PKM2, cancer metabolism, and the road ahead

Discovery of Functional Alternatively Spliced PKM Transcripts in Human Cancers

Simple Summary

Pyruvate kinase muscle type (PKM) is a key enzyme in glycolysis and is a mediator of the Warburg effect in tumors. The association of PKM with survival of cancer patients is controversial. In this study, we investigated the associations of the alternatively spliced transcripts of PKM with cancer patients’ survival outcomes and explained the conflicts in previous studies. We discovered three poorly studied alternatively spliced PKM transcripts that exhibited opposite prognostic indications in different human cancers based on integrative systems analysis. We also detected their protein products and explored their potential biological functions based on in-vitro experiments. Our analysis demonstrated that alternatively spliced transcripts of not only PKM but also other genes should be considered in cancer studies, since it may enable the discovery and targeting of the right protein product for development of the efficient treatment strategies.

Abstract

Pyruvate kinase muscle type (PKM) is a key enzyme in glycolysis and plays an important oncological role in cancer. However, the association of PKM expression and the survival outcome of patients with different cancers is controversial. We employed systems biology methods to reveal prognostic value and potential biological functions of PKM transcripts in different human cancers. Protein products of transcripts were shown and detected by western blot and mass spectrometry analysis. We focused on different transcripts of PKM and investigated the associations between their mRNA expression and the clinical survival of the patients in 25 different cancers. We find that the transcripts encoding PKM2 and three previously unstudied transcripts, namely ENST00000389093, ENST00000568883, and ENST00000561609, exhibited opposite prognostic indications in different cancers. Moreover, we validated the prognostic effect of these transcripts in an independent kidney cancer cohort. Finally, we revealed that ENST00000389093 and ENST00000568883 possess pyruvate kinase enzymatic activity and may have functional roles in metabolism, cell invasion, and hypoxia response in cancer cells. Our study provided a potential explanation to the controversial prognostic indication of PKM, and could invoke future studies focusing on revealing the biological and oncological roles of these alternative spliced variants of PKM.

Role of Glucose Metabolism and Mitochondrial Function in Diabetic Kidney Disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) continues to be the primary cause of chronic kidney disease in the USA and around the world. The numbers of people with DKD also continue to rise despite current treatments. Certain newer hypoglycemic drugs offer a promise of slowing progression, but it remains to be seen how effective these will be over time. Thus, continued exploration of the mechanisms underlying the development and progression of DKD is essential in order to discover new treatments. Hyperglycemia is the main cause of the cellular damage seen in DKD. But, exactly how hyperglycemia leads to the activation of processes that are ultimately deleterious is incompletely understood.

RECENT FINDINGS

Studies primarily over the past 10 years have provided novel insights into the interplay of hyperglycemia, glucose metabolic pathways, mitochondrial function, and the potential importance of what has been called the Warburg effect on the development and progression of DKD. This review will provide a brief overview of glucose metabolism and the hypotheses concerning the pathogenesis of DKD and then discuss in more detail the supporting data that indicate a role for the interplay of glucose metabolic pathways and mitochondrial function.

Proteins moonlighting in tumor metabolism and epigenetics

Cancer development is a complicated process controlled by the interplay of multiple signaling pathways and restrained by oxygen and nutrient accessibility in the tumor microenvironment. High plasticity in using diverse nutrients to adapt to metabolic stress is one of the hallmarks of cancer cells. To respond to nutrient stress and to meet the requirements for rapid cell proliferation, cancer cells reprogram metabolic pathways to take up more glucose and coordinate the production of energy and intermediates for biosynthesis. Such actions involve gene expression and activity regulation by the moonlighting function of oncoproteins and metabolic enzymes. The signal - moonlighting protein - metabolism axis facilitates the adaptation of tumor cells under varying environment conditions and can be therapeutically targeted for cancer treatment.

Characterization of novel USP6 gene rearrangements in a subset of so-called cellular fibroma of tendon sheath

Fibroma of tendon sheath (FTS) is an uncommon benign fibroblastic/myofibroblastic neoplasm that typically arises in the tenosynovial tissue of the distal extremities. Histologically, it is a well-circumscribed proliferation of spindle cells within collagenous stroma with peripheral slit-like vessels. Most examples are relatively hypocellular and more densely collagenous than nodular fasciitis; however, a cellular variant has been described, which has considerable morphologic overlap with nodular fasciitis and has been shown to harbor USP6 translocations in a subset of cases. The incidence of these rearrangements and the identity of the USP6 fusion partners have not been described in detail. In this study we evaluate 13 cases of cellular fibroma of tendon sheath by anchored multiplex PCR/next generation sequencing in order to detect potential gene fusions. Nucleic acids of adequate quality were obtained in 11 cases, demonstrating gene fusions in 7/11 (64%), all of which involve USP6 with a variety of partners, including PKM, RCC1, ASPN, COL1A1, COL3A1, and MYH9. Some unusual histomorphologic findings were present in a subset of cases including palisading growth pattern, epithelioid cells, and osteoclast-like multinucleated giant cells, particularly in the tumors with PKM and ASPN gene partners. Overall, the findings support a biologic relationship between cellular fibroma of tendon sheath and other lesions within the spectrum of USP6-rearranged neoplasms, particularly nodular fasciitis.

The Establishment of a Fast and Safe Orthotopic Colon Cancer Model Using a Tissue Adhesive Technique

Purpose

We aimed to develop a novel method for orthotopic colon cancer model, using tissue adhesive in place of conventional surgical method.

Materials and Methods

RFP HCT 116 cell line were used to establish the colon cancer model. Fresh tumor tissue harvested from a subcutaneous injection was grafted into twenty nude mice, divided into group A (suture method) and group B (tissue adhesive method). For the group A, we fixed the tissue on the serosa layer of proximal colon by 8-0 surgical suture. For the group B, tissue adhesive (10 μL) was used to fix the tumor. The mortality, tumor implantation success, tumor metastasis, primary tumor size, and operation time were compared between the two groups. Dissected tumor tissue was analyzed for the histology and immunohistochemistry. Also, we performed tumor marker analysis.

Results

We observed 30% increase in graft success and 20% decrease in mortality, by using tissue adhesive method, respectively. The median colon tumor size was significantly increased by 4 mm and operation time was shortened by 6.5 minutes. The H&E showed similar tumor structure between the two groups. The immunohistochemistry staining for cancer antigen 19-9, carcinoembryonic antigen, cytokeratin 20, and Ki-67 showed comparable intensities in both groups. Real-time quantitative reverse transcription analysis showed eight out of nine tumor markers are unchanged in the tissue adhesive group. Western blot indicated the tissue adhesive group expressed less p-JNK (apototic marker) and more p-MEK/p-p38 (proliferation marker) levels.

Conclusion

We concluded the tissue adhesive method is a quick and safe way to generate orthotopic, colon cancer model.

Interrogation of kinase genetic interactions provides a global view of PAK1-mediated signal transduction pathways

Kinases are critical components of intracellular signaling pathways and have been extensively investigated with regard to their roles in cancer. p21-activated kinase-1 (PAK1) is a serine/threonine kinase that has been previously implicated in numerous biological processes, such as cell migration, cell cycle progression, cell motility, invasion, and angiogenesis, in glioma and other cancers. However, the signaling network linked to PAK1 is not fully defined. We previously reported a large-scale yeast genetic interaction screen using toxicity as a readout to identify candidate PAK1 genetic interactions. En masse transformation of the PAK1 gene into 4,653 homozygous diploid Saccharomyces cerevisiae yeast deletion mutants identified ∼400 candidates that suppressed yeast toxicity. Here we selected 19 candidate PAK1 genetic interactions that had human orthologs and were expressed in glioma for further examination in mammalian cells, brain slice cultures, and orthotopic glioma models. RNAi and pharmacological inhibition of potential PAK1 interactors confirmed that DPP4, KIF11, mTOR, PKM2, SGPP1, TTK, and YWHAE regulate PAK1-induced cell migration and revealed the importance of genes related to the mitotic spindle, proteolysis, autophagy, and metabolism in PAK1-mediated glioma cell migration, drug resistance, and proliferation. AKT1 was further identified as a downstream mediator of the PAK1-TTK genetic interaction. Taken together, these data provide a global view of PAK1-mediated signal transduction pathways and point to potential new drug targets for glioma therapy.

