Tyrosine phosphorylation inhibits PKM2 to promote the Warburg effect and tumor growth

Characterization of an in vitro steatosis model simulating activated de novo lipogenesis in MAFLD patients

Activated de novo lipogenesis (DNL) is the critical pathway involved in the progression of metabolic-associated fatty liver disease (MAFLD). We present an in vitro steatosis model for MAFLD that induces steatosis through activated DNL. This model utilizes insulin and LXR receptor ligand T0901317, eliminating the need for fatty acid treatment. Significant increases in triglycerides (TAGs) and expression of DNL-related transcription factors were observed. Transcriptomic analysis revealed distinct gene expression profiles between the DNL and conventional oleic acid (OA)-induced steatosis model. DNL steatosis model exhibited elevated pathways related to glycolysis, cholesterol homeostasis, and bile acid metabolism, reflecting its clinical relevance to MAFLD. Moreover, C75 and JNK-IN-5A compounds effectively reduced TAG accumulation and steatosis-related protein expression in the DNL model, whereas they had no significant impact on TAG accumulation in the OA model. In conclusion, we introduce an ideal model for steatosis study, which could help in understanding the MAFLD mechanisms.

Dissecting the Role of Autophagy-Related Proteins in Cancer Metabolism and Plasticity

Modulation of autophagy as an anticancer strategy has been widely studied and evaluated in several cell models. However, little attention has been paid to the metabolic changes that occur in a cancer cell when autophagy is inhibited or induced. In this review, we describe how the expression and regulation of various autophagy-related (ATGs) genes and proteins are associated with cancer progression and cancer plasticity. We present a comprehensive review of how deregulation of ATGs affects cancer cell metabolism, where inhibition of autophagy is mainly reflected in the enhancement of the Warburg effect. The importance of metabolic changes, which largely depend on the cancer type and form part of a cancer cell's escape strategy after autophagy modulation, is emphasized. Consequently, pharmacological strategies based on a dual inhibition of metabolic and autophagy pathways emerged and are reviewed critically here.

CD44 Intracellular Domain: A Long Tale of a Short Tail

CD44 is a single-chain transmembrane receptor that exists in multiple forms due to alternative mRNA splicing and post-translational modifications. CD44 is the main cell surface receptor of hyaluronan as well as other extracellular matrix molecules, cytokines, and growth factors that play important roles in physiological processes (such as hematopoiesis and lymphocyte homing) and the progression of various diseases, the predominant one being cancer. Currently, CD44 is an established cancer stem cell marker in several tumors, implying a central functional role in tumor biology. The present review aims to highlight the contribution of the CD44 short cytoplasmic tail, which is devoid of any enzymatic activity, in the extraordinary functional diversity of the receptor. The interactions of CD44 with cytoskeletal proteins through specific structural motifs within its intracellular domain drives cytoskeleton rearrangements and affects the distribution of organelles and transport of molecules. Moreover, the CD44 intracellular domain specifically interacts with various cytoplasmic effectors regulating cell-trafficking machinery, signal transduction pathways, the transcriptome, and vital cell metabolic pathways. Understanding the cell type- and context-specificity of these interactions may unravel the high complexity of CD44 functions and lead to novel improved therapeutic interventions.

Pyruvate kinase M2 regulates mitochondrial homeostasis in cisplatin-induced acute kidney injury

An important pathophysiological process of acute kidney injury (AKI) is mitochondrial fragmentation in renal tubular epithelial cells, which leads to cell death. Pyruvate kinase M2 (PKM2) is an active protein with various biological functions that participates in regulating glycolysis and plays a key role in regulating cell survival. However, the role and mechanism of PKM2 in regulating cell survival during AKI remain unclear. Here, we found that the phosphorylation of PKM2 contributed to the formation of the PKM2 dimer and translocation of PKM2 into the mitochondria after treatment with staurosporine or cisplatin. Mitochondrial PKM2 binds myosin heavy chain 9 (MYH9) to promote dynamin-related protein 1 (DRP1)-mediated mitochondrial fragmentation. Both in vivo and in vitro, PKM2-specific loss or regulation PKM2 activity partially limits mitochondrial fragmentation, alleviating renal tubular injury and cell death, including apoptosis, necroptosis, and ferroptosis. Moreover, staurosporine or cisplatin-induced mitochondrial fragmentation and cell death were reversed in cultured cells by inhibiting MYH9 activity. Taken together, our results indicate that the regulation of PKM2 abundance and activity to inhibit mitochondrial translocation may maintain mitochondrial integrity and provide a new therapeutic strategy for treating AKI.

NSUN2 is a glucose sensor suppressing cGAS/STING to maintain tumorigenesis and immunotherapy resistance

Glucose metabolism is known to orchestrate oncogenesis. Whether glucose serves as a signaling molecule directly regulating oncoprotein activity for tumorigenesis remains elusive. Here, we report that glucose is a cofactor binding to methyltransferase NSUN2 at amino acid 1-28 to promote NSUN2 oligomerization and activation. NSUN2 activation maintains global m5C RNA methylation, including TREX2, and stabilizes TREX2 to restrict cytosolic dsDNA accumulation and cGAS/STING activation for promoting tumorigenesis and anti-PD-L1 immunotherapy resistance. An NSUN2 mutant defective in glucose binding or disrupting glucose/NSUN2 interaction abolishes NSUN2 activity and TREX2 induction leading to cGAS/STING activation for oncogenic suppression. Strikingly, genetic deletion of the glucose/NSUN2/TREX2 axis suppresses tumorigenesis and overcomes anti-PD-L1 immunotherapy resistance in those cold tumors through cGAS/STING activation to facilitate apoptosis and CD8+ T cell infiltration. Our study identifies NSUN2 as a direct glucose sensor whose activation by glucose drives tumorigenesis and immunotherapy resistance by maintaining TREX2 expression for cGAS/STING inactivation.

Pantothenate Kinase 4 Governs Lens Epithelial Fibrosis by Negatively Regulating Pyruvate Kinase M2-Related Glycolysis

Lens fibrosis is one of the leading causes of cataract in the elderly population. The primary energy substrate of the lens is glucose from the aqueous humor, and the transparency of mature lens epithelial cells (LECs) is dependent on glycolysis for ATP. Therefore, the deconstruction of reprogramming of glycolytic metabolism can contribute to further understanding of LEC epithelial-mesenchymal transition (EMT). In the present study, we found a novel pantothenate kinase 4 (PANK4)-related glycolytic mechanism that regulates LEC EMT. The PANK4 level was correlated with aging in cataract patients and mice. Loss of function of PANK4 significantly contributed to alleviating LEC EMT by upregulating pyruvate kinase M2 isozyme (PKM2), which was phosphorylated at Y105, thus switching oxidative phosphorylation to glycolysis. However, PKM2 regulation did not affect PANK4, demonstrating the downstream role of PKM2. Inhibition of PKM2 in Pank4-/- mice caused lens fibrosis, which supports the finding that the PANK4-PKM2 axis is required for LEC EMT. Glycolytic metabolism-governed hypoxia inducible factor (HIF) signaling is involved in PANK4-PKM2-related downstream signaling. However, HIF-1α elevation was independent of PKM2 (S37) but PKM2 (Y105) when PANK4 was deleted, which demonstrated that PKM2 and HIF-1α were not involved in a classic positive feedback loop. Collectively, these results indicate a PANK4-related glycolysis switch that may contribute to HIF-1 stabilization and PKM2 phosphorylation at Y105 and inhibit LEC EMT. The mechanism elucidation in our study may also shed light on fibrosis treatments for other organs.

The role and mechanism of action of microRNA-122 in cancer: Focusing on the liver

microRNA-122 (miR-122) is a highly conserved microRNA that is predominantly expressed in the liver and plays a critical role in the regulation of liver metabolism. Recent studies have shown that miR-122 is involved in the pathogenesis of various types of cancer, particularly liver cancer. In this sense, The current findings highlighted the potential role of miR-122 in regulating many vital processes in cancer pathophysiology, including apoptosis, signaling pathway, cell metabolism, immune system response, migration, and invasion. These results imply that miR-122, which has been extensively studied for its biological functions and potential therapeutic applications, acts as a tumor suppressor or oncogene in cancer development. We first provide an overview and summary of the physiological function and mode of action of miR-122 in liver cancer. We will examine the various signaling pathways and molecular mechanisms through which miR-122 exerts its effects on cancer cells, including the regulation of oncogenic and tumor suppressor genes, the modulation of cell proliferation and apoptosis, and the regulation of metastasis. Most importantly, we will also discuss the potential diagnostic and therapeutic applications of miR-122 in cancer, including the development of miRNA-based biomarkers for cancer diagnosis and prognosis, and the potential use of miR-122 as a therapeutic target for cancer treatment.

