Small ubiquitin-related modifier (SUMO)-1 promotes glycolysis in hypoxia

Compartmentation of multiple metabolic enzymes and their preparation in vitro and in cellulo

Compartmentalization of multiple enzymes in cellulo and in vitro is a means of controlling the cascade reaction of metabolic enzymes. The compartmentation of enzymes through liquid-liquid phase separation may facilitate the reversible control of biocatalytic cascade reactions, thereby reducing the transcriptional and translational burden. This has attracted attention as a potential application in bioproduction. Recent research has demonstrated the existence and regulatory mechanisms of various enzyme compartments within cells. Mounting evidence suggests that enzyme compartmentation allows in vitro and in vivo regulation of cellular metabolism. However, the comprehensive regulatory mechanisms of enzyme condensates in cells and ideal organization of cellular systems remain unknown. This review provides an overview of the recent progress in multiple enzyme compartmentation in cells and summarizes strategies to reconstruct multiple enzyme assemblies in vitro and in cellulo. By examining parallel examples, we have evaluated the consensus and future perspectives of enzyme condensation.

Exploring the Molecular Interplay Between Oxygen Transport, Cellular Oxygen Sensing, and Mitochondrial Respiration

Significance: The mitochondria play a key role in maintaining oxygen homeostasis under normal oxygen tension (normoxia) and during oxygen deprivation (hypoxia). This is a critical balancing act between the oxygen content of the blood, the tissue oxygen sensing mechanisms, and the mitochondria, which ultimately consume most oxygen for energy production. Recent Advances: We describe the well-defined role of the mitochondria in oxygen metabolism with a special focus on the impact on blood physiology and pathophysiology. Critical Issues: Fundamental questions remain regarding the impact of mitochondrial responses to changes in overall blood oxygen content under normoxic and hypoxic states and in the case of impaired oxygen sensing in various cardiovascular and pulmonary complications including blood disorders involving hemolysis and hemoglobin toxicity, ischemia reperfusion, and even in COVID-19 disease. Future Directions: Understanding the nature of the crosstalk among normal homeostatic pathways, oxygen carrying by hemoglobin, utilization of oxygen by the mitochondrial respiratory chain machinery, and oxygen sensing by hypoxia-inducible factor proteins, may provide a target for future therapeutic interventions. Antioxid. Redox Signal. 42, 730-750.

CHAC1 blockade suppresses progression of lung adenocarcinoma by interfering with glucose metabolism via hijacking PKM2 nuclear translocation

Patients with lung adenocarcinoma (LUAD) generally have poor prognosis. Abnormal cellular energy metabolism is a hallmark of LUAD. Glutathione-specific gamma-glutamylcyclotransferase 1 (CHAC1) is a member of the γ-glutamylcyclotransferase family and an unfolded protein response pathway regulatory gene. Its biological function and molecular regulatory mechanism, especially regarding energy metabolism underlying LUAD, remain unclear. By utilizing tissue microarray and data from The Cancer Genome Atlas and Gene Expression Omnibus, we found that CHAC1 expression was markedly higher in LUAD tissues than in non-tumor tissues, and was positively correlated with poor prognosis. Phenotypically, CHAC1 overexpression enhanced the proliferation, migration, invasion, tumor sphere formation, and glycolysis ability of LUAD cells, resulting in tumor growth both in vitro and in vivo. Mechanistically, through a shotgun mass spectrometry-based proteomic approach and high-throughput RNA sequencing, we found that CHAC1 acted as a bridge connecting UBA2 and PKM2, enhancing the SUMOylation of PKM2. The SUMOylated PKM2 then transferred from the cytoplasm to the nucleus, activating the expression of glycolysis-related genes and enhancing the Warburg effect. Lastly, E2F Transcription Factor 1 potently activated CHAC1 transcription by directly binding to the CHAC1 promoter in LUAD cells. The results of this study implied that CHAC1 regulates energy metabolism and promotes glycolysis in LUAD progression.

Hypoxia-inducible factor-driven glycolytic adaptations in host-microbe interactions

Mammalian cells utilize glucose as a primary carbon source to produce energy for most cellular functions. However, the bioenergetic homeostasis of cells can be perturbed by environmental alterations, such as changes in oxygen levels which can be associated with bacterial infection. Reduction in oxygen availability leads to a state of hypoxia, inducing numerous cellular responses that aim to combat this stress. Importantly, hypoxia strongly augments cellular glycolysis in most cell types to compensate for the loss of aerobic respiration. Understanding how this host cell metabolic adaptation to hypoxia impacts the course of bacterial infection will identify new anti-microbial targets. This review will highlight developments in our understanding of glycolytic substrate channeling and spatiotemporal enzymatic organization in response to hypoxia, shedding light on the integral role of the hypoxia-inducible factor (HIF) during host-pathogen interactions. Furthermore, the ability of intracellular and extracellular bacteria (pathogens and commensals alike) to modulate host cellular glucose metabolism will be discussed.

HERC5 downregulation in non-small cell lung cancer is associated with altered energy metabolism and metastasis

BACKGROUND

Metastasis is the leading cause of cancer-related death in non-small cell lung cancer (NSCLC) patients. We previously showed that low HERC5 expression predicts early tumor dissemination and a dismal prognosis in NSCLC patients. Here, we performed functional studies to unravel the mechanism underlying the "metastasis-suppressor" effect of HERC5, with a focus on mitochondrial metabolism pathways.

METHODS

We assessed cell proliferation, colony formation potential, anchorage-independent growth, migration, and wound healing in NSCLC cell line models with HERC5 overexpression (OE) or knockout (KO). To study early tumor cell dissemination, we used these cell line models in zebrafish experiments and performed intracardial injections in nude mice. Mass spectrometry (MS) was used to analyze protein changes in whole-cell extracts. Furthermore, electron microscopy (EM) imaging, cellular respiration, glycolytic activity, and lactate production were used to investigate the relationships with mitochondrial energy metabolism pathways.

RESULTS

Using different in vitro NSCLC cell line models, we showed that NSCLC cells with low HERC5 expression had increased malignant and invasive properties. Furthermore, two different in vivo models in zebrafish and a xenograft mouse model showed increased dissemination and metastasis formation (in particular in the brain). Functional enrichment clustering of MS data revealed an increase in mitochondrial proteins in vitro when HERC5 levels were high. Loss of HERC5 leads to an increased Warburg effect, leading to improved adaptation and survival under prolonged inhibition of oxidative phosphorylation.

CONCLUSIONS

Taken together, these results indicate that low HERC5 expression increases the metastatic potential of NSCLC in vitro and in vivo. Furthermore, HERC5-induced proteomic changes influence mitochondrial pathways, ultimately leading to alterations in energy metabolism and demonstrating its role as a new potential metastasis suppressor gene.

SUMOylation of Smad2 mediates TGF-β-regulated endothelial-mesenchymal transition

Endothelial-mesenchymal transition (EndoMT) is a complex biological process in which endothelial cells are transformed into mesenchymal cells, and dysregulated EndoMT causes a variety of pathological processes. Transforming growth factor beta (TGF-β) signaling effectively induces the EndoMT process in endothelial cells, and Smad2 is the critical protein of the TGF-β signaling pathway. However, whether small ubiquitin-like modifier modification (SUMOylation) is involved in EndoMT remains unclear. Here, we show that Smad2 is predominantly modified by SUMO1 at two major SUMOylation sites with PIAS2α as the primary E3 ligase, whereas SENP1 (sentrin/SUMO-specific protease 1) mediates the deSUMOylation of Smad2. In addition, we identified that SUMOylation significantly enhances the transcriptional activity and protein stability of Smad2, regulating the expression of downstream target genes. SUMOylation increases the phosphorylation of Smad2 and the formation of the Smad2-Smad4 complex, thus promoting the nuclear translocation of Smad2. Ultimately, the wildtype, but not SUMOylation site mutant Smad2 facilitated the EndoMT process. More importantly, TGF-β enhances the nuclear translocation of Smad2 by enhancing its SUMOylation and promoting the EndoMT process. These results demonstrate that SUMOylation of Smad2 plays a critical role in the TGF-β-mediated EndoMT process, providing a new theoretical basis for the treatment and potential drug targets of EndoMT-related clinical diseases.