SEMG1/2 augment energy metabolism of tumor cells

SEMG1 and SEMG2 genes belong to the family of cancer-testis antigens (CTAs), whose expression normally is restricted to male germ cells but is often restored in various malignancies. High levels of SEMG1 and SEMG2 expression are detected in prostate, renal, and lung cancer as well as hemoblastosis. However, the functional importance of both SEMGs proteins in human neoplasms is still largely unknown. In this study, by using a combination of the bioinformatics and various cellular and molecular assays, we have demonstrated that SEMG1 and SEMG2 are frequently expressed in lung cancer clinical samples and cancer cell lines of different origins and are negatively associated with the survival rate of cancer patients. Using the pull-down assay followed by LC-MS/MS mass-spectrometry, we have identified 119 proteins associated with SEMG1 and SEMG2. Among the SEMGs interacting proteins we noticed two critical glycolytic enzymes-pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA). Importantly, we showed that SEMGs increased the protein level and activity of both PKM2 and LDHA. Further, both SEMGs increased the membrane mitochondrial potential (MMP), glycolysis, respiration, and ROS production in several cancer cell lines. Taken together, these data provide first evidence that SEMGs can up-regulate the energy metabolism of cancer cells, exemplifying their oncogenic features.

Non-coding RNAs: emerging regulators of glucose metabolism in hepatocellular carcinoma

Reprogramming of metabolism is one of the hallmarks of cancer, among which glucose metabolism dysfunction is the most prominent feature. The glucose metabolism of tumor cells is significantly different from that of normal cells. Glucose metabolism reprogramming of hepatocellular carcinoma (HCC) has become an important research hotspot in the field of HCC, a variety of tumor metabolic interventions have been applied clinically. Moreover, various Non-coding RNAs (ncRNAs) including microRNAs (miRNAs), long non-coding (lncRNAs) as well as circular RNAs (circRNAs), have recently been proved to play potential roles in glucose metabolism. This review summarizes the effects of ncRNAs on HCC that participate in glucose metabolism and discuss the related mechanisms to find potential and effective targeted treatments for HCC.

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.

Serine and Metabolism Regulation: A Novel Mechanism in Antitumor Immunity and Senescence

As one of the nonessential amino acids (NEAAs), serine is involved in the anabolism of multiple macromolecular substances by participating in one-carbon unit metabolism. Thus, rapidly proliferating cells such as tumor cells and activated immune cells are highly dependent on serine. Serine supports the proliferation of various immune cells through multiple pathways to enhance the antitumor immune response. Moreover, serine influences aging specificity in an epigenetic and metabolic manner. In this review, we focus on recent advances in the relationship between serine metabolism, antitumor immunity, and senescence. The metabolic regulation of serine seems to be a key point of intervention in antitumor immunity and aging-related disease, providing an opportunity for several novel therapeutics.

The synergistic antitumour effect of multi-components from Pulsatilla chinensis saponins in NCI-H460 lung cancer cell line through induction of apoptosis

Context: Pulsatilla chinensis (Bunge) Regel (Ranunculaceae) possess antitumour effects; however, its antitumour potential has not been extensively investigated.Objective: To investigate the synergetic effect of multi-components from P. chinensis induced cell apoptosis and explore the mechanism.Materials and methods: The cytotoxicity was measured against NCI-H460, SMMC-7721, HCT-116 and U251 cell lines treated with eight monomers from P. chinensis. The synergetic effect of a combination of Pulsatilla saponin D (PSD), Raddeanoside R13 (R13), and Pulsatilla saponin A (PSA) was assessed using CalcuSyn3.0. Annexin V-FITC/PI and DAPI staining analyzed apoptosis of NCI-H460 cells treated with PSD, R13 and PSA alone or in combination. Proteins differential expression was analyzed using proteomic, DAVID Bioinformatics Resources, R software environment and KEGG database, and verified by western blotting.Results: PSD, R13, and PSA displayed greater antitumor activity with IC₅₀ values of 5.6, 5.1 and 10.5 µM against NCI-H460 cells compared with other monomers. The combination of PSD, R13, and PSA had a synergistic effect at CI = 0.27 and induced 17.53% cells apoptotic detected by flow cytometric. Bioinformatic analysis showed an overview of the differentially expressed proteins and some signalling pathways. Moreover, some candidate proteins (LDHA, PI3K, NOL3 and cleaved-caspase-3) were validated by western blotting.Discussion and Conclusion: These results show PSD, R13, and PSA are good candidates as natural products for use in the treatment of lung cancer. Potential signalling pathways and protein targets need to be further validated. The application of the drug combination approach also provides a therapeutic strategy for cancer.

The Two-Way Relationship Between Calcium and Metabolism in Cancer

Calcium ion (Ca²⁺) signaling is critical to many physiological processes, and its kinetics and subcellular localization are tightly regulated in all cell types. All Ca²⁺ flux perturbations impact cell function and may contribute to various diseases, including cancer. Several modulators of Ca²⁺ signaling are attractive pharmacological targets due to their accessibility at the plasma membrane. Despite this, the number of specific inhibitors is still limited, and to date there are no anticancer drugs in the clinic that target Ca²⁺ signaling. Ca²⁺ dynamics are impacted, in part, by modifications of cellular metabolic pathways. Conversely, it is well established that Ca²⁺ regulates cellular bioenergetics by allosterically activating key metabolic enzymes and metabolite shuttles or indirectly by modulating signaling cascades. A coordinated interplay between Ca²⁺ and metabolism is essential in maintaining cellular homeostasis. In this review, we provide a snapshot of the reciprocal interaction between Ca²⁺ and metabolism and discuss the potential consequences of this interplay in cancer cells. We highlight the contribution of Ca²⁺ to the metabolic reprogramming observed in cancer. We also describe how the metabolic adaptation of cancer cells influences this crosstalk to regulate protumorigenic signaling pathways. We suggest that the dual targeting of these processes might provide unprecedented opportunities for anticancer strategies. Interestingly, promising evidence for the synergistic effects of antimetabolites and Ca²⁺-modulating agents is emerging.

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.

Platelet-rich plasma improves chronic inflammatory pain by inhibiting PKM2-mediated aerobic glycolysis in astrocytes

Background

Astrocytes are highly glycolytic cells that play a crucial role in chronic pain. Recently it has been found that inflammation and metabolism are related to the inflammatory stimuli closely that cause cellular metabolic changes. Pyruvate kinase M2 (PKM2) is a critical metabolic kinase in aerobic glycolysis or the Warburg effect. Besides, it also plays a crucial role in cell proliferation and signal transduction, but its role in astrocytes is still unclear.

Methods

The chronic inflammatory pain model was set up by intraplantar injection of complete Freund’s adjuvant (CFA) in Sprague Dawley (SD) rats as well as the cell model was constructed by lipopolysaccharide-treated primary astrocytes. Von Frey filament stimulation was used to continuously observe the changes of pain behavior in rats after modeling. Then, immunofluorescence staining and Western blot tests were used to observe the expression levels of glial fibrillary acidic protein (GFAP), pyruvate kinase (PKM2), signal transducers and activators of transcription 3 (STAT3) and high mobility group box-1 protein (HMGB1). After that, specific kits measured lactate contents. Finally, we observed the platelet-rich plasma’s (PRP) effect on mechanical hyperalgesia in rats with inflammatory pain induced by CFA and its effect on related signal molecules.

