Hypoxia regulates beta-enolase and pyruvate kinase-M promoters by modulating Sp1/Sp3 binding to a conserved GC element

Hypoxic microenvironment in cancer: molecular mechanisms and therapeutic interventions

Having a hypoxic microenvironment is a common and salient feature of most solid tumors. Hypoxia has a profound effect on the biological behavior and malignant phenotype of cancer cells, mediates the effects of cancer chemotherapy, radiotherapy, and immunotherapy through complex mechanisms, and is closely associated with poor prognosis in various cancer patients. Accumulating studies have demonstrated that through normalization of the tumor vasculature, nanoparticle carriers and biocarriers can effectively increase the oxygen concentration in the tumor microenvironment, improve drug delivery and the efficacy of radiotherapy. They also increase infiltration of innate and adaptive anti-tumor immune cells to enhance the efficacy of immunotherapy. Furthermore, drugs targeting key genes associated with hypoxia, including hypoxia tracers, hypoxia-activated prodrugs, and drugs targeting hypoxia-inducible factors and downstream targets, can be used for visualization and quantitative analysis of tumor hypoxia and antitumor activity. However, the relationship between hypoxia and cancer is an area of research that requires further exploration. Here, we investigated the potential factors in the development of hypoxia in cancer, changes in signaling pathways that occur in cancer cells to adapt to hypoxic environments, the mechanisms of hypoxia-induced cancer immune tolerance, chemotherapeutic tolerance, and enhanced radiation tolerance, as well as the insights and applications of hypoxia in cancer therapy.

Hypoxia- and Inflammation-Related Transcription Factor SP3 May Be Involved in Platelet Activation and Inflammation in Intracranial Hemorrhage

The purpose of this study was to identify the biomarkers implicated in the development of intracranial hemorrhage (ICH) and potential regulatory pathways. In the transcriptomic data for patients with ICH, we identified DEmiRNAs and DEmRNAs related to hypoxia, inflammation, and their transcription factors (TFs). An ICH-based miRNA-TF-mRNA regulatory network was thus constructed, and four biomarkers (TIMP1, PLAUR, DDIT3, and CD40) were screened for their association with inflammation or hypoxia by machine learning. Following this, SP3 was found to be a transcription factor involved in hypoxia and inflammation, which regulates TIMP1 and PLAUR. From the constructed miRNA-TF-mRNA regulatory network, we identified three axes, hsa-miR-940/RUNX1/TIMP1, hsa-miR-571/SP3/TIMP1, and hsa-miR-571/SP3/PLAUR, which may be involved in the development of ICH. Upregulated TIMP1 and PLAUR were validated in an independent clinical cohort 3 days after ICH onset. According to Gene Set Enrichment Analysis (GSEA), SP3 was discovered to be important in interleukin signaling and platelet activation for hemostasis. Transcription factor SP3 associated with hypoxia or inflammation plays an important role in development of ICH. This study provides potential targets for monitoring the severity of inflammation and hypoxia in patients with ICH.

Metabolic Phenotype of Daphnia Under Hypoxia: Macroevolution, Microevolution, and Phenotypic Plasticity

Daphnia is a freshwater crustacean that is able to upregulate hemoglobin (Hb) in response to hypoxia, imparting a red color. We combine multiple field surveys across season with a lab experiment to evaluate changes in the metabolic phenotype of Daphnia in relation to environmental hypoxia. Looking at the zooplankton community, we found that D. pulicaria was restricted to lakes with a hypoxic hypolimnion. Comparing D. pulicaria with different amounts of Hb, red animals showed higher mRNA levels for several Hb genes, whereas most glycolytic genes showed red/pale differences of less than 50%. We also observed seasonal changes in the metabolic phenotype that differed between red and pale animals. Hb was upregulated early in the season in hypoxic lakes, and a relationship between Hb and lactate dehydrogenase only emerged later in the season in a temporal pattern that was lake specific. To evaluate whether these differences were due to specific lake environments or microevolutionary differences, we tested the induction of genes under controlled hypoxia in isofemale lines from each of four lakes. We found a strong response to 18 h hypoxia exposure in both Hb and lactate dehydrogenase mRNA, although the magnitude of the acute response was greater than the steady state differences in mRNA levels between pale and red Daphnia. The baseline expression of Hb and lactate dehydrogenase also varied between isofemale lines with different lake origins. These results, in combination with comparison of glycogen measurements, suggests that Hb functions primarily to facilitate oxygen delivery, mitigating systemic hypoxia, rather than an oxygen store. The combination of lab and field studies suggest that the metabolic phenotype of the animal is influenced by both microevolutionary differences (within and between lakes) as well as the spatial and temporal environmental heterogeneity of the lakes. The differences between Daphnia species, and the unexpected lack of hypoxia sensitivity of select glycolytic genes provide evidence of macroevolutionary differences in metabolic strategies to cope with hypoxia.

Identification and functional characterization of the siRNA pathway in Taenia crassiceps by silencing Enolase A

A gene silencing procedure on cysticerci of the taeniid cestode Taenia crassiceps is described. This is the first time this technique is reported in this species that is widely used as an animal model for human cysticercosis. Genome database searches were performed in order to find out if relevant genes involved in gene silencing and non-coding RNA processing, Argonaute and Dicer (AGO and Dcr) are present in T. crassiceps. We found three AGO and two Dcr orthologues that were designed TcAGO1, Tc2 and Tc3, as well as TcDcr1 and TcDcr2. In order to elucidate the evolutionary relationships of T. crassiceps TcAGO and TcDcr genes, separate phylogenetic analyses were carried out for each, including AGO and Dcr orthologues of other 20 platyhelminthes. Our findings showed a close phylogenetic relationship of TcAGO and TcDcr with those previously described for Echinococcus spp. Our RT-PCR studies demonstrated expression of all TcAGO and TcDcr orthologues. Our results show that the gene silencing machinery in T. crassiceps is functionally active by inducing silencing of TcEnoA (∼90%). These results clearly show that gene silencing using siRNAs can be used as a molecular methodology to study gene function in taeniid cestodes.

Potential role for pyruvate kinase M2 in the regulation of murine cardiac glycolytic flux during in vivo chronic hypoxia

Carbohydrate metabolism in heart failure shares similarities to that following hypoxic exposure, and is thought to maintain energy homoeostasis in the face of reduced O₂ availability. As part of these in vivo adaptations during sustained hypoxia, the heart up-regulates and maintains a high glycolytic flux, but the underlying mechanism is still elusive. We followed the cardiac glycolytic responses to a chronic hypoxic (CH) intervention using [5-³H]-glucose labelling in combination with detailed and extensive enzymatic and metabolomic approaches to provide evidence of the underlying mechanism that allows heart survivability. Following 3 weeks of in vivo hypoxia (11% oxygen), murine hearts were isolated and perfused in a retrograde mode with function measured via an intraventricular balloon and glycolytic flux quantified using [5-³H]-glucose labelling. At the end of perfusion, hearts were flash-frozen and central carbon intermediates determined via liquid chromatography tandem mass spectrometry (LC-MS/MS). The maximal activity of glycolytic enzymes considered rate-limiting was assessed enzymatically, and protein abundance was determined using Western blotting. Relative to normoxic hearts, CH increased ex vivo cardiac glycolytic flux 1.7-fold with no effect on cardiac function. CH up-regulated cardiac pyruvate kinase (PK) flux 3.1-fold and cardiac pyruvate kinase muscle isoenzyme M2 (PKM2) protein content 1.4-fold compared with normoxic hearts. CH also augmented cardiac pentose phosphate pathway (PPP) flux, reflected by higher ribose-5-phosphate (R5P) content. These findings support an increase in the covalent (protein expression) and allosteric (flux) control of PKM2 as being central to the sustained up-regulation of the glycolytic flux in the chronically hypoxic heart.