Omentin-1 induces mechanically activated fibroblasts lipogenic differentiation through pkm2/yap/pparγ pathway to promote lung fibrosis resolution

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease characterized by extensive extracellular matrix (ECM) deposition by activated myofibroblasts, which are specialized hyper-contractile cells that promote ECM remodeling and matrix stiffening. New insights on therapeutic strategies aimed at reversing fibrosis by targeting myofibroblast fate are showing promise in promoting fibrosis resolution. Previously, we showed that a novel adipocytokine, omentin-1, attenuated bleomycin (BLM)-induced lung fibrosis by reducing the number of myofibroblasts. Apoptosis, deactivation, and reprogramming of myofibroblasts are important processes in the resolution of fibrosis. Here we report that omentin-1 reverses established lung fibrosis by promoting mechanically activated myofibroblasts dedifferentiation into lipofibroblasts. Omentin-1 promotes myofibroblasts lipogenic differentiation by inhibiting dimerization and nuclear translocation of glycolytic enzymes pyruvate kinase isoform M2 (PKM2) and activation of the downstream Yes-associated protein (YAP) by increasing the cofactor fructose-1,6-bisphosphate (F1, 6BP, FBP). Moreover, omentin-1 activates proliferator-activated receptor gamma (PPARγ) signaling, the master regulator of lipogenesis, and promotes the upregulation of the lipogenic differentiation-related protein perilipin 2 (PLIN2) by suppressing the PKM2-YAP pathway. Ultimately, omentin-1 facilitates myofibroblasts transformation into the lipofibroblast phenotype, with reduced collagen synthesis and enhanced degradation properties, which are crucial mechanisms to clear the ECM deposition in fibrotic tissue, leading to fibrosis resolution. Our results indicate that omentin-1 targets mechanical signal accelerates fibrosis resolution and reverses established lung fibrosis by promoting myofibroblasts lipogenic differentiation, which is closely associated with ECM clearance in fibrotic tissue. These findings suggest that targeting mechanical force to promote myofibroblast lipogenic differentiation is a promising therapeutic strategy against persistent lung fibrosis.

Pyruvate Kinase Activity Regulates Cystine Starvation Induced Ferroptosis through Malic Enzyme 1 in Pancreatic Cancer Cells

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with high mortality and limited efficacious therapeutic options. PDAC cells undergo metabolic alterations to survive within a nutrient-depleted tumor microenvironment. One critical metabolic shift in PDAC cells occurs through altered isoform expression of the glycolytic enzyme, pyruvate kinase (PK). Pancreatic cancer cells preferentially upregulate pyruvate kinase muscle isoform 2 isoform (PKM2). PKM2 expression reprograms many metabolic pathways, but little is known about its impact on cystine metabolism. Cystine metabolism is critical for supporting survival through its role in defense against ferroptosis, a non-apoptotic iron-dependent form of cell death characterized by unchecked lipid peroxidation. To improve our understanding of the role of PKM2 in cystine metabolism and ferroptosis in PDAC, we generated PKM2 knockout (KO) human PDAC cells. Fascinatingly, PKM2KO cells demonstrate a remarkable resistance to cystine starvation mediated ferroptosis. This resistance to ferroptosis is caused by decreased PK activity, rather than an isoform-specific effect. We further utilized stable isotope tracing to evaluate the impact of glucose and glutamine reprogramming in PKM2KO cells. PKM2KO cells depend on glutamine metabolism to support antioxidant defenses against lipid peroxidation, primarily by increased glutamine flux through the malate aspartate shuttle and utilization of ME1 to produce NADPH. Ferroptosis can be synergistically induced by the combination of PKM2 activation and inhibition of the cystine/glutamate antiporter in vitro. Proof-of-concept in vivo experiments demonstrate the efficacy of this mechanism as a novel treatment strategy for PDAC.

Anti-Warburg effect via generation of ROS and inhibition of PKM2/β-catenin mediates apoptosis of lambertianic acid in prostate cancer cells

To elucidate the underlying antitumor mechanism of lambertianic acid (LA) derived from Pinus koraiensis, the role of cancer metabolism related molecules was investigated in the apoptotic effect of LA in DU145 and PC3 prostate cancer cells. MTT assay for cytotoxicity, RNA interference, cell cycle analysis for sub G1 population, nuclear and cytoplasmic extraction, lactate, Glucose and ATP assay by ELISA, Measurement of reactive oxygen species (ROS) generation, Western blotting, and immunoprecipitation assay were conducted in DU145 and PC3 prostate cancer cells. Herein LA exerted cytotoxicity, increased sub G1 population and attenuated the expression of pro-Caspase3 and pro-poly (ADP-ribose) polymerase (pro-PARP) in DU145 and PC3 cells. Also, LA reduced the expression of lactate dehydrogenase A (LDHA), glycolytic enzymes such as hexokinase 2 and pyruvate kinase M2 (PKM2) with reduced production of lactate in DU145 and PC3 cells. Notably, LA decreased phosphorylation of PKM2 on Tyr105 and inhibited the expression of p-STAT3, cyclin D1, C-Myc, β-catenin, and p-GSK3β with the decrease of nuclear translocation of p-PKM2. Furthermore, LA disturbed the binding of p-PKM2 and β-catenin in DU145 cells, which was supported by Spearman coefficient (0.0463) of cBioportal database. Furthermore, LA generated ROS in DU145 and PC3 cells, while ROS scavenger NAC (N-acetyl L-cysteine) blocked the ability of LA to reduce p-PKM2, PKM2, β-catenin, LDHA, and pro-caspase3 in DU145 cells. Taken together, these findings provide evidence that LA induces apoptosis via ROS generation and inhibition of PKM2/β-catenin signaling in prostate cancer cells.

Platelet mitochondria: the mighty few

PURPOSE OF REVIEW

Platelet mitochondrial dysfunction is both caused by, as well as a source of oxidative stress. Oxidative stress is a key hallmark of metabolic disorders such as dyslipidemia and diabetes, which are known to have higher risks for thrombotic complications.

RECENT FINDINGS

Increasing evidence supports a critical role for platelet mitochondria beyond energy production and apoptosis. Mitochondria are key regulators of reactive oxygen species and procoagulant platelets, which both contribute to pathological thrombosis. Studies targeting platelet mitochondrial pathways have reported promising results suggesting antithrombotic effects with limited impact on hemostasis in animal models.

SUMMARY

Targeting platelet mitochondria holds promise for the reduction of thrombotic complications in patients with metabolic disorders. Future studies should aim at validating these preclinical findings and translate them to the clinic.

Remodelling of the Mitochondrial Bioenergetic Pathways in Human Cultured Fibroblasts with Carbohydrates

Mitochondrial oxidative phosphorylation defects underlie many neurological and neuromuscular diseases. Patients' primary dermal fibroblasts are one of the most commonly used in vitro models to study mitochondrial pathologies. However, fibroblasts tend to rely more on glycolysis than oxidative phosphorylation for their energy when cultivated in standard high-glucose medium, rendering it difficult to expose mitochondrial dysfunctions. This study aimed to systematically investigate to which extent the use of galactose- or fructose-based medium switches the fibroblasts' energy metabolism to a more oxidative state. Highly proliferative cells depend more on glycolysis than less proliferative cells. Therefore, we investigated two primary dermal fibroblast cultures from healthy subjects: a highly proliferative neonatal culture and a slower-growing adult culture. Cells were cultured with 25 mM glucose, galactose or fructose, and 4 mM glutamine as carbon sources. Compared to glucose, both galactose and fructose reduce the cellular proliferation rate, but the galactose-induced drop in proliferation is much more profound than the one observed in cells cultivated in fructose. Both galactose and fructose result in a modest increase in mitochondrial content, including mitochondrial DNA, and a disproportionate increase in protein levels, assembly, and activity of the oxidative phosphorylation enzyme complexes. Galactose- and fructose-based media induce a switch of the prevalent biochemical pathway in cultured fibroblasts, enhancing aerobic metabolism when compared to glucose-based medium. While both galactose and fructose stimulate oxidative phosphorylation to a comparable degree, galactose decreases the cellular proliferation rate more than fructose, suggesting that a fructose-based medium is a better choice when studying partial oxidative phosphorylation defects in patients' fibroblasts.