Results

We found that in the CFA-induced inflammatory pain model, astrocytes were significantly activated, GFAP was increased, PKM2 was significantly up-regulated, and the glycolytic product lactate was increased. Also, intrathecal injection of PRP increased the pain threshold, inhibited the activation of astrocytes, and decreased the expression of PKM2 and aerobic glycolysis; in LPS-activated primary astrocytes as an in vitro model, we found PKM2 translocation activationSTAT3 signaling resulted in sustained activation of astrocyte marker GFAP, and the expression level and localization of p-STAT3 were correlated with PKM2. PRP could inhibit the activation of astrocytes, reduce the expression of PKM2 and the expression levels of glycolysis and GFAP, GLUT1, and p-STAT3 in astrocytes.

Conclusions

Our findings suggest PKM2 not only plays a glycolytic role in astrocytes, but also plays a crucial role in astrocyte-activated signaling pathways, and PRP attenuates CFA induced inflammatory pain by inhibiting aerobic glycolysis in astrocytes, providing a new therapeutic target for the treatment of inflammatory pain.

Modulation of PKM activity affects the differentiation of TH17 cells

Small molecules that promote the metabolic activity of the pyruvate kinase isoform PKM2, such as TEPP-46 and DASA-58, limit tumorigenesis and inflammation. To understand how these compounds alter T cell function, we assessed their therapeutic activity in a mouse model of T cell-mediated autoimmunity that mimics multiple sclerosis (MS). TH17 cells are believed to orchestrate MS pathology, in part, through the production of two proinflammatory cytokines: interleukin-17 (IL-17) and GM-CSF. We found that both TEPP-46 and DASA-58 suppressed the development of IL-17-producing TH17 cells but increased the generation of those producing GM-CSF. This switch redirected disease pathology from the spinal cord to the brain. In addition, we found that activation of PKM2 interfered with TGF-β1 signaling, which is necessary for the development of TH17 and regulatory T cells. Collectively, our data clarify the therapeutic potential of PKM2 activators in MS-like disease and how these agents alter T cell function.

Digging deeper through glucose metabolism and its regulators in cancer and metastasis

Glucose metabolism enzymes and transporters play major role in cancer development and metastasis. In this study, we discuss glucose metabolism, transporters, receptors, hormones, oncogenes and tumor suppressors which interact with glucose metabolism and we try to discuss their major role in cancer development and cancer metabolism. We try to highlight the. Metabolic changes in cancer and metastasis upregulation of glycolysis is observed in many primary and metastatic cancers and aerobic glycolysis is the most favorable mechanism for glucose metabolism in cancer cells, and it is a kind of evolutionary change. The question that is posed at this juncture is: Can we use aerobic glycolysis phenotype and enzymes beyond this mechanism in estimating cancer prognosis and metastasis? Lactate is a metabolite of glucose metabolism and it is a key player in cancer and metastasis in both normoxic and hypoxic condition so lactate dehydrogenase can be a good prognostic biomarker. Furthermore, monocarboxylic transporter which is the main lactate transporter can be good target in therapeutic studies. Glycolysis enzymes are valuable enzymes in cancer and metastasis diagnosis and can be used as therapeutic targets in cancer treatment. Designing a diagnostic and prognostic profile for cancer metastasis seems to be possible base on glycolysis enzymes and glucose transporters. Also, glucose metabolism enzymes and agents can give us a clear vision in estimating cancer metastasis. We can promote a panel of genes that detect genetic changes in glucose metabolism agents to diagnose cancer metastasis.

Functional interplay among thiol-based redox signaling, metabolism, and ferroptosis unveiled by a genetic variant of TP53

The p53 tumor suppressor protein is a transcription factor and master stress response mediator, and it is subject to reduction-oxidation (redox)-dependent regulation. The P47S variant of TP53, which exists primarily in African-descent populations, associates with an elevated abundance of low molecular weight (LMW) thiols, including glutathione (GSH) and coenzyme A (CoA). Here we show that S47 and P47 cells exhibit distinct metabolic profiles, controlled by their different redox states and expression of Activating Transcription Factor-4 (ATF4). We find that S47 cells exhibit decreased catabolic glycolysis but increased use of the pentose phosphate pathway (PPP), and an enhanced abundance of the antioxidant, NADPH. We identify ATF4 as differentially expressed in P47 and S47 cells and show that ATF4 can reverse the redox status and rescue metabolism of S47 cells, as well as increase sensitivity to ferroptosis. This adaptive metabolic switch is rapid, reversible, and accompanied by thiol-mediated changes in the structures and activities of key glycolytic signaling pathway proteins, including GAPDH and G6PD. The results presented here unveil the important functional interplay among pathways regulating thiol-redox status, metabolic adaptation, and cellular responses to oxidative stress.

Long Non-Coding RNAs as Regulators of Interactions between Cancer-Associated Fibroblasts and Cancer Cells in the Tumor Microenvironment

Long non-coding RNAs (lncRNAs) regulate diverse physiological and pathological processes via post-transcriptional, post-translational, and epigenetic mechanisms. They are also involved in tumor initiation, progression, and metastasis by functioning as key players in the tumor microenvironment. Cancer-associated fibroblasts (CAFs) promote tumor initiation, progression, metastasis, drug resistance, and immunosuppression, which can be modulated by lncRNAs. LncRNAs regulate the intrinsic properties of CAFs or cancer cells intracellularly or function extracellularly through exosomal secretion. In-depth studies on the mechanisms of lncRNA functions will enable their clinical use as diagnosis/prognosis markers and therapeutic targets in cancer treatment.

Pyruvate Kinase M2 Promotes Prostate Cancer Metastasis Through Regulating ERK1/2-COX-2 Signaling

Pyruvate kinase M2 (PKM2) is a key enzyme of glycolysis, which is highly expressed in many tumor cells, and has emerged as an important player in tumor progression and metastasis. However, the functional roles of PKM2 in tumor metastasis remain elusive. Here we showed that PKM2 promoted prostate cancer metastasis via extracellular-regulated protein kinase (ERK)-cyclooxygenase (COX-2) signaling. Based on public databases, we found that PKM2 expression was upregulated in prostate cancer and positively associated with tumor metastasis. Further analysis showed that PKM2 promoted prostate cancer cell migration/invasion and epithelial-mesenchymal transition (EMT) through upregulation of COX-2. Mechanistically, PKM2 interacted with ERK1/2 and regulated its phosphorylation, leading to phosphorylation of transcription factor c-Jun, downstream of ERK1/2, to activate COX-2 transcription by IP and ChIP assay, while inhibition of COX-2 significantly reversed the promotion effect of PKM2 on tumor metastasis in vivo. Taken together, our results suggest that a novel of PKM2-ERK1/2-c-Jun-COX-2 axis is a potential target in controlling prostate cancer metastasis.

J. de Wit G, Vogel ISP, Offringa C, Schönfelder M, Jaspers RT, Wackerhage H. PKM2 Determines Myofiber Hypertrophy In Vitro and Increases in Response to Resistance Exercise in Human Skeletal Muscle

Nearly 100 years ago, Otto Warburg investigated the metabolism of growing tissues and discovered that tumors reprogram their metabolism. It is poorly understood whether and how hypertrophying muscle, another growing tissue, reprograms its metabolism too. Here, we studied pyruvate kinase muscle (PKM), which can be spliced into two isoforms (PKM1, PKM2). This is of interest, because PKM2 redirects glycolytic flux towards biosynthetic pathways, which might contribute to muscle hypertrophy too. We first investigated whether resistance exercise changes PKM isoform expression in growing human skeletal muscle and found that PKM2 abundance increases after six weeks of resistance training, whereas PKM1 decreases. Second, we determined that Pkm2 expression is higher in fast compared to slow fiber types in rat skeletal muscle. Third, by inducing hypertrophy in differentiated C2C12 cells and by selectively silencing Pkm1 and/or Pkm2 with siRNA, we found that PKM2 limits myotube growth. We conclude that PKM2 contributes to hypertrophy in C2C12 myotubes and indicates a changed metabolic environment within hypertrophying human skeletal muscle fibers. PKM2 is preferentially expressed in fast muscle fibers and may partly contribute to the increased potential for hypertrophy in fast fibers.