MP-Pt(IV): A MAOB-Sensitive Mitochondrial-Specific Prodrug for Treating Glioblastoma

We have previously reported the in vitro and in vivo efficacy of N,N-bis(2-chloroethyl)-2-(1-methyl-1,2,3,6-tetrahydropyridin-4-yl)propenamide (MP-MUS), a prodrug that targeted the mitochondria of glioblastoma (GBM). The mitochondrial enzyme, monoamine oxidase B (MAOB), is highly expressed in GBM and oxidizes an uncharged methyl-tetrahydropyridine (MP-) moiety into the mitochondrially targeted cationic form, methyl-pyridinium (P⁺-). Coupling this MAOB-sensitive group to a nitrogen mustard produced a prodrug that damaged GBM mitochondria and killed GBM cells. Unfortunately, the intrinsic reactivity of the nitrogen mustard group and low solubility of MP-MUS precluded clinical development. In our second-generation prodrug, MP-Pt(IV), we coupled the MP group to an unreactive cisplatin precursor. The enzymatic conversion of MP-Pt(IV) to P⁺-Pt(IV) was tested using recombinant human MAOA and rhMAOB. The generation of cisplatin from Pt(IV) by ascorbate was studied optically and using mass spectroscopy. Efficacy toward primary GBM cells and tumors was studied in vitro and in an intracranial patient-derived xenograft mice GBM model. Our studies demonstrate that MP-Pt(IV) is selectively activated by MAOB. MP-Pt(IV) is highly toxic toward GBM cells in vitro MP-Pt(IV) toxicity against GBM is potentiated by elevating mitochondrial ascorbate and can be arrested by MAOB inhibition. In in vitro studies, sublethal MP-Pt(IV) doses elevated mitochondrial MAOB levels in surviving GBM cells. MP-Pt(IV) is a potent chemotherapeutic in intracranial patient-derived xenograft mouse models of primary GBM and potentiates both temozolomide and temozolomide-chemoradiation therapies. MP-Pt(IV) was well tolerated and is highly effective against GBM in both in vitro and in vivo models.

Hypoxia in chronic kidney disease: towards a paradigm shift?

Chronic kidney disease (CKD) is defined as an alteration of kidney structure and/or function lasting for >3 months [1]. CKD affects 10% of the general adult population and is responsible for large healthcare costs [2]. Since the end of the last century, the role of hypoxia in CKD progression has controversially been discussed. To date, there is evidence of the presence of hypoxia in late-stage renal disease, but we lack time-course evidence, stage correlation and also spatial co-localization with fibrotic lesions to ensure its causative role. The classical view of hypoxia in CKD progression is that it is caused by peritubular capillary alterations, renal anaemia and increased oxygen consumption regardless of the primary injury. In this classical view, hypoxia is assumed to further induce pro-fibrotic and pro-inflammatory responses, as well as oxidative stress, leading to CKD worsening as part of a vicious circle. However, recent investigations tend to question this paradigm, and both the presence of hypoxia and its role in CKD progression are still not clearly demonstrated. Hypoxia-inducible factor (HIF) is the main transcriptional regulator of the hypoxia response. Genetic HIF modulation leads to variable effects on CKD progression in different murine models. In contrast, pharmacological modulation of the HIF pathway [i.e. by HIF hydroxylase inhibitors (HIs)] appears to be generally protective against fibrosis progression experimentally. We here review the existing literature on the role of hypoxia, the HIF pathway and HIF HIs in CKD progression and summarize the evidence that supports or rejects the hypoxia hypothesis, respectively.

The synthetic oleanane triterpenoid CDDO-Me binds and inhibits pyruvate kinase M2

BACKGROUND

The M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2) is one of the key components in the Warburg effect, and an important regulator of cancer cell metabolism. Elevated PKM2 expression is a hallmark of numerous tumor types, making it a promising target for cancer therapy.

METHODS

Migration of H1299 lung tumor cells treated with synthetic oleanane triterpenoid derivatives CDDO-Me and CDDO-Im was monitored using scratch and transwell assays. Direct binding and inhibition of PKM2 activity by CDDO-Me was demonstrated by pull-down and activity assays. PKM2 localization in the absence and presence of CDDO-Me or CDDO-Im was determined by subcellular fractionation and immunofluorescence microscopy. Involvement of PKM2 in tumor cell migration was assessed using a stable PKM2 knockdown cell line.

RESULTS

We demonstrate that migration of H1299 lung tumor cells is inhibited by CDDO-Me and CDDO-Im in scratch and transwell assays. CDDO-Me binds directly and specifically to recombinant PKM2, leading to a reduction of its catalytic activity. PKM2 knockdown cells exhibit significantly lower migration compared to control cells when subjected to glucose and oxygen deprivation, but not under regular conditions.

CONCLUSIONS

The results suggest that PKM2 expression in a tumor-like environment contributes to cell migration, and that PKM2 activity can be down regulated by synthetic triterpenoid derivatives.

Oxidized ATM-mediated glycolysis enhancement in breast cancer-associated fibroblasts contributes to tumor invasion through lactate as metabolic coupling

BACKGROUND

Cancer-associated fibroblasts (CAFs) are the predominant residents in the breast tumor microenvironment. In our work, we found activation of DNA damage-independent ATM (oxidized ATM), enhanced glycolysis and aberrant metabolism-associated gene expressions in breast CAFs. Nevertheless, whether and how oxidized ATM regulates the glycolytic activity of CAFs keep in unveil. Recently, a reverse Warburg effect was observed in tumor tissues, in which host cells (such as CAFs, PSCs) in the tumor microenvironment have been found to "fuel" the cancer cells via metabolites transfer. However, the molecular mechanisms of the metabolites from stromal cells playing a role to the progression of cancer cells remain to be determined.

METHODS

Oxidized ATM activation in stromal CAFs was assessed by western blotting and immunofluorescence. The increased glycolytic ability of CAFs was validated by measurements of OCR and ECAR and detections of glucose consumption and lactate production. Kinase assay and western blotting were performed to confirm the phosphorylation of GLUT1. The membrane location of phosphorylated GLUT1 was determined by biotin pull-down assay and immunofluorescence staining. The regulation of PKM2 through oxidized ATM was evaluated by western blots. In addition, the impact of lactate derived from hypoxic CAFs on cancer cell invasion was investigated both in vitro (transwell assays, western blots) and in vivo (orthotopic xenografts).

FINDINGS

Hypoxia-induced oxidized ATM promotes glycolytic activity of CAFs by phosphorylating GLUT1 at S490 and increasing PKM2 expression. Moreover, lactate derived from hypoxic CAFs, acting as a metabolic coupling between CAFs and breast cancer cells, promotes breast cancer cell invasion by activating the TGFβ1/p38 MAPK/MMP2/9 signaling axis and fueling the mitochondrial activity in cancer cells.