Intracellular energy production and distribution in hypoxia

The hydrolysis of ATP is the primary source of metabolic energy for eukaryotic cells. Under physiological conditions, cells generally produce more than sufficient levels of ATP to fuel the active biological processes necessary to maintain homeostasis. However, mechanisms underpinning the distribution of ATP to subcellular microenvironments with high local demand remain poorly understood. Intracellular distribution of ATP in normal physiological conditions has been proposed to rely on passive diffusion across concentration gradients generated by ATP producing systems such as the mitochondria and the glycolytic pathway. However, subcellular microenvironments can develop with ATP deficiency due to increases in local ATP consumption. Alternatively, ATP production can be reduced during bioenergetic stress during hypoxia. Mammalian cells therefore need to have the capacity to alter their metabolism and energy distribution strategies to compensate for local ATP deficits while also controlling ATP production. It is highly likely that satisfying the bioenergetic requirements of the cell involves the regulated distribution of ATP producing systems to areas of high ATP demand within the cell. Recently, the distribution (both spatially and temporally) of ATP-producing systems has become an area of intense investigation. Here, we review what is known (and unknown) about intracellular energy production and distribution and explore potential mechanisms through which this targeted distribution can be altered in hypoxia, with the aim of stimulating investigation in this important, yet poorly understood field of research.

The emerging roles of SUMOylation in the tumor microenvironment and therapeutic implications

Tumor initiation, progression, and response to therapies depend to a great extent on interactions between malignant cells and the tumor microenvironment (TME), which denotes the cancerous/non-cancerous cells, cytokines, chemokines, and various other factors around tumors. Cancer cells as well as stroma cells can not only obtain adaption to the TME but also sculpt their microenvironment through a series of signaling pathways. The post-translational modification (PTM) of eukaryotic cells by small ubiquitin-related modifier (SUMO) proteins is now recognized as a key flexible pathway. Proteins involved in tumorigenesis guiding several biological processes including chromatin organization, DNA repair, transcription, protein trafficking, and signal conduction rely on SUMOylation. The purpose of this review is to explore the role that SUMOylation plays in the TME formation and reprogramming, emphasize the importance of targeting SUMOylation to intervene in the TME and discuss the potential of SUMOylation inhibitors (SUMOi) in ameliorating tumor prognosis.

Systems approaches to understand oxygen sensing: how multi-omics has driven advances in understanding oxygen-based signalling

Hypoxia is a common denominator in the pathophysiology of a variety of human disease states. Insight into how cells detect, and respond to low oxygen is crucial to understanding the role of hypoxia in disease. Central to the hypoxic response is rapid changes in the expression of genes essential to carry out a wide range of functions to adapt the cell/tissue to decreased oxygen availability. These changes in gene expression are co-ordinated by specialised transcription factors, changes to chromatin architecture and intricate balances between protein synthesis and destruction that together establish changes to the cellular proteome. In this article, we will discuss the advances of our understanding of the cellular oxygen sensing machinery achieved through the application of 'omics-based experimental approaches.

Condensate Formation by Metabolic Enzymes in Saccharomyces cerevisiae

Condensate formation by a group of metabolic enzymes in the cell is an efficient way of regulating cell metabolism through the formation of "membrane-less organelles." Because of the use of green fluorescent protein (GFP) for investigating protein localization, various enzymes were found to form condensates or filaments in living Saccharomyces cerevisiae, mammalian cells, and in other organisms, thereby regulating cell metabolism in the certain status of the cells. Among different environmental stresses, hypoxia triggers the spatial reorganization of many proteins, including more than 20 metabolic enzymes, to form numerous condensates, including "Glycolytic body (G-body)" and "Purinosome." These individual condensates are collectively named "Metabolic Enzymes Transiently Assembling (META) body". This review overviews condensate or filament formation by metabolic enzymes in S. cerevisiae, focusing on the META body, and recent reports in elucidating regulatory machinery of META body formation.

MicroRNA‑25 protects nucleus pulposus cells against apoptosis via targeting SUMO2 in intervertebral disc degeneration

It has been reported that microRNA (miRNA/miR)‑25 is downregulated in patients with intervertebral disc degeneration (IVDD). However, the potential role of miR‑25 in IVDD remains unclear. Therefore, the present study aimed to investigate the effects of miR‑25 on human intervertebral disc nucleus pulposus cells (NPCs). The expression levels of miR‑25 and those of small ubiquitin‑related modifier 2 (SUMO2) were determined in human nucleus pulposus (NP) tissues by reverse transcription‑quantitative PCR (RT‑qPCR) and western blot analyses. Subsequently, the potential interaction between miR‑25 and SUMO2 was validated via dual‑luciferase reporter assay and RNA pull‑down assay with biotinylated miRNA. The effects of miR‑25 on NPC proliferation and apoptosis were evaluated using Cell Counting Kit‑8 assay, 5‑ethynyl‑2'‑deoxyuridine incorporation assay, and flow cytometry. The results showed that miR‑25 was downregulated in patients with IVDD. In addition, miR‑25 increased the proliferation of NPCs and inhibited their apoptosis. Furthermore, the current study verified that miR‑25 could directly target SUMO2 and regulate its expression via the p53 signaling pathway. Additionally, the effects of miR‑25 on NPCs were abrogated following SUMO2 overexpression. Overall, the results of the present study demonstrated that miR‑25 could promote the proliferation and inhibit the apoptosis of NPCs via targeting SUMO2, suggesting that miR‑25 may be a potential target in the treatment of IVDD.

HIF-1-Independent Mechanisms Regulating Metabolic Adaptation in Hypoxic Cancer Cells

In solid tumours, cancer cells exist within hypoxic microenvironments, and their metabolic adaptation to this hypoxia is driven by HIF-1 transcription factor, which is overexpressed in a broad range of human cancers. HIF inhibitors are under pre-clinical investigation and clinical trials, but there is evidence that hypoxic cancer cells can adapt metabolically to HIF-1 inhibition, which would provide a potential route for drug resistance. Here, we review accumulating evidence of such adaptions in carbohydrate and creatine metabolism and other HIF-1-independent mechanisms that might allow cancers to survive hypoxia despite anti-HIF-1 therapy. These include pathways in glucose, glutamine, and lipid metabolism; epigenetic mechanisms; post-translational protein modifications; spatial reorganization of enzymes; signalling pathways such as Myc, PI3K-Akt, 2-hyxdroxyglutarate and AMP-activated protein kinase (AMPK); and activation of the HIF-2 pathway. All of these should be investigated in future work on hypoxia bypass mechanisms in anti-HIF-1 cancer therapy. In principle, agents targeted toward HIF-1β rather than HIF-1α might be advantageous, as both HIF-1 and HIF-2 require HIF-1β for activation. However, HIF-1β is also the aryl hydrocarbon nuclear transporter (ARNT), which has functions in many tissues, so off-target effects should be expected. In general, cancer therapy by HIF inhibition will need careful attention to potential resistance mechanisms.

Hyper-SUMOylation of ERG Is Essential for the Progression of Acute Myeloid Leukemia

Leukemia is a malignant disease of hematopoietic tissue characterized by the differentiation arrest and malignant proliferation of immature hematopoietic precursor cells in bone marrow. ERG (ETS-related gene) is an important member of the E26 transformation-specific (ETS) transcription factor family that plays a crucial role in physiological and pathological processes. However, the role of ERG and its modification in leukemia remains underexplored. In the present study, we stably knocked down or overexpressed ERG in leukemia cells and observed that ERG significantly promotes the proliferation and inhibits the differentiation of AML (acute myeloid leukemia) cells. Further experiments showed that ERG was primarily modified by SUMO2, which was deconjugated by SENP2. PML promotes the SUMOylation of ERG, enhancing its stability. Arsenic trioxide decreased the expression level of ERG, further promoting cell differentiation. Furthermore, the mutation of SUMO sites in ERG inhibited its ability to promote the proliferation and inhibit the differentiation of leukemia cells. Our results demonstrated the crucial role of ERG SUMOylation in the development of AML, providing powerful targeted therapeutic strategies for the clinical treatment of AML.

