Pyruvate Kinase Type M2: A Key Regulator Within the Tumour Metabolome and a Tool for Metabolic Profiling of Tumours

Single-cell and spatial transcriptomics reveal a high glycolysis B cell and tumor-associated macrophages cluster correlated with poor prognosis and exhausted immune microenvironment in diffuse large B-cell lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous malignancy characterized by varied responses to treatment and prognoses. Understanding the metabolic characteristics driving DLBCL progression is crucial for developing personalized therapies.

METHODS

This study utilized multiple omics technologies including single-cell transcriptomics (n = 5), bulk transcriptomics (n = 966), spatial transcriptomics (n = 10), immunohistochemistry (n = 34), multiple immunofluorescence (n = 20) and to elucidate the metabolic features of highly malignant DLBCL cells and tumor-associated macrophages (TAMs), along with their associated tumor microenvironment. Metabolic pathway analysis facilitated by scMetabolism, and integrated analysis via hdWGCNA, identified glycolysis genes correlating with malignancy, and the prognostic value of glycolysis genes (STMN1, ENO1, PKM, and CDK1) and TAMs were verified.

RESULTS

High-glycolysis malignant DLBCL tissues exhibited an immunosuppressive microenvironment characterized by abundant IFN_TAMs (CD68+CXCL10+PD-L1+) and diminished CD8+ T cell infiltration. Glycolysis genes were positively correlated with malignancy degree. IFN_TAMs exhibited high glycolysis activity and closely communicating with high-malignancy DLBCL cells identified within datasets. The glycolysis score, evaluated by seven genes, emerged as an independent prognostic factor (HR = 1.796, 95% CI: 1.077-2.995, p = 0.025 and HR = 2.631, 95% CI: 1.207-5.735, p = 0.015) along with IFN_TAMs were positively correlated with poor survival (p < 0.05) in DLBCL. Immunohistochemical validation of glycolysis markers (STMN1, ENO1, PKM, and CDK1) and multiple immunofluorescence validation of IFN_TAMs underscored their prognostic value (p < 0.05) in DLBCL.

CONCLUSIONS

This study underscores the significance of glycolysis in tumor progression and modulation of the immune microenvironment. The identified glycolysis genes and IFN_TAMs represent potential prognostic markers and therapeutic targets in DLBCL.

Spectroscopic insights with molecular docking and molecular dynamic simulation studies of anticancer drug 5-Fluorouracil targeting human pyruvate kinase m2

This study was conducted to test the efficacy of 5-fluorouracil (5-FU) as an anticancer drug against the human pyruvate kinase isozyme M2 (PKM2) using spectroscopic, molecular docking and molecular dynamic simulation studies. PKM2 fluorescence quenching studies in the presence of 5-FU performed at three different temperatures indicates dynamic quenching processes with single-set of binding (n ≈ 1) profile. The biomolecular quenching constants (kq) and the effective binding constants (Kb) obtained are shown to increase with temperature. The calculated enthalpy (ΔH) and entropy changes (ΔS) are estimated to be -118.06 kJ/mol and 146.14 kJ/mol/K respectively, which suggest the possible mode of interaction as electrostatic and hydrogen bonding. Further, these values were used to estimate the free energy changes (ΔG) and that increases with temperature. The negative ΔG values clearly indicates spontaneous binding process that stabilizes the complex formed between 5-FU and PKM2. Far-UV CD spectra of PKM2 in the presence of 5-FU shows decrease in α-helix contents which point towards the destabilization of secondary structure that weakens the biological activity of PKM2. The intrinsic fluorescence study and circular dichroism (CD) spectra showed minor conformational changes of PKM2 in the presence of 5-FU. Additionally, the results obtained from molecular docking and all-atom molecular dynamic simulation study supports the insight of the spectroscopic binding studies, and strengthens the dynamic stability of the complex between 5-FU and PKM2 through H-bonding. This study establishes a paradigm of 5-FU-PKM2 complexation and the efficacy of 5-FU that compromises the biological activity of the targeted PKM2.Communicated by Ramaswamy H. Sarma.

Metformin Increases the Response of Cholangiocarcinoma Cells to Gemcitabine by Suppressing Pyruvate Kinase M2 to Activate Mitochondrial Apoptosis

BACKGROUND

Cholangiocarcinoma (CCA) is a malignant tumor with a high mortality rate. Resistance to chemotherapy remains a major challenge related to cancer treatment, and increasing the sensitivity of cancer cells to therapeutic drugs is a major focus of cancer treatment.

AIMS

We purposed to explore the role of Metformin in CCA involved in chemotherapeutic sensitivity and Pyruvate kinase M2 (PKM2) through regulating mitochondrial apoptosis in the present study.

METHODS

CCA cell lines of HCC9810 and RBE were treated with Metformin companied with antagonists or agonists of PKM2, cells sensitivity to Gemcitabine, cell migration and invasion along with apoptosis, which is mediated by JC-1 and LDH were assayed.

RESULTS

Our results indicated that Metformin and Gemcitabine exhibit synergistic effect on inhibition of cholangiocarcinoma cell viability, cell migration and invasion as well as promotion apoptosis of cholangiocarcinoma cells. In vivo, Metformin combined with Gemcitabine has cooperation in inhibiting the growth of cholangiocarcinoma cell-derived tumors. Moreover, Metformin and Gemcitabine inhibited expression of PKM2 and PDHB in HCC9810 and RBE.

CONCLUSION

Our study suggested that Metformin may increase the response of cholangiocarcinoma cells to Gemcitabine by suppressing PKM2 to activate mitochondrial apoptosis.

MNX1-AS1, a c-Myc induced lncRNA, promotes the Warburg effect by regulating PKM2 nuclear translocation

BACKGROUND

Altered glycolysis is the most fundamental metabolic change associated with the Warburg effect. Some glycolytic enzymes such as PKM2, the dominant pyruvate kinase in cancer cells, have been shown to engage in non-glycolytic functions that contribute to tumor metabolism. However, the precise mechanisms are not completely understood.

METHODS

The role of MNX1-AS1 in hepatocellular carcinoma progression was assessed both in vitro and in vivo. Northern blotting, RNA pulldown, mass spectrometry, RNA-binding protein immunoprecipitation, ChIP, luciferase reporter assays, RNA FISH and immunofluorescence staining were used to explore the detail molecular mechanism of MNX1-AS1 in hepatocellular carcinoma (HCC).

RESULTS

Here we dissect how MNX1-AS1, a long non-coding RNA (lncRNA), reinforces the Warburg effect through facilitating the non-glycolytic actions of PKM2 in the cell nucleus. We found that MNX1-AS1 expression was frequently overexpressed in HCC-derived cell lines and tissues compared to their normal hepatic cell counterparts, a finding consistent with its status as pan-cancer expressed lncRNA. In the context of HCC, we show MNX1-AS1 acts as a scaffold to promote interactions between PKM2 and importin α5. In response to EGFR activation, the resulting ternary complex drives the translocation of PKM2 into the nucleus. In consequence, glycolytic pathway components including key mediators of the Warburg effect (LDHA, GLUT1 and PDK1) are upregulated though the coactivator function of PKM2. Manipulating MNX1-AS1 elicited robust effects on glycolysis associated with marked changes in HCC growth in vitro and in xenograft models, indicative of the significant contribution of MNX1-AS1 to tumorigenic phenotypes. Moreover, while MNX1-AS1 expression is driven by c-Myc, its actions associated with PKM2 were shown to be downstream and independent of c-Myc.