INTERPRETATION

Our work shows that oxidized ATM-mediated glycolysis enhancement in hypoxic stromal fibroblasts plays an essential role in cancer cell invasion and metastasis and may implicate oxidized ATM as a target for breast tumor treatment. FUND: This research was supported by National Natural Science Foundation of China.

Molecular Cloning and Expression Analysis of Lactate Dehydrogenase from the Oriental River Prawn Macrobrachium nipponense in Response to Hypoxia

Metabolic adaption to hypoxic stress in crustaceans implies a shift from aerobic to anaerobic metabolism. Lactate dehydrogenase (LDH) is a key enzyme in glycolysis in prawns. However, very little is known about the role of LDH in hypoxia inducible factor (HIF) pathways of prawns. In this study, full-length cDNA of LDH (MnLDH) was obtained from the oriental river prawn Macrobrachium nipponense, and was characterized. The full-length cDNA is 2267-bp with an open reading frame of 999 bp coding for a protein of 333 amino acids with conserved domains important for function and regulation. Phylogenetic analysis showed that MnLDH is close to LDHs from other invertebrates. Quantitative real-time PCR revealed that MnLDH is expressed in various tissues with the highest expression level in muscle. MnLDH mRNA transcript and protein abundance in muscle, but not in hepatopancreas, were induced by hypoxia. Silencing of hypoxia-inducible factor 1 (HIF-1) α or HIF-1β subunits blocked the hypoxia-dependent increase of LDH expression and enzyme activity in muscle. A series of MnLDH promoter sequences, especially the full-length promoter, generated an increase in luciferase expression relative to promoterless vector; furthermore, the expression of luciferase was induced by hypoxia. These results demonstrate that MnLDH is probably involved a HIF-1-dependent pathway during hypoxia in the highly active metabolism of muscle.

HIF1 mediates a switch in pyruvate kinase isoforms after myocardial infarction

Alternative splicing of RNA is an underexplored area of transcriptional response. We expect that early changes in alternatively spliced genes may be important for responses to cardiac injury. Hypoxia inducible factor 1 (HIF1) is a key transcription factor that rapidly responds to loss of oxygen through alteration of metabolism and angiogenesis. The goal of this study was to investigate the transcriptional response after myocardial infarction (MI) and to identify novel, hypoxia-driven changes, including alternative splicing. After ligation of the left anterior descending artery in mice, we observed an abrupt loss of cardiac contractility and upregulation of hypoxic signaling. We then performed RNA sequencing on ischemic heart tissue 1 and 3 days after infarct to assess early transcriptional changes and identified 89 transcripts with altered splicing. Of particular interest was the switch in Pkm isoform expression (pyruvate kinase, muscle). The usually predominant Pkm1 isoform was less abundant in ischemic hearts, while Pkm2 and associated splicing factors (hnRNPA1, hnRNPA2B1, Ptbp1) rapidly increased. Despite increased Pkm2 expression, total pyruvate kinase activity remained reduced in ischemic myocardial tissue. We also demonstrated HIF1 binding to PKM by chromatin immunoprecipitation, indicating a direct role for HIF1 in mediating this isoform switch. Our study provides a new, detailed characterization of the early transcriptome after MI. From this analysis, we identified an HIF1-mediated alternative splicing event in the PKM gene. Pkm1 and Pkm2 play distinct roles in glycolytic metabolism and the upregulation of Pkm2 is likely to have important consequences for ATP synthesis in infarcted cardiac muscle.

Site-specific expression of amine oxidases in breast cancer metastases

We aimed to evaluate the expression of amine oxidase-related proteins in metastatic breast cancer tissue and determine its clinical implication. A tissue microarray was constructed from a total of 126 metastatic breast tumors (31 bone metastases (24.6%), 36 brain metastases (28.6%), 11 liver metastases (8.7%), and 48 lung metastases (38.1%)). Immunohistochemical staining for amine oxidase-related proteins (lysyl oxidase, diamine oxidase, and monoamine oxidase A and B) was performed. In metastatic breast cancer tissue, lysyl oxidase ( p = 0.001), tumoral diamine oxidase ( p = 0.003), stromal diamine oxidase ( p = 0.047), and stromal monoamine oxidase B ( p = 0.002) were differentially expressed in different metastatic sites. Bone metastases showed low expression of lysyl oxidase, tumoral diamine oxidase, and stromal diamine oxidase. We observed high expression of lysyl oxidase in brain metastases, tumoral diamine oxidase in liver metastases, stromal diamine oxidase in lung metastases, and stromal monoamine oxidase B in bone metastases. Lysyl oxidase positivity was associated with progesterone receptor negativity ( p = 0.001), and monoamine oxidase A positivity was associated with human epidermal growth factor receptor-2 negativity ( p = 0.003) and the luminal A subtype ( p = 0.003). On univariate analysis shorter overall survival was associated with stromal diamine oxidase negativity ( p = 0.008), especially in lung metastases ( p = 0.025), and stromal monoamine oxidase B positivity ( p < 0.001). Stromal monoamine oxidase B positivity was an independent prognostic factor for shorter overall survival in multivariate Cox analysis (hazard ratio, 4.069; 95% confidence interval, 1.649–10.04; p = 0.002). Finally, in metastatic breast cancer, amine oxidase-related proteins were differentially expressed in a manner specific to metastatic site, and stromal monoamine oxidase B expression was correlated with prognosis.

Acute hypoxia stress induced abundant differential expression genes and alternative splicing events in heart of tilapia

Hypoxia is one of the critical environmental stressors for fish in aquatic environments. Although accumulating evidences indicate that gene expression is regulated by hypoxia stress in fish, how genes undergoing differential gene expression and/or alternative splicing (AS) in response to hypoxia stress in heart are not well understood. Using RNA-seq, we surveyed and detected 289 differential expressed genes (DEG) and 103 genes that undergo differential usage of exons and splice junctions events (DUES) in heart of a hypoxia tolerant fish, Nile tilapia, Oreochromis niloticus following 12h hypoxic treatment. The spatio-temporal expression analysis validated the significant association of differential exon usages in two randomly selected DUES genes (fam162a and ndrg2) in 5 tissues (heart, liver, brain, gill and spleen) sampled at three time points (6h, 12h, and 24h) under acute hypoxia treatment. Functional analysis significantly associated the differential expressed genes with the categories related to energy conservation, protein synthesis and immune response. Different enrichment categories were found between the DEG and DUES dataset. The Isomerase activity, Oxidoreductase activity, Glycolysis and Oxidative stress process were significantly enriched for the DEG gene dataset, but the Structural constituent of ribosome and Structural molecule activity, Ribosomal protein and RNA binding protein were significantly enriched only for the DUES genes. Our comparative transcriptomic analysis reveals abundant stress responsive genes and their differential regulation function in the heart tissues of Nile tilapia under acute hypoxia stress. Our findings will facilitate future investigation on transcriptome complexity and AS regulation during hypoxia stress in fish.

miR-361-5p modulates metabolism and autophagy via the Sp1-mediated regulation of PKM2 in prostate cancer