Profiling the Murine SUMO Proteome in Response to Cardiac Ischemia and Reperfusion Injury

SUMOylation is a reversible posttranslational modification pathway catalyzing the conjugation of small ubiquitin-related modifier (SUMO) proteins to lysine residues of distinct target proteins. SUMOylation modifies a wide variety of cellular regulators thereby affecting a multitude of key processes in a highly dynamic manner. The SUMOylation pathway displays a hallmark in cellular stress-adaption, such as heat or redox stress. It has been proposed that enhanced cellular SUMOylation protects the brain during ischemia, however, little is known about the specific regulation of the SUMO system and the potential target proteins during cardiac ischemia and reperfusion injury (I/R). By applying left anterior descending (LAD) coronary artery ligation and reperfusion in mice, we detect dynamic changes in the overall cellular SUMOylation pattern correlating with decreased SUMO deconjugase activity during I/R injury. Further, unbiased system-wide quantitative SUMO-proteomics identified a sub-group of SUMO targets exhibiting significant alterations in response to cardiac I/R. Notably, transcription factors that control hypoxia- and angiogenesis-related gene expression programs, exhibit altered SUMOylation during ischemic stress adaptation. Moreover, several components of the ubiquitin proteasome system undergo dynamic changes in SUMO conjugation during cardiac I/R suggesting an involvement of SUMO signaling in protein quality control and proteostasis in the ischemic heart. Altogether, our study reveals regulated candidate SUMO target proteins in the mouse heart, which might be important in coping with hypoxic/proteotoxic stress during cardiac I/R injury.

Regulation of glycolysis by the hypoxia-inducible factor (HIF): implications for cellular physiology

Under conditions of hypoxia, most eukaryotic cells can shift their primary metabolic strategy from predominantly mitochondrial respiration towards increased glycolysis to maintain ATP levels. This hypoxia-induced reprogramming of metabolism is key to satisfying cellular energetic requirements during acute hypoxic stress. At a transcriptional level, this metabolic switch can be regulated by several pathways including the hypoxia inducible factor-1α (HIF-1α) which induces an increased expression of glycolytic enzymes. While this increase in glycolytic flux is beneficial for maintaining bioenergetic homeostasis during hypoxia, the pathways mediating this increase can also be exploited by cancer cells to promote tumour survival and growth, an area which has been extensively studied. It has recently become appreciated that increased glycolytic metabolism in hypoxia may also have profound effects on cellular physiology in hypoxic immune and endothelial cells. Therefore, understanding the mechanisms central to mediating this reprogramming are of importance from both physiological and pathophysiological standpoints. In this review, we highlight the role of HIF-1α in the regulation of hypoxic glycolysis and its implications for physiological processes such as angiogenesis and immune cell effector function.

Increased SUMO-activating enzyme SAE1/UBA2 promotes glycolysis and pathogenic behavior of rheumatoid fibroblast-like synoviocytes

Fibroblast-like synoviocytes (FLSs) are critical to joint inflammation and destruction in rheumatoid arthritis (RA). Increased glycolysis in RA FLSs contributes to persistent joint damage. SUMOylation, a posttranslational modification of proteins, plays an important role in initiation and development of many diseases. However, the role of small ubiquitin-like modifier–activating (SUMO-activating) enzyme 1 (SAE1)/ubiquitin like modifier activating enzyme 2 (UBA2) in regulating the pathogenic FLS behaviors is unknown. Here, we found an increased expression of SAE1 and UBA2 in FLSs and synovial tissues from patients with RA. SAE1 or UBA2 knockdown by siRNA and treatment with GA, an inhibitor of SAE1/UBA2-mediated SUMOylation, resulted in reduced glycolysis, aggressive phenotype, and inflammation. SAE1/UBA2-mediated SUMOylation of pyruvate kinase M2 (PKM2) promoted its phosphorylation and nuclear translocation and decreased PK activity. Moreover, inhibition of PKM2 phosphorylation increased PK activity and suppressed glycolysis, aggressive phenotype, and inflammation. We further demonstrated that STAT5A mediated SUMOylated PKM2-induced glycolysis and biological behaviors. Interestingly, GA treatment attenuated the severity of arthritis in mice with collagen-induced arthritis and human TNF-α transgenic mice. These findings suggest that an increase in synovial SAE1/UBA2 may contribute to synovial glycolysis and joint inflammation in RA and that targeting SAE1/UBA2 may have therapeutic potential in patients with RA.

SUMO-activating enzyme SAE1/UBA2 promotes glycolysis and pathogenic behavior of rheumatoid fibroblast-like synoviocytes through SUMOylation of pyruvate kinase M2.

The HIF target ATG9A is essential for epithelial barrier function and tight junction biogenesis

Intestinal epithelial cells (IECs) exist in a metabolic state of low oxygen tension termed "physiologic hypoxia." An important factor in maintaining intestinal homeostasis is the transcription factor hypoxia-inducible factor (HIF), which is stabilized under hypoxic conditions and mediates IEC homeostatic responses to low oxygen tension. To identify HIF transcriptional targets in IEC, chromatin immunoprecipitation (ChIP) was performed in Caco-2 IECs using HIF-1α- or HIF-2α-specific antibodies. ChIP-enriched DNA was hybridized to a custom promoter microarray (termed ChIP-chip). This unbiased approach identified autophagy as a major HIF-1-targeted pathway in IEC. Binding of HIF-1 to the ATG9A promoter, the only transmembrane component within the autophagy pathway, was particularly enriched by exposure of IEC to hypoxia. Validation of this ChIP-chip revealed prominent induction of ATG9A, and luciferase promoter assays identified a functional hypoxia response element upstream of the TSS. Hypoxia-mediated induction of ATG9A was lost in cells lacking HIF-1. Strikingly, we found that lentiviral-mediated knockdown (KD) of ATG9A in IECs prevents epithelial barrier formation by >95% and results in significant mislocalization of multiple tight junction (TJ) proteins. Extensions of these findings showed that ATG9A KD cells have intrinsic abnormalities in the actin cytoskeleton, including mislocalization of the TJ binding protein vasodilator-stimulated phosphoprotein. These results implicate ATG9A as essential for multiple steps of epithelial TJ biogenesis and actin cytoskeletal regulation. Our findings have novel applicability for disorders that involve a compromised epithelial barrier and suggest that targeting ATG9A may be a rational strategy for future therapeutic intervention.

SUMOylation in α-Synuclein Homeostasis and Pathology

The accumulation and aggregation of α-synuclein are central to Parkinson’s disease (PD), yet the molecular mechanisms responsible for these events are not fully understood. Post-translational modifications of α-synuclein regulate several of its properties, including degradation, interaction with proteins and membranes, aggregation and toxicity. SUMOylation is a post-translational modification involved in various nuclear and extranuclear processes, such as subcellular protein targeting, mitochondrial fission and synaptic plasticity. Protein SUMOylation increases in response to several stressful situations, from viral infections to trauma. In this framework, an increasing amount of evidence has implicated SUMOylation in several neurodegenerative diseases, including PD. This review will discuss recent findings in the role of SUMOylation as a regulator of α-synuclein accumulation, aggregation and toxicity, and its possible implication in neurodegeneration that underlies PD.

