysis and Western blotting with an emphasis on phosphorylation variant Tyr105 and two reagents known to impair PKM2 activity. Our results show that in HNSCC, PKM2 is commonly phosphorylated at Tyrosine 105. Its levels depended on tyrosine kinase activity, emphasizing the importance of growth factors such as EGF (epidermal growth factor) on HNSCC metabolism. Furthermore, its correlation with the expression of CD44 indicates a role in cancer stemness. Cells generally reacted with higher glycolysis to PKM2 activator DASA-58 and lower glycolysis to PKM2 inhibitor Compound 3k, but some were more susceptible to activation and others to inhibition. Our findings emphasize the need to further investigate the role of PKM2 in HNSCC, as it could aid understanding and treatment of the disease.

ASO-based PKM splice-switching therapy inhibits hepatocellular carcinoma growth

The M2 pyruvate kinase (PKM2) isoform is upregulated in most cancers and plays a crucial role in regulation of the Warburg effect, which is characterized by the preference for aerobic glycolysis over oxidative phosphorylation for energy metabolism. PKM2 is an alternative-splice isoform of the PKM gene and is a potential therapeutic target. Antisense oligonucleotides (ASO) that switch PKM splicing from the cancer-associated PKM2 to the PKM1 isoform have been shown to induce apoptosis in cultured glioblastoma cells when delivered by lipofection. Here, we explore the potential of ASO-based PKM splice switching as a targeted therapy for liver cancer. A more potent lead cEt/DNA ASO induced PKM splice-switching and inhibited the growth of cultured hepatocellular carcinoma (HCC) cells. This PKM isoform switch increased pyruvate-kinase activity and altered glucose metabolism. In an orthotopic HCC xenograft mouse model, the lead ASO and a second ASO targeting a non-overlapping site inhibited tumor growth. Finally, in a genetic HCC mouse model, a surrogate mouse-specific ASO induced Pkm splice switching and inhibited tumorigenesis, without observable toxicity. These results lay the groundwork for a potential ASO-based splicing therapy for HCC.

Targeting Pyruvate Kinase M2 Phosphorylation Reverses Aggressive Cancer Phenotypes

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype with low survival rate and a lack of biomarkers and targeted treatments. Here, we target pyruvate kinase M2 (PKM2), a key metabolic component of oncogenesis. In patients with TNBC, PKM2pS37 was identified as a prominent phosphoprotein corresponding to the aggressive breast cancer phenotype that showed a characteristic nuclear staining pattern and prognostic value. Phosphorylation of PKM2 at S37 was connected with a cyclin-dependent kinase (CDK) pathway in TNBC cells. In parallel, pyruvate kinase activator TEPP-46 bound PKM2pS37 and reduced its nuclear localization. In a TNBC mouse xenograft model, treatment with either TEPP-46 or the potent CDK inhibitor dinaciclib reduced tumor growth and diminished PKM2pS37. Combinations of dinaciclib with TEPP-46 reduced cell invasion, impaired redox balance, and triggered cancer cell death. Collectively, these data support an approach to identify PKM2pS37-positive TNBC and target the PKM2 regulatory axis as a potential treatment. SIGNIFICANCE: PKM2 phosphorylation marks aggressive breast cancer cell phenotypes and targeting PKM2pS37 could be an effective therapeutic approach for treating triple-negative breast cancer.

From Glucose to Lactate and Transiting Intermediates Through Mitochondria, Bypassing Pyruvate Kinase: Considerations for Cells Exhibiting Dimeric PKM2 or Otherwise Inhibited Kinase Activity

A metabolic hallmark of many cancers is the increase in glucose consumption coupled to excessive lactate production. Mindful that L-lactate originates only from pyruvate, the question arises as to how can this be sustained in those tissues where pyruvate kinase activity is reduced due to dimerization of PKM2 isoform or inhibited by oxidative/nitrosative stress, posttranslational modifications or mutations, all widely reported findings in the very same cells. Hereby 17 pathways connecting glucose to lactate bypassing pyruvate kinase are reviewed, some of which transit through the mitochondrial matrix. An additional 69 converging pathways leading to pyruvate and lactate, but not commencing from glucose, are also examined. The minor production of pyruvate and lactate by glutaminolysis is scrutinized separately. The present review aims to highlight the ways through which L-lactate can still be produced from pyruvate using carbon atoms originating from glucose or other substrates in cells with kinetically impaired pyruvate kinase and underscore the importance of mitochondria in cancer metabolism irrespective of oxidative phosphorylation.