CONCLUSIONS

Given the status of MNX1-AS1 as a pan-cancer upregulated lncRNA, this implicitly highlights the potential of targeting MNX1-AS1 to selectively counter the Warburg effect in a range of tumor types.

A brief glimpse of a tangled web in a small world: Tumor microenvironment

A tumor is a result of stepwise accumulation of genetic and epigenetic alterations. This notion has deepened the understanding of cancer biology and has introduced the era of targeted therapies. On the other hand, there have been a series of attempts of using the immune system to treat tumors, dating back to ancient history, to sporadic reports of inflamed tumors undergoing spontaneous regression. This was succeeded by modern immunotherapies and immune checkpoint inhibitors. The recent breakthrough has broadened the sight to other players within tumor tissue. Tumor microenvironment is a niche or a system orchestrating reciprocal and dynamic interaction of various types of cells including tumor cells and non-cellular components. The output of this complex communication dictates the functions of the constituent elements present within it. More complicated factors are biochemical and biophysical settings unique to TME. This mini review provides a brief guide on a range of factors to consider in the TME research.

Early cleaving embryos result in blastocysts with increased aspartate and glucose consumption, which exhibit different metabolic gene expression that persists in placental and fetal tissues

OBJECTIVES

Using time-lapse microscopy, previous research has shown that IVF mouse embryos that cleave earlier at the first division ('fast') develop into blastocysts with increased glucose consumption and lower likelihood of post-implantation loss as compared to slower cleaving embryos ('slow'). Further, metabolomics analysis employing LC-MS conducted on groups of 'fast' blastocysts revealed that more aspartate was consumed. With the worldwide adoption of single blastocyst transfer as the standard of care, the need for quantifiable biomarkers of viability, such as metabolism of specific nutrients, would greatly assist in embryo selection for transfer.

METHODS

Here we describe the development of a targeted enzymatic assay to quantitate aspartate uptake of single blastocysts.

RESULTS

Results demonstrate that the rates of aspartate and glucose consumption were significantly higher in individual 'fast' blastocysts. Blastocysts, together with placental and fetal liver tissue collected following transfer, were analysed for the expression of genes involved in aspartate and carbohydrate metabolism. In 'fast' blastocysts, expressions of B3gnt5, Slc2a1, Slc2a3, Got1 and Pkm2 were found to be significantly higher. In placental tissue derived from 'fast' blastocysts, expression of Slc2a1, Got1 and Pkm2 were significantly higher, while levels of Got1 and Pkm2 were lower in fetal liver tissue compared to tissue from 'slow' blastocysts.

CONCLUSIONS

Importantly, this study shows that genes regulating aspartate and glucose metabolism were increased in blastocysts that have higher viability, with differences maintained in resultant placentae and fetuses. Consequently, the analysis of aspartate uptake in combination with glucose represents biomarkers of development and may improve embryo selection efficacy and pregnancy rates.

Detection of Nail Oncometabolite SAICAR in Oral Cancer Patients and Its Molecular Interactions with PKM2 Enzyme

Oncometabolites are known to drive metabolic adaptations in oral cancer. Several oncometabolites are known to be shared between cancer cells and non-cancer cells including microbiotas to modulate the tumor microenvironment. Among potential oncometabolites, succinylaminoimidazolecarboxamide ribose5′-phosphate (SAICAR) supports the growth and invasiveness of cancer cells by pyruvate kinase M2 (PKM2) enzyme in a glucose starved tumor microenvironment. There is a significant gap that shows the detection of SAICAR in biological samples including nails of oral cancer patients. Metabolite identification of SAICAR was investigated in the nails of oral cancer patients using novel vertical tube gel electrophoresis (VTGE) and LC-HRMS. Further molecular docking and molecular dynamics simulations (MDS) were employed to determine the nature of molecular interactions of SAICAR (CHEBI ID:18319) with PKM2 (PDB ID: 4G1N). Molecular docking of SAICAR (CHEBI ID:18319) was performed against pyruvate kinase M2 (PDB ID: 4G1N). Data suggest the presence of oncometabolite SAICAR in nails of oral cancer. Molecular docking of SAICAR with PKM2 showed appreciable binding affinity (−8.0 kcal/mol) with residues including ASP407, THR405, GLU410, ARG443, GLY321, ARG436, HIS439, LYS266, and TYR466. Furthermore, MDS confirmed the specific binding of SAICAR within the activator site of PKM2 and the stability of SAICAR and PKM2 molecular interactions. In conclusion, SAICAR is a promising oncometabolite biomarker present in the nails of oral cancer patients. A significant activation potential of SAICAR exists with the PKM2 enzyme.

Non-Metabolic Functions of PKM2 Contribute to Cervical Cancer Cell Proliferation Induced by the HPV16 E7 Oncoprotein

Pyruvate kinase M2 (PKM2) mainly catalyzes glycolysis, but it also exerts non-glycolytic functions in several cancers. While it has been shown to interact with the human papillomavirus 16 (HPV16) E7 oncoprotein, the functional significance of PKM2 in HPV-associated cervical cancer has been elusive. Here, we show that HPV16 E7 increased the expression of PKM2 in cervical cancer cells. TCGA data analyses revealed a higher level of PKM2 in HPV+ than HPV- cervical cancers and a worse prognosis for patients with high PKM2 expression. Functionally, we demonstrate that shRNA-mediated PKM2 knockdown decreased the proliferation of HPV+ SiHa cervical cancer cells. PKM2 knockdown also inhibited the E7-induced proliferation of cervical cancer cells. ML265 activating the pyruvate kinase function of PKM2 inhibited cell cycle progression and colony formation. ML265 treatments decreased phosphorylation of PKM2 at the Y105 position that has been associated with non-glycolytic functions. On the contrary, HPV16 E7 increased the PKM2 phosphorylation. Our results indicate that E7 increases PKM2 expression and activates a non-glycolytic function of PKM2 to promote cervical cancer cell proliferation.

Pyruvate Kinase M2 Tetramerization Protects against Hepatic Stellate Cell Activation and Liver Fibrosis

Liver fibrosis is an increasing health problem worldwide, for which no effective antifibrosis drugs are available. Although the involvement of aerobic glycolysis in hepatic stellate cell (HSC) activation has been reported, the role of pyruvate kinase M2 (PKM2) in liver fibrogenesis still remains unknown. We examined PKM2 expression and location in liver tissues and primary hepatic cells. The in vitro and in vivo effects of a PKM2 antagonist (shikonin) and its allosteric agent (TEPP-46) on liver fibrosis were investigated in HSCs and liver fibrosis mouse model. Chromatin immunoprecipitation sequencing and immunoprecipitation were performed to identify the relevant molecular mechanisms. PKM2 expression was significantly up-regulated in both mouse and human fibrotic livers compared with normal livers, and mainly detected in activated, rather than quiescent, HSCs. PKM2 knockdown markedly inhibited the activation and proliferation of HSCs in vitro. Interestingly, the PKM2 dimer, rather than the tetramer, induced HSC activation. PKM2 tetramerization induced by TEPP-46 effectively inhibited HSC activation, reduced aerobic glycolysis, and decreased MYC and CCND1 expression via regulating histone H3K9 acetylation in activated HSCs. TEPP-46 and shikonin dramatically attenuated liver fibrosis in vivo. Our findings demonstrate a nonmetabolic role of PKM2 in liver fibrosis. PKM2 tetramerization or suppression could prevent HSC activation and protects against liver fibrosis.