Transmission of ALS pathogenesis by the cerebrospinal fluid

To test the hypothesis that the cerebrospinal fluid (CSF) could provide a spreading route for pathogenesis of amyotrophic lateral sclerosis (ALS), we have examined the effects of intraventricular infusion during 2 weeks of pooled CSF samples from sporadic ALS patients or control CSF samples into transgenic mice expressing human TDP43^WT which do not develop pathological phenotypes. Infusion of ALS-CSF, but not of control CSF, triggered motor and cognitive dysfunction, as well as ALS-like pathological changes including TDP43 proteinopathy, neurofilament disorganization and neuroinflammation. In addition, the neuron-specific translational profiles from peptide analyses of immunoprecipitated ribosomes revealed dysregulation of multiple protein networks in response to ALS-CSF altering cytoskeletal organization, vesicle trafficking, mitochondrial function, and cell metabolism. With normal mice, similar ALS-CSF infusion induced mild motor dysfunction but without significant TDP43 pathology in spinal neurons. We conclude that the CSF from sporadic ALS contains factors that can transmit and disseminate disease including TDP43 proteinopathy into appropriate recipient animal model expressing human TDP43. These findings open new research avenues for the discovery of etiogenic factors for sporadic ALS and for the testing of drugs aiming to neutralize the ALS-CSF toxicity.

HIF hydroxylase inhibitors decrease cellular oxygen consumption depending on their selectivity

Pharmacologic HIF hydroxylase inhibitors (HIs) are effective for the treatment of anemia in chronic kidney disease patients and may also be beneficial for the treatment of diseases such as chronic inflammation and ischemia-reperfusion injury. The selectivities of many HIs for HIF hydroxylases and possible off-target effects in cellulo are unclear, delaying the translation from preclinical studies to clinical trials. We developed a novel assay that discriminates between the inhibition of HIF-α prolyl-4-hydroxylase domain (PHD) enzymes and HIF-α asparagine hydroxylase factor inhibiting HIF (FIH). We characterized 15 clinical and preclinical HIs, categorizing them into pan-HIF-α hydroxylase (broad spectrum), PHD-selective, and FIH-selective inhibitors, and investigated their effects on HIF-dependent transcriptional regulation, erythropoietin production, and cellular energy metabolism. While energy homeostasis was generally maintained following HI treatment, the pan-HIs led to a stronger increase in pericellular pO₂ than the PHD/FIH-selective HIs. Combined knockdown of FIH and PHD-selective inhibition did not further increase pericellular pO₂ . Hence, the additional increase in pericellular pO₂ by pan- over PHD-selective HIs likely reflects HIF hydroxylase independent off-target effects. Overall, these analyses demonstrate that HIs can lead to oxygen redistribution within the cellular microenvironment, which should be considered as a possible contributor to HI effects in the treatment of hypoxia-associated diseases.

Prioritizing natural-selection signals from the deep-sequencing genomic data suggests multi-variant adaptation in Tibetan highlanders

Human genetic adaptation to high altitudes (>2500 m) has been extensively studied over the last few years, but few functional adaptive genetic variants have been identified, largely owing to the lack of deep-genome sequencing data available to previous studies. Here, we build a list of putative adaptive variants, including 63 missense, 7 loss-of-function, 1,298 evolutionarily conserved variants and 509 expression quantitative traits loci. Notably, the top signal of selection is located in TMEM247, a transmembrane protein-coding gene. The Tibetan version of TMEM247 harbors one high-frequency (76.3%) missense variant, rs116983452 (c.248C > T; p.Ala83Val), with the T allele derived from archaic ancestry and carried by >94% of Tibetans but absent or in low frequencies (<3%) in non-Tibetan populations. The rs116983452-T is strongly and positively correlated with altitude and significantly associated with reduced hemoglobin concentration (p = 5.78 × 10-5), red blood cell count (p = 5.72 × 10-7) and hematocrit (p = 2.57 × 10-6). In particular, TMEM247-rs116983452 shows greater effect size and better predicts the phenotypic outcome than any EPAS1 variants in association with adaptive traits in Tibetans. Modeling the interaction between TMEM247-rs116983452 and EPAS1 variants indicates weak but statistically significant epistatic effects. Our results support that multiple variants may jointly deliver the fitness of the Tibetans on the plateau, where a complex model is needed to elucidate the adaptive evolution mechanism.

Hypoxia-induced Changes in SUMO Conjugation Affect Transcriptional Regulation Under Low Oxygen

Hypoxia occurs in pathological conditions, such as cancer, as a result of the imbalance between oxygen supply and consumption by proliferating cells. HIFs are critical molecular mediators of the physiological response to hypoxia but also regulate multiple steps of carcinogenesis including tumor progression and metastasis. Recent data support that sumoylation, the covalent attachment of the Small Ubiquitin-related MOdifier (SUMO) to proteins, is involved in the activation of the hypoxic response and the ensuing signaling cascade. To gain insights into differences of the SUMO1 and SUMO2/3 proteome of HeLa cells under normoxia and cells grown for 48 h under hypoxic conditions, we employed endogenous SUMO-immunoprecipitation in combination with quantitative mass spectrometry (SILAC). The group of proteins whose abundance was increased both in the total proteome and in the SUMO IPs from hypoxic conditions was enriched in enzymes linked to the hypoxic response. In contrast, proteins whose SUMOylation status changed without concomitant change in abundance were predominantly transcriptions factors or transcription regulators. Particularly interesting was transcription factor TFAP2A (Activating enhancer binding Protein 2 alpha), whose sumoylation decreased on hypoxia. TFAP2A is known to interact with HIF-1 and we provide evidence that deSUMOylation of TFAP2A enhances the transcriptional activity of HIF-1 under hypoxic conditions. Overall, these results support the notion that SUMO-regulated signaling pathways contribute at many distinct levels to the cellular response to low oxygen.

SUMOylation in Glioblastoma: A Novel Therapeutic Target

Protein SUMOylation is a dynamic post-translational modification which is involved in a diverse set of physiologic processes throughout the cell. Of note, SUMOylation also plays a role in the pathobiology of a myriad of cancers, one of which is glioblastoma (GBM). Accordingly, herein, we review core aspects of SUMOylation as it relates to GBM and in so doing highlight putative methods/modalities capable of therapeutically engaging the pathway for treatment of this deadly neoplasm.

Hypoxia-induced Slug SUMOylation enhances lung cancer metastasis

Background

The Slug-E-cadherin axis plays a critical role in non-small-cell lung cancers (NSCLCs) where aberrant upregulation of Slug promotes cancer metastasis. Now, the post-translational modifications of Slug and their regulation mechanisms still remain unclear in lung cancer. Hence, exploring the protein linkage map of Slug is of great interest for investigating the scenario of how Slug protein is regulated in lung cancer metastasis.

Methods

The Slug associated proteins, Ubc9 and SUMO-1, were identified using yeast two-hybrid screening; and in vitro SUMOylation assays combined with immunoprecipitation and immunoblotting were performed to explore the detail events and regulations of Slug SUMOylation. The functional effects of SUMOylation on Slug proteins were examined by EMSA, reporter assay, ChIP assay, RT-PCR, migration and invasion assays in vitro, tail vein metastatic analysis in vivo, and also evaluated the association with clinical outcome of NSCLC patients.

Results

Slug protein could interact with Ubc9 and SUMO-1 and be SUMOylated in cells. Amino acids 130–212 and 33–129 of Slug are responsible for its binding to Ubc9 and protein inhibitor of activated STAT (PIAS)y, respectively. SUMOylation could enhance the transcriptional repression activity of Slug via recruiting more HDAC1, resulting in reduced expression of downstream Slug target genes and enhanced lung cancer metastasis. In addition, hypoxia could increase Slug SUMOylation through attenuating the interactions of Slug with SENP1 and SENP2. Finally, high expression Slug and Ubc9 levels were associated with poor overall survival among NSCLC patients.

Conclusions

Ubc9/PIASy-mediated Slug SUMOylation and subsequent HDAC1 recruitment may play a crucial role in hypoxia-induced lung cancer progression, and these processes may serve as therapeutic targets for NSCLC.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0996-8) contains supplementary material, which is available to authorized users.