Prostate cancer (PCa) is a leading cause of death among men. The dysregulation of metabolism and autophagy contributes to the progression of PCa. The transcription factor specificity protein 1 (Sp1) is implicated in the regulation of metabolism and autophagy. We confirmed that Sp1 is overexpressed in castration-resistant prostate cancer (CRPC) cells. However, the roles of Sp1 in PCa metabolism and autophagy remain unclear. Thus, in the present study, we retrieved the GSE35988 dataset from Gene Expression Omnibus (GEO) database to reinvestigate Sp1 expression and its role in PCa.We found that in PCa, Sp1 knockdown significantly inhibited cell growth, aerobic glycolysis, and hypoxia-induced autophagy, which were accompanied by an increased G1 cell cycle arrest. Pearson correlation indicated that pyruvate kinase isoenzyme type M2 (PKM2) is positively correlated with Sp1 expression. Western blot analysis demonstrated that Sp1 directly regulates PKM2; therefore, Sp1 modulates metabolism and autophagy in CRPC. Western blot analysis and luciferase reporter assay also indicated that the tumor suppressor miR-361-5p inversely regulates Sp1 by directly targeting the binding site in the 3'UTR of Sp1. miR-361-5p overexpression presented effects that are similar to Sp1 depletion in PCa. In summary, this study is the first to demonstrate that miR-361-5p suppresses the Sp1/PKM2 axis, consequently affecting the progression of PCa and the metabolism and autophagy of PCa cells. Therefore, targeting the miR-361-5p/Sp1/PKM2 pathway has considerable clinical significance in preventing the malignant progression of PCa.

Impact of Metabolism on T-Cell Differentiation and Function and Cross Talk with Tumor Microenvironment

The immune system and metabolism are highly integrated and multilevel interactions between metabolic system and T lymphocyte signaling and fate exist. Accumulating evidence indicates that the regulation of nutrient uptake and utilization in T cells is critically important for the control of their differentiation and manipulating metabolic pathways in these cells can shape their function and survival. This review will discuss some potential cell metabolism pathways involved in shaping T lymphocyte function and differentiation. It will also describe show subsets of T cells have specific metabolic requirements and signaling pathways that contribute to their respective function. Examples showing the apparent similarity between cancer cell metabolism and T cells during activation are illustrated and finally some mechanisms being used by tumor microenvironment to orchestrate T-cell metabolic dysregulation and the subsequent emergence of immune suppression are discussed. We believe that targeting T-cell metabolism may provide an additional opportunity to manipulate T-cell function in the development of novel therapeutics.

Role of HIF-1α in the hypoxia inducible expression of the thiamine transporter, SLC19A3

Ensuring continuous intracellular supply of thiamine is essential to maintain metabolism. Cellular homeostasis requires the function of the membrane bound thiamine transporters THTR1 and THTR2. In the absence of increased dietary intake of thiamine, varying intracellular levels to meet metabolic demands during pathophysiological stressors, such as hypoxia, requires adaptive regulatory mechanisms to increase thiamine transport capacity. Previous work has established the up-regulation of SLC19A3 (THTR2) gene expression and activity during hypoxic stress through the activity of the hypoxia inducible transcription factor 1 alpha (HIF-1α). However, it is unknown whether HIF-1α acts directly or indirectly to trans-activate expression of SLC19A3. This work utilized the breast cancer cell line BT-474 treated with 1% O2 or a hypoxia chemical mimetic deferoxamine to determine the minimal promoter region of SLC19A3 responsible for hypoxia responsiveness. In silico sequence analysis determined two contiguous hypoxia responsive elements in close proximity to the transcriptional start site of the SLC19A3 gene. Using a HIF-1α transcriptional factor ELISA assay, HIF-1α was capable of binding to a dsDNA construct of the SLC19A3 minimal promoter. Chromatin immunoprecipitation assay established that SP1 was bound to the SLC19A3 minimal promoter region under normoxic conditions. However, HIF-1α binding to the minimal promoter region occurred during hypoxic treatments, while no SP1 binding was observed under these conditions. This work demonstrates the direct binding and activation of SLC19A3 expression by HIF-1α during hypoxic stress, suggesting an important adaptive regulatory role for HIF-1α in maintaining thiamine homeostasis.

Monoamine oxidase B levels are highly expressed in human gliomas and are correlated with the expression of HiF-1α and with transcription factors Sp1 and Sp3

Monoamine oxidases A and B (MAOA and MAOB) are highly expressed in many cancers. Here we investigated the level of MAOB in gliomas and confirmed its high expression. We found that MAOB levels correlated with tumor grade and hypoxia-inducible factor 1-alpha (HiF-1α) expression. HiF-1α was localized to the nuclei in high-grade gliomas, but it was primarily cytosolic in low-grade gliomas and normal human astrocytes. Expression of both glial fibrillary acidic protein (GFAP) and MAOB are correlated to HiF-1α expression levels. Levels of MAOB are correlated by the levels of transcription factor Sp3 in the majority of GBM examined, but this control of MAOB expression by Sp3 in low grade astrocytic gliomas is significantly different from control in the in the majority of glioblastomas. The current findings support previous suggestions that MAOB can be exploited for the killing of cancer cells. Selective cell toxicity can be achieved by designing non-toxic prodrugs that require MAOB for their catalytic conversion into mature cytotoxic chemotherapeutics.

An alternative mode of CD43 signal transduction activates pro-survival pathways of T lymphocytes

CD43 is one of the most abundant co-stimulatory molecules on a T-cell surface; it transduces activation signals through its cytoplasmic domain, contributing to modulation of the outcome of T-cell responses. The aim of this study was to uncover new signalling pathways regulated by this sialomucin. Analysis of changes in protein abundance allowed us to identify pyruvate kinase isozyme M2 (PKM2), an enzyme of the glycolytic pathway, as an element potentially participating in the signalling cascade resulting from the engagement of CD43 and the T-cell receptor (TCR). We found that the glycolytic activity of this enzyme was not significantly increased in response to TCR+CD43 co-stimulation, but that PKM2 was tyrosine phosphorylated, suggesting that it was performing moonlight functions. We report that phosphorylation of both Y¹⁰⁵ of PKM2 and of Y⁷⁰⁵ of signal transducer and activator of transcription 3 was induced in response to TCR+CD43 co-stimulation, resulting in activation of the mitogen-activated protein kinase kinase 5/extracellular signal-regulated kinase 5 (MEK5/ERK5) pathway. ERK5 and the cAMP response element binding protein (CREB) were activated, and c-Myc and nuclear factor-κB (p65) nuclear localization, as well as Bad phosphorylation, were augmented. Consistent with this, expression of human CD43 in a murine T-cell hybridoma favoured cell survival. Altogether, our data highlight novel signalling pathways for the CD43 molecule in T lymphocytes, and underscore a role for CD43 in promoting cell survival through non-glycolytic functions of metabolic enzymes.