Pyruvate Kinase M2 Coordinates Metabolism Switch between Glycolysis and Glutaminolysis in Cancer Cells

Cancer cells alter their nutrition metabolism to cope the stressful environment. One important metabolism adjustment is that cancer cells activate glutaminolysis in response to the reduced carbon from glucose entering into the TCA cycle due to inactivation of several enzymes in glycolysis. An important question is how the cancer cells coordinate the changes of glycolysis and glutaminolysis. In this report, we demonstrate that the pyruvate kinase inactive dimer PKM2 facilitates activation of glutaminolysis. Our experiments show that growth stimulations promote PKM2 dimer. The dimer PKM2 plays a role in regulation of glutaminolysis by upregulation of mitochondrial glutaminase I (GLS-1). PKM2 dimer regulates the GLS-1 expression by controlling internal ribosome entry site (IRES)-dependent c-myc translation. Growth stimulations promote PKM2 interacting with c-myc IRES-RNA, thus facilitating c-myc IRES-dependent translation. Our study reveals an important linker that coordinates the metabolism adjustment in cancer cells.

Pyruvate Kinase M2 and Cancer: The Role of PKM2 in Promoting Tumorigenesis

Pyruvate kinase plays a pivotal role in regulating cell metabolism. The final and rate-limiting step of glycolysis is the conversion of Phosphoenolpyruvate (PEP) to Pyruvate, which is catalyzed by Pyruvate Kinase. There are four isomeric, tissue-specific forms of Pyruvate Kinase found in mammals: PKL, PKR, PKM1, and PKM2. PKM1 and PKM2 are formed bya single mRNA transcript of the PKM gene by alternative splicing. The oligomers of PKM2 exist in high activity tetramer and low activity dimer forms. The dimer PKM2 regulates the rate-limiting step of glycolysis that shifts the glucose metabolism from the normal respiratory chain to lactate production in tumor cells. Besides its role as a metabolic regulator, it also acts as protein kinase, which contributes to tumorigenesis. This review is focused on the metabolic role of pyruvate kinase M2 in normal cells vs. cancerous cells and its regulation at the transcriptional level. The review also highlights the role of PKM2 as a potential diagnostic marker and as a therapeutic target in cancer treatment.

Knockdown of Pyruvate Kinase M Inhibits Cell Growth and Migration by Reducing NF-kB Activity in Triple-Negative Breast Cancer Cells

Altered genetic features in cancer cells lead to a high rate of aerobic glycolysis and metabolic reprogramming that is essential for increased cancer cell viability and rapid proliferation. Pyruvate kinase muscle (PKM) is a rate-limiting enzyme in the final step of glycolysis. Herein, we report that PKM is a potential therapeutic target in triple-negative breast cancer (TNBC) cells. We found that PKM1 or PKM2 is highly expressed in TNBC tissues or cells. Knockdown of PKM significantly suppressed cell proliferation and migration, and strongly reduced S phase and induced G2 phase cell cycle arrest by reducing phosphorylation of the CDC2 protein in TNBC cells. Additionally, knockdown of PKM significantly suppressed NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity by reducing the phosphorylation of p65 at serine 536, and also decreased the expression of NF-kB target genes. Taken together, PKM is a potential target that may have therapeutic implications for TNBC cells.

HERCing: Structural and Functional Relevance of the Large HERC Ubiquitin Ligases

Homologous to the E6AP carboxyl terminus (HECT) and regulator of chromosome condensation 1 (RCC1)-like domain-containing proteins (HERCs) belong to the superfamily of ubiquitin ligases. HERC proteins are divided into two subfamilies, Large and Small HERCs. Despite their similarities in terms of both structure and domains, these subfamilies are evolutionarily very distant and result from a convergence phenomenon rather than from a common origin. Large HERC genes, HERC1 and HERC2, are present in most metazoan taxa. They encode very large proteins (approximately 5,000 amino acid residues in a single polypeptide chain) that contain more than one RCC1-like domain as a structural characteristic. Accumulating evidences show that these unusually large proteins play key roles in a wide range of cellular functions which include neurodevelopment, DNA damage repair, and cell proliferation. To better understand the origin, evolution, and function of the Large HERC family, this minireview provides with an integrated overview of their structure and function and details their physiological implications. This study also highlights and discusses how dysregulation of these proteins is associated with severe human diseases such as neurological disorders and cancer.

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

It is becoming generally accepted in recent literature that the Warburg effect in cancer depends on inhibition of M₂PYK, the pyruvate kinase isozyme most commonly expressed in tumors. We remain skeptical. There continues to be a general lack of solid experimental evidence for the underlying idea that a bottle neck in aerobic glycolysis at the level of M₂PYK results in an expanded pool of glycolytic intermediates (which are thought to serve as building blocks necessary for proliferation and growth of cancer cells). If a bottle neck at M₂PYK exists, then the remarkable increase in lactate production by cancer cells is a paradox, particularly since a high percentage of the carbons of lactate originate from glucose. The finding that pyruvate kinase activity is invariantly increased rather than decreased in cancer undermines the logic of the M₂PYK bottle neck, but is consistent with high lactate production. The "inactive" state of M₂PYK in cancer is often described as a dimer (with reduced substrate affinity) that has dissociated from an active tetramer of M₂PYK. Although M₂PYK clearly dissociates easier than other isozymes of pyruvate kinase, it is not clear that dissociation of the tetramer occurs in vivo when ligands are present that promote tetramer formation. Furthermore, it is also not clear whether the dissociated dimer retains any activity at all. A number of non-canonical functions for M₂PYK have been proposed, all of which can be challenged by the finding that not all cancer cell types are dependent on M₂PYK expression. Additional in-depth studies of the Warburg effect and specifically of the possible regulatory role of M₂PYK in the Warburg effect are needed.

Metabolic Reprogramming in Thyroid Carcinoma

Among all the adaptations of cancer cells, their ability to change metabolism from the oxidative to the glycolytic phenotype is a hallmark called the Warburg effect. Studies on tumor metabolism show that improved glycolysis and glutaminolysis are necessary to maintain rapid cell proliferation, tumor progression, and resistance to cell death. Thyroid neoplasms are common endocrine tumors that are more prevalent in women and elderly individuals. The incidence of thyroid cancer has increased in the Past decades, and recent findings describing the metabolic profiles of thyroid tumors have emerged. Currently, several drugs are in development or clinical trials that target the altered metabolic pathways of tumors are undergoing. We present a review of the metabolic reprogramming in cancerous thyroid tissues with a focus on the factors that promote enhanced glycolysis and the possible identification of promising metabolic targets in thyroid cancer.