Diabetes and PKM2 affect prognosis in patients with intrahepatic cholangiocarcinoma

Diabetes mellitus (DM) is a common disease, but its effect on the prognosis of patients with intrahepatic cholangiocarcinoma (ICC) has not been reported. The aim of the present study was to explore the prognostic significance of diabetes in patients with ICC treated with hepatectomy and to clarify the role of pyruvate kinase M2 (PKM2). A consecutive retrospective cohort of 110 patients with ICC (28 with DM and 82 without DM) who underwent therapeutic hepatectomy was evaluated between January 2006 and January 2011. The clinicopathological characteristics of the two groups and the differences between overall survival (OS) and recurrence-free survival (RFS) were analyzed. The Cox proportional hazards model was further used to identify independent prognostic predictors. PKM2 expression was measured using immunohistochemical staining in tissues collected, after obtaining informed consent. Patients with ICC with DM exhibited significantly lower OS and RFS rates at 1, 3 and 5 years compared with patients with ICC without DM. Cox multivariate analysis revealed that DM was an independent predictor of poor OS and RFS. Additionally, high PKM2 expression was significantly higher in patients with ICC with DM compared with that in patients without DM. Overall, DM was associated with significantly lower OS and RFS rates in patients with ICC. The underlying biological rationale may be attributed to the higher PKM2 expression rate.

IGF2BP3 May Contributes to Lung Tumorigenesis by Regulating the Alternative Splicing of PKM

RNA binding proteins (RBPs) play a key role in genome regulation. Here we report the post-transcript regulation of IGF2BP3, which belongs to the insulin-like growth factor 2 mRNA binding protein family. We used iRIP-seq and RNA-seq to analyze the transcript regulation and alternative splicing on IGF2BP3 treated with overexpression cells and control. Overexpressed IGF2BP3 has broadly increased genes expression which involved in G-protein coupled receptor signaling pathway, positive regulation of cell proliferation, and signal transduction. IGF2BP3 regulated alternative splicing of multiple genes mainly clustered at response to hypoxia, negative regulation of transcription, and embryonic development. This study first provides alternative splicing analysis on transcription level of IGF2BP3 regulation, which laid the foundation for later research on IGF2BP3 critical functions.

Flavonoids against the Warburg phenotype-concepts of predictive, preventive and personalised medicine to cut the Gordian knot of cancer cell metabolism

The Warburg effect is characterised by increased glucose uptake and lactate secretion in cancer cells resulting from metabolic transformation in tumour tissue. The corresponding molecular pathways switch from oxidative phosphorylation to aerobic glycolysis, due to changes in glucose degradation mechanisms known as the 'Warburg reprogramming' of cancer cells. Key glycolytic enzymes, glucose transporters and transcription factors involved in the Warburg transformation are frequently dysregulated during carcinogenesis considered as promising diagnostic and prognostic markers as well as treatment targets. Flavonoids are molecules with pleiotropic activities. The metabolism-regulating anticancer effects of flavonoids are broadly demonstrated in preclinical studies. Flavonoids modulate key pathways involved in the Warburg phenotype including but not limited to PKM2, HK2, GLUT1 and HIF-1. The corresponding molecular mechanisms and clinical relevance of 'anti-Warburg' effects of flavonoids are discussed in this review article. The most prominent examples are provided for the potential application of targeted 'anti-Warburg' measures in cancer management. Individualised profiling and patient stratification are presented as powerful tools for implementing targeted 'anti-Warburg' measures in the context of predictive, preventive and personalised medicine.

Revisiting cancer hallmarks: insights from the interplay between oxidative stress and non-coding RNAs

Cancer is one of the most common disease worldwide, with complex changes and certain traits which have been described as “The Hallmarks of Cancer.” Despite increasing studies on in-depth investigation of these hallmarks, the molecular mechanisms associated with tumorigenesis have still not yet been fully defined. Recently, accumulating evidence supports the observation that microRNAs and long noncoding RNAs (lncRNAs), two main classes of noncoding RNAs (ncRNAs), regulate most cancer hallmarks through their binding with DNA, RNA or proteins, or encoding small peptides. Reactive oxygen species (ROS), the byproducts generated during metabolic processes, are known to regulate every step of tumorigenesis by acting as second messengers in cancer cells. The disturbance in ROS homeostasis leads to a specific pathological state termed “oxidative stress”, which plays essential roles in regulation of cancer progression. In addition, the interplay between oxidative stress and ncRNAs is found to regulate the expression of multiple genes and the activation of several signaling pathways involved in cancer hallmarks, revealing a potential mechanistic relationship involving ncRNAs, oxidative stress and cancer. In this review, we provide evidence that shows the essential role of ncRNAs and the interplay between oxidative stress and ncRNAs in regulating cancer hallmarks, which may expand our understanding of ncRNAs in the cancer development from the new perspective.

ATP Synthase c-Subunit Leak Causes Aberrant Cellular Metabolism in Fragile X Syndrome

Loss of the gene (Fmr1) encoding Fragile X mental retardation protein (FMRP) causes increased mRNA translation and aberrant synaptic development. We find neurons of the Fmr1^-/y mouse have a mitochondrial inner membrane leak contributing to a "leak metabolism." In human Fragile X syndrome (FXS) fibroblasts and in Fmr1^-/y mouse neurons, closure of the ATP synthase leak channel by mild depletion of its c-subunit or pharmacological inhibition normalizes stimulus-induced and constitutive mRNA translation rate, decreases lactate and key glycolytic and tricarboxylic acid (TCA) cycle enzyme levels, and triggers synapse maturation. FMRP regulates leak closure in wild-type (WT), but not FX synapses, by stimulus-dependent ATP synthase β subunit translation; this increases the ratio of ATP synthase enzyme to its c-subunit, enhancing ATP production efficiency and synaptic growth. In contrast, in FXS, inability to close developmental c-subunit leak prevents stimulus-dependent synaptic maturation. Therefore, ATP synthase c-subunit leak closure encourages development and attenuates autistic behaviors.

The rational discovery of multipurpose inhibitors of the ornithine decarboxylase

Metabolic reprograming is a hallmark of cancer, and the polyamine metabolic network is dysregulated in many cancers. Ornithine decarboxylase (ODC) is a rate-limiting enzyme for polyamine synthesis in the polyamine metabolic network. In many cancer cells, ODC is over-expressed, so this enzyme has been an attracting anti-cancer drug target. In the catalysis axis (pathway), ODC converts ornithine to putrescine. Meanwhile, ODC's activity is regulated by protein-protein interactions (PPIs), including the ODC-OAZ1-AZIN1 PPI axis and its monomer-dimer equilibrium. Previous studies showed that when ODC's activity is inhibited, the PPIs might counteract the inhibition efficiency. Therefore, we proposed that multipurpose inhibitors that can simultaneously inhibit ODC's activity and perturb the PPIs would be very valuable as drug candidates and molecular tools. To discover multipurpose ODC inhibitors, we established a computational pipeline by combining positive screening and negative screening. We used this pipeline for the forward screening of multipurpose ligands that might inhibit ODC's activity, block ODC-OAZ1 interaction and enhance ODC non-functional dimerization. With a combination of different experimental assays, we identified three multipurpose ODC inhibitors. At last, we showed that one of these inhibitors is a promising drug candidate. This work demonstrated that our computational pipeline is useful for discovering multipurpose ODC inhibitors, and multipurpose inhibitors would be very valuable. Similar with ODC, there are a lot of proteins in human proteome that act as both enzymes and PPI components. Therefore, this work is not only presenting new molecular tools for polyamine study, but also providing potential insights and protocols for discovering multipurpose inhibitors to target more important protein targets.