Diverse Mechanisms of Sp1-Dependent Transcriptional Regulation Potentially Involved in the Adaptive Response of Cancer Cells to Oxygen-Deficient Conditions

The inside of a tumor often contains a hypoxic area caused by a limited supply of molecular oxygen due to aberrant vasculature. Hypoxia-inducible factors (HIFs) are major transcription factors that are required for cancer cells to adapt to such stress conditions. HIFs, complexed with the aryl hydrocarbon receptor nuclear translocator, bind to and activate target genes as enhancers of transcription. In addition to this common mechanism, the induction of the unfolded protein response and mTOR signaling in response to endoplasmic reticulum stress is also known to be involved in the adaptation to hypoxia conditions. Sp1 is a ubiquitously-expressed transcription factor that plays a vital role in the regulation of numerous genes required for normal cell function. In addition to the well-characterized stress response mechanisms described above, increasing experimental evidence suggests that Sp1 and HIFs collaborate to drive gene expression in cancer cells in response to hypoxia, thereby regulating additional adaptive responses to cellular oxygen deficiency. However, these characteristics of Sp1 and their biological merits have not been summarized. In this review, we will discuss the diverse mechanisms of transcriptional regulation by Sp1 and their potential involvement in the adaptive response of cancer cells to hypoxic tumor microenvironments.

SREBP maintains lipid biosynthesis and viability of cancer cells under lipid- and oxygen-deprived conditions and defines a gene signature associated with poor survival in glioblastoma multiforme

Oxygen and nutrient limitation are common features of the tumor microenvironment and are associated with cancer progression and induction of metastasis. The inefficient vascularization of tumor tissue also limits the penetration of other serum-derived factors, such as lipids and lipoproteins, which can be rate limiting for cell proliferation and survival. Here we have investigated the effect of hypoxia and serum deprivation on sterol regulatory element-binding protein (SREBP) activity and the expression of lipid metabolism genes in human glioblastoma multiforme (GBM) cancer cells. We found that SREBP transcriptional activity was induced by serum depletion both in normoxic and hypoxic cells and that activation of SREBP was required to maintain the expression of fatty acid and cholesterol metabolism genes under hypoxic conditions. Moreover, expression of stearoyl-CoA desaturase, the enzyme required for the generation of mono-unsaturated fatty acids, and fatty acid-binding protein 7, a regulator of glioma stem cell function, was strongly dependent on SREBP function. Inhibition of SREBP function blocked lipid biosynthesis in hypoxic cancer cells and impaired cell survival under hypoxia and in a three-dimensional spheroid model. Finally, gene expression analysis revealed that SREBP defines a gene signature that is associated with poor survival in glioblastoma.

Dysregulated glycolysis as an oncogenic event

Enhanced glycolysis in cancer, called the Warburg effect, is a well-known feature of cancer metabolism. Recent advances revealed that the Warburg effect is coupled to many other cancer properties, including adaptation to hypoxia and low nutrients, immortalisation, resistance to oxidative stress and apoptotic stimuli, and elevated biomass synthesis. These linkages are mediated by various oncogenic molecules and signals, such as c-Myc, p53, and the insulin/Ras pathway. Furthermore, several regulators of glycolysis have been recently identified as oncogene candidates, including the hypoxia-inducible factor pathway, sirtuins, adenosine monophosphate-activated kinase, glycolytic pyruvate kinase M2, phosphoglycerate mutase, and oncometabolites. The interplay between glycolysis and oncogenic events will be the focus of this review.

Pyruvate kinase M2 at a glance

Reprogrammed metabolism is a key feature of cancer cells. The pyruvate kinase M2 (PKM2) isoform, which is commonly upregulated in many human cancers, has been recently shown to play a crucial role in metabolism reprogramming, gene transcription and cell cycle progression. In this Cell Science at a glance article and accompanying poster, we provide a brief overview of recent advances in understanding the mechanisms underlying the regulation of PKM2 expression, enzymatic activity, metabolic functions and subcellular location. We highlight the instrumental role of the non-metabolic functions of PKM2 in tumorigenesis and evaluate the potential to target PKM2 for cancer treatment.

HIV-1 transcriptional regulation in the central nervous system and implications for HIV cure research

Human immunodeficiency virus type-1 (HIV-1) invades the central nervous system (CNS) during acute infection which can result in HIV-associated neurocognitive disorders in up to 50% of patients, even in the presence of combination antiretroviral therapy (cART). Within the CNS, productive HIV-1 infection occurs in the perivascular macrophages and microglia. Astrocytes also become infected, although their infection is restricted and does not give rise to new viral particles. The major barrier to the elimination of HIV-1 is the establishment of viral reservoirs in different anatomical sites throughout the body and viral persistence during long-term treatment with cART. While the predominant viral reservoir is believed to be resting CD4(+) T cells in the blood, other anatomical compartments including the CNS, gut-associated lymphoid tissue, bone marrow, and genital tract can also harbour persistently infected cellular reservoirs of HIV-1. Viral latency is predominantly responsible for HIV-1 persistence and is most likely governed at the transcriptional level. Current clinical trials are testing transcriptional activators, in the background of cART, in an attempt to purge these viral reservoirs and reverse viral latency. These strategies aim to activate viral transcription in cells constituting the viral reservoir, so they can be recognised and cleared by the immune system, while new rounds of infection are blocked by co-administration of cART. The CNS has several unique characteristics that may result in differences in viral transcription and in the way latency is established. These include CNS-specific cell types, different transcription factors, altered immune surveillance, and reduced antiretroviral drug bioavailability. A comprehensive understanding of viral transcription and latency in the CNS is required in order to determine treatment outcomes when using transcriptional activators within the CNS.

PKM2 regulates the Warburg effect and promotes HMGB1 release in sepsis

Increasing evidence suggests the important role of metabolic reprogramming in the regulation of the innate inflammatory response, but the underlying mechanism remains unclear. Here we provide evidence to support a novel role for the pyruvate kinase M2 (PKM2)-mediated Warburg effect, namely aerobic glycolysis, in the regulation of high-mobility group box 1 (HMGB1) release. PKM2 interacts with hypoxia-inducible factor 1α (HIF1α) and activates the HIF-1α-dependent transcription of enzymes necessary for aerobic glycolysis in macrophages. Knockdown of PKM2, HIF1α and glycolysis-related genes uniformly decreases lactate production and HMGB1 release. Similarly, a potential PKM2 inhibitor, shikonin, reduces serum lactate and HMGB1 levels, and protects mice from lethal endotoxemia and sepsis. Collectively, these findings shed light on a novel mechanism for metabolic control of inflammation by regulating HMGB1 release and highlight the importance of targeting aerobic glycolysis in the treatment of sepsis and other inflammatory diseases.

Oxygen-sensing pathways and the development of mammalian gas exchange

Oxygen-sensing pathways have been extensively explored in the context of homeostatic responses to hypoxic episodes; however, little is known of their involvement in the morphogenesis of respiratory structures (mitochondria, placenta, lung) during development in utero. This review identifies four essential loci where oxygen signalling pathways may cue the development of respiratory structures as: (i). mitochondrial biogenesis coupled with muted oxidative function dependent on the hypoxia-sustained production of NO; (ii). the generation of oxygen gradients which drive trophoblast differentiation and the formation of the chorionic gas exchange interface of the placenta; (iii). the proliferation and epithelial/endothelial differentiation of mesenchyme during the initiation of lung morphogenesis; and (iv). the regulation of epithelial fluid secretion/absorption in the lung. The identification of these oxygen-regulated developmental stages clarifies the close association between oxygen availability, reactive oxygen species and the morphogenesis of gas exchange structures and bears with it the implication that these pathways set the scope for aerobic metabolic performance throughout life.