Lapatinib Inhibits Breast Cancer Cell Proliferation by Influencing PKM2 Expression

Pyruvate kinase type M2, which is expressed in multiple tumor cell types and plays a key role in aerobic glycolysis, also has nonglycolytic functions and can regulate transcription and cell proliferation. The results of this study show that epidermal growth factor receptor activation induces pyruvate kinase type M2 nuclear translocation. To further determine the relationship between pyruvate kinase type M2 and epidermal growth factor receptor, we analyzed pathological data from mammary glands and performed epidermal growth factor receptor/human epidermal growth factor receptor 2 knockdown to reveal that pyruvate kinase type M2 is associated with epidermal growth factor receptor and human epidermal growth factor receptor 2. Lapatinib is a small molecule epidermal growth factor receptor tyrosine kinase inhibitor that can inhibit epidermal growth factor receptor and human epidermal growth factor receptor 2, though its effect on pyruvate kinase type M2 remains elusive. Accordingly, we performed Western blotting and reverse transcription polymerase chain reaction and analyzed pathological data from mammary glands, with results suggesting that lapatinib inhibits pyruvate kinase type M2 expression. We further found that the antitumor drug lapatinib inhibits breast cancer cell proliferation by influencing pyruvate kinase type M2 expression, as based on Cell Counting Kit-8 analyses and pyruvate kinase type M2 overexpression experiments. Signal transducer and activator of transcription 3, which is a transcription factor-associated cell proliferation and the only transcription factor that interacts with pyruvate kinase type M2, we performed pyruvate kinase type M2 knockdown experiments in Human breast cancer cells MDA-MB-231 and Human breast cancer cells SK-BR-3 cell lines and examined the effect on levels of Signal transducer and activator of transcription 3 and phosphorylated Signal transducer and activator of transcription 3. The results indicate that pyruvate kinase type M2 regulates Signal transducer and activator of transcription 3 and phospho-Stat3 (Tyr705) expression. Together with previous reports, our findings show that lapatinib inhibits breast cancer cell proliferation by influencing pyruvate kinase type M2 expression, which results in a reduction in both Signal transducer and activator of transcription 3 and phosphorylated Signal transducer and activator of transcription 3.

LincRNA-p21 suppresses development of human prostate cancer through inhibition of PKM2

OBJECTIVES

Previously, we found that long intergenic non-coding RNA-p21 (lincRNA-p21) inhibited the development of human prostate cancer. However, the underlying molecular mechanisms are poorly understood. Here, we attempted to investigate the downstream targets of lincRNA-p21 in prostate cancer.

MATERIALS AND METHODS

Expression of lincRNA-p21 and PKM2 was determined by qRT-PCR and Western blot. Lentivirus expressing shPKM2 or shCtrl was used to explore the role of PKM2 on the enhanced cell proliferation and glycolysis of lincRNA-p21-silenced prostate cancer cells. A xenograft mouse model was performed to investigate the effect of PKM2 suppression, glycolytic or mammalian target of rapamycin (mTOR) inhibitor on the tumorigenic capacity of lincRNA-p21-silenced prostate cancer cells.

RESULTS

We revealed that lincRNA-p21 silencing in DU145 and LNCaP cells induced up-regulation of PKM2 and activation of glycolysis, which could be reversed by PKM2 knockdown or rapamycin treatment. We also found that the proliferation and tumorigenesis of lincRNA-p21-silenced prostate cancer cells were significantly inhibited after knocking down PKM2. 3-bromopyruvate (3-Brpa) or rapamycin treatment largely decreased the tumour burden. Importantly, PKM2 expression was inversely correlated with the lincRNA-p21 level and the survival of prostate cancer patients.

CONCLUSIONS

We demonstrated that lincRNA-p21 blunted the prostate cancer cell proliferation and tumorigenic capacity through down-regulation of PKM2. Therefore, targeting PKM2 or glycolysis might be a therapeutic strategy in prostate cancer patients with lowly expressed lincRNA-p21.

Associations among Metabolism, Circadian Rhythm and Age-Associated Diseases

Accumulating epidemiological studies have implicated a strong link between age associated metabolic diseases and cancer, though direct and irrefutable evidence is missing. In this review, we discuss the connection between Warburg effects and tumorigenesis, as well as adaptive responses to environment such as circadian rhythms on molecular pathways involved in metabolism. We also review the central role of the sirtuin family of proteins in physiological modulation of cellular processes and age-associated metabolic diseases. We also provide a macroscopic view of how the circadian rhythm affects metabolism and may be involved in cell metabolism reprogramming and cancer pathogenesis. The aberrations in metabolism and the circadian system may lead to age-associated diseases directly or through intermediates. These intermediates may be either mutated or reprogrammed, thus becoming responsible for chromatin modification and oncogene transcription. Integration of circadian rhythm and metabolic reprogramming in the holistic understanding of metabolic diseases and cancer may provide additional insights into human diseases.

Knockdown of the M2 Isoform of Pyruvate Kinase (PKM2) with shRNA Enhances the Effect of Docetaxel in Human NSCLC Cell Lines In Vitro

PURPOSE

The aim of our study was to explore the relationships between the M2 isoform of pyruvate kinase (PKM2) and the sensitivity of human non-small cell lung cancer (NSCLC) cells to docetaxel in vitro.

MATERIALS AND METHODS

With the method of plasmid transfection, we silenced the expression of PKM2 successfully in A549 and H460 cells. Western blotting and real-time PCR were applied to detect PKM2 expression at protein and gene levels. Cell viability was examined by CCK8 assay. Cell cycle distribution and apoptosis were examined by flow cytometry. P21 and Bax were detected.

RESULTS

Expression of PKM2 mRNA and protein were significantly decreased by shRNA targeting PKM2. Silencing of PKM2 increased docetaxel sensitivity of human NSCLC A549 and H460 cells in a collaborative manner, resulting in strong suppression of cell viability. The results of flow cytometric assays suggested that knockdown of PKM2 or docetaxel treatment, whether used singly or in combination, blocked the cells in the G2/M phase, which is in consistent with the effect of the two on the expression of p21. Cells with PKM2 silencing were more likely to be induced into apoptosis by docetaxel although knockdown of PKM2 alone can't induce apoptosis significantly, which is in consistent with the effect of the two on Bax expression.

CONCLUSION

The results suggest that PKM2 knockdown could serve as a chemosensitizer to docetaxel in non-small lung cancer cells through targeting PKM2, leading to inhibition of cell viability, increase of cell arrest of G2/M phase and apoptosis.

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

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

c-Myc Alters Substrate Utilization and O-GlcNAc Protein Posttranslational Modifications without Altering Cardiac Function during Early Aortic Constriction

Hypertrophic stimuli cause transcription of the proto-oncogene c-Myc (Myc). Prior work showed that myocardial knockout of c-Myc (Myc) attenuated hypertrophy and decreased expression of metabolic genes after aortic constriction. Accordingly, we assessed the interplay between Myc, substrate oxidation and cardiac function during early pressure overload hypertrophy. Mice with cardiac specific, inducible Myc knockout (MycKO-TAC) and non-transgenic littermates (Cont-TAC) were subjected to transverse aortic constriction (TAC; n = 7/group). Additional groups underwent sham surgery (Cont-Sham and MycKO-Sham, n = 5 per group). After two weeks, function was measured in isolated working hearts along with substrate fractional contributions to the citric acid cycle by using perfusate with ¹³C labeled mixed fatty acids, lactate, ketone bodies and unlabeled glucose and insulin. Cardiac function was similar between groups after TAC although +dP/dT and -dP/dT trended towards improvement in MycKO-TAC versus Cont-TAC. In sham hearts, Myc knockout did not affect cardiac function or substrate preferences for the citric acid cycle. However, Myc knockout altered fractional contributions during TAC. The unlabeled fractional contribution increased in MycKO-TAC versus Cont-TAC, whereas ketone and free fatty acid fractional contributions decreased. Additionally, protein posttranslational modifications by O-GlcNAc were significantly greater in Cont-TAC versus both Cont-Sham and MycKO-TAC. In conclusion, Myc alters substrate preferences for the citric acid cycle during early pressure overload hypertrophy without negatively affecting cardiac function. Myc also affects protein posttranslational modifications by O-GlcNAc during hypertrophy, which may regulate Myc-induced metabolic changes.