CB2R agonist GW405833 alleviates acute liver failure in mice via inhibiting HIF-1α-mediated reprogramming of glycometabolism and macrophage proliferation

The inflammatory responses involving infiltration and activation of liver macrophages play a vital role in acute liver failure (ALF). In the liver of ALF mice, cannabinoid receptor 2 (CB2R) is significantly upregulated on macrophages, while CB2R agonist GW405833 (GW) could protect against cell death in acute liver damage. In this study, we investigated the molecular mechanisms underlying the protective effects of GW against ALF in vivo and in vitro from a perspective of macrophage glycometabolism. Mice were pretreated with GW (10 mg/kg, i.p.), then were injected with D-GalN (750 mg/kg, i.p.) and LPS (10 mg/kg, i.p.) to induce ALF. We verified the protective effects of GW pretreatment in ALF mice. Furthermore, GW pretreatment significantly reduced liver macrophage infiltration and M1 polarization, and inhibited the release of inflammatory factors TNF-α and IL-1β in ALF mice. These protective effects were eliminated by CB2R antagonist SR144528 or in CB2R-/- ALF mice. We used LPS-stimulated RAW264.7 cells as an in vitro M1 macrophage-centered model of inflammatory response, and demonstrated that pretreatment with GW (10 μM) significantly reduced glucose metabolism by inhibiting glycolysis, which inhibited LPS-induced macrophage proliferation and inflammatory cytokines release. We verified these results in a stable CB2R-/- RAW264.7 cell line. Moreover, we found that GW significantly inhibited the expression of hypoxia inducible factor 1α (HIF-1α). Using a stable HIF-1α-/- RAW264.7 cell line, we confirmed that GW reduced the release of inflammatory cytokines from macrophages and inhibited glycolysis by downregulating HIF-1α expression. In conclusion, activation of CB2Rs inhibits the proliferation of hepatic macrophages and release of inflammatory factors in ALF mice through downregulating HIF-1α to inhibit glycolysis.

Significance of liquid-liquid phase separation (LLPS)-related genes in breast cancer: a multi-omics analysis

Currently, the role of liquid-liquid phase separation (LLPS) in cancer has been preliminarily explained. However, the significance of LLPS in breast cancer is unclear. In this study, single cell sequencing datasets GSE188600 and GSE198745 for breast cancer were downloaded from the GEO database. Transcriptome sequencing data for breast cancer were downloaded from UCSC database. We divided breast cancer cells into high-LLPS group and low-LLPS group by down dimension clustering analysis of single-cell sequencing data set, and obtained differentially expressed genes between the two groups. Subsequently, weighted co-expression network analysis (WGCNA) was performed on transcriptome sequencing data, and the module genes most associated with LLPS were obtained. COX regression and Lasso regression were performed and the prognostic model was constructed. Subsequently, survival analysis, principal component analysis, clinical correlation analysis, and nomogram construction were used to evaluate the significance of the prognostic model. Finally, cell experiments were used to verify the function of the model's key gene, PGAM1. We constructed a LLPS-related prognosis model consisting of nine genes: POLR3GL, PLAT, NDRG1, HMGB3, HSPH1, PSMD7, PDCD2, NONO and PGAM1. By calculating LLPS-related risk scores, breast cancer patients could be divided into high-risk and low-risk groups, with the high-risk group having a significantly worse prognosis. Cell experiments showed that the activity, proliferation, invasion and healing ability of breast cancer cell lines were significantly decreased after knockdown of the key gene PGAM1 in the model. Our study provides a new idea for prognostic stratification of breast cancer and provides a novel marker: PGAM1.

Anti-tumor effects of novel alkannin derivatives with potent selectivity on comprehensive analysis

BACKGROUND

Therapeutic approaches based on glycolysis and energy metabolism of tumor cells are new promising strategies for the treatment of cancer. Currently, researches on the inhibition of pyruvate kinase M2, a key rate limiting enzyme in glycolysis, have been corroborated as an effective cancer therapy. Alkannin is a potent pyruvate kinase M2 inhibitor. However, its non-selective cytotoxicity has affected its subsequent clinical application. Thus, it needs to be structurally modified to develop novel derivatives with high selectivity.

PURPOSE

Our study aimed to ameliorate the toxicity of alkannin through structural modification and elucidate the mechanism of the superior derivative 23 in lung cancer therapy.

METHODS

On the basis of the principle of collocation, different amino acids and oxygen-containing heterocycles were introduced into the hydroxyl group of the alkannin side chain. We examined the cell viability of all derivatives on three tumor cells (HepG2, A549 and HCT116) and two normal cells (L02 and MDCK) by MTT assay. Besides, the effect of derivative 23 on the morphology of A549 cells as observed by Giemsa and DAPI staining, respectively. Flow cytometry was performed to assess the effects of derivative 23 on apoptosis and cell cycle arrest. To further assess the effect of derivative 23 on the Pyruvate kinase M2 in glycolysis, an enzyme activity assay and western blot assay were performed. Finally, in vivo the antitumor activity and safety of the derivative 23 were evaluated by using Lewis mouse lung cancer xenograft model.

RESULTS

Twenty-three novel alkannin derivatives were designed and synthesized to improve the cytotoxicity selectivity. Among these derivatives, derivative 23 showed the highest cytotoxicity selectivity between cancer and normal cells. The anti-proliferative activity of derivative 23 on A549 cells (IC₅₀ = 1.67 ± 0.34 μM) was 10-fold higher than L02 cells (IC₅₀ = 16.77 ± 1.44 μM) and 5-fold higher than MDCK cells (IC₅₀ = 9.23 ± 0.29 μM) respectively. Subsequently, fluorescent staining and flow cytometric analysis showed that derivative 23 was able to induce apoptosis of A549 cells and arrest the cell cycle in the G0/G1 phase. In addition, the mechanistic studies suggested derivative 23 was an inhibitor of pyruvate kinase; it could regulate glycolysis by inhibiting the activation of the phosphorylation of PKM2/STAT3 signaling pathway. Furthermore, studies in vivo demonstrated derivative 23 significantly inhibited the growth of xenograft tumor.

CONCLUSION

In this study, alkannin selectivity is reported to be significantly improved following structural modification, and derivative 23 is first shown to be able to inhibit lung cancer growth via the PKM2/STAT3 phosphorylation signaling pathway in vitro, indicating the potential value of derivative 23 in treating lung cancer.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

HIF-1α Mediates Arsenic-Induced Metabolic Reprogramming in Lung Bronchial Epithelial Cells

Arsenic is a common environmental pollutant that can cause damage to multiple systems and organs in the body. The lungs are particularly sensitive to arsenic exposure, and respiratory disease is thought to be the leading cause of death from arsenic poisoning. Our previous study found that human bronchial epithelial (HBE) cells treated with NaAsO₂ exhibited mitochondrial dysfunction accompanied by elevated HIF-1α; however, the molecular mechanism was unclear. The aim of the current study was to confirm the role of HIF-1α in arsenic-induced mitochondrial damage. The results of this study indicated that NaAsO₂ treatment induced mitochondrial ultrastructure impairment and depolarization of the mitochondrial membrane potential. Furthermore, NaAsO₂ induced a significant decrease in basal respiration, maximal respiration, spare respiratory capacity, ATP (adenosine-triphosphate)-associated mitochondrial respiration and proton leakage in HBE cells (P < 0.05), while promoting an increase in ECAR (extracellular acidification rate) values. To clarify the role of HIF-1α, the effect of HIF-1α siRNA on NaAsO₂-induced glycolysis in HBE cells was examined, and the results showed that HIF-1α siRNA reversed the NaAsO₂-induced elevation in PKM2 (Tyr105), HIF-1α, GLUT1 and HK2 protein expression and decreased the NaAsO₂-mediated glycolysis level, glycolytic capacity and glycolytic reserve. These findings suggest that targeting metabolic dysregulation has significant implications for targeting arsenic-induced lung injury and that HIF-1α is an exciting new therapeutic target for the treatment of arsenic-induced lung injury.