Pyruvate Kinase Controls Signal Strength in the Insulin Secretory Pathway

Pancreatic β cells couple nutrient metabolism with appropriate insulin secretion. Here, we show that pyruvate kinase (PK), which converts ADP and phosphoenolpyruvate (PEP) into ATP and pyruvate, underlies β cell sensing of both glycolytic and mitochondrial fuels. Plasma membrane-localized PK is sufficient to close K_ATP channels and initiate calcium influx. Small-molecule PK activators increase the frequency of ATP/ADP and calcium oscillations and potently amplify insulin secretion. PK restricts respiration by cyclically depriving mitochondria of ADP, which accelerates PEP cycling until membrane depolarization restores ADP and oxidative phosphorylation. Our findings support a compartmentalized model of β cell metabolism in which PK locally generates the ATP/ADP required for insulin secretion. Oscillatory PK activity allows mitochondria to perform synthetic and oxidative functions without any net impact on glucose oxidation. These findings suggest a potential therapeutic route for diabetes based on PK activation that would not be predicted by the current consensus single-state model of β cell function.

Multi-Tissue Acceleration of the Mitochondrial Phosphoenolpyruvate Cycle Improves Whole-Body Metabolic Health

The mitochondrial GTP (mtGTP)-dependent phosphoenolpyruvate (PEP) cycle couples mitochondrial PEPCK (PCK2) to pyruvate kinase (PK) in the liver and pancreatic islets to regulate glucose homeostasis. Here, small molecule PK activators accelerated the PEP cycle to improve islet function, as well as metabolic homeostasis, in preclinical rodent models of diabetes. In contrast, treatment with a PK activator did not improve insulin secretion in pck2^-/- mice. Unlike other clinical secretagogues, PK activation enhanced insulin secretion but also had higher insulin content and markers of differentiation. In addition to improving insulin secretion, acute PK activation short-circuited gluconeogenesis to reduce endogenous glucose production while accelerating red blood cell glucose turnover. Four-week delivery of a PK activator in vivo remodeled PK phosphorylation, reduced liver fat, and improved hepatic and peripheral insulin sensitivity in HFD-fed rats. These data provide a preclinical rationale for PK activation to accelerate the PEP cycle to improve metabolic homeostasis and insulin sensitivity.

The Role of Erastin in Ferroptosis and Its Prospects in Cancer Therapy

Erastin was initially discovered as a small molecule compound that selectively kills tumor cells expressing ST and RAS^V12 and was later widely investigated as an inducer of ferroptosis. Ferroptosis is a recently discovered form of cell death caused by peroxidation induced by the accumulation of intracellular lipid reactive oxygen species (L-ROS) in an iron-dependent manner. Erastin can mediate ferroptosis through a variety of molecules including the cystine-glutamate transport receptor (system X_C⁻), the voltage-dependent anion channel (VDAC), and p53. Erastin is able to enhance the sensitivity of chemotherapy and radiotherapy, suggesting a promising future in cancer therapy. We hope that this review will help to better understand the role of erastin in ferroptosis and lay the foundation for further research and the development of erastin-based cancer therapies in the future.

Metabolic alterations in the tumor microenvironment and their role in oncogenesis

Metabolic reprogramming is a characteristic feature of both cancer cells and their neighbouring cells in the tumor microenvironment (TME). The latter include stroma fibroblasts and adipocytes, that respectively differentiate to become cancer associated fibroblasts (CAFs) and cancer associated adipocytes (CAAs), and infiltrated immune cells, that collaborate with the stromal cells to provide the tumor a pro-tumorigenic niche. Here we discuss the association between the reprogramming of glucose metabolism in the TME and oncogenic signaling and its reflection in the non-canonical functions of metabolic enzymes. We also discuss the non-canonical actions of oncometabolites and the contribution to oncogenesis of external metabolites that accumulate in the TME as result of crosstalk between the tumor and the TME. Special emphasis is given in this regard to lysophosphatidic acid (LPA) and adenosine, two powerful metabolites, the concentrations of which rise in the TME due to altered metabolism of the tumor and its surrounding cells, allowing their action as external signals.

Cancer-associated mutations in human pyruvate kinase M2 impair enzyme activity

Mammalian pyruvate kinase catalyzes the final step of glycolysis, and its M2 isoform (PKM2) is widely expressed in proliferative tissues. Mutations in PKM2 are found in some human cancers; however, the effects of these mutations on enzyme activity and regulation are unknown. Here, we characterized five cancer-associated PKM2 mutations, occurring at various locations on the enzyme, with respect to substrate kinetics and activation by the allosteric activator fructose-1,6-bisphosphate (FBP). The mutants exhibit reduced maximal velocity, reduced substrate affinity, and/or altered activation by FBP. The kinetic parameters of five additional PKM2 mutants that have been used to study enzyme function or regulation also demonstrate the deleterious effects of mutations on PKM2 function. Our findings indicate that PKM2 is sensitive to many amino acid changes and support the hypothesis that decreased PKM2 activity is selected for in rapidly proliferating cells.