Phosphorylation of pyruvate kinase M2 and lactate dehydrogenase A by fibroblast growth factor receptor 1 in benign and malignant thyroid tissue

BACKGROUND

Lactate dehydrogenase A (LDHA) and Pyruvate Kinase M2 (PKM2) are important enzymes of glycolysis. Both of them can be phosphorylated and therefore regulated by Fibroblast growth factor receptor 1 (FGFR1). While phosphorylation of LDHA at tyrosine10 leads to tetramerization and activation, phosphorylation of PKM2 at tyrosine105 promotes dimerization and inactivation. Dimeric PKM2 is found in the nucleus and regulates gene transcription. Up-regulation and phosphorylation of LDHA and PKM2 contribute to faster proliferation under hypoxic conditions and promote the Warburg effect.

METHODS

Using western blot and SYBR Green Real time PCR we investigated 77 thyroid tissues including 19 goiter tissues, 11 follicular adenomas, 16 follicular carcinomas, 15 papillary thyroid carcinomas, and 16 undifferentiated thyroid carcinomas for total expression of PKM2, LDHA and FGFR1. Additionally, phosphorylation status of PKM2 and LDHA was analysed. Inhibition of FGFR was performed on FTC133 cells with SU-5402 and Dovitinib.

RESULTS

All examined thyroid cancer subtypes overexpressed PKM2 as compared to goiter. LDHA was overexpressed in follicular and papillary thyroid cancer as compared to goiter. Elevated phosphorylation of LDHA and PKM2 was detectable in all analysed cancer subtypes. The highest relative phosphorylation levels of PKM2 and LDHA compared to overall expression were found in undifferentiated thyroid cancer. Inhibition of FGFR led to significantly decreased phosphorylation levels of PKM2 and LDHA.

CONCLUSIONS

Our data shows that overexpression and increased phosphorylation of PKM2 and LHDA is a common finding in thyroid malignancies. Phospho-PKM2 and Phospho-LDHA could be valuable tumour markers for thyroglobulin negative thyroid cancer.

Analysis and interpretation of transcriptomic data obtained from extended Warburg effect genes in patients with clear cell renal cell carcinoma

Background

Many cancers adopt a metabolism that is characterized by the well-known Warburg effect (aerobic glycolysis). Recently, numerous attempts have been made to treat cancer by targeting one or more gene products involved in this pathway without notable success. This work outlines a transcriptomic approach to identify genes that are highly perturbed in clear cell renal cell carcinoma (CCRCC).

Methods

We developed a model of the extended Warburg effect and outlined the model using Cytoscape. Following this, gene expression fold changes (FCs) for tumor and adjacent normal tissue from patients with CCRCC (GSE6344) were mapped on to the network. Gene expression values with FCs of greater than two were considered as potential targets for treatment of CCRCC.

Results

The Cytoscape network includes glycolysis, gluconeogenesis, the pentose phosphate pathway (PPP), the TCA cycle, the serine/glycine pathway, and partial glutaminolysis and fatty acid synthesis pathways. Gene expression FCs for nine of the 10 CCRCC patients in the GSE6344 data set were consistent with a shift to aerobic glycolysis. Genes involved in glycolysis and the synthesis and transport of lactate were over-expressed, as was the gene that codes for the kinase that inhibits the conversion of pyruvate to acetyl-CoA. Interestingly, genes that code for unique proteins involved in gluconeogenesis were strongly under-expressed as was also the case for the serine/glycine pathway. These latter two results suggest that the role attributed to the M2 isoform of pyruvate kinase (PKM2), frequently the principal isoform of PK present in cancer: i.e. causing a buildup of glucose metabolites that are shunted into branch pathways for synthesis of key biomolecules, may not be operative in CCRCC. The fact that there was no increase in the expression FC of any gene in the PPP is consistent with this hypothesis. Literature protein data generally support the transcriptomic findings.

Conclusions

A number of key genes have been identified that could serve as valid targets for anti-cancer pharmaceutical agents. Genes that are highly over-expressed include ENO2, HK2, PFKP, SLC2A3, PDK1, and SLC16A1. Genes that are highly under-expressed include ALDOB, PKLR, PFKFB2, G6PC, PCK1, FBP1, PC, and SUCLG1.

The combination of the expression of hexokinase 2 and pyruvate kinase M2 is a prognostic marker in patients with pancreatic cancer

Metabolism may determine the biologically malignant behavior of pancreatic cancer. To investigate the significance and prognostic value of cancer metabolism in cancer patients, we investigated the expression of two key enzymes in anaerobic glycolysis, hexokinase 2 (HK2) and pyruvate kinase isoenzyme type M2 (PKM2), in surgical specimens obtained from 36 patients who underwent curative resection of pancreatic ductal carcinoma. The hk2-glycolysis axis is a key system in the clinical imaging of tumors via positron emission tomography. Immunohistochemical staining for hk2 and pkm2 was performed and the data were statistically analyzed to evaluate their prognostic power. The expression of hk2 and pkm2 was associated with clinicopathological variables and patient prognosis, including overall survival, local recurrence-free survival and distant metastasis-free survival. Staining for hk2 was negative and positive in 42 and 58% of the patients, respectively, whereas staining for pkm2 was negative and positive in 56 and 44%, respectively; hk2-positive staining was correlated with progressive pathological tumor stage (pT3 vs. pT1 and pT2; P=0.017). In the univariate analysis, the positive expression of hk2 and pkm2, pathological stage (pT3 vs. pT1 and pT2) and nodal metastasis were significantly correlated with poor prognosis (P<0.03). In the multivariate analysis, pathological nodal metastasis was an independent prognostic factor for overall survival, whereas the positive expression of hk2 and pkm2 exhibited borderline significance (P=0.08 and 0.12, hazard ratio = 2.57 and 2.16, respectively). In addition, the combination of high expression of hk2 as well as pkm2 was found to be significant (P<0.05). These results suggested that the expression of hk2 and pkm2, particularly their combination, in surgical specimens obtained during curative resection, may predict an unfavorable clinical outcome in patients with pancreatic cancer.

PKM2 phosphorylates MLC2 and regulates cytokinesis of tumour cells

Pyruvate kinase M2 (PKM2) is expressed at high levels during embryonic development and tumour progression and is important for cell growth. However, it is not known whether it directly controls cell division. Here, we found that Aurora B phosphorylates PKM2, but not PKM1, at T45; this phosphorylation is required for PKM2's localization and interaction with myosin light chain 2 (MLC2) in the contractile ring region of mitotic cells during cytokinesis. PKM2 phosphorylates MLC2 at Y118, which primes the binding of ROCK2 to MLC2 and subsequent ROCK2-dependent MLC2 S15 phosphorylation. PKM2-regulated MLC2 phosphorylation, which is greatly enhanced by EGF stimulation or EGFRvIII, K-Ras G12V and B-Raf V600E mutant expression, plays a pivotal role in cytokinesis, cell proliferation and brain tumour development. These findings underscore the instrumental function of PKM2 in oncogenic EGFR-, K-Ras- and B-Raf-regulated cytokinesis and tumorigenesis.

Identification of protein biomarkers for cervical cancer using human cervicovaginal fluid

Objectives

Cervicovaginal fluid (CVF) can be considered as a potential source of biomarkers for diseases of the lower female reproductive tract. The fluid can easily be collected, thereby offering new opportunities such as the development of self tests. Our objective was to identify a CVF protein biomarker for cervical cancer or its precancerous state.