Regulation of tumor metabolism by post translational modifications on metabolic enzymes

Metabolic reprogramming is a hallmark of cancer development, progression, and metastasis. Several metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, lipid metabolism, and glutamine catabolism are frequently altered to support cancer growth. Importantly, the activity of the rate-limiting metabolic enzymes in these pathways are specifically modulated in cancer cells. This is achieved by transcriptional, translational, and post translational regulations that enhance the expression, activity, stability, and substrate sensitivity of the rate-limiting enzymes. These mechanisms allow the enzymes to retain increased activity supporting the metabolic needs of rapidly growing tumors, sustain their survival in the hostile tumor microenvironments and in the metastatic lesions. In this review, we primarily focused on the post translational modifications of the rate-limiting enzymes in the glucose and glutamine metabolism, TCA cycle, and fatty acid metabolism promoting tumor progression and metastasis.

IgSF11-mediated phosphorylation of pyruvate kinase M2 regulates osteoclast differentiation and prevents pathological bone loss

Osteoclasts are primary bone-resorbing cells, and receptor-activated NF-kB ligand (RANKL) stimulation is the key driver of osteoclast differentiation. During late-stage differentiation, osteoclasts become multinucleated and enlarged (so-called "maturation"), suggesting their need to adapt to changing metabolic demands and a substantial increase in size. Here, we demonstrate that immunoglobulin superfamily 11 (IgSF11), which is required for osteoclast differentiation through an association with the postsynaptic scaffolding protein PSD-95, regulates osteoclast differentiation by controlling the activity of pyruvate kinase M isoform 2 (PKM2). By using a system that directly induces the activation of IgSF11 in a controlled manner, we identified PKM2 as a major IgSF11-induced tyrosine-phosphorylated protein. IgSF11 activates multiple Src family tyrosine kinases (SFKs), including c-Src, Fyn, and HcK, which phosphorylate PKM2 and thereby inhibit PKM2 activity. Consistently, IgSF11-deficient cells show higher PKM2 activity and defective osteoclast differentiation. Furthermore, inhibiting PKM2 activities with the specific inhibitor Shikonin rescues the impaired osteoclast differentiation in IgSF11-deficient cells, and activating PKM2 with the specific activator TEPP46 suppresses osteoclast differentiation in wild-type cells. Moreover, PKM2 activation further suppresses osteoclastic bone loss without affecting bone formation in vivo. Taken together, these results show that IgSF11 controls osteoclast differentiation through PKM2 activity, which is a metabolic switch necessary for optimal osteoclast maturation.

Identification of residues involved in allosteric signal transmission from amino acid binding site of pyruvate kinase muscle isoform 2

PKM2 is a rate-limiting enzyme in the glycolytic process and is involved in regulating tumor proliferation. Several amino acids (AAs) such as Asn, Asp, Val, and Cys have been shown to bind to the AA binding pocket of PKM2 and modulate its oligomeric state, substrate binding affinity, and activity. Although previous studies have attributed that the main chain and side chain of bound AAs are responsible for initiating signal to regulate PKM2, the signal transduction pathway remains elusive. To identify the residues involved in signal transfer process, N70 and N75 located at two ends of a β strand connecting the active site and AA binding pocket were altered. Biochemical studies of these variants with various AA ligands (Asn, Asp, Val, and Cys), illustrate that N70 and N75, along with β1 connecting these residues are part of the signal transduction pathway between the AA binding pocket and the active site. The results demonstrate that mutation of N70 to D prevents the transfer of the inhibitory signal mediated by Val and Cys, whereas N75 to L alteration blocks the activating signal initiated by Asn and Asp. Taken together, this study confirms that N70 is one of the residues responsible for transmitting the inhibitory signal and N75 is involved in the activation signal flow.

USP25-PKM2-glycolysis axis contributes to ischemia reperfusion-induced acute kidney injury by promoting M1-like macrophage polarization and proinflammatory response

M1-like macrophages have been reported to play critical roles in acute kidney injury (AKI). Here, we elucidated the role of ubiquitin-specific protease 25 (USP25) in M1-like macrophages polarization and AKI. High USP25 expression was correlated with a decline in renal function in patients with acute kidney tubular injury and in mice with AKI. In contrast, USP25 knockout reduced M1-like macrophage infiltration, suppressed M1-like polarization, and improved AKI in mice, indicating that USP25 was necessary for M1-like polarization and proinflammatory response. Immunoprecipitation assay and liquid chromatography-tandem mass spectrometry showed that the M2 isoform of pyruvate kinase, muscle (PKM2) was a target substrate of USP25. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated the USP25 regulated aerobic glycolysis and lactate production during M1-like polarization via PKM2. Further analysis showed that the USP25-PKM2-aerobic glycolysis axis positively regulated M1-like polarization and exacerbated AKI in mice, providing potential therapeutic targets for AKI treatment.

Intersection of immune and oncometabolic pathways drives cancer hyperprogression during immunotherapy

Immune checkpoint blockade (ICB) can produce durable responses against cancer. We and others have found that a subset of patients experiences paradoxical rapid cancer progression during immunotherapy. It is poorly understood how tumors can accelerate their progression during ICB. In some preclinical models, ICB causes hyperprogressive disease (HPD). While immune exclusion drives resistance to ICB, counterintuitively, patients with HPD and complete response (CR) following ICB manifest comparable levels of tumor-infiltrating CD8+ T cells and interferon γ (IFNγ) gene signature. Interestingly, patients with HPD but not CR exhibit elevated tumoral fibroblast growth factor 2 (FGF2) and β-catenin signaling. In animal models, T cell-derived IFNγ promotes tumor FGF2 signaling, thereby suppressing PKM2 activity and decreasing NAD+, resulting in reduction of SIRT1-mediated β-catenin deacetylation and enhanced β-catenin acetylation, consequently reprograming tumor stemness. Targeting the IFNγ-PKM2-β-catenin axis prevents HPD in preclinical models. Thus, the crosstalk of core immunogenic, metabolic, and oncogenic pathways via the IFNγ-PKM2-β-catenin cascade underlies ICB-associated HPD.

Human scattered tubular cells represent a heterogeneous population of glycolytic dedifferentiated proximal tubule cells

Scattered tubular cells (STCs) are a phenotypically distinct cell population in the proximal tubule that increase in number after acute kidney injury. We aimed to characterize the human STC population. Three-dimensional human tissue analysis revealed that STCs are preferentially located within inner bends of the tubule and are barely present in young kidney tissue (<2 years), and their number increases with age. Increased STC numbers were associated with acute tubular injury (kidney injury molecule 1) and interstitial fibrosis (alpha smooth muscle actin). Isolated CD13⁺ CD24^- CD133^- proximal tubule epithelial cells (PTECs) and CD13⁺ CD24+ and CD13⁺ CD133⁺ STCs were analyzed using RNA sequencing. Transcriptome analysis revealed an upregulation of nuclear factor κB, tumor necrosis factor alpha, and inflammatory pathways in STCs, whereas metabolism, especially the tricarboxylic acid cycle and oxidative phosphorylation, was downregulated, without showing signs of cellular senescence. Using immunostaining and a publicly available single-cell sequencing database of human kidneys, we demonstrate that STCs represent a heterogeneous population in a transient state. In conclusion, STCs are dedifferentiated PTECs showing a metabolic shift toward glycolysis, which could facilitate cellular survival after kidney injury. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Screening Kinase-Dependent Phosphorylation of Key Metabolic Reprogramming Regulators

Aerobic glycolysis has been commonly linked to cell proliferation, especially in cancer cells where it serves to generate sufficient energy and biosynthesis of new cell constituents needed for cell growth and division. The M2 isoform of pyruvate kinase (PKM2) catalyzes the last reaction of the glycolytic process. PKM2 promotes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, generating ATP and releasing pyruvate. This rate-limiting reaction relies therefore on the enzymatic activity of PKM2. The switching between the high- and low-activity states of PKM2 is subjected to a combination of allosteric mechanisms and fine-tuned regulation by oncogenes and tumor suppressor genes. These regulatory mechanisms involve primarily post-translational modifications of PKM2. Recent findings suggest that phosphorylation contributes to the regulation of PKM2 activity.Here, we describe an in vitro kinase assay we used to assess PKM2 phosphorylation by c-Jun N-terminal kinase (JNK), a master regulator of apoptosis, cell proliferation, and differentiation. While the use of phospho-specific antibodies gives information in terms of measuring the effects of a given kinase on its substrate, specific antibodies for newly identified phospho-groups are not readily available. The in vitro kinase assay allows the immediate measuring of phosphorylation of any substrate of interest. Although there are several options that do not use radioactive materials, we continue to rely on this biochemical method for robust quantitation of results. More interestingly, this protocol can be easily adapted to measure the activity of other kinases by using their specific substrates.