Post-translational modifications of transporters

Drug transporter proteins are critical to the distribution of a wide range of endogenous compounds and xenobiotics such as hormones, bile acids, peptides, lipids, sugars, and drugs. There are two classes of drug transporters- the solute carrier (SLC) transporters and ATP-binding cassette (ABC) transporters -which predominantly differ in the energy source utilized to transport substrates across a membrane barrier. Despite their hydrophobic nature and residence in the membrane bilayer, drug transporters have dynamic structures and adopt many conformations during the translocation process. Whereas there is significant literature evidence for the substrate specificity and structure-function relationship for clinically relevant drug transporters proteins, there is less of an understanding in the regulatory mechanisms that contribute to the functional expression of these proteins. Post-translational modifications have been shown to modulate drug transporter functional expression via a wide range of molecular mechanisms. These modifications commonly occur through the addition of a functional group (e.g. phosphorylation), a small protein (e.g. ubiquitination), sugar chains (e.g. glycosylation), or lipids (e.g. palmitoylation) on solvent accessible amino acid residues. These covalent additions often occur as a result of a signaling cascade and may be reversible depending on the type of modification and the intended fate of the signaling event. Here, we review the significant role in which post-translational modifications contribute to the dynamic regulation and functional consequences of SLC and ABC drug transporters and highlight recent progress in understanding their roles in transporter structure, function, and regulation.

Silencing SUMO2 promotes protection against degradation and apoptosis of nucleus pulposus cells through p53 signaling pathway in intervertebral disc degeneration

Objective: Intervertebral disc degeneration (IDD), as a common cause of back pain, is related to the promotion of cellular senescence and reduction in proliferation. Based on recent studies, small ubiquitin-related modifier (SUMO) proteins have been implicated in various biological functions. Therefore, in the present study, we investigated the effects of SUMO2 on proliferation and senescence of nucleus pulposus cells (NPCs) via mediation of p53 signaling pathway in rat models of IDD.

Methods: After the establishment of rat models of IDD for the measurement of positive expression of SUMO2/3 protein, the mRNA and protein levels of SUMO2, molecular phenotype [matrix metalloproteinase-2 (MMP-2) and hypoxia-inducible factor-1α (HIF-1α)] and p53 signaling pathway-related genes [p21, murine double minute-2 (MDM2), growth arrest and DNA-damage-inducible protein 45 α (GADD45α), cyclin-dependent kinase 2/4 (CDK2/4), and CyclinB1] were determined, followed by the detection of cell proliferation, cell cycle, apoptosis, and cell senescence.

Results: The rat models of IDD were successfully constructed. The results obtained showed that there was a higher positive expression of SUMO2/3 protein in IDD rats. Moreover, the silencing of the SUMO2 gene decreases the levels of SUMO2, p53, p21, MDM2, GADD45α, MMP-2, and HIF-1α expressions and p53 phosphorylation level while it increases the levels of CDK2/4 and CyclinB1 expressions. In addition, SUMO2 gene silencing enhances proliferation and suppresses apoptosis and cell senescence of NPCs.

Conclusion: In conclusion, SUMO2 gene silencing promotes proliferation, and inhibits the apoptosis and senescence of NPCs in rats with IDD through the down-regulation of the p53 signaling pathway. Thus, SUMO2 is a potential target in the treatment of IDD.

Ubc9 overexpression and SUMO1 deficiency blunt inflammation after intestinal ischemia/reperfusion

The intestinal epithelium constitutes a crucial defense to the potentially life-threatening effects of gut microbiota. However, due to a complex underlying vasculature, hypoperfusion and resultant tissue ischemia pose a particular risk to function and integrity of the epithelium. The small ubiquitin-like modifier (SUMO) conjugation pathway critically regulates adaptive responses to metabolic stress and is of particular significance in the gut, as inducible knockout of the SUMO-conjugating enzyme Ubc9 results in rapid intestinal epithelial disintegration. Here we analyzed the pattern of individual SUMO isoforms in intestinal epithelium and investigated their roles in intestinal ischemia/reperfusion (I/R) damage. Immunostaining revealed that epithelial SUMO2/3 expression was almost exclusively limited to crypt epithelial nuclei in unchallenged mice. However, intestinal I/R or overexpression of Ubc9 caused a remarkable enhancement of epithelial SUMO2/3 staining along the crypt-villus axis. Unexpectedly, a similar pattern was found in SUMO1 knockout mice. Ubc9 transgenic mice, but also SUMO1 knockout mice were protected from I/R injury as evidenced by better preserved barrier function and blunted inflammatory responses. PCR array analysis of microdissected villus-tip epithelia revealed a specific epithelial contribution to reduced inflammatory responses in Ubc9 transgenic mice, as key chemotactic signaling molecules such as IL17A were significantly downregulated. Together, our data indicate a critical role particularly of the SUMO2/3 isoforms in modulating responses to I/R and provide the first evidence that SUMO1 deletion activates a compensatory process that protects from ischemic damage.

Small ubiquitin-like modifier 1 modification of pyruvate kinase M2 promotes aerobic glycolysis and cell proliferation in A549 human lung cancer cells

Objective

Lung cancer is the leading cause of cancer-related death worldwide. Aerobic glycolysis is considered the seventh hallmark of cancer. The M2 isoform of pyruvate kinase (PKM2) is an important rate-limiting enzyme in glycolytic pathway, and is strongly expressed in several types of cancer. Thus, understanding the underlying mechanisms of regulation of PKM2 is of great value for targeted therapy for lung cancer.

Patients and methods

Seventy-three lung adenocarcinoma patients were analyzed in our study. The expression levels of PKM2 were analyzed by immunohistochemistry on tissues. The effect of small ubiquitin-like modifier 1 (SUMO1) on PKM2 expression was investigated using Western blot assay and quantitative polymerase chain reaction. PKM2 SUMO1 modification was determined by in vitro and in vivo SUMOylation assays. ¹⁸F-deoxyglucose uptake and lactate production measurements were conducted to research the levels of glycolysis. The level of oxidative phosphorylation in cells was determined by cellular oxygen consumption rate measurements. Cell proliferation assays were carried out to confirm the growth ability of tumor cells.

Results

PKM2 was overexpressed in lung adenocarcinoma patients based on immunohistochemical staining. Patients with high PKM2 expression had reduced overall survival rate (P=0.017) and disease-free survival rate (P=0.027) compared with those with low PKM2 expression. SUMO1 promoted PKM2-dependent glycolysis. Western blotting analysis showed that SUMO1 knockdown in A549 cells led to a significant decrease in PKM2 protein expression. PKM2 could be covalently modified by SUMO1 at K336 (Lys336) site. SUMO1 modification of PKM2 at Lys-336 site increased glycolysis and promoted its cofactor functions. Moreover, PKM2 SUMO1 modification promoted the proliferation of A549 cells in vitro.

Conclusion

This information is important in elucidating a new mechanism of regulation of PKM2, and suggested that SUMO1 modification of PKM2 could be a potential therapeutic target in lung cancer.

The post-translational modification, SUMOylation, and cancer (Review)

SUMOylation is a reversible post-translational modification which has emerged as a crucial molecular regulatory mechanism, involved in the regulation of DNA damage repair, immune responses, carcinogenesis, cell cycle progression and apoptosis. Four SUMO isoforms have been identified, which are SUMO1, SUMO2/3 and SUMO4. The small ubiquitin-like modifier (SUMO) pathway is conserved in all eukaryotes and plays pivotal roles in the regulation of gene expression, cellular signaling and the maintenance of genomic integrity. The SUMO catalytic cycle includes maturation, activation, conjugation, ligation and de-modification. The dysregulation of the SUMO system is associated with a number of diseases, particularly cancer. SUMOylation is widely involved in carcinogenesis, DNA damage response, cancer cell proliferation, metastasis and apoptosis. SUMO can be used as a potential therapeutic target for cancer. In this review, we briefly outline the basic concepts of the SUMO system and summarize the involvement of SUMO proteins in cancer cells in order to better understand the role of SUMO in human disease.