Methods

A differential proteomics study was set up using CVF samples from healthy and precancerous women. Label-free spectral counting was applied to quantify protein abundances.

Results

The proteome analysis revealed 16 candidate biomarkers of which alpha-actinin-4 (p = 0.001) and pyruvate kinase isozyme M1/M2 (p = 0.014) were most promising. Verification of alpha-actinin-4 by ELISA (n = 28) showed that this candidate biomarker discriminated between samples from healthy and both low-risk and high-risk HPV-infected women (p = 0.009). Additional analysis of longitudinal samples (n = 29) showed that alpha-actinin-4 levels correlated with virus persistence and clearing, with a discrimination of approximately 18 pg/ml.

Conclusions

Our results show that CVF is an excellent source of protein biomarkers for detection of lower female genital tract pathologies and that alpha-actinin-4 derived from CVF is a promising candidate biomarker for the precancerous state of cervical cancer. Further studies regarding sensitivity and specificity of this biomarker will demonstrate its utility for improving current screening programs and/or its use for a cervical cancer self-diagnosis test.

Pyruvate kinase M2 in blood circulation facilitates tumor growth by promoting angiogenesis

It is long known that pyruvate kinase isoform M2 (PKM2) is released into the circulation of cancer patients. The PKM2 levels in patients have been suggested as a diagnostic marker for many types of cancers. However, it is not known how PKM2 is released in the blood, and whether the circulating PKM2 has any physiological function(s) in tumor progression. In this report, we demonstrate that PKM2 in the blood facilitates tumor growth by promoting tumor angiogenesis. Our experiments show that PKM2 promotes tumor angiogenesis by increasing endothelial cell proliferation, migration, and cell-ECM adhesion. Only the dimeric PKM2 possess the activity in promoting tumor angiogenesis, which is consistent with the observations that PKM2 in circulation of cancer patients is a dimer form.

mTOR in viral hepatitis and hepatocellular carcinoma: function and treatment

As the fifth most common cancer in men and the eighth most common cancer in women, hepatocellular carcinoma (HCC) is the leading cause of cancer-related deaths worldwide, with standard chemotherapy and radiation being minimally effective in prolonging survival. Virus hepatitis, particularly HBV and HCV infection is the most prominent risk factor for HCC development. Mammalian target of rapamycin (mTOR) pathway is activated in viral hepatitis and HCC. mTOR inhibitors have been tested successfully in clinical trials for their antineoplastic potency and well tolerability. Treatment with mTOR inhibitor alone or in combination with cytotoxic drugs or targeted therapy drug scan significantly reduces HCC growth and improves clinical outcome, indicating that mTOR inhibition is a promising strategy for the clinical management of HCC.

PKM2 regulates chromosome segregation and mitosis progression of tumor cells

Tumor-specific pyruvate kinase M2 (PKM2) is instrumental in both aerobic glycolysis and gene transcription. PKM2 regulates G1-S phase transition by controlling cyclin D1 expression. However, it is not known whether PKM2 directly controls cell-cycle progression. We show here that PKM2, but not PKM1, binds to the spindle checkpoint protein Bub3 during mitosis and phosphorylates Bub3 at Y207. This phosphorylation is required for Bub3-Bub1 complex recruitment to kinetochores, where it interacts with Blinkin and is essential for correct kinetochore-microtubule attachment, mitotic/spindle-assembly checkpoint, accurate chromosome segregation, cell survival and proliferation, and active EGF receptor-induced brain tumorigenesis. In addition, the level of Bub3 Y207 phosphorylation correlated with histone H3-S10 phosphorylation in human glioblastoma specimens and with glioblastoma prognosis. These findings highlight the role of PKM2 as a protein kinase controlling the fidelity of chromosome segregation, cell-cycle progression, and tumorigenesis.

Regulation and function of pyruvate kinase M2 in cancer

Altered metabolism is fundamental to the growth and survival of cancer cells. Pyruvate kinase M2 (PKM2), a key enzyme in cancer metabolism, has been demonstrated to play a central role not only in metabolic reprogramming but also in direct regulation of gene expression and subsequent cell cycle progression. This review outlines the current understanding of PKM2 protein kinase activity and regulatory mechanisms underlying PKM2 expression, enzymatic activity, and nuclear localization, thus highlighting PKM2 as a potential therapeutic target.

Insulin promotes glucose consumption via regulation of miR-99a/mTOR/PKM2 pathway

Insulin is known to regulate multiple cellular functions and is used for the treatment of diabetes. MicroRNAs have been demonstrated to be involved in many human diseases, including Type 2 diabetes. In this study, we showed that insulin decreased miR-99a expression levels, but induced glucose consumption and lactate production, and increased the expression of mTOR, HIF-1α and PKM2 in HepG2 and HL7702 cells. Forced expression of miR-99a or rapamycin treatment blocked insulin-induced PKM2 and HIF-1α expression, and glucose consumption and lactate production. Meanwhile, knockdown of HIF-1α inhibited PKM2 expression and insulin-induced glucose consumption. Taken together, these findings will reveal the role and mechanism of insulin in regulating glycolytic activities via miR-99a/mTOR.

PKM2, a Central Point of Regulation in Cancer Metabolism

Aerobic glycolysis is the dominant metabolic pathway utilized by cancer cells, owing to its ability to divert glucose metabolites from ATP production towards the synthesis of cellular building blocks (nucleotides, amino acids, and lipids) to meet the demands of proliferation. The M2 isoform of pyruvate kinase (PKM2) catalyzes the final and also a rate-limiting reaction in the glycolytic pathway. In the PK family, PKM2 is subjected to a complex regulation by both oncogenes and tumour suppressors, which allows for a fine-tone regulation of PKM2 activity. The less active form of PKM2 drives glucose through the route of aerobic glycolysis, while active PKM2 directs glucose towards oxidative metabolism. Additionally, PKM2 possesses protein tyrosine kinase activity and plays a role in modulating gene expression and thereby contributing to tumorigenesis. We will discuss our current understanding of PKM2's regulation and its many contributions to tumorigenesis.

STAT6 promotes bi-directional modulation of PKM2 in liver and adipose inflammatory cells in rosiglitazone-treated mice

STAT6 interacts with PPARγ to elicit macrophage polarization towards an anti-inflammatory, insulin-sensitizing phenotype. Mice deficient in STAT6 display liver lipid accumulation (hepatosteatosis). Rosiglitazone (RSG), a PPARγ agonist, ameliorates hepatosteatosis and enhances insulin sensitivity. To elucidate the role of STAT6 in PPARγ action on hepatosteatosis we compared liver proteomes of RSG-treated wild type and STAT6-deficient mice and we identified pyruvate kinase M2 (PKM2), a glycolysis and proliferation-regulating enzyme that displayed STAT6-dependent expression. RSG induced PKM2 within inflammatory cells in liver but suppressed its expression in adipose tissue. RSG diminished hepatosteatosis and oxidative stress, enhanced fat accumulation and improved insulin sensitivity in STAT6-deficient mice. Our data reveal a complex interaction between STAT6 and PPARγ in the regulation of liver and adipose tissue lipid depot distribution and design STAT6 as a novel link between inflammatory cell metabolism and adipocyte and hepatocyte function.