Pan-Cancer Analysis of the Oncogenic and Prognostic Role of PKM2: A Potential Target for Survival and Immunotherapy

Background

No pan-cancer study has been conducted till date to explore the comprehensive oncogenic roles of pyruvate kinase M2 (PKM2).

Methods

TCGA, TIMER, GEPIA, UALCAN, STRING, and other databases were used to analyze the expression, prognostic roles, epigenetic variants, and possible oncogenic mechanisms of PKM2. Proteomic sequencing data and PRM were applied to validate.

Results

PKM2 showed higher expression in majority of cancers, the expression being significantly correlated with the clinical stage. Higher expression of PKM2 was associated with lower OS and DFS in several cancers, such as MESO and PAAD. In addition, the epigenetic variation of PKM2, including gene alteration, mutation type and sites, DNA methylation, and phosphorylation, showed diversity in different cancers. All four methods indicated that PKM2 is positively associated with the immune infiltration of tumor-associated fibroblasts, such as in THCA, GBM, and SARC. Further mechanistic exploration suggested that the ribosome pathway might play an essential role in the regulation of PKM2, and interestingly, four out of ten hub genes were found to be highly related to OS in several cancers. Finally, in thyroid cancer specimen, we validated the expression and potential mechanisms by proteomic sequencing and PRM validation.

Conclusion

In the majority of cancers, the higher expression of PKM2 was highly associated with poor prognosis. Further molecular mechanism exploration implied that PKM2 might serve as a potential target for cancer survival and immunotherapy by regulating the ribosome pathway.

Protein kinase C epsilon promotes de novo lipogenesis and tumor growth in prostate cancer cells by regulating the phosphorylation and nuclear translocation of pyruvate kinase isoform M2

Protein kinase C epsilon (PKCε) belongs to a family of serine/threonine kinases that control cell proliferation, differentiation and survival. Aberrant PKCε activation and overexpression is a frequent feature of numerous cancers. However, its role in regulation of lipid metabolism in cancer cells remains elusive. Here we report a novel function of PKCε in regulating of prostate cancer cell proliferation by modulation of PKM2-mediated de novo lipogenesis. We show that PKCε promotes de novo lipogenesis and tumor cell proliferation via upregulation of lipogenic enzymes and lipid contents in prostate cancer cells. Mechanistically, PKCε interacts with NABD (1-388) domain of C-terminal deletion on pyruvate kinase isoform M2 (PKM2) and enhances the Tyr105 phosphorylation of PKM2, leading to its nuclear localization. Moreover, forced expression of mutant Tyr105 (Y105F) or PKM2 inhibition suppressed de novo lipogenesis and cell proliferation induced by overexpression of PKCε in prostate cancer cells. In a murine tumor model, inhibitor of PKM2 antagonizes lipogenic enzymes expression and prostate cancer growth induced by overexpression of PKCε in vivo. These data indicate that PKCε is a critical regulator of de novo lipogenesis, which may represent a potential therapeutic target for the treatment of prostate cancer.

Hindering NAT8L expression in hepatocellular carcinoma increases cytosolic aspartate delivery that fosters pentose phosphate pathway and purine biosynthesis promoting cell proliferation

N-acetylaspartate (NAA) is synthesized by the mitochondrial enzyme NAT8L, which uses acetyl-CoA and aspartate as substrates. These metabolites are fundamental for bioenergetics and anabolic requirements of highly proliferating cells, thus, NAT8L modulation may impinge on the metabolic reprogramming of cancer cells. Specifically, aspartate represents a limiting amino acid for nucleotide synthesis in cancer. Here, the expression of the NAT8L enzyme was modulated to verify how it impacts the metabolic adaptations and proliferative capacity of hepatocellular carcinoma. We demonstrated that NAT8L downregulation is associated with increased proliferation of hepatocellular carcinoma cells and immortalized hepatocytes. The overexpression of NAT8L instead decreased cell growth. The pro-tumoral effect of NAT8L silencing depended on glutamine oxidation and the rewiring of glucose metabolism. Mechanistically, NAT8L downregulation triggers aspartate outflow from mitochondria via the exporter SLC25A13 to promote glucose flux into the pentose phosphate pathway, boosting purine biosynthesis. These results were corroborated by the analyses of human and mouse hepatocellular carcinoma samples revealing a decrease in NAT8L expression compared to adjacent non-tumoral tissues. Overall, this work demonstrates that NAT8L expression in liver cells limits the cytosolic availability of aspartate necessary for enhancing the pentose phosphate pathway and purine biosynthesis, counteracting cell proliferation.

The emerging role of PKM in keratinocyte homeostasis and pathophysiology

Increased aerobic glycolysis in keratinocytes has been reported as a hallmark of skin diseases while its pharmacological inhibition restores keratinocyte homeostasis. Pyruvate kinase muscle (PKM) isoforms are key enzymes in the glycolytic pathway and, therefore, an attractive therapeutic target. Simon Nold and colleagues used CRISPR/Cas9-mediated gene editing to investigate the outcomes of PKM splicing perturbations and specific PKM1 or PKM2 deficiency in human HaCaT keratinocytes. Collectively, the study demonstrated different effects of PKM1 or PKM2 depletion on the reciprocal PKM isoform and on keratinocyte gene expression, metabolism and proliferation. Findings from this study provide novel insights into the role of PKM in keratinocyte homeostasis, warranting additional investigations into the underlying molecular mechanisms and potential therapeutic applications.

Glucose metabolism and tumour microenvironment in pancreatic cancer: A key link in cancer progression

Early and accurate diagnosis and treatment of pancreatic cancer (PC) remain challenging endeavors globally. Late diagnosis lag, high invasiveness, chemical resistance, and poor prognosis are unresolved issues of PC. The concept of metabolic reprogramming is a hallmark of cancer cells. Increasing evidence shows that PC cells alter metabolic processes such as glucose, amino acids, and lipids metabolism and require continuous nutrition for survival, proliferation, and invasion. Glucose metabolism, in particular, regulates the tumour microenvironment (TME). Furthermore, the link between glucose metabolism and TME also plays an important role in the targeted therapy, chemoresistance, radiotherapy ineffectiveness, and immunosuppression of PC. Altered metabolism with the TME has emerged as a key mechanism regulating PC progression. This review shed light on the relationship between TME, glucose metabolism, and various aspects of PC. The findings of this study provide a new direction in the development of PC therapy targeting the metabolism of cancer cells.

Tracing the electron flow in redox metabolism: The appropriate distribution of electrons is essential to maintain redox balance in cancer cells

Cancer cells are characterized by sustained proliferation, which requires a huge demand of fuels to support energy production and biosynthesis. Energy is produced by the oxidation of the fuels during catabolism, and biosynthesis is achieved by the reduction of smaller units or precursors. Therefore, the oxidation-reduction (redox) reactions in cancer cells are more active compared to those in the normal counterparts. The higher activity of redox metabolism also induces a more severe oxidative stress, raising the question of how cancer cells maintain the redox balance. In this review, we overview the redox metabolism of cancer cells in an electron-tracing view. The electrons are derived from the nutrients in the tumor microenvironment and released during catabolism. Most of the electrons are transferred to NAD(P) system and then directed to four destinations: energy production, ROS generation, reductive biosynthesis and antioxidant system. The appropriate distribution of these electrons achieved by the function of redox regulation network is essential to maintain redox homeostasis in cancer cells. Interfering with the electron distribution and disrupting redox balance by targeting the redox regulation network may provide therapeutic implications for cancer treatment.

Control of cell metabolism by the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) triggers the activation of many intracellular signals that control cell proliferation, growth, survival, migration, and differentiation. Given its wide expression, EGFR has many functions in development and tissue homeostasis. Some of the cellular outcomes of EGFR signaling involve alterations of specific aspects of cellular metabolism, and alterations of cell metabolism are emerging as driving influences in many physiological and pathophysiological contexts. Here we review the mechanisms by which EGFR regulates cell metabolism, including by modulation of gene expression and protein function leading to control of glucose uptake, glycolysis, biosynthetic pathways branching from glucose metabolism, amino acid metabolism, lipogenesis, and mitochondrial function. We further examine how this regulation of cell metabolism by EGFR may contribute to cell proliferation and differentiation and how EGFR-driven control of metabolism can impact certain diseases and therapy outcomes.