Phosphoribosyl Pyrophosphate Amidotransferase Promotes the Progression of Thyroid Cancer via Regulating Pyruvate Kinase M2

Background

Pyruvate kinase is an enzyme that catalyzes the conversion of phosphoenolpyruvate and ADP to pyruvate and ATP in glycolysis and plays a role in regulating cell metabolism. It is reported that the activity of pyruvate kinase is increased in cancers. Phosphoribosyl amidotransferase (PPAT) is reported to be a crucial regulator for pyruvate kinase activity in lung cancer. However, its role in thyroid cancer remains largely unknown.

Materials and Methods

Immunohistochemical analysis and qRT-PCR were used to detect the expression of PPAT in thyroid cancer samples. Both gain-of-function and loss-of-function models were constructed in thyroid cancer cell lines and the biological functions of PPAT on cellular phenotypes were studied using CCK-8 assay and transwell assay in vitro, respectively. Then, Western blot was used to evaluate the change of PKM2 and downstream signal pathways after PPAT was overexpressed or knocked down.

Results

Immunohistochemical analysis showed increased expression of PPAT in thyroid cancer tissues, and it was associated with unfavorable pathological characteristics. Knockdown and overexpression assays suggested that altering PPAT expression modulated cell proliferation, migration, and invasion. In terms of mechanism, PPAT could positively regulate the expression of PKM2 and activate ERK and STAT3 signaling pathways.

Conclusion

PPAT plays crucial roles in regulating proliferation, migration, and invasion of thyroid cancer cells via activating PKM2, ERK, and STAT3.

Ribosome profiling unveils translational regulation of metabolic enzymes in primary CD4+ Th1 cells

The transition from a naïve to an effector T cell is an essential event that requires metabolic reprogramming. We have recently demonstrated that the rapid metabolic changes that occur following stimulation of naïve T cells require the translation of preexisting mRNAs. Here, we provide evidence that translation regulates the metabolic asset of effector T cells. By performing ribosome profiling in human CD4⁺ Th1 cells, we show that the metabolism of glucose, fatty acids and pentose phosphates is regulated at the translational level. In Th1 cells, each pathway has at least one enzyme regulated at the translational level and selected enzymes have high translational efficiencies. mRNA expression does not predict protein expression. For instance, PKM2 mRNA is equally present in naïve T and Th1 cells, but the protein is abundant only in Th1. 5'-untranslated regions (UTRs) may partly account for this regulation. Overall we suggest that immunometabolism is controlled by translation.

Peroxidan Plays a Tumor-Promoting Role in Oral Squamous Cell Carcinoma

Despite dramatic progress in cancer diagnosis and treatment, the five-year survival rate of oral squamous cell carcinoma (OSCC) is still only about 50%. Thus, the need for elucidating the molecular mechanisms underlying OSCC is urgent. We previously identified the peroxidasin gene (PXDN) as one of several novel genes associated with OSCC. Although the PXDN protein is known to act as a tumor-promoting factor associated with the Warburg effect, its function and role in OSCC are poorly understood. In this study, we investigated the expression, function, and relationship with the Warburg effect of PXDN in OSCC. In immunohistochemical analysis of OSCC specimens, we observed that elevated PXDN expression correlated with lymph node metastasis and a diffuse invasion pattern. High PXDN expression was confirmed as an independent predictor of poor prognosis by multivariate analysis. The PXDN expression level correlated positively with that of pyruvate kinase (PKM2) and heme oxygenase-1 (HMOX1) and with lactate and ATP production. No relationship between PXDN expression and mitochondrial activation was observed, and PXDN expression correlated inversely with reactive oxygen species (ROS) production. These results suggest that PXDN might be a tumor progression factor causing a Warburg-like effect in OSCC.

PKM2 Expression as Biomarker for Resistance to Oxaliplatin-Based Chemotherapy in Colorectal Cancer

The purpose of the current study is to investigate the prognostic significance of M2 isoform of pyruvate kinase (PKM2) mRNA expression loss in patients with operable colon cancer (CC). Two hundred sixty-two specimens from patients with stage-III or high-risk stage-II CC (group-A) treated with adjuvant fluoropyrimidine and oxaliplatin chemotherapy (FOLFOX), 118 specimens from metastatic CC patients (group-B) treated with FOLFOX, and 104 metastatic CC patients (group-C) treated with irinotecan-based chemotherapy were analyzed for PKM2, TS, ERCC1, MYC, and NEDD9 mRNA expression, as well as KRAS exon2 and BRAF^V600E mutations. High PKM2 mRNA expression was correlated with left-sided located primaries (p = 0.001, group-A; p = 0.003, group-B; p = 0.001, group-C), high-grade tumors (p = 0.001, group-A; p = 0.017, group-B; p = 0.021, group-C), microsatellite-stable tumors (p < 0.001, group-A), pericolic lymph nodes involvement (p = 0.018, group-A), and cMYC mRNA expression (p = 0.002, group-A; p = 0.008, group-B; p = 0.006, group-C). High PKM2 mRNA expression was correlated with significantly lower disease free survival (DFS) (p = 0.002) and overall survival (OS) (p = 0.001) in the group-A. Similarly, PKM2 mRNA expression was associated with significantly decreased progression free survival (PFS) (p = 0.001) and OS (p = 0.001) in group-B. On the contrary, no significant association for the PKM2 mRNA expression has been observed with either PFS (p = 0.612) or OS (p = 0.517) in group-C. To conclude, the current study provides evidence for the prediction of PKM2 mRNA expression oxaliplatin-based treatment resistance.

ATP synthase c-subunit ring as the channel of mitochondrial permeability transition: Regulator of metabolism in development and degeneration

The mitochondrial permeability transition pore (mPTP) or mitochondrial megachannel is arguably one of the most mysterious phenomena in biology today. mPTP has been at the center of ongoing extensive scientific research for the last several decades. In this review we will discuss recent advances in the field that enhance our understanding of the molecular composition of mPTP, its regulatory mechanisms and its pathophysiological role. We will describe our recent findings on the role of ATP synthase c-subunit ring as a central player in mitochondrial permeability transition and as an important metabolic regulator during development and in degenerative diseases.

Stable isotope resolved metabolomics classification of prostate cancer cells using hyperpolarized NMR data

Metabolic fingerprinting is a strong tool for characterization of biological phenotypes. Classification with machine learning is a critical component in the discrimination of molecular determinants. Cellular activity can be traced using stable isotope labelling of metabolites from which information on cellular pathways may be obtained. Nuclear magnetic resonance (NMR) spectroscopy is, due to its ability to trace labelling in specific atom positions, a method of choice for such metabolic activity measurements. In this study, we used hyperpolarization in the form of dissolution Dynamic Nuclear Polarization (dDNP) NMR to measure signal enhanced isotope labelled metabolites reporting on pathway activity from four different prostate cancer cell lines. The spectra have a high signal-to-noise, with less than 30 signals reporting on 10 metabolic reactions. This allows easy extraction and straightforward interpretation of spectral data. Four metabolite signals selected using a Random Forest algorithm allowed a classification with Support Vector Machines between aggressive and indolent cancer cells with 96.9% accuracy, -corresponding to 31 out of 32 samples. This demonstrates that the information contained in the few features measured with dDNP NMR, is sufficient and robust for performing binary classification based on the metabolic activity of cultured prostate cancer cells.

ERK signalling: a master regulator of cell behaviour, life and fate

The proteins extracellular signal-regulated kinase 1 (ERK1) and ERK2 are the downstream components of a phosphorelay pathway that conveys growth and mitogenic signals largely channelled by the small RAS GTPases. By phosphorylating widely diverse substrates, ERK proteins govern a variety of evolutionarily conserved cellular processes in metazoans, the dysregulation of which contributes to the cause of distinct human diseases. The mechanisms underlying the regulation of ERK1 and ERK2, their mode of action and their impact on the development and homeostasis of various organisms have been the focus of much attention for nearly three decades. In this Review, we discuss the current understanding of this important class of kinases. We begin with a brief overview of the structure, regulation, substrate recognition and subcellular localization of ERK1 and ERK2. We then systematically discuss how ERK signalling regulates six fundamental cellular processes in response to extracellular cues. These processes are cell proliferation, cell survival, cell growth, cell metabolism, cell migration and cell differentiation.