Proteomic identification of PKM2 and HSPA5 as potential biomarkers for predicting high-risk endometrial carcinoma

AIM

Endometrial carcinoma (EC) is a common gynecologic malignancy. EC has a favorable prognosis because it is usually diagnosed at an early stage. However, the recurrence rate is high and the prognosis is poor for high-risk EC. Identification of new biomarkers for the prediction of high-risk features will help to guide the treatment and improve the prognosis of patients with EC.

MATERIAL AND METHODS

Differentially expressed proteins among high-risk EC, low-risk EC, and normal endometrial tissues were determined by two-dimensional gel electrophoresis (2-DE) and a liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) proteomics approach. Then, the candidate proteins were examined by immunohistochemical analysis.

RESULTS

Thirteen protein spots were differentially expressed between the high- and low-risk groups, and 25 protein spots were differentially expressed between the high-risk and normal endometrium groups. Twenty-two proteins were identified by MS analysis. PKM2 and HSPA5 were elevated in the high-risk EC tissues compared with both the low-risk EC and normal endometrial tissues. The elevated expression of PKM2 and HSPA5 in high-risk EC tissue was confirmed by immunohistochemical analysis.

DISCUSSION

PKM2 and HSPA5 may play an important role in the progression of EC. These two proteins are potential biomarkers to better predict high-risk EC and thereby guide clinical therapy.

PKM2 phosphorylates histone H3 and promotes gene transcription and tumorigenesis

Tumor-specific pyruvate kinase M2 (PKM2) is essential for the Warburg effect. In addition to its well-established role in aerobic glycolysis, PKM2 directly regulates gene transcription. However, the mechanism underlying this nonmetabolic function of PKM2 remains elusive. We show here that PKM2 directly binds to histone H3 and phosphorylates histone H3 at T11 upon EGF receptor activation. This phosphorylation is required for the dissociation of HDAC3 from the CCND1 and MYC promoter regions and subsequent acetylation of histone H3 at K9. PKM2-dependent histone H3 modifications are instrumental in EGF-induced expression of cyclin D1 and c-Myc, tumor cell proliferation, cell-cycle progression, and brain tumorigenesis. In addition, levels of histone H3 T11 phosphorylation correlate with nuclear PKM2 expression levels, glioma malignancy grades, and prognosis. These findings highlight the role of PKM2 as a protein kinase in its nonmetabolic functions of histone modification, which is essential for its epigenetic regulation of gene expression and tumorigenesis.

Targeting cancer metabolism--aiming at a tumour's sweet-spot

Targeting cancer metabolism has emerged as a hot topic for drug discovery. Most cancers have a high demand for metabolic inputs (i.e. glucose/glutamine), which aid proliferation and survival. Interest in targeting cancer metabolism has been renewed in recent years with the discovery that many cancer-related (e.g. oncogenic and tumour suppressor) pathways have a profound effect on metabolism and that many tumours become dependent on specific metabolic processes. Considering the recent increase in our understanding of cancer metabolism and the increasing knowledge of the enzymes and pathways involved, the question arises: could metabolism be cancer's Achilles heel? During recent years, interest into the possible therapeutic benefit of targeting metabolic pathways in cancer has increased dramatically with academic and pharmaceutical groups actively pursuing this aspect of tumour physiology. Therefore, what has fuelled this revived interest in targeting cancer metabolism and what are the major advances and potential challenges faced in the race to develop new therapeutics in this area? This review will attempt to answer these questions by summarising recent developments in this field. We aim to illustrate why we, and others, believe that targeting metabolism in cancer presents such a promising therapeutic rationale.

Glycolysis inhibition inactivates ABC transporters to restore drug sensitivity in malignant cells

Cancer cells eventually acquire drug resistance largely via the aberrant expression of ATP-binding cassette (ABC) transporters, ATP-dependent efflux pumps. Because cancer cells produce ATP mostly through glycolysis, in the present study we explored the effects of inhibiting glycolysis on the ABC transporter function and drug sensitivity of malignant cells. Inhibition of glycolysis by 3-bromopyruvate (3BrPA) suppressed ATP production in malignant cells, and restored the retention of daunorubicin or mitoxantrone in ABC transporter-expressing, RPMI8226 (ABCG2), KG-1 (ABCB1) and HepG2 cells (ABCB1 and ABCG2). Interestingly, although side population (SP) cells isolated from RPMI8226 cells exhibited higher levels of glycolysis with an increased expression of genes involved in the glycolytic pathway, 3BrPA abolished Hoechst 33342 exclusion in SP cells. 3BrPA also disrupted clonogenic capacity in malignant cell lines including RPMI8226, KG-1, and HepG2. Furthermore, 3BrPA restored cytotoxic effects of daunorubicin and doxorubicin on KG-1 and RPMI8226 cells, and markedly suppressed subcutaneous tumor growth in combination with doxorubicin in RPMI8226-implanted mice. These results collectively suggest that the inhibition of glycolysis is able to overcome drug resistance in ABC transporter-expressing malignant cells through the inactivation of ABC transporters and impairment of SP cells with enhanced glycolysis as well as clonogenic cells.

Human pyruvate kinase M2: a multifunctional protein

Glycolysis, a central metabolic pathway, harbors evolutionary conserved enzymes that modulate and potentially shift the cellular metabolism on requirement. Pyruvate kinase, which catalyzes the last but rate-limiting step of glycolysis, is expressed in four isozymic forms, depending on the tissue requirement. M2 isoform (PKM2) is exclusively expressed in embryonic and adult dividing/tumor cells. This tetrameric allosterically regulated isoform is intrinsically designed to downregulate its activity by subunit dissociation (into dimer), which results in partial inhibition of glycolysis at the last step. This accumulates all upstream glycolytic intermediates as an anabolic feed for synthesis of lipids and nucleic acids, whereas reassociation of PKM2 into active tetramer replenishes the normal catabolism as a feedback after cell division. In addition, involvement of this enzyme in a variety of pathways, protein-protein interactions, and nuclear transport suggests its potential to perform multiple nonglycolytic functions with diverse implications, although multidimensional role of this protein is as yet not fully explored. This review aims to provide an overview of the involvement of PKM2 in various physiological pathways with possible functional implications.

Profiling the effects of isocitrate dehydrogenase 1 and 2 mutations on the cellular metabolome

Point mutations of the NADP(+)-dependent isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) occur early in the pathogenesis of gliomas. When mutated, IDH1 and IDH2 gain the ability to produce the metabolite (R)-2-hydroxyglutarate (2HG), but the downstream effects of mutant IDH1 and IDH2 proteins or of 2HG on cellular metabolism are unknown. We profiled >200 metabolites in human oligodendroglioma (HOG) cells to determine the effects of expression of IDH1 and IDH2 mutants. Levels of amino acids, glutathione metabolites, choline derivatives, and tricarboxylic acid (TCA) cycle intermediates were altered in mutant IDH1- and IDH2-expressing cells. These changes were similar to those identified after treatment of the cells with 2HG. Remarkably, N-acetyl-aspartyl-glutamate (NAAG), a common dipeptide in brain, was 50-fold reduced in cells expressing IDH1 mutants and 8.3-fold reduced in cells expressing IDH2 mutants. NAAG also was significantly lower in human glioma tissues containing IDH mutations than in gliomas without such mutations. These metabolic changes provide clues to the pathogenesis of tumors associated with IDH gene mutations.