SUMO Signaling by Hypoxic Inactivation of SUMO-Specific Isopeptidases

Post-translational modification of proteins with ubiquitin-like SUMO modifiers is a tightly regulated and highly dynamic process. The SENP family of SUMO-specific isopeptidases comprises six cysteine proteases. They are instrumental in counterbalancing SUMO conjugation, but their regulation is not well understood. We demonstrate that in hypoxic cell extracts, the catalytic activity of SENP family members, in particular SENP1 and SENP3, is inhibited in a rapid and fully reversible process. Comparative mass spectrometry from normoxic and hypoxic cells defines a subset of hypoxia-induced SUMO1 targets, including SUMO ligases RanBP2 and PIAS2, glucose transporter 1, and transcriptional regulators. Among the most strongly induced targets, we identified the transcriptional co-repressor BHLHE40, which controls hypoxic gene expression programs. We provide evidence that SUMOylation of BHLHE40 is reversed by SENP1 and contributes to transcriptional repression of the metabolic master regulator gene PGC-1α. We propose a pathway that connects oxygen-controlled SENP activity to hypoxic reprogramming of metabolism.

The Roles of SUMO in Metabolic Regulation

Protein modification with the small ubiquitin-related modifier (SUMO) can affect protein function, enzyme activity, protein-protein interactions, protein stability, protein targeting and cellular localization. SUMO influences the function and regulation of metabolic enzymes within pathways, and in some cases targets entire metabolic pathways by affecting the activity of transcription factors or by facilitating the translocation of entire metabolic pathways to subcellular compartments. SUMO modification is also a key component of nutrient- and metabolic-sensing mechanisms that regulate cellular metabolism. In addition to its established roles in maintaining metabolic homeostasis, there is increasing evidence that SUMO is a key factor in facilitating cellular stress responses through the regulation and/or adaptation of the most fundamental metabolic processes, including energy and nucleotide metabolism. This review focuses on the role of SUMO in cellular metabolism and metabolic disease.

Topotecan is a potent inhibitor of SUMOylation in glioblastoma multiforme and alters both cellular replication and metabolic programming

Protein SUMOylation is a dynamic post-translational modification shown to be involved in a diverse set of physiologic processes throughout the cell. SUMOylation has also been shown to play a role in the pathobiology of myriad cancers, one of which is glioblastoma multiforme (GBM). As such, the clinical significance and therapeutic utility offered via the selective control of global SUMOylation is readily apparent. There are, however, relatively few known/effective inhibitors of global SUMO-conjugation. Herein we describe the identification of topotecan as a novel inhibitor of global SUMOylation. We also provide evidence that inhibition of SUMOylation by topotecan is associated with reduced levels of CDK6 and HIF-1α, as well as pronounced changes in cell cycle progression and cellular metabolism, thereby highlighting its putative role as an adjuvant therapy in defined GBM patient populations.

Spatial Organization of Metabolic Enzyme Complexes in Cells

The organization of metabolic multienzyme complexes has been hypothesized to benefit metabolic processes and provide a coordinated way for the cell to regulate metabolism. Historically, their existence has been supported by various in vitro techniques. However, it is only recently that the existence of metabolic complexes inside living cells has come to light to corroborate this long-standing hypothesis. Indeed, subcellular compartmentalization of metabolic enzymes appears to be widespread and highly regulated. On the other hand, it is still challenging to demonstrate the functional significance of these enzyme complexes in the context of the cellular milieu. In this review, we discuss the current understanding of metabolic enzyme complexes by primarily focusing on central carbon metabolism and closely associated metabolic pathways in a variety of organisms, as well as their regulation and functional contributions to cells.

ROS homeostasis and metabolism: a critical liaison for cancer therapy

Evidence indicates that hypoxia and oxidative stress can control metabolic reprogramming of cancer cells and other cells in tumor microenvironments and that the reprogrammed metabolic pathways in cancer tissue can also alter the redox balance. Thus, important steps toward developing novel cancer therapy approaches would be to identify and modulate critical biochemical nodes that are deregulated in cancer metabolism and determine if the therapeutic efficiency can be influenced by changes in redox homeostasis in cancer tissues. In this review, we will explore the molecular mechanisms responsible for the metabolic reprogramming of tumor microenvironments, the functional modulation of which may disrupt the effects of or may be disrupted by redox homeostasis modulating cancer therapy.

Prostaglandin E2 (PGE2) promotes proliferation and invasion by enhancing SUMO-1 activity via EP4 receptor in endometrial cancer

Prostaglandin E2 (PGE2), a derivative of arachidonic acid, has been identified as a tumorigenic factor in many cancers in recent studies. Prostaglandin E synthase 2 (PTGES2) is an enzyme that in humans is encoded by the PTGES2 gene located on chromosome 9, and it synthesizes PGE2 in human cells. In our study, we selected 119 samples from endometrial cancer patients, with 50 normal endometrium tissue samples as controls, in which we examined the expression of PTGES2. Both immunohistochemistry (IHC) and Western blot analyses demonstrated that synthase PTGES2, which is required for PGE2 synthesis, was highly expressed in endometrium cancer tissues compared with normal endometrium. Stable PTGES2-shRNA transfectants were generated in Ishikawa and Hec-1B endometrial cancer cell lines, and transfection efficiencies were confirmed by RT-PCR and Western blot analyses. We found that PGE2 promoted proliferation and invasion of cells in Ishikawa and Hec-1B cells by cell counting kit-8 tests (CCK8) and transwell assays, respectively. PGE2 stimulation enhanced the expression of SUMO-1, via PGE2 receptor subtype 4 (EP4). Further analysis implicated the Wnt/β-catenin signaling pathway function as the major mediator of EP4 and SUMO-1. The increase in SUMO-1 activity prompted the SUMOlyation of target proteins which may be involved in proliferation and invasion. These findings suggest SUMO-1 and EP4 as two potential targets for new therapeutic or prevention strategies for endometrial cancers.

Intense Resistance Exercise Promotes the Acute and Transient Nuclear Translocation of Small Ubiquitin-Related Modifier (SUMO)-1 in Human Myofibres

Protein sumoylation is a posttranslational modification triggered by cellular stress. Because general information concerning the role of small ubiquitin-related modifier (SUMO) proteins in adult skeletal muscle is sparse, we investigated whether SUMO-1 proteins will be subjected to time-dependent changes in their subcellular localization in sarcoplasmic and nuclear compartments of human type I and II skeletal muscle fibers in response to acute stimulation by resistance exercise (RE). Skeletal muscle biopsies were taken at baseline (PRE), 15, 30, 60, 240 min and 24 h post RE from 6 male subjects subjected to a single bout of one-legged knee extensions. SUMO-1 localization was determined via immunohistochemistry and confocal laser microscopy. At baseline SUMO-1 was localized in perinuclear regions of myonuclei. Within 15 and up to 60 min post exercise, nuclear SUMO-1 localization was significantly increased (p < 0.01), declining towards baseline levels within 240 min post exercise. Sarcoplasmic SUMO-1 localization was increased at 15 min post exercise in type I and up to 30 min post RE in type II myofibres. The changing localization of SUMO-1 proteins acutely after intense muscle contractions points to a role for SUMO proteins in the acute regulation of the skeletal muscle proteome after exercise.

Identification and detoxification of glycolaldehyde, an unattended bioethanol fermentation inhibitor

Although there have been approximately 60 chemical compounds identified as potent fermentation inhibitors in lignocellulose hydrolysate, our research group recently discovered glycolaldehyde as a key fermentation inhibitor during second generation biofuel production. Accordingly, we have developed a yeast S. cerevisiae strain exhibiting tolerance to glycolaldehyde. During this glycolaldehyde study, we established novel approaches for rational engineering of inhibitor-tolerant S. cerevisiae strains, including engineering redox cofactors and engineering the SUMOylation pathway. These new technical dimensions provide a novel platform for engineering S. cerevisiae strains to overcome one of the key barriers for industrialization of lignocellulosic ethanol production. As such, this review discusses novel biochemical insight of glycolaldehyde in the context of the biofuel industry.