Protein Stability of Pyruvate Kinase Isozyme M2 Is Mediated by HAUSP

The ubiquitin–proteasome system (UPS) is responsible for proteasomal degradation, regulating the half-life of the protein. Deubiquitinating enzymes (DUBs) are components of the UPS and inhibit degradation by removing ubiquitins from protein substrates. Herpesvirus-associated ubiquitin-specific protease (HAUSP) is one such deubiquitinating enzyme and has been closely associated with tumor development. In a previous study, we isolated putative HAUSP binding substrates by two-dimensional electrophoresis (2-DE) and identified them by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF/MS) analysis. The analysis showed that pyruvate kinase isoenzyme M2 (PKM2) was likely to be one of the substrates for HAUSP. Further study revealed that PKM2 binds to HAUSP, confirming the interaction between these proteins, and that PKM2 possesses the putative HAUSP binding motif, E or P/AXXS. Therefore, we generated mutant forms of PKM2 S57A, S97A, and S346A, and found that S57A had less binding affinity. In a previous study, we demonstrated that PKM2 is regulated by the UPS, and that HAUSP- as a DUB-acted on PKM2, thus siRNA for HAUSP increases PKM2 ubiquitination. Our present study newly highlights the direct interaction between HAUSP and PKM2.

The cysteine residue at 424th of pyruvate kinase M2 is crucial for tetramerization and responsiveness to oxidative stress

Alternative splicing of the pyruvate kinase M (PKM) pre-mRNA generates two isoforms, PKM1 and PKM2. PKM catalyzes the conversion of phosphoenol-pyruvate to pyruvate in glycolytic pathway. PKM1 exist as a stable tetramer that is at an active enzyme state, while PKM2 is in equilibrium among monomer, dimer and tetramer under the regulation of its allosteric activators. Many cancer cells show the feature of higher glucose uptake and lactate production in spite of oxygen availability, which is known as the Warburg effect. PKM2 is upregulated in most cancer types and the inactive PKM2 lead to the cancer metabolism. In addition, dimeric PKM2 induces its nuclear translocation through posttranslational modification and acts as a transcriptional co-activator for the expression of oncogenes. Therefore, it is important to elucidate mechanisms for modulation of an active or inactive state of PKM2, namely the tetramer-to-dimer-transition. The definitive difference between PKM1 and PKM2 is to constitutively form tetramer or not in the cytoplasm, which is ascribed to 22 amino acids derived from exon 9 (PKM1) or exon 10 (PKM2). In this study, we generated 22 different PKM1-mimetic point mutants of PKM2, and demonstrated that replacement of cysteine424 residue of PKM2 with leucine424 conserved in PKM1 (C424L) promote its tetramerization. PKM2(C424L) formed a tetramer without allosteric activator, and escaped the inhibitory effects by oxidative stress, like PKM1. Our findings intensely suggest that C424 or L424 determines the different catalytic and modulatory properties between PKM splicing isoforms.

Biomarkers of tumor invasiveness in proteomics (Review)

Over the past two decades, quantitative proteomics has emerged as an important tool for deciphering the complex molecular events involved in cancers. The number of references involving studies on the cancer metastatic process has doubled since 2010, while the last 5 years have seen the development of novel technologies combining deep proteome coverage capabilities with quantitative consistency and accuracy. To highlight key findings within this huge amount of information, the present review identified a list of tumor invasive biomarkers based on both the literature and data collected on a biocollection of experimental cell lines, tumor models of increasing invasiveness and tumor samples from patients with colorectal or breast cancer. Crossing these different data sources led to 76 proteins of interest out of 1,245 mentioned in the literature. Information on these proteins can potentially be translated into clinical prospects, since they represent potential targets for the development and evaluation of innovative therapies, alone or in combination. Herein, a systematical review of the biology of each of these proteins, including their specific subcellular/extracellular or multiple localizations is presented. Finally, as an important advantage of quantitative proteomics is the ability to provide data on all these molecules simultaneously in cell pellets, body fluids or paraffin‑embedded sections of tumors/invaded tissues, the significance of some of their interconnections is discussed.

Bcl2 inhibitor ABT737 reverses the Warburg effect via the Sirt3-HIF1α axis to promote oxidative stress-induced apoptosis in ovarian cancer cells

AIMS

Compared to normal cells, tumor cells maintain higher concentrations of reactive oxygen species (ROS) to support proliferation, invasion, and metastasis. Chemotherapeutic drugs often induce tumor cell apoptosis by increasing intracellular ROS concentrations to highly toxic levels. ABT737, which inhibits the apoptosis regulator B cell lymphoma 2 (Bcl2), increases the sensitivity of ovarian cancer cells to chemotherapeutic drugs by regulating the glucose metabolism, but the underlying mechanisms remain unclear. Therefore, we aimed to determine whether ABT737 promoted H₂O₂-induced tumor cell apoptosis by reversing glycolysis in ovarian cancer cells.

MAIN METHODS

SKOV3 ovarian cancer cells were treated with H₂O₂, ABT737, or both. Cell viability was compared using methyl thiazolyl tetrazolium (MTT), and flow cytometry was used to detect differences in apoptosis, ROS, and mitochondrial membrane potential. The relative expression levels of proteins associated with apoptosis and the glucose metabolism were measured using immunoblotting. Finally, glucose uptake and lactate secretion were measured using kits and compared.

KEY FINDINGS

ABT737 downregulated proteins associated with glucose uptake (GLUT1) and glycolysis (LHDA, PKM2 and HK2) via the Sirt3-HIF1α axis, reducing glucose uptake and lactate secretion in SKOV3 cells. This reversed glycolysis in the tumor cells, and promoted H₂O₂-induced apoptosis.

SIGNIFICANCE

The Bcl2 inhibitor ABT737 enhanced the anti-tumor effect of oxidative stress by reversing the Warburg effect in ovarian cancer cells, providing powerful theoretical support for further clinical applications of Bcl2 inhibitors.

Altered photoreceptor metabolism in mouse causes late stage age-related macular degeneration-like pathologies

The main cause for blindness in the elderly worldwide is age-related macular degeneration (AMD). What causes AMD remains unknown. The high metabolic demands of photoreceptors are thought to contribute to disease pathogenesis, yet whether photoreceptor metabolism differs in individuals with AMD has not been determined. Here, we show that photoreceptor metabolism does differ between diseased and nondiseased individuals. Mimicking the metabolic profile of diseased individuals in mouse resulted in the similar advanced pathologies as those that cause blindness in humans. A disease model with photoreceptors as a contributing factor explains also why AMD affects preferentially the macula; it is the region of highest photoreceptor density. The data might open new avenues to study the role of PRs in disease pathogenesis.

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly. While the histopathology of the different disease stages is well characterized, the cause underlying the progression, from the early drusen stage to the advanced macular degeneration stage that leads to blindness, remains unknown. Here, we show that photoreceptors (PRs) of diseased individuals display increased expression of two key glycolytic genes, suggestive of a glucose shortage during disease. Mimicking aspects of this metabolic profile in PRs of wild-type mice by activation of the mammalian target of rapamycin complex 1 (mTORC1) caused early drusen-like pathologies, as well as advanced AMD-like pathologies. Mice with activated mTORC1 in PRs also displayed other early disease features, such as a delay in photoreceptor outer segment (POS) clearance and accumulation of lipofuscin in the retinal-pigmented epithelium (RPE) and of lipoproteins at the Bruch’s membrane (BrM), as well as changes in complement accumulation. Interestingly, formation of drusen-like deposits was dependent on activation of mTORC1 in cones. Both major types of advanced AMD pathologies, including geographic atrophy (GA) and neovascular pathologies, were also seen. Finally, activated mTORC1 in PRs resulted in a threefold reduction in di-docosahexaenoic acid (DHA)–containing phospholipid species. Feeding mice a DHA-enriched diet alleviated most pathologies. The data recapitulate many aspects of the human disease, suggesting that metabolic adaptations in photoreceptors could contribute to disease progression in AMD. Identifying the changes downstream of mTORC1 that lead to advanced pathologies in mouse might present new opportunities to study the role of PRs in AMD pathogenesis.