Identification of novel molecular targets for endometrial cancer using a drill-down LC-MS/MS approach with iTRAQ

Background

The number of patients with endometrial carcinoma (EmCa) with advanced stage or high histological grade is increasing and prognosis has not improved for over the last decade. There is an urgent need for the discovery of novel molecular targets for diagnosis, prognosis and treatment of EmCa, which will have the potential to improve the clinical strategy and outcome of this disease.

Methodology and Results

We used a “drill-down” proteomics approach to facilitate the identification of novel molecular targets for diagnosis, prognosis and/or therapeutic intervention for EmCa. Based on peptide ions identified and their retention times in the first LC-MS/MS analysis, an exclusion list was generated for subsequent iterations. A total of 1529 proteins have been identified below the Proteinpilot® 5% error threshold from the seven sets of iTRAQ experiments performed. On average, the second iteration added 78% new peptides to those identified after the first run, while the third iteration added 36% additional peptides. Of the 1529 proteins identified, only 40 satisfied our criteria for significant differential expression in EmCa in comparison to normal proliferative tissues. These proteins included metabolic enzymes (pyruvate kinase M2 and lactate dehydrogenase A); calcium binding proteins (S100A6, calcyphosine and calumenin), and proteins involved in regulating inflammation, proliferation and invasion (annexin A1, interleukin enhancer-binding factor 3, alpha-1-antitrypsin, macrophage capping protein and cathepsin B). Network analyses revealed regulation of these molecular targets by c-myc, Her2/neu and TNF alpha, suggesting intervention with these pathways may be a promising strategy for the development of novel molecular targeted therapies for EmCa.

Conclusions

Our analyses revealed the significance of drill-down proteomics approach in combination with iTRAQ to overcome some of the limitations of current proteomics strategies. This study led to the identification of a number of novel molecular targets having therapeutic potential for targeted molecular therapies for endometrial carcinoma.

Prolactin inhibits activity of pyruvate kinase M2 to stimulate cell proliferation

Mitogenic and prosurvival effects underlie the tumorigenic roles of prolactin (PRL) in the pathogenesis of breast cancer. PRL signaling is mediated through its receptor (PRLr). A proteomics screen identified the pyruvate kinase M2 (PKM2), a glycolytic enzyme known to play an important role in tumorigenesis, as a protein that constitutively interacts with PRLr. Treatment of cells with PRL inhibited pyruvate kinase activity and increased the lactate content in human cells in a manner that was dependent on the abundance of PRLr, activation of Janus kinase 2, and tyrosine phosphorylation of the intracellular domain of PRLr. Knockdown of PKM2 attenuated PRL-stimulated cell proliferation. The extent of this proliferation was rescued by the knock-in of the wild-type PKM2 but not of its mutant insensitive to PRL-mediated inhibition. We discuss a hypothesis that the inhibition of PKM2 by PRL contributes to the PRL-stimulated cell proliferation.

Adding a combination of hydroxycitrate and lipoic acid (METABLOC™) to chemotherapy improves effectiveness against tumor development: experimental results and case report

Altered metabolism of cancer first highlighted by Otto Warburg has a long history. Although ignored for a considerable amount of time, it is now receiving substantial attention. We recently published results obtained with a combination of two drugs, lipoic acid and hydroxycitrate, targeting metabolic enzymes particularly affected in cancer: ATP citrate lyase and pyruvate dehydrogenase kinase. This treatment was as efficient as chemotherapy in the three mouse cancer models that were tested. In this work, we asked if our drug combination could be used in conjunction with standard cytotoxic chemotherapy, in particular cisplatin, to improve basic protocol efficacy. A combination of lipoic acid and hydroxycitrate was administered to mice implanted with syngeneic cancer cells, LL/2 lung carcinoma and MBT-2 bladder carcinoma, concommitantly with classical chemotherapy (cisplatin or methotrexate). We demonstrate that the triple combination lipoic acid + hydroxycitrate + cisplatin or methotrexate is more efficient than cisplatin or methotrexate used individually or the combination of lipoic acid and hydroxycitrate administered alone. Of particular note are the results obtained in the treatment of an 80 year-old female who presented with ductal adenocarcinoma of the pancreas accompanied by liver metastases. A treatment course using gemcitabine plus α-lipoic acid and hydroxycitrate gave highly promising results. The in vivo data, coupled with the case study results, suggest a possible advantage in using a treatment targeted at cancer metabolism in association with classical chemotherapy.

Multiplex N-terminome analysis of MMP-2 and MMP-9 substrate degradomes by iTRAQ-TAILS quantitative proteomics

Proteolysis is a major protein posttranslational modification that, by altering protein structure, affects protein function and, by truncating the protein sequence, alters peptide signatures of proteins analyzed by proteomics. To identify such modified and shortened protease-generated neo-N-termini on a proteome-wide basis, we developed a whole protein isobaric tag for relative and absolute quantitation (iTRAQ) labeling method that simultaneously labels and blocks all primary amines including protein N- termini and lysine side chains. Blocking lysines limits trypsin cleavage to arginine, which effectively elongates the proteolytically truncated peptides for improved MS/MS analysis and peptide identification. Incorporating iTRAQ whole protein labeling with terminal amine isotopic labeling of substrates (iTRAQ-TAILS) to enrich the N-terminome by negative selection of the blocked mature original N-termini and neo-N-termini has many advantages. It enables simultaneous characterization of the natural N-termini of proteins, their N-terminal modifications, and proteolysis product and cleavage site identification. Furthermore, iTRAQ-TAILS also enables multiplex N-terminomics analysis of up to eight samples and allows for quantification in MS2 mode, thus preventing an increase in spectral complexity and extending proteome coverage by signal amplification of low abundance proteins. We compared the substrate degradomes of two closely related matrix metalloproteinases, MMP-2 (gelatinase A) and MMP-9 (gelatinase B), in fibroblast secreted proteins. Among 3,152 unique N-terminal peptides identified corresponding to 1,054 proteins, we detected 201 cleavage products for MMP-2 and unexpectedly only 19 for the homologous MMP-9 under identical conditions. Novel substrates identified and biochemically validated include insulin-like growth factor binding protein-4, complement C1r component A, galectin-1, dickkopf-related protein-3, and thrombospondin-2. Hence, N-terminomics analyses using iTRAQ-TAILS links gelatinases with new mechanisms of action in angiogenesis and reveals unpredicted restrictions in substrate repertoires for these two very similar proteases.

Dominant negative mutations affect oligomerization of human pyruvate kinase M2 isozyme and promote cellular growth and polyploidy

This study was designed to understand the mechanism and functional implication of the two heterozygous mutations (H391Y and K422R) of human pyruvate kinase M2 isozyme (PKM(2)) observed earlier in a Bloom syndrome background. The co-expression of homotetrameric wild type and mutant PKM(2) in the cellular milieu resulting in the interaction between the two at the monomer level was substantiated further by in vitro experiments. The cross-monomer interaction significantly altered the oligomeric state of PKM(2) by favoring dimerization and heterotetramerization. In silico study provided an added support in showing that hetero-oligomerization was energetically favorable. The hetero-oligomeric populations of PKM(2) showed altered activity and affinity, and their expression resulted in an increased growth rate of Escherichia coli as well as mammalian cells, along with an increased rate of polyploidy. These features are known to be essential to tumor progression. This study provides insight in understanding the modulated role of large oligomeric multifunctional proteins such as PKM(2) by affecting cellular behavior, which is an essential observation to understand tumor sustenance and progression and to design therapeutic intervention in future.