Hypoxia-induced regulation of the very low density lipoprotein receptor

The very low density lipoprotein receptor (VLDLr) is highly upregulated during hypoxia in mouse cardiomyocytes and in human and mouse ischemic hearts causing a detrimental lipid accumulation. To know how the gene is regulated is important for future studies. In this study, we have thoroughly mapped the 5'-flanking region of the mouse VLDLr promoter and show that the hypoxia-mediated increase in VLDLr expression is dependent on Hif-1α binding to a hypoxia responsive element (HRE) located at -162 to -158bp 5'of translation start. We show that classical HRE sites and the previously described PPARγ and Sp1 binding are not involved in the hypoxia-induced regulation of the VLDLr promoter. Using a chromatin immunoprecipitation (ChIP) assay, we show that Hif-1α specifically binds and activates the mouse VLDLr promoter at the previously described non-classical HRE in HL-1 cells. We also show that the same HRE is present and active in response to hypoxia in human cardiomyocytes, however at a different location (-812bp from translation start). These results conclude that in the hypoxic hearts of mice and men, the VLDLr gene is regulated by a direct binding of Hif-1α to the VLDLr promoter.

Regulation and function of pyruvate kinase M2 in cancer

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

PKM2, a Central Point of Regulation in Cancer Metabolism

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

Energetic coupling between an oxidizable cysteine and the phosphorylatable N-terminus of human liver pyruvate kinase

During our efforts to characterize the regulatory properties of human liver pyruvate kinase (L-PYK), we have noted that the affinity of the protein for phosphoenolpyruvate (PEP) becomes reduced several days after cell lysis. A 1.8 Å crystallographic structure of L-PYK with the S12D mimic of phosphorylation indicates that Cys436 is oxidized, the first potential insight into explaining the effect of "aging". Interestingly, the oxidation is only to sulfenic acid despite the crystal growth time period of 2 weeks. Mutagenesis confirms that the side chain of residue 436 is energetically coupled to PEP binding. Mass spectrometry confirms that the oxidation is present in solution and is not an artifact caused by X-ray exposure. Exposure of the L-PYK mutations to H₂O₂ also confirms that PEP affinity is sensitive to the nature of the side chain at position 436. A 1.95 Å structure of the C436M mutant of L-PYK, the only mutation at position 436 that has been shown to strengthen PEP affinity, revealed that the methionine substitution results in the ordering of several N-terminal residues that have not been ordered in previous structures. This result allowed speculation that oxidation of Cys436 and phosphorylation of the N-terminus at Ser12 may function through a similar mechanism, namely the interruption of an activating interaction between the nonphosphorylated N-terminus with the nonoxidized main body of the protein. Mutant cycles were used to provide evidence that mutations of Cys436 are energetically synergistic with N-terminal modifications, a result that is consistent with phosphorylation of the N-terminus and oxidation of Cys436 functioning through mechanisms with common features. Alanine-scanning mutagenesis was used to confirm that the newly ordered N-terminal residues were important to the regulation of enzyme function by the N-terminus of the enzyme (i.e., not an artifact caused by the introduced methionine substitution) and to further define which residues in the N-terminus are energetically coupled to PEP affinity. Collectively, these studies indicate energetic coupling (and potentially mechanistic similarities) between the oxidation of Cys436 and phosphorylation of Ser12 in the N-terminus of L-PYK.

Low oxygen tension enhances hepatitis C virus replication

Low oxygen tension exerts a significant effect on the replication of several DNA and RNA viruses in cultured cells. In vitro propagation of hepatitis C virus (HCV) has thus far been studied under atmospheric oxygen levels despite the fact that the liver tissue microenvironment is hypoxic. In this study, we investigated the efficiency of HCV production in actively dividing or differentiating human hepatoma cells cultured under low or atmospheric oxygen tensions. By using both HCV replicons and infection-based assays, low oxygen was found to enhance HCV RNA replication whereas virus entry and RNA translation were not affected. Hypoxia signaling pathway-focused DNA microarray and real-time quantitative reverse transcription-PCR (qRT-PCR) analyses revealed an upregulation of genes related to hypoxic stress, glycolytic metabolism, cell growth, and proliferation when cells were kept under low (3% [vol/vol]) oxygen tension, likely reflecting cell adaptation to anaerobic conditions. Interestingly, hypoxia-mediated enhancement of HCV replication correlated directly with the increase in anaerobic glycolysis and creatine kinase B (CKB) activity that leads to elevated ATP production. Surprisingly, activation of hypoxia-inducible factor alpha (HIF-α) was not involved in the elevation of HCV replication. Instead, a number of oncogenes known to be associated with glycolysis were upregulated and evidence that these oncogenes contribute to hypoxia-mediated enhancement of HCV replication was obtained. Finally, in liver biopsy specimens of HCV-infected patients, the levels of hypoxia and anaerobic metabolism markers correlated with HCV RNA levels. These results provide new insights into the impact of oxygen tension on the intricate HCV-host cell interaction.

Emerging roles of PKM2 in cell metabolism and cancer progression

Increased conversion of glucose to lactate is a key feature of many cancer cells that promotes rapid growth. Pyruvate kinase M2 (PKM2) expression is increased and facilitates lactate production in cancer cells. Modulation of PKM2 catalytic activity also regulates the synthesis of DNA and lipids that are required for cell proliferation, and of NADPH that is required for redox homeostasis. In addition to its role as a pyruvate kinase, PKM2 also functions as a protein kinase and as a transcriptional coactivator. These biochemical activities are controlled by allosteric regulators and post-translational modifications of PKM2 that include acetylation, oxidation, phosphorylation, prolyl hydroxylation, and sumoylation. Given its pleiotropic effects on cancer biology, PKM2 represents an attractive target for cancer therapy.

Identification of a novel enhancer that binds Sp1 and contributes to induction of cold-inducible RNA-binding protein (cirp) expression in mammalian cells

Background

There are a growing number of reports on the sub-physiological temperature culturing of mammalian cells for increased recombinant protein yields. However, the effect varies and the reasons for the enhancement are not fully elucidated. Expression of cold-inducible RNA-binding protein (cirp, also called cirbp or hnRNP A18) is known to be induced in response to mild, but not severe, hypothermia in mammalian cells. To clarify the molecular mechanism underlying the induction and to exploit this to improve the productivity of recombinant proteins, we tried to identify the regulatory sequence(s) in the 5′ flanking region of the mouse cirp gene.