Screening and identification of SUMP-proteins in sub-acute treatment with diazinon

OBJECTIVES

Small ubiquitin-like modifiers (SUMOs) are a family of ubiquitin-related, proteins that are involved in a wide variety of signaling pathways. SUMOylation, as a vital post translational modification, regulate protein function in manycellular processes. Diazinon (DZN), an organophosphate insecticide, causses oxidative stress and subsequently programmed cell death in different tissues. The aim of this study was to evaluate the role and pattern of SUMO modificationas a defense mechanism against stress oxidative, in the heart tissuesof the DZN treated rats.

MATERIALS AND METHODS

Diazinon (15 mg/kg/day), corn oil (control) were administered via gavageto male Wistar rats for four weeks. SUMO1 antibody was covalently crosslinked to protein A/G agarose. heart tissue lysate were added to agarosebeads, After isolation of target proteins(SUMO1- protein)SDS-PAGE gel electrophoresis was performed. Protein bands were identified using MALDI-TOF/TOF and MASCOT). Fold change of (DZN/Ctrl) separated proteins was evaluated using UVband software (UVITEC, UK).

RESULTS

Our result showed that subacute exposure to DZN increased SUMOylationoffour key proteins involved in the metabolic process including; Acyl-CoA dehydrogenase, creatine kinase, glyceraldehyde-3-phosphate dehydrogenase and ATP synthase, in the heart tissue of animals. A probability value of less than 0.05 was considered significant (P<0.05).

CONCLUSION

It seems that protein SUMOylation provides a safeguard mechanism against DZN Toxicity.

Glucose Starvation in Cardiomyocytes Enhances Exosome Secretion and Promotes Angiogenesis in Endothelial Cells

Cardiomyocytes (CMs) and endothelial cells (ECs) have an intimate anatomical relationship that is essential for maintaining normal development and function in the heart. Little is known about the mechanisms that regulate cardiac and endothelial crosstalk, particularly in situations of acute stress when local active processes are required to regulate endothelial function. We examined whether CM-derived exosomes could modulate endothelial function. Under conditions of glucose deprivation, immortalized H9C2 cardiomyocytes increase their secretion of exosomes. CM-derived exosomes are loaded with a broad repertoire of miRNA and proteins in a glucose availability-dependent manner. Gene Ontology (GO) analysis of exosome cargo molecules identified an enrichment of biological process that could alter EC activity. We observed that addition of CM-derived exosomes to ECs induced changes in transcriptional activity of pro-angiogenic genes. Finally, we demonstrated that incubation of H9C2-derived exosomes with ECs induced proliferation and angiogenesis in the latter. Thus, exosome-mediated communication between CM and EC establishes a functional relationship that could have potential implications for the induction of local neovascularization during acute situations such as cardiac injury.

Chronic hyperglycemia downregulates GLP-1 receptor signaling in pancreatic β-cells via protein kinase A

Objective

Glucagon-like peptide 1 (GLP-1) enhances insulin secretion and protects β-cell mass. Diabetes therapies targeting the GLP-1 receptor (GLP-1R), expressed in numerous tissues, have diminished dose-response in patients with type 2 diabetes compared with healthy human controls. The aim of this study was to determine the mechanistic causes underlying the reduced efficacy of GLP-1R ligands.

Methods

Using primary mouse islets and the β-cell line MIN6, outcomes downstream of the GLP-1R were analyzed: Insulin secretion; phosphorylation of the cAMP-response element binding protein (CREB); cAMP responses. Signaling systems were studied by immunoblotting and qRT-PCR, and PKA activity was assayed. Cell surface localization of the GLP-1R was studied by confocal microscopy using a fluorescein-tagged exendin-4 and GFP-tagged GLP-1R.

Results

Rodent β-cells chronically exposed to high glucose had diminished responses to GLP-1R agonists including: diminished insulin secretory response; reduced phosphorylation of (CREB); impaired cAMP response, attributable to chronically increased cAMP levels. GLP-1R signaling systems were affected by hyperglycemia with increased expression of mRNAs encoding the inducible cAMP early repressor (ICER) and adenylyl cyclase 8, reduced PKA activity due to increased expression of the PKA-RIα subunit, reduced GLP-1R mRNA expression and loss of GLP-1R from the cell surface. To specifically examine the loss of GLP-1R from the plasma membrane a GLP-1R-GFP fusion protein was employed to visualize subcellular localization. Under low glucose conditions or when PKA activity was inhibited, GLP-1R-GFP was found at the plasma membrane. Conversely high glucose, expression of a constitutively active PKA subunit, or exposure to exendin-4 or forskolin led to GLP-1R-GFP internalization. Mutation of serine residue 301 of the GLP-1R abolished the glucose-dependent loss of the receptor from the plasma membrane. This was associated with a loss of an interaction between the receptor and the small ubiquitin-related modifier (SUMO), an interaction that was found to be necessary for internalization of the receptor.

Conclusions

These data show that glucose acting, at least in part, via PKA leads to the loss of the GLP-1R from the cell surface and an impairment of GLP-1R signaling, which may underlie the reduced clinical efficacy of GLP-1R based therapies in individuals with poorly controlled hyperglycemia.

Analysis of changes in SUMO-2/3 modification during breast cancer progression and metastasis

SUMOylation is an essential posttranslational modification and regulates many cellular processes. Dysregulation of SUMOylation plays a critical role in metastasis, yet how its perturbation affects this lethal process of cancer is not well understood. We found that SUMO-2/3 modification is greatly up-regulated in metastatic breast cancer cells compared with nonmetastatic control cells. To identify proteins differentially modified by SUMO-2/3 between metastatic and nonmetastatic cells, we established a method in which endogenous SUMO-2/3 conjugates are labeled by stable isotope labeling by amino acids in cell culture (SILAC), immunopurified by SUMO-2/3 monoclonal antibodies and epitope-peptide elution, and analyzed by quantitative mass spectrometry. We identified 66 putative SUMO-2/3-conjugated proteins, of which 15 proteins show a significant increase/decrease in SUMO-2/3 modification in metastatic cells. Targets with altered SUMOylation are involved in cell cycle, migration, inflammation, glycolysis, gene expression, and SUMO/ubiquitin pathways, suggesting that perturbations of SUMO-2/3 modification might contribute to metastasis by affecting these processes. Consistent with this, up-regulation of PML SUMO-2/3 modification corresponds to an increased number of PML nuclear bodies (PML-NBs) in metastatic cells, whereas up-regulation of global SUMO-2/3 modification promotes 3D cell migration. Our findings provide a foundation for further investigating the effects of SUMOylation on breast cancer progression and metastasis.

A monoclonal antibody against the human SUMO-1 protein obtained by immunization with recombinant protein and CpG-DNA-liposome complex

Post-translational modification regulated by conjugation of a small ubiquitin-like modifier (SUMO) is involved in various cellular processes. In this study, we expressed and purified recombinant human SUMO-1 (hSUMO-1). BALB/c mice were immunized with a complex of hSUMO-1 protein and Lipoplex(O) to produce hSUMO-1-specific antibodies. Using conventional hybridoma technology, we obtained four hybridoma clones derived from the mouse with the highest antibody titer against hSUMO-1. Based on Western blot analysis, our hSUMO-1 monoclonal antibody specifically recognizes hSUMO-1, but not other SUMO proteins. These results support that the anti-hSUMO-1 monoclonal antibody produced with the aid of Lipoplex(O) adjuvant is specific and that Lipoplex(O) is useful for development of monoclonal antibodies against recombinant protein. In addition, we analyzed human tissues to examine the distribution of hSUMO-1. Higher expression of hSUMO-1 was detected in normal adrenal gland, esophagus, pancreas, liver, stomach, kidney, and uterus than in corresponding cancer tissues, suggesting a tumor suppressive function of hSUMO-1.