Short-chain lipid peroxidation products form covalent adducts with pyruvate kinase and inhibit its activity in vitro and in breast cancer cells

Pyruvate kinase catalyses the last step in glycolysis and has been suggested to contribute to the regulation of aerobic glycolysis in cancer cells. It can be inhibited by oxidation of cysteine residues in vitro and in vivo, which is relevant to the more pro-oxidant state in cancer and proliferating tissues. These conditions also favour lipid peroxidation and the formation of electrophilic fragmentation products, including short-chain aldehydes that can covalently modify proteins. However, as yet few studies have investigated their interactions with pyruvate kinase, so we investigated the effects of three different aldehydes, acrolein, malondialdehyde and 4-hydroxy-2(E)-hexenal (HHE), on the structure and activity of the enzyme. Analysis by LC-MS/MS showed unique modification profiles for each aldehyde, but Cys152, Cys423 and Cys474 were the residues most susceptible to electrophilic modification. Analysis of enzymatic activity under these conditions showed that acrolein was the strongest inhibitor, and at incubation times longer than 2 h, pathophysiological concentrations induced significant effects. Treatment of MCF-7 cells with the aldehydes caused similar losses of pyruvate kinase activity to those observed in vitro, and at lower concentrations than those required to cause cell death, with time and dose-dependent effects; acrolein adducts on Cys152 and Cys358 were detected. Cys358 and Cys474 are located at or near the allosteric or active sites, and formation of adducts on these residues probably contributes to loss of activity at low treatment concentrations. This study provides the first detailed analysis of the structure-activity relationship of C3 and C6 aldehydes with pyruvate kinase, and suggests that reactive short-chain aldehydes generated in diseases with an oxidative aetiology or from environmental exposure such as smoking could be involved in the metabolic alterations observed in cancer cells, through alteration of pyruvate kinase activity.

ROCK2 promotes osteosarcoma growth and metastasis by modifying PFKFB3 ubiquitination and degradation

Rho-associated coiled-coil-containing protein kinase 2 (ROCK2) and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) are widely involved in cell biological activities and play a key role in controlling various cell phenomena. However, the underlying mechanisms connecting ROCK2 and PFKFB3 in osteosarcoma growth and metastasis are poorly understood. In this study, we explored and analysed the role and molecular mechanism of ROCK2 and PFKFB3 in osteosarcoma. We analysed ROCK2 and PFKFB3 protein expression in 51 surgical specimens from osteosarcoma patients and determined the correlation between ROCK2 and PFKFB3. In addition, we used Transwell and wound-healing assays to detect cell invasion and migration and CCK8 and EdU assays to assess cell proliferation. Herein, we confirmed that ROCK2 and PFKFB3 proteins were significantly upregulated in osteosarcoma compared with adjacent normal tissues. Further studies revealed that knockdown of ROCK2 significantly decreased the expression levels of PFKFB3; moreover, growth and metastasis were decreased in shROCK2 osteosarcoma cells. Additionally, upregulation of PFKFB3 rescued the decreased proliferation and metastasis induced by ROCK2 knockdown, whereas knockdown of PFKFB3 decreased ROCK2-enhanced osteosarcoma proliferation and metastasis. These results suggest that PFKFB3 is essential for ROCK2-mediated proliferation and metastasis of osteosarcoma cells. Mechanistically, ROCK2 stabilizes PFKFB3 expression by modifying its ubiquitination and degradation. Taken together, our results link two drivers of proliferation and metastasis in osteosarcoma and identify a novel pathway for PFKFB3 regulation. Thus, we provide new evidence of the biological and clinical significance of PFKFB3 as a potential biomarker for osteosarcoma.

An overview of structure, function, and regulation of pyruvate kinases

In the last step of glycolysis Pyruvate kinase catalyzes the irreversible conversion of ADP and phosphoenolpyruvate to ATP and pyruvic acid, both crucial for cellular metabolism. Thus pyruvate kinase plays a key role in controlling the metabolic flux and ATP production. The hallmark of the activity of different pyruvate kinases is their tight modulation by a variety of mechanisms including the use of a large number of physiological allosteric effectors in addition to their homotropic regulation by phosphoenolpyruvate. Binding of effectors signals precise and orchestrated movements in selected areas of the protein structure that alter the catalytic action of these evolutionarily conserved enzymes with remarkably conserved architecture and sequences. While the diverse nature of the allosteric effectors has been discussed in the literature, the structural basis of their regulatory effects is still not well understood because of the lack of data representing conformations in various activation states. Results of recent studies on pyruvate kinases of different families suggest that members of evolutionarily related families follow somewhat conserved allosteric strategies but evolutionarily distant members adopt different strategies. Here we review the structure and allosteric properties of pyruvate kinases of different families for which structural data are available.