Girdin Promotes Tumorigenesis and Chemoresistance in Lung Adenocarcinoma by Interacting with PKM2

Girdin, an Akt substrate, has been reported to promote tumorigenesis in various tumors. However, the role of Girdin in a spontaneous tumor model has not yet been explored. Here, we studied the role of Girdin in lung adenocarcinoma (LUAD) using the autochthonous mouse model and found that Girdin led to LUAD progression and chemoresistance by enhancing the Warburg effect. Mechanistically, Girdin interacted with pyruvate kinase M2 (PKM2), which played a vital role in aerobic glycolysis. Furthermore, Girdin impaired Platelet Derived Growth Factor Receptor Beta (PDGFRβ) degradation, which in turn, promoted PKM2 tyrosine residue 105 (Y105) phosphorylation and inhibited PKM2 activity, subsequently promoting aerobic glycolysis in cancer cells. Taken together, our study demonstrates that Girdin is a crucial regulator of tumor growth and may be a potential therapeutic target for overcoming the resistance of LUAD cells to chemotherapy.

Oncometabolism: A Paradigm for the Metabolic Remodeling of the Failing Heart

Heart failure is associated with profound alterations in cardiac intermediary metabolism. One of the prevailing hypotheses is that metabolic remodeling leads to a mismatch between cardiac energy (ATP) production and demand, thereby impairing cardiac function. However, even after decades of research, the relevance of metabolic remodeling in the pathogenesis of heart failure has remained elusive. Here we propose that cardiac metabolic remodeling should be looked upon from more perspectives than the mere production of ATP needed for cardiac contraction and relaxation. Recently, advances in cancer research have revealed that the metabolic rewiring of cancer cells, often coined as oncometabolism, directly impacts cellular phenotype and function. Accordingly, it is well feasible that the rewiring of cardiac cellular metabolism during the development of heart failure serves similar functions. In this review, we reflect on the influence of principal metabolic pathways on cellular phenotype as originally described in cancer cells and discuss their potential relevance for cardiac pathogenesis. We discuss current knowledge of metabolism-driven phenotypical alterations in the different cell types of the heart and evaluate their impact on cardiac pathogenesis and therapy.

Salvianolic acid A regulates pyroptosis of endothelial cells via directly targeting PKM2 and ameliorates diabetic atherosclerosis

Rescuing endothelial cells from pyroptotic cell death emerges as a potential therapeutic strategy to combat diabetic atherosclerosis. Salvianolic acid A (SAA) is a major water-soluble phenolic acid in the Salvia miltiorrhiza Bunge, which has been used in traditional Chinese medicine (TCM) and health food products for a long time. This study investigated whether SAA-regulated pyruvate kinase M2 (PKM2) functions to protect endothelial cells. In streptozotocin (STZ)-induced diabetic ApoE-/- mice subjected to a Western diet, SAA attenuated atherosclerotic plaque formation and inhibited pathological changes in the aorta. In addition, SAA significantly prevented NLRP3 inflammasome activation and pyroptosis of endothelial cells in the diabetic atherosclerotic aortic sinus or those exposed to high glucose. Mechanistically, PKM2 was verified to be the main target of SAA. We further revealed that SAA directly interacts with PKM2 at its activator pocket, inhibits phosphorylation of Y105, and hinders the nuclear translocation of PKM2. Also, SAA consistently decreased high glucose-induced overproduction of lactate and partially lactate-dependent phosphorylation of PKR (a regulator of the NLRP3 inflammasome). Further assay on Phenylalanine (PKM2 activity inhibitor) proved that SAA exhibits the function in high glucose-induced pyroptosis of endothelial cells dependently on PKM2 regulation. Furthermore, an assay on c16 (inhibitor of PKR activity) with co-phenylalanine demonstrated that the regulation of the phosphorylated PKR partially drives PKM2-dependent SAA modulation of cell pyroptosis. Therefore, this article reports on the novel function of SAA in the pyroptosis of endothelial cells and diabetic atherosclerosis, which provides important insights into immunometabolism reprogramming that is important for diabetic cardiovascular disease complications therapy.

Gut fungi enhances immunosuppressive function of myeloid-derived suppressor cells by activating PKM2-dependent glycolysis to promote colorectal tumorigenesis

Background

Accumulating evidence implicates that gut fungi are associated with the pathogenesis of colorectal cancer (CRC). Our previous study has revealed that Candida tropicalis (C. tropicalis) promotes colorectal tumorigenesis by enhancing immunosuppressive function of myeloid-derived suppressor cells (MDSCs) and increasing accumulation of MDSCs, but the underlying mechanisms remain unestablished.

Methods

Bone marrow–derived MDSCs were stimulated with C. tropicalis. RNA-sequencing analysis was performed to screen the differentially expressed genes. Quantitative real-time PCR and western blot were used to measure the expression of related proteins. Co-culture assay of MDSCs and CD8+ T cells was used to determine the immunosuppressive ability of MDSCs. Metabolomic analysis was conducted to detect metabolic reprogramming of MDSCs. Aerobic glycolysis of MDSCs was assessed by extracellular acidification rate (ECAR), glucose consumption and lactate production. A CAC mouse model was induced by AOM and DSS to determine the therapeutic action of TEPP-46. IHC and immunofluorescence were performed to examine the expression of PKM2, PKM2 (p-Y105) and iNOS in human CRC-infiltrated MDSCs.

Results

C. tropicalis facilitates immunosuppressive function of MDSCs by increasing the expression of iNOS, COX2 and NOX2, production of nitric oxide (NO) and reactive oxygen species (ROS). Mechanistically, C. tropicalis facilitates the immunosuppressive function of MDSCs through the C-type lectin receptors Dectin-3 and Syk. C. tropicalis-enhanced immunosuppressive function of MDSCs is further dependent on aerobic glycolysis. On the one hand, NO produced by MDSCs enhanced aerobic glycolysis in a positive feedback manner. On the other hand, C. tropicalis promotes p-Syk binding to PKM2, which results in PKM2 Tyr105 phosphorylation and PKM2 nuclear translocation in MDSCs. Nuclear PKM2 interacts with HIF-1α and subsequently upregulates the expression of HIF-1α target genes encoding glycolytic enzymes, GLUT1, HK2, PKM2, LDHA and PDK1, which are required for the C. tropicalis-induced aerobic glycolysis of MDSCs. Blockade of PKM2 nuclear translocation attenuates C. tropicalis-mediated colorectal tumorigenesis. The high expression of PKM2, PKM2 (p-Y105) and iNOS in CRC-infiltrated MDSCs correlates with the development of human CRC.

Conclusion

C. tropicalis enhances immunosuppressive function of MDSCs via Syk-PKM2-HIF-1α-glycolysis signaling axis, which drives CRC. Therefore, we identify the Syk-PKM2-HIF-1α-glycolysis signaling axis as a potential therapeutic target for CRC.

TRIM35-mediated degradation of nuclear PKM2 destabilizes GATA4/6 and induces P53 in cardiomyocytes to promote heart failure

Pyruvate kinase M2 (PKM2) is a glycolytic enzyme that translocates to the nucleus to regulate transcription factors in different tissues or pathologic states. Although studied extensively in cancer, its biological role in the heart remains unresolved. PKM1 is more abundant than the PKM2 isoform in cardiomyocytes, and thus, we speculated that PKM2 is not genetically redundant to PKM1 and may be critical in regulating cardiomyocyte-specific transcription factors important for cardiac survival. Here, we showed that nuclear PKM2 ( S37 P-PKM2) in cardiomyocytes interacts with prosurvival and proapoptotic transcription factors, including GATA4, GATA6, and P53. Cardiomyocyte-specific PKM2-deficient mice ( Pkm2 Mut Cre + ) developed age-dependent dilated cardiac dysfunction and had decreased amounts of GATA4 and GATA6 (GATA4/6) but increased amounts of P53 compared to Control Cre +  hearts. Nuclear PKM2 prevented caspase-1–dependent cleavage and degradation of GATA4/6 while also providing a molecular platform for MDM2-mediated reduction of P53. In a preclinical heart failure mouse model, nuclear PKM2 and GATA4/6 were decreased, whereas P53 was increased in cardiomyocytes. Loss of nuclear PKM2 was ubiquitination dependent and associated with the induction of the E3 ubiquitin ligase TRIM35. In mice, cardiomyocyte-specific TRIM35 overexpression resulted in decreased S37 P-PKM2 and GATA4/6 along with increased P53 in cardiomyocytes compared to littermate controls and similar cardiac dysfunction to Pkm2 Mut Cre +  mice. In patients with dilated left ventricles, increase in TRIM35 was associated with decreased S37 P-PKM2 and GATA4/6 and increased P53. This study supports a previously unrecognized role for PKM2 as a molecular platform that mediates cell signaling events essential for cardiac survival.