EAF2 suppresses hypoxia-induced factor 1α transcriptional activity by disrupting its interaction with coactivator CBP/p300

Previous studies revealed that the potential tumor suppressor EAF2 binds to and stabilizes pVHL, suggesting that EAF2 may function by disturbing the hypoxia signaling pathway. However, the extent to which EAF2 affects hypoxia and the mechanisms underlying this activity remain largely unknown. In this study, we found that EAF2 is a hypoxia response gene harboring the hypoxia response element (HRE) in its promoter. By taking advantage of the pVHL-null cell lines RCC4 and 786-O, we demonstrated that hypoxia-induced factor 1α (HIF-1α), but not HIF-2α, induced EAF2 under hypoxia. Subsequent experiments showed that EAF2 bound to and suppressed HIF-1α but not HIF-2α transactivity. In addition, we observed that EAF2 inhibition of HIF-1α activity resulted from the disruption of p300 recruitment and that this occurred independently of FIH-1 (factor inhibiting HIF-1) and Sirt1. Furthermore, we found that EAF2 protected cells against hypoxia-induced cell death and inhibited cellular uptake of glucose under hypoxic conditions, suggesting that EAF2 indeed may act by modulating the hypoxia-signaling pathway. Our findings not only uncover a unique feedback regulation loop between EAF2 and HIF-1α but also provide a novel insight into the mechanism of EAF2 tumor suppression.

Spatial reorganization of Saccharomyces cerevisiae enolase to alter carbon metabolism under hypoxia

Hypoxia has critical effects on the physiology of organisms. In the yeast Saccharomyces cerevisiae, glycolytic enzymes, including enolase (Eno2p), formed cellular foci under hypoxia. Here, we investigated the regulation and biological functions of these foci. Focus formation by Eno2p was inhibited temperature independently by the addition of cycloheximide or rapamycin or by the single substitution of alanine for the Val22 residue. Using mitochondrial inhibitors and an antioxidant, mitochondrial reactive oxygen species (ROS) production was shown to participate in focus formation. Focus formation was also inhibited temperature dependently by an SNF1 knockout mutation. Interestingly, the foci were observed in the cell even after reoxygenation. The metabolic turnover analysis revealed that [U-(13)C]glucose conversion to pyruvate and oxaloacetate was accelerated in focus-forming cells. These results suggest that under hypoxia, S. cerevisiae cells sense mitochondrial ROS and, by the involvement of SNF1/AMPK, spatially reorganize metabolic enzymes in the cytosol via de novo protein synthesis, which subsequently increases carbon metabolism. The mechanism may be important for yeast cells under hypoxia, to quickly provide both energy and substrates for the biosynthesis of lipids and proteins independently of the tricarboxylic acid (TCA) cycle and also to fit changing environments.

The impact of biosampling procedures on molecular data interpretation

The separation between biological and technical variation without extensive use of technical replicates is often challenging, particularly in the context of different forms of protein and peptide modifications. Biosampling procedures in the research laboratory are easier to conduct within a shorter time frame and under controlled conditions as compared with clinical sampling, with the latter often having issues of reproducibility. But is the research laboratory biosampling really less variable? Biosampling introduces within minutes rapid tissue-specific changes in the cellular microenvironment, thus inducing a range of different pathways associated with cell survival. Biosampling involves hypoxia and, depending on the circumstances, hypothermia, circumstances for which there are evolutionarily conserved defense strategies in the range of species and also are relevant for the range of biomedical conditions. It remains unclear to what extent such adaptive processes are reflected in different biosampling procedures or how important they are for the definition of sample quality. Lately, an increasing number of comparative studies on different biosampling approaches, post-mortem effects and pre-sampling biological state, have investigated such immediate early biosampling effects. Commonalities between biosampling effects and a range of ischemia/reperfusion- and hypometabolism/anoxia-associated biological phenomena indicate that even small variations in post-sampling time intervals are likely to introduce a set of nonrandom and tissue-specific effects of experimental importance (both in vivo and in vitro). This review integrates the information provided by these comparative studies and discusses how an adaptive biological perspective in biosampling procedures may be relevant for sample quality issues.

Role of SUMO-specific protease 2 in reprogramming cellular glucose metabolism

Most cancer cells exhibit a shift in glucose metabolic strategy, displaying increased glycolysis even with adequate oxygen supply. SUMO-specific proteases (SENPs) de-SUMOylate substrates including HIF1α and p53,two key regulators in cancer glucose metabolism, to regulate their activity, stability and subcellular localization. However, the role of SENPs in tumor glucose metabolism remains unclear. Here we report that SUMO-specific protease 2 (SENP2) negatively regulates aerobic glycolysis in MCF7 and MEF cells. Over-expression of SENP2 reduces the glucose uptake and lactate production, increasing the cellular ATP levels in MCF7 cells, while SENP2 knockout MEF cells show increased glucose uptake and lactate production along with the decreased ATP levels. Consistently, the MCF7 cells over-expressing SENP2 exhibit decreased expression levels of key glycolytic enzymes and an increased rate of glucose oxidation compared with control MCF7 cells, indicating inhibited glycolysis but enhanced oxidative mitochondrial respiration. Moreover, SENP2 over-expressing MCF7 cells demonstrated a reduced amount of phosphorylated AKT, whereas SENP2 knockout MEFs exhibit increased levels of phosphorylated AKT. Furthermore, inhibiting AKT phosphorylation by LY294002 rescued the phenotype induced by SENP2 deficiency in MEFs. In conclusion, SENP2 represses glycolysis and shifts glucose metabolic strategy, in part through inhibition of AKT phosphorylation. Our study reveals a novel function of SENP2 in regulating glucose metabolism.

A dynamic model of the hypoxia-inducible factor 1α (HIF-1α) network

Activation of the hypoxia-inducible factor (HIF) pathway is a critical step in the transcriptional response to hypoxia. Although many of the key proteins involved have been characterised, the dynamics of their interactions in generating this response remain unclear. In the present study, we have generated a comprehensive mathematical model of the HIF-1α pathway based on core validated components and dynamic experimental data, and confirm the previously described connections within the predicted network topology. Our model confirms previous work demonstrating that the steps leading to optimal HIF-1α transcriptional activity require sequential inhibition of both prolyl- and asparaginyl-hydroxylases. We predict from our model (and confirm experimentally) that there is residual activity of the asparaginyl-hydroxylase FIH (factor inhibiting HIF) at low oxygen tension. Furthermore, silencing FIH under conditions where prolyl-hydroxylases are inhibited results in increased HIF-1α transcriptional activity, but paradoxically decreases HIF-1α stability. Using a core module of the HIF network and mathematical proof supported by experimental data, we propose that asparaginyl hydroxylation confers a degree of resistance upon HIF-1α to proteosomal degradation. Thus, through in vitro experimental data and in silico predictions, we provide a comprehensive model of the dynamic regulation of HIF-1α transcriptional activity by hydroxylases and use its predictive and adaptive properties to explain counter-intuitive biological observations.

Protein SUMOylation, an emerging pathway in amyotrophic lateral sclerosis

The covalent attachment of SUMO proteins (small ubiquitin-like modifier) to specific proteins or SUMOylation regulates their functional properties in the nucleus and cytoplasm of neurons. Recent studies reported dysfunction of the SUMO pathway in molecular and cellular abnormalities associated with amyotrophic lateral sclerosis (ALS). Furthermore, several observations support a direct role for SUMOylation in diverse pathogenic mechanisms involved in ALS, such as response to hypoxia, oxidative stress, glutamate excitotoxicity and proteasome impairment. Recent results also suggest that SUMO modifications of superoxide dismutase 1, transactive response DNA-binding protein 43, CTE (COOH terminus of EAAT2) (proteolytic C-terminal fragment of the glutamate transporter excitatory amino acid transporter 2, EAAT2) and proteins regulating the turnover of ALS-related proteins can participate in the pathogenesis of ALS. Moreover, the fused in sarcoma (FUS) gene, mutated in ALS, encodes a protein with a SUMO E3 ligase activity. In this review, we summarize the functioning of the SUMO pathway in normal conditions and in response to stresses, its action on ALS-related proteins and discuss the need for further research on this pathway in ALS.