Results

By transiently transfecting HEK293 cells with plasmids expressing chloramphenicol acetyltransferase as a reporter, we found that the cirp 5′ flanking region octanucleotide 5′-TCCCCGCC-3′ is a mild-cold responsive element (MCRE). When 3 copies of MCRE were placed upstream of the CMV promoter and used in transient transfection, reporter gene expression was increased 3- to 7-fold at 32°C relative to 37°C in various cell lines including HEK293, U-2 OS, NIH/3T3, BALB/3T3 and CHO-K1 cells. In stable transfectants, MCRE also enhanced the reporter gene expression at 32°C, although more copy numbers of MCRE were necessary. Sp1 transcription factor bound to MCRE in vitro. Immunohistochemistry and chromatin immunoprecipitation assays demonstrated that more Sp1, but not Sp3, was localized in the nucleus to bind to the cirp regulatory region containing MCRE at 32°C than 37°C. Overexpression of Sp1 protein increased the expression of endogenous Cirp as well as a reporter gene driven by the 5′ flanking region of the cirp gene, and down-regulation of Sp1 had the opposite effect. Mutations within the MCRE sequence in the 5′ flanking region abolished the effects of Sp1 on the reporter gene expression both at 37°C and 32°C.

Conclusions

Cold-induced, as well as constitutive, expression of cirp is dependent, at least partly, on MCRE and Sp1. The present novel enhancer permits conditional high-level gene expression at moderately low culture temperatures and could be utilized to increase the yield of recombinant proteins in mammalian cells.

Adaptive and maladaptive cardiorespiratory responses to continuous and intermittent hypoxia mediated by hypoxia-inducible factors 1 and 2

Hypoxia is a fundamental stimulus that impacts cells, tissues, organs, and physiological systems. The discovery of hypoxia-inducible factor-1 (HIF-1) and subsequent identification of other members of the HIF family of transcriptional activators has provided insight into the molecular underpinnings of oxygen homeostasis. This review focuses on the mechanisms of HIF activation and their roles in physiological and pathophysiological responses to hypoxia, with an emphasis on the cardiorespiratory systems. HIFs are heterodimers comprised of an O(2)-regulated HIF-1α or HIF-2α subunit and a constitutively expressed HIF-1β subunit. Induction of HIF activity under conditions of reduced O(2) availability requires stabilization of HIF-1α and HIF-2α due to reduced prolyl hydroxylation, dimerization with HIF-1β, and interaction with coactivators due to decreased asparaginyl hydroxylation. Stimuli other than hypoxia, such as nitric oxide and reactive oxygen species, can also activate HIFs. HIF-1 and HIF-2 are essential for acute O(2) sensing by the carotid body, and their coordinated transcriptional activation is critical for physiological adaptations to chronic hypoxia including erythropoiesis, vascularization, metabolic reprogramming, and ventilatory acclimatization. In contrast, intermittent hypoxia, which occurs in association with sleep-disordered breathing, results in an imbalance between HIF-1α and HIF-2α that causes oxidative stress, leading to cardiorespiratory pathology.

Elevated SP-1 transcription factor expression and activity drives basal and hypoxia-induced vascular endothelial growth factor (VEGF) expression in non-small cell lung cancer

VEGF plays a central role in angiogenesis in cancer. Non-small cell lung cancer (NSCLC) tumors have increased microvascular density, localized hypoxia, and high VEGF expression levels; however, there is a lack of understanding of how oncogenic and tumor microenvironment changes such as hypoxia lead to greater VEGF expression in lung and other cancers. We show that NSCLC cells secreted higher levels of VEGF than normal airway epithelial cells. Actinomycin D inhibited all NSCLC VEGF secretion, and VEGF minimal promoter-luciferase reporter constructs were constitutively active until the last 85 base pairs before the transcription start site containing three SP-1 transcription factor-binding sites; mutation of these VEGF promoter SP-1-binding sites eliminated VEGF promoter activity. Furthermore, dominant negative SP-1, mithramycin A, and SP-1 shRNA decreased VEGF promoter activity, whereas overexpression of SP-1 increased VEGF promoter activity. Chromatin immunoprecipitation assays demonstrated SP-1, p300, and PCA/F histone acetyltransferase binding and histone H4 hyperacetylation at the VEGF promoter in NSCLC cells. Cultured NSCLC cells expressed higher levels of SP-1 protein than normal airway epithelial cells, and double-fluorescence immunohistochemistry showed a strong correlation between SP-1 and VEGF in human NSCLC tumors. In addition, hypoxia-driven VEGF expression in NSCLC cells was SP-1-dependent, with hypoxia increasing SP-1 activity and binding to the VEGF promoter. These studies are the first to demonstrate that overexpression of SP-1 plays a central role in hypoxia-induced VEGF secretion.

Role of sp transcription factors in the regulation of cancer cell metabolism

Cancer cells exhibit altered metabolism characterized by the generation of adenosine triphosphate by glycolysis and generation of fatty acids by de novo synthesis. The majority of genes involved in these pathways have binding sites for specificity protein (Sp) transcription factors in their promoters. Studies showing that Sp transcription factors, particularly Sp1, are involved in the regulation in cancer cells of hexokinase, pyruvate kinase, lactate dehydrogenase, fatty acid synthase, and hypoxia-inducible factor-1α are reviewed. Glycolysis and lipogenesis in cancers are also known to be stimulated by the constitutive activation of the PI3K/Akt signaling pathway. Evidence is presented for the notion that Sp transcription factors may act in concert with Akt to regulate the abnormal metabolism of cancer cells.

Rocking cell metabolism: revised functions of the key glycolytic regulator PKM2 in cancer

Cancer cell metabolism is exemplified by high glucose consumption and lactate production. Pyruvate kinase (PK), which catalyzes the final step of glycolysis, has emerged as a potential regulator of this metabolic phenotype. The M2 isoform of PK (PKM2) is highly expressed in cancer cells. However, the mechanisms by which PKM2 coordinates high energy requirements with high anabolic activities to support cancer cell proliferation are still not completely understood. Current research has elucidated novel regulatory mechanisms for PKM2, contributing to its important role in cancer. This review summarizes the current understanding and explores future directions in the field, highlighting controversies regarding the activity and specificity of PKM2 in cancer. In light of this knowledge, the potential therapeutic implications and strategies are critically discussed.

Sequential activation of hypoxia-inducible factor 1 and specificity protein 1 is required for hypoxia-induced transcriptional stimulation of Abcc8

Cerebral ischemia causes increased transcription of sulfonylurea receptor 1 (SUR1), which forms SUR1-regulated NC(Ca-ATP) channels linked to cerebral edema. We tested the hypothesis that hypoxia is an initial signal that stimulates transcription of Abcc8, the gene encoding SUR1, via activation of hypoxia-inducible factor 1 (HIF1). In the brain microvascular endothelial cells, hypoxia increased SUR1 abundance and expression of functional SUR1-regulated NC(Ca-ATP) channels. Luciferase reporter activity driven by the Abcc8 promoter was increased by hypoxia and by coexpression of HIF1α. Surprisingly, a series of luciferase reporter assays studying the Abcc8 promoter revealed that binding sites for specificity protein 1 (Sp1), but not for HIF, were required for stimulation of Abcc8 transcription by HIF1α. Luciferase reporter assays studying Sp1 promoters of three species, and chromatin immunoprecipitation analysis in rats after cerebral ischemia, indicated that HIF binds to HIF-binding sites on the Sp1 promoter to stimulate transcription of the Sp1 gene. We conclude that sequential activation of two transcription factors, HIF and Sp1, is required to stimulate transcription of Abcc8 following cerebral ischemia. Sequential gene activation in cerebral ischemia provides a plausible molecular explanation for the prolonged treatment window observed for inhibition of the end-target gene product, SUR1, by glibenclamide.