Advances in energy metabolism in renal fibrosis

Renal fibrosis is a common pathway toward chronic kidney disease (CKD) and is the main pathological predecessor for end-stage renal disease; thus, preventing progressive CKD and renal fibrosis is essential to reducing their consequential morbidity and mortality. Emerging evidence has connected renal fibrosis to metabolic reprogramming; abnormalities in energy metabolism pathways, such as glycolysis, the tricarboxylic acid cycle, and lipid metabolism, are known to cause diseases of diverse etiologies. Cytokine interventions in affected metabolic pathways may significantly reduce the degree of fibrosis, highlighting therapeutic targets for drug development for renal fibrosis. Here, we discuss the relationship between glycolysis, lipid metabolism, mitochondrial and peroxisome dysfunction, and renal fibrosis in detail and propose that targeted therapies for specific metabolic pathways are expected to represent the next generation of treatments for renal fibrosis.

Exploring metabolism in scleroderma reveals opportunities for pharmacological intervention for therapy in fibrosis

Background

Recent evidence has indicated that alterations in energy metabolism play a critical role in the pathogenesis of fibrotic diseases. Studies have suggested that ‘metabolic reprogramming’ involving the glycolysis and oxidative phosphorylation (OXPHOS) in cells lead to an enhanced generation of energy and biosynthesis. The aim of this study was to assess the molecular basis of changes in fibrotic metabolism in systemic sclerosis (Scleroderma; SSc) and highlight the most appropriate targets for anti-fibrotic therapies.

Materials and methods

Dermal fibroblasts were isolated from five SSc patients and five healthy donors. Cells were cultured in medium with/without TGF-β1 and with/without ALK5, pan-PIM or ATM kinase inhibitors. Extracellular flux analyses were performed to evaluate glycolytic and mitochondrial respiratory function. The mitochondrial network in TMRM-stained cells was visualized by confocal laser-scanning microscopy, followed by semi-automatic analysis on the ImageJ platform. Protein expression of ECM and fibroblast components, glycolytic enzymes, subunits of the five OXPHOS complexes, and dynamin-related GTPases and receptors involved in mitochondrial fission/fusion were assessed by western blotting.

Results

Enhanced mitochondrial respiration coupled to ATP production was observed in SSc fibroblasts at the expense of spare respiratory capacity. Although no difference was found in glycolysis when comparing SSc with healthy control fibroblasts, levels of phophofructokinase-1 isoform PFKM were significantly lower in SSc fibroblasts (P<0.05). Our results suggest that the number of respirasomes is decreased in the SSc mitochondria; however, the organelles formed a hyperfused network, which is thought to increase mitochondrial ATP production through complementation. The increased mitochondrial fusion correlated with a change in expression levels of regulators of mitochondrial morphology, including decreased levels of DRP1, increased levels of MIEF2 and changes in OPA1 isoform ratios. TGF-β1 treatment strongly stimulated glycolysis and mitochondrial respiration and induced the expression of fibrotic markers. The pan-PIM kinase inhibitor had no effect, whereas both ALK5 and ATM kinase inhibition abrogated TGF-β1-mediated fibroblast activation, and upregulation of glycolysis and respiration.

Conclusions

Our data provide evidence for a novel mechanism(s) by which SSc fibroblasts exhibit altered metabolic programs and highlight changes in respiration and dysregulated mitochondrial morphology and function, which can be selectively targeted by small molecule kinase inhibitors.

Role of Pyruvate Kinase M2 (PKM2) in Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the world's leading cause of death, accounting for 32% of all fatalities. Although therapeutic agents are available for CVDs, however, most of them have significant limitations such as the time-dependency effect, hypotension, and bradycardia. To overcome the limitations of current pharmacological therapies, new molecular targets and pathways need to be identified and investigated to provide better treatment options for CVDs. Recent evidence suggested the involvement of pyruvate kinase M2 (PKM2) and targeting PKM2 by its modulators (inhibitors and activators) has shown promising results in several CVDs. PKM2 regulates gene activation in the context of apoptosis, mitosis, hypoxia, inflammation, and metabolic reprogramming. PKM2 modulators might have a significant impact on the molecular pathways involved in CVD pathogenesis. Therefore, PKM2 modulators can be one of the therapeutic options for CVDs. This review provides an insight into PKM2 involvement in various CVDs along with their therapeutic potential.

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

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

Reactive Oxygen Species and Long Non-Coding RNAs, an Unexpected Crossroad in Cancer Cells

Long non-coding RNAs (lncRNA) have recently been identified as key regulators of oxidative stress in several malignancies. The level of reactive oxygen species (ROS) must be constantly regulated to maintain cancer cell proliferation and chemoresistance and to prevent apoptosis. This review will discuss how lncRNAs alter the ROS level in cancer cells. We will first describe the role of lncRNAs in the nuclear factor like 2 (Nrf-2) coordinated antioxidant response of cancer cells. Secondly, we show how lncRNAs can promote the Warburg effect in cancer cells, thus shifting the cancer cell’s “building blocks” towards molecules important in oxidative stress regulation. Lastly, we explain the role that lncRNAs play in ROS-induced cancer cell apoptosis and proliferation.

Metabolic reprogramming: A novel therapeutic target in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most common microvascular complications of diabetes mellitus. However, the pathological mechanisms contributing to DKD are multifactorial and poorly understood. Diabetes is characterized by metabolic disorders that can bring about a series of changes in energy metabolism. As the most energy-consuming organs secondary only to the heart, the kidneys must maintain energy homeostasis. Aberrations in energy metabolism can lead to cellular dysfunction or even death. Metabolic reprogramming, a shift from mitochondrial oxidative phosphorylation to glycolysis and its side branches, is thought to play a critical role in the development and progression of DKD. This review focuses on the current knowledge about metabolic reprogramming and the role it plays in DKD development. The underlying etiologies, pathological damages in the involved cells, and potential molecular regulators of metabolic alterations are also discussed. Understanding the role of metabolic reprogramming in DKD may provide novel therapeutic approaches to delay its progression to end-stage renal disease.

Revisited Metabolic Control and Reprogramming Cancers by Means of the Warburg Effect in Tumor Cells

Aerobic glycolysis is an emerging hallmark of many human cancers, as cancer cells are defined as a "metabolically abnormal system". Carbohydrates are metabolically reprogrammed by its metabolizing and catabolizing enzymes in such abnormal cancer cells. Normal cells acquire their energy from oxidative phosphorylation, while cancer cells acquire their energy from oxidative glycolysis, known as the "Warburg effect". Energy-metabolic differences are easily found in the growth, invasion, immune escape and anti-tumor drug resistance of cancer cells. The glycolysis pathway is carried out in multiple enzymatic steps and yields two pyruvate molecules from one glucose (Glc) molecule by orchestral reaction of enzymes. Uncontrolled glycolysis or abnormally activated glycolysis is easily observed in the metabolism of cancer cells with enhanced levels of glycolytic proteins and enzymatic activities. In the "Warburg effect", tumor cells utilize energy supplied from lactic acid-based fermentative glycolysis operated by glycolysis-specific enzymes of hexokinase (HK), keto-HK-A, Glc-6-phosphate isomerase, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase, phosphofructokinase (PFK), phosphor-Glc isomerase (PGI), fructose-bisphosphate aldolase, phosphoglycerate (PG) kinase (PGK)1, triose phosphate isomerase, PG mutase (PGAM), glyceraldehyde-3-phosphate dehydrogenase, enolase, pyruvate kinase isozyme type M2 (PKM2), pyruvate dehydrogenase (PDH), PDH kinase and lactate dehydrogenase. They are related to glycolytic flux. The key enzymes involved in glycolysis are directly linked to oncogenesis and drug resistance. Among the metabolic enzymes, PKM2, PGK1, HK, keto-HK-A and nucleoside diphosphate kinase also have protein kinase activities. Because glycolysis-generated energy is not enough, the cancer cell-favored glycolysis to produce low ATP level seems to be non-efficient for cancer growth and self-protection. Thus, the Warburg effect is still an attractive phenomenon to understand the metabolic glycolysis favored in cancer. If the basic properties of the Warburg effect, including genetic mutations and signaling shifts are considered, anti-cancer therapeutic targets can be raised. Specific therapeutics targeting metabolic enzymes in aerobic glycolysis and hypoxic microenvironments have been developed to kill tumor cells. The present review deals with the tumor-specific Warburg effect with the revisited viewpoint of recent progress.