Role of pyruvate kinase M2-mediated metabolic reprogramming during podocyte differentiation

Podocytes, a type of highly specialized epithelial cells, require substantial levels of energy to maintain glomerular integrity and function, but little is known on the regulation of podocytes’ energetics. Lack of metabolic analysis during podocyte development led us to explore the distribution of mitochondrial oxidative phosphorylation and glycolysis, the two major pathways of cell metabolism, in cultured podocytes during in vitro differentiation. Unexpectedly, we observed a stronger glycolytic profile, accompanied by an increased mitochondrial complexity in differentiated podocytes, indicating that mature podocytes boost both glycolysis and mitochondrial metabolism to meet their augmented energy demands. In addition, we found a shift of predominant energy source from anaerobic glycolysis in immature podocyte to oxidative phosphorylation during the differentiation process. Furthermore, we identified a crucial metabolic regulator for podocyte development, pyruvate kinase M2. Pkm2-knockdown podocytes showed dramatic reduction of energy metabolism, resulting in defects of cell differentiation. Meanwhile, podocyte-specific Pkm2-knockout (KO) mice developed worse albuminuria and podocyte injury after adriamycin treatment. We identified mammalian target of rapamycin (mTOR) as a critical regulator of PKM2 during podocyte development. Pharmacological inhibition of mTOR potently abrogated PKM2 expression and disrupted cell differentiation, indicating the existence of metabolic checkpoint that need to be satisfied in order to allow podocyte differentiation.

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.

Large-Scale Differential Gene Expression Transcriptomic Analysis Identifies a Metabolic Signature Shared by All Cancer Cells

Cancer-dependent metabolic rewiring is often manifested by selective expression of enzymes essential for the transformed cells’ viability. However, the metabolic variations between normal and transformed cells are not fully characterized, and therefore, a systematic analysis will result in the identification of unknown cellular mechanisms crucial for tumorigenesis. Here, we applied differential gene expression transcriptome analysis to examine the changes in metabolic gene profiles between a wide range of normal tissues and cancer samples. We found that, in contrast to normal tissues which exhibit a tissue-specific expression profile, cancer samples are more homogenous despite their diverse origins. This similarity is due to a “proliferation metabolic signature” (PMS), composed of 158 genes (87 upregulated and 71 downregulated gene sets), where 143 are common to all proliferative cells but 15 are cancer specific. Intriguingly, the PMS gene set is enriched for genes encoding rate-limiting enzymes, and its upregulated set with genes associated with poor patient outcome and essential genes. Among these essential genes is ribulose-5-phosphate-3-epimerase (RPE), which encodes a pentose phosphate pathway enzyme and whose role in cancer is still unclear. Collectively, we identified a set of metabolic genes that can serve as novel cancer biomarkers and potential targets for drug development.

TRAF4 acts as a fate checkpoint to regulate the adipogenic differentiation of MSCs by activating PKM2

BACKGROUND

Mesenchymal stem cells (MSCs) selectively differentiate into adipocytes or osteoblasts, and several molecules control the fate determination of MSCs. Understanding these key checkpoints greatly contributes to the ability to induce specific MSC differentiation for clinical applications. In this study, we aimed to explore whether TNF receptor-associated factor 4 (TRAF4) affects MSC adipogenic differentiation, which we previously reported that could positively regulated the osteogenic differentiation.

METHODS

Western blotting and Real-time Polymerase Chain Reaction were used to detected the expression pattern of TRAF4 during adipogenic differentiation. Lentivirus was constructed to regulate TRAF4 expression, and oil red O staining and Western blotting were used to assess its role in adipogenesis, which was confirmed in vivo by implanting an MSC-matrigel mixture into nude mice. Western blotting was used to detect the activated signaling pathways, and a specific inhibitor and agonist were used to clear the roles of the key signaling pathways. Additionaly, Co-Immunoprecipitation was conducted to find that Pyruvate kinase isozyme type M2 (PKM2) interacts with TRAF4, and to further explore their binding and functional domains. Finally, an RNA-binding protein immunoprecipitation assay and Western blotting were used to detect whether N6-methyladenosine mediates the decreased TRAF4 expression during adipogenic differentiation.

FINDINGS

The results demonstrated that TRAF4 negatively regulates MSC adipogenesis in vitro and in vivo. Mechanistically, we revealed that TRAF4 binds to PKM2 to activate the kinase activity of PKM2, which subsequently activates β-catenin signaling and then inhibits adipogenesis. Furthermore, TRAF4 downregulation during adipogenesis is regulated by ALKBH5-mediated N6-methyladenosine RNA demethylation.

INTERPRETATION

TRAF4 negatively regulates the adipogenesis of MSCs by activating PKM2 kinase activity, which may act as a checkpoint to fine-tune the balance of adipo-osteogenic differentiation, and suggests that TRAF4 may be a novel target of MSCs in clinical use and may also illuminate the underlying mechanisms of bone metabolic diseases.

FUNDING

This study was supported by the National Natural Science Foundation of China (81871750 and 81971518) and the Science and Technology Project of Guangdong Province (2019B02023600 and 2017A020215070).

Hypoxia-induced lncRNA-AC020978 promotes proliferation and glycolytic metabolism of non-small cell lung cancer by regulating PKM2/HIF-1α axis

Rationale: Non-small cell lung cancer (NSCLC) is a deadly disease with a hallmark of aberrant metabolism. The mechanism of glycolysis associated lncRNA underlying the aggressive behaviors of NSCLC is poorly understood. Methods: The expression level of AC020978 in NSCLC was measured by quantitative real-time PCR and fluorescence in situ hybridization (FISH) assay. The biological role of AC020978 in cell proliferation and aerobic glycolysis was determined by functional experiments in vitro and in vivo. The transcription of AC020978 was assessed by dual-luciferase reporter and chromatin immunoprecipitation (ChIP) assay. RNA pull-down, mass spectrometry and RNA immunoprecipitation (RIP) assays were used to identify the interaction protein with AC020978. Western blotting, in situ proximity ligation assay (PLA), and co-immunoprecipitation (co-IP) were performed to reveal the potential mechanism of AC020978. Results: The present study indicated that AC020978 was upregulated in NSCLC, significantly correlated with advanced TNM stage and poor clinical outcomes, representing as an independent prognostic predictor. Functional assays revealed AC020978's role in promoting cell growth and metabolic reprogramming. Moreover, AC020978 was an upregulated lncRNA under glucose starvation as well as hypoxia conditions, and directly transactivated by HIF-1α. Mechanistic investigations identified that AC020978 directly interacted with Pyruvate kinase isozymes M2 (PKM2) and enhanced PKM2 protein stability. Besides, this study uncovered that AC020978 could promote the nuclear translocation of PKM2 and regulate PKM2-enhanced HIF-1α transcription activity. Conclusions: Together, these data provided evidence that AC020978 conferred an aggressive phenotype to NSCLC and was a poor prognosticator. Targeting AC020978 might be an effective therapeutic strategy for NSCLC.

Addressing the heterogeneity in liver diseases using biological networks

The abnormalities in human metabolism have been implicated in the progression of several complex human diseases, including certain cancers. Hence, deciphering the underlying molecular mechanisms associated with metabolic reprogramming in a disease state can greatly assist in elucidating the disease aetiology. An invaluable tool for establishing connections between global metabolic reprogramming and disease development is the genome-scale metabolic model (GEM). Here, we review recent work on the reconstruction of cell/tissue-type and cancer-specific GEMs and their use in identifying metabolic changes occurring in response to liver disease development, stratification of the heterogeneous disease population and discovery of novel drug targets and biomarkers. We also discuss how GEMs can be integrated with other biological networks for generating more comprehensive cell/tissue models. In addition, we review the various biological network analyses that have been employed for the development of efficient treatment strategies. Finally, we present three case studies in which independent studies converged on conclusions underlying liver disease.

Hypoxia-Induced Adaptations of miRNomes and Proteomes in Melanoma Cells and Their Secreted Extracellular Vesicles

Reduced levels of intratumoural oxygen are associated with hypoxia-induced pro-oncogenic events such as invasion, metabolic reprogramming, epithelial–mesenchymal transition, metastasis and resistance to therapy, all favouring cancer progression. Small extracellular vesicles (EV) shuttle various cargos (proteins, miRNAs, DNA and others). Tumour-derived EVs can be taken up by neighbouring or distant cells in the tumour microenvironment, thus facilitating intercellular communication. The quantity of extracellular vesicle secretion and their composition can vary with changing microenvironmental conditions and disease states. Here, we investigated in melanoma cells the influence of hypoxia on the content and number of secreted EVs. Whole miRNome and proteome profiling revealed distinct expression patterns in normoxic or hypoxic growth conditions. Apart from the well-known miR-210, we identified miR-1290 as a novel hypoxia-associated microRNA, which was highly abundant in hypoxic EVs. On the other hand, miR-23a-5p and -23b-5p were consistently downregulated in hypoxic conditions, while the protein levels of the miR-23a/b-5p-predicted target IPO11 were concomitantly upregulated. Furthermore, hypoxic melanoma EVs exhibit a signature consisting of six proteins (AKR7A2, DDX39B, EIF3C, FARSA, PRMT5, VARS), which were significantly associated with a poor prognosis for melanoma patients, indicating that proteins and/or miRNAs secreted by cancer cells may be exploited as biomarkers.

Long non‑coding RNA BCYRN1 promotes glycolysis and tumor progression by regulating the miR‑149/PKM2 axis in non‑small‑cell lung cancer

Cancer cells use aerobic glycolysis to sustain their proliferation. Long non‑coding RNA brain cytoplasmic RNA 1 (BCYRN1) has been reported to act as an oncogene in non‑small‑cell lung cancer (NSCLC). The present study investigated the role of BCYRN1 in NSCLC glycolysis. BCYRN1 expression was detected in NSCLC cells and tissues using reverse transcription‑quantitative PCR. The effect of BCYRN1 on aerobic glycolysis was examined by measuring NSCLC cell glucose catabolism and lactate synthesis. The relationships between BCYRN1 and microRNA (miR)‑149, and between miR‑149 and pyruvate kinase M1/2 (PKM2) were measured using a dual‑luciferase reporter assay. Cell proliferation and invasion were analyzed by the Cell Counting kit‑8 assay and the Matrigel invasion assay, respectively. High BCYRN1 expression was observed in NSCLC tissues and cells compared with the corresponding controls. BCYRN1 induced glycolysis and upregulated the expression levels of PKM2 in NSCLC cells. In addition, BCYRN1 regulated miR‑149 expression levels, and miR‑149 inhibitor rescued the effects of si‑BCYRN1 on glucose consumption and lactate production. miR‑149 knockdown significantly enhanced the expression of PKM2. Furthermore, PKM2 inhibition significantly reversed the effects of miR‑149 inhibitor on glucose catabolism and lactate synthesis. Furthermore, PKM2 was involved in NSCLC cell proliferation and invasion, and BCYRN1 knockdown and miR‑149 overexpression inhibited both processes. The present study suggested that BCYRN1 was involved in cell glycolysis, proliferation and invasion during NSCLC via regulating miR‑149 and PKM2.

Antitumor Effect of miR-1294/Pyruvate Kinase M2 Signaling Cascade in Osteosarcoma Cells

Background

MicroRNAs (miRNAs) can act as negative regulators of gene expression, and play a crucial role in cancer progression. The aim of this study was to investigate the role of miR-1294/pyruvate kinase M2 (PKM2) axis in osteosarcoma cells in vitro and in vivo.

Methods

The function of miR-1294 and its association with PKM2 in osteosarcoma cells were studied by real-time PCR, CCK-8, Western blot, scratch test, transwell assay, flow cytometry, and dual-luciferase reporter assays. The effect of miR-1294 on tumor growth in vivo was evaluated in a subcutaneous xenograft model of osteosarcoma.

Results

miR-1294 was downregulated in osteosarcoma cells. Forced overexpression of miR-1294 inhibited cell proliferation, migration, and invasion, and induced G0/G1 arrest and apoptosis. Consistently, protein expression levels of proliferating cell nuclear antigen, c-Myc, cyclin D1, active matrix metalloproteinase 2, and active matrix metalloproteinase 9 were decreased, and cleaved caspase 3 and cleaved PARP were increased following miR-1294 overexpression. Moreover, we demonstrated that PKM2 was a target of miR-1294 in osteosarcoma cells, and the effects caused by miR-1294 mimic were reversed by the overexpression of PKM2. Furthermore, we found that upregulation of miR-1294 inhibited tumorigenesis of osteosarcoma cells in vivo, which was accompanied by downregulation of PKM2.

Conclusion

Our results revealed that miR-1294/PKM2 signaling cascade exerts important roles in the regulation of tumor progression, implying that this pathway may serve as a potential therapeutic target in osteosarcoma.

Upregulated expression of pyruvate kinase M2 mRNA predicts poor prognosis in lung adenocarcinoma

Background

Pyruvate kinase M2 (PKM2) is critical regulator contributing to Warburg effect. However, the expression pattern and prognostic value of PKM2 remain unknown in lung adenocarcinoma (LUAD). The aim of this study is to clarify the prognostic value of PKM2 via intergrated bioinformatics analysis.

Methods

Firstly, mRNA expression levels of PKM2 in LUAD were systematically analyzed using the ONCOMINE and TCGA databases. Then, the association between PKM2 expression and clinical parameters was investigated by UALCAN. The Kaplan-Meier Plotter was used to assess the prognostic significance of PKM2. Finally, the relationship between PKM2 expression and its genetic and epigenetic changes was evaluated with MEXPRESS and MethHC database.

Results

Pooled analysis showed that PKM2 is frequently upregulated expression in LUAD. Subsequently, PKM2 expression was identified to be positively associated with tumor stage and lymph node metastasis and also strongly correlated with worse OS (P = 2.80e-14), PPS (P = 0.022), FP (P = 1.30e-6) and RFS (P = 3.41e-8). Importantly, our results demonstrated that over-expressed PKM2 is associated with PKM2 hypomethylation and copy number variations (CNVs).

Conclusion

This study confirms that over-expressed PKM2 in LUAD is associated with poor prognosis, suggesting that PKM2 might act as a promising prognostic biomarker and novel therapeutic target for LUAD.

Pyridoxine induces glutathione synthesis via PKM2-mediated Nrf2 transactivation and confers neuroprotection

Oxidative stress is a major pathogenic mechanism in Parkinson's disease (PD). As an important cellular antioxidant, glutathione (GSH) balances the production and incorporation of free radicals to protect neurons from oxidative damage. GSH level is decreased in the brains of PD patients. Hence, clarifying the molecular mechanism of GSH deficiency may help deepen our knowledge of PD pathogenesis. Here we report that the astrocytic dopamine D2 receptor (DRD2) regulates GSH synthesis via PKM2-mediated Nrf2 transactivation. In addition we find that pyridoxine can dimerize PKM2 to promote GSH biosynthesis. Further experiments show that pyridoxine supplementation increases the resistance of nigral dopaminergic neurons to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in wild-type mice as well as in astrocytic Drd2 conditional knockout mice. We conclude that dimerizing PKM2 may be a potential target for PD treatment.