Methionine oxidation activates pyruvate kinase M2 to promote pancreatic cancer metastasis

Cancer mortality is primarily a consequence of its metastatic spread. Here, we report that methionine sulfoxide reductase A (MSRA), which can reduce oxidized methionine residues, acts as a suppressor of pancreatic ductal adenocarcinoma (PDA) metastasis. MSRA expression is decreased in the metastatic tumors of PDA patients, whereas MSRA loss in primary PDA cells promotes migration and invasion. Chemoproteomic profiling of pancreatic organoids revealed that MSRA loss results in the selective oxidation of a methionine residue (M239) in pyruvate kinase M2 (PKM2). Moreover, M239 oxidation sustains PKM2 in an active tetrameric state to promote respiration, migration, and metastasis, whereas pharmacological activation of PKM2 increases cell migration and metastasis in vivo. These results demonstrate that methionine residues can act as reversible redox switches governing distinct signaling outcomes and that the MSRA-PKM2 axis serves as a regulatory nexus between redox biology and cancer metabolism to control tumor metastasis.

Shikonin ameliorated mice colitis by inhibiting dimerization and tetramerization of PKM2 in macrophages

Dysregulated immune response plays a pivotal role in Ulcerative colitis. In lamina propria of inflammatory colonic mucosa, macrophages tend to polarize into M1 type and metabolically reprogram to aerobic glycolysis. PKM2 orchestrates glucose metabolic switch in macrophages, which tetramer has high pyruvate kinase activity, while which dimer mainly works as a protein kinase to stabilize HIF-1α and mediate anabolism. Shikonin is a potent PKM2 inhibitor derived from traditional Chinese medicine Arnebiae Radix with anti-inflammatory and anticarcinogen activities. However, it is unclear which conformation of PKM2 is inhibited by Shikonin, and whether this inhibition mediates pharmacological effect of Shikonin. In this study, we examined the efficacy of Shikonin on dextran sulfate sodium-induced mice colitis and determined the states of PKM2 aggregation after Shikonin treatment. Results showed that Shikonin dose-dependently alleviated mice colitis, down-regulated expression of F4/80, iNOS and CD86, decreased IFN-γ, IL-1β, IL-6 and TNF-α, while increased IL-10 in mice colon. Furthermore, Shikonin suppressed the pyruvate, lactate production and glucose consumption, inhibited the pyruvate kinase activity and nuclear translocation of PKM2, and decreased both dimerization and tetramerization of PKM2 in macrophages. In vitro assay revealed that Shikonin bounded to PKM2 protein, inhibited the formation of both dimer and tetramer, while promoted aggregation of PKM2 macromolecular polymer. TEPP-46, an activator of PKM2 tetramerization, attenuated the ameliorative effect of Shikonin on disuccinimidyl suberate mice. In summary, Shikonin improved mice colitis, which mechanism may be mediated by inhibiting dimerization and tetramerization of PKM2, suppressing aerobic glycolysis reprogram, improving mitochondrial dynamic, and therefore alleviating inflammatory response of macrophages.

lncRNA HITT Inhibits Lactate Production by Repressing PKM2 Oligomerization to Reduce Tumor Growth and Macrophage Polarization

Lactic acid acidifies the tumor microenvironment and promotes multiple critical oncogenic processes, including immune evasion. Pyruvate kinase M2 (PKM2) is a dominant form of pyruvate kinase (PK) expressed in cancers that plays essential roles in metabolic reprograming and lactate production, rendering it as an attractive therapeutic target of cancer. However, the mechanism underlying PKM2 regulation remains unclear. Here, we show that long noncoding RNA (lncRNA) HIF-1α inhibitor at transcription level (HITT) inhibits lactate production in a PKM2-dependent manner. Mechanistically, it physically interacts with PKM2 mapped to a region that has been involved in both dimer (less-active) and tetramer (more-active) formation, inhibiting PKM2 oligomerization and leading to dramatic reduction of PK activity. Under glucose starvation, HITT was reduced as a result of miR-106 induction, which subsequently facilitates PKM2 oligomerization and increases vulnerability to apoptosis under glucose starvation stress. In addition, the interaction also reduces lactate secretion from cancer cells, which subsequently polarizes macrophages toward an M2-like anti-inflammatory phenotype and thus possibly contributes to immune escape in vivo. This study highlights an important role of an lncRNA in regulating PKM2 activity and also reveals a metabolic regulatory effect of PKM2 on macrophage polarization.

Sulforaphane diminishes moonlighting of pyruvate kinase M2 and interleukin 1β expression in M1 (LPS) macrophages

Murine macrophages activated by the Toll-like receptor 4 agonist lipopolysaccharide (LPS) polarize to the M1 type by inducing proinflammatory marker proteins and changing their energy metabolism to increased aerobic glycolysis and reduced respiration. We here show that the aliphatic isothiocyanate sulforaphane (Sfn) diminishes M1 marker expression (IL-1β, IL-6, TNF-α, iNOS, NO, and ROS) and leads to highly energetic cells characterized by both high glycolytic and high respiratory activity as assessed by extracellular flux analysis. Focusing on a potential connection between high glycolytic activity and low IL-1β expression in M1 (LPS/Sfn) macrophages, we reveal that Sfn impedes the moonlighting function of pyruvate kinase M2 (PKM2) in M1 macrophages. Sfn limits mono/dimerization and nuclear residence of PKM2 accompanied by reduced HIF-1α levels, Stat3 phosphorylation at tyrosine 705, and IL-1β expression while preserving high levels of cytosolic PKM2 tetramer with high glycolytic enzyme activity. Sfn prevents glutathionylation of PKM2 in LPS-stimulated macrophages which may account for the reduced loss of PKM2 tetramer. Overall, we uncover PKM2 as a novel affected hub within the anti-inflammatory activity profile of Sfn.

The C-Terminal Acidic Tail Modulates the Anticancer Properties of HMGB1

Energy metabolism reprogramming was recently listed as a hallmark of cancer. In this process, the switch from pyruvate kinase isoenzyme type M1 to pyruvate kinase isoenzyme type M2 (PKM2) is believed to play a crucial role. Interestingly, the activity of the active form of PKM2 can efficiently be inhibited by the high-mobility group box 1 (HMGB1) protein, leading to a rapid blockage of glucose-dependent aerobic respiration and cancer cell death. HMGB1 is a member of the HMG protein family. It contains two DNA-binding HMG-box domains and an acidic C-terminal tail capable of positively or negatively modulating its biological properties. In this work, we report that the deletion of the C-terminal tail of HMGB1 increases its activity towards a large panel of cancer cells without affecting the viability of normal immortalized fibroblasts. Moreover, in silico analysis suggests that the truncated form of HMGB1 retains the capacity of the full-length protein to interact with PKM2. However, based on the capacity of the cells to circumvent oxidative phosphorylation inhibition, we were able to identify either a cytotoxic or cytostatic effect of the proteins. Together, our study provides new insights in the characterization of the anticancer activity of HMGB1.

Research progress on the interaction between long non‑coding RNAs and RNA‑binding proteins to influence the reprogramming of tumor glucose metabolism (Review)

As epigenetic regulators, long non-coding RNAs (lncRNAs) are involved in various important regulatory processes and typically interact with RNA-binding proteins (RBPs) to exert their core functional effects. An increasing number of studies have demonstrated that lncRNAs can regulate the occurrence and development of cancer through a variety of complex mechanisms and can also participate in tumor glucose metabolism by directly or indirectly regulating the Warburg effect. As one of the metabolic characteristics of tumor cells, the Warburg effect provides a large amount of energy and numerous intermediate products to meet the consumption demands of tumor metabolism, providing advantages for the occurrence and development of tumors. The present review article summarizes the regulatory effects of lncRNAs on the reprogramming of glucose metabolism after interacting with RBPs in tumors. The findings discussed herein may aid in the better understanding of the pathogenesis of malignancies, and may provide novel therapeutic targets, as well as new diagnostic and prognostic markers for human cancers.