Pyruvate kinase M2 regulates glucose metabolism by functioning as a coactivator for hypoxia-inducible factor 1 in cancer cells

Cancer cells feature altered glucose metabolism that allows their rapid growth. They consume large amounts of glucose to produce lactate, even in the presence of ample oxygen, which is known as the Warburg effect. Pyruvate kinase M2 (PKM2) contributes to the Warburg effect by previously unknown mechanisms. Hypoxia-inducible factor 1 (HIF-1) mediates PKM2 gene transcription and glucose reprogramming in cancer cells. The recent discovery of novel physical and functional interactions between PKM2 and HIF-1 in cancer cells has provided insight into molecular mechanisms underlying the Warburg effect.

Functional characterization of the human translocator protein (18kDa) gene promoter in human breast cancer cell lines

The translocator protein (18kDa; TSPO) is a mitochondrial drug- and cholesterol-binding protein that has been implicated in several processes, including steroidogenesis, cell proliferation, and apoptosis. Expression of the human TSPO gene is elevated in several cancers. To understand the molecular mechanisms that regulate TSPO expression in human breast cancer cells, the TSPO promoter was identified, cloned, and functionally characterized in poor-in-TSPO hormone-dependent, non-aggressive MCF-7 cells and rich-in-TSPO hormone-independent, aggressive, and metastatic MDA-MB-231 breast cancer cells. RNA ligase-mediated 5'-rapid amplification of cDNA ends analysis indicated transcription initiated at multiple sites downstream of a GC-rich promoter that lacks functional TATA and CCAAT boxes. Deletion analysis indicated that the region from -121 to +66, which contains five putative regulatory sites known as GC boxes, was sufficient to induce reporter activity up to 24-fold in MCF-7 and nearly 120-fold in MDA-MB-231 cells. Electrophoretic mobility shift and chromatin immunoprecipitation assays indicated that Sp1, Sp3 and Sp4 bind to these GC boxes in vitro and to the endogenous TSPO promoter. Silencing of Sp1, Sp3 and Sp4 gene expression reduced TSPO levels. In addition, TSPO expression was epigenetically regulated at one or more of the identified GC boxes. Disruption of the sequence downstream of the main start site of TSPO differentially regulated TSPO promoter activity in MCF-7 and MDA-MB-231 cells, indicating that essential elements contribute to its differential expression in these cells. Taken together, these experiments constitute the first in-depth functional analysis of the human TSPO gene promoter and its transcriptional regulation.

Enzymatic features of the glucose metabolism in tumor cells

Many tumor types exhibit an impaired Pasteur effect, i.e. despite the presence of oxygen, glucose is consumed at an extraordinarily high rate compared with the tissue from which they originate - the so-called 'Warburg effect'. Glucose has to serve as the source for a diverse array of cellular functions, including energy production, synthesis of nucleotides and lipids, membrane synthesis and generation of redox equivalents for antioxidative defense. Tumor cells acquire specific enzyme-regulatory mechanisms to direct the main flux of glucose carbons to those pathways most urgently required under challenging external conditions such as varying substrate availability, presence of anti-cancer drugs or different phases of the cell cycle. In this review we summarize the currently available information on tumor-specific expression, activity and kinetic properties of enzymes involved in the main pathways of glucose metabolism with due regard to the explanation of the regulatory basis and physiological significance of the Warburg effect. We conclude that, besides the expression level of the metabolic enzymes involved in the glucose metabolism of tumor cells, the unique tumor-specific pattern of isozymes and accompanying changes in the metabolic regulation below the translation level enable tumor cells to drain selfishly the blood glucose pool that non-transformed cells use as sparingly as possible.

Circadian rhythm of enolase in suprachiasmatic nucleus depends on mitochondrial function

Metabolic activity in the suprachiasmatic nucleus (SCN), a center of biological rhythm, is higher during the daytime than at night. The rhythmic oscillation in the SCN is feedback controlled by the CLOCK/BMAL1 heterodimer binding to the E-box in target genes (e.g., Arg- vasopressin). Similar transcriptional regulation by NPAS2/BMAL1 heterodimer formation operates in the brain, which depends on the redox state (i.e., NAD/NADH). To clarify the metabolic function of SCN in relation to the redox state, two-dimensional electrophoresis was carried out on the mitochondrial fraction of SCN, obtained from rats kept under a light:dark cycle and constant under dim light. The electrophoretic pattern with TOF-mass spectrometry analysis revealed that enolase catalyzes the interconversion of 2-phosphoglycerate and phosphoenolpyruvate. The enolase activity, coupled with lactate dehydrogenase, was higher during the light period than that in the dark. However, enolase mRNA, analyzed by RT-PCR, showed higher levels during the dark period than in the light. The clock gene products Per2, Bmal1, Rev-erbα, and AVP mRNA in the mitochondrial fraction of SCN developed a circadian rhythm showing almost the same peak time as that in whole SCN. These mRNA rhythms ran free except for that of Rev-erbα mRNA. The results indicate that, in the glycolysis-related energy pathway, enolase might be involved in higher metabolic activity during the day than at night, at least in part.

Oxygen homeostasis

Metazoan life is dependent upon the utilization of O(2) for essential metabolic processes and oxygen homeostasis is an organizing principle for understanding metazoan evolution, ontology, physiology, and pathology. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that is expressed by all metazoan species and functions as a master regulator of oxygen homeostasis. Recent studies have elucidated complex mechanisms by which HIF-1 activity is regulated and by which HIF-1 regulates gene expression, with profound consequences for prenatal development, postnatal physiology, and disease pathogenesis.

Hemoglobin regulates the metabolic, synthetic, detoxification, and biotransformation functions of hepatoma cells cultured in a hollow fiber bioreactor

Hepatic hollow fiber (HF) bioreactors constitute one type of extracorporeal bioartificial liver assist device (BLAD). Ideally, cultured hepatocytes in a BLAD should closely mimic the in vivo oxygenation environment of the liver sinusoid to yield a device with optimal performance. However, most BLADs, including hepatic HF bioreactors, suffer from O2 limited transport toward cultured hepatocytes, which reduces their performance. We hypothesize that supplementation of hemoglobin-based O2 carriers into the circulating cell culture medium of hepatic HF bioreactors is a feasible and effective strategy to improve bioreactor oxygenation and performance. We examined the effect of bovine hemoglobin (BvHb) supplementation (15g/L) in the circulating cell culture medium of hepatic HF bioreactors on hepatocyte proliferation, metabolism, and varied liver functions, including biosynthesis, detoxification, and biotransformation. It was observed that BvHb supplementation supported the maintenance of a higher cell mass in the extracapillary space, improved hepatocyte metabolic efficiency (i.e., hepatocytes consumed much less glucose), improved hepatocyte capacity for drug metabolism, and conserved both albumin synthesis and ammonia detoxification functions compared to controls (no BvHb supplementation) under the same experimental conditions.

Oxidative-stress-induced alterations in Sp factors mediate transcriptional regulation of the NR1 subunit in hippocampus during hypoxia

Ascent to high altitude is associated with tissue hypoxia resulting from the decrease in partial pressure of atmospheric oxygen. The hippocampus, in particular, is highly vulnerable to hypoxic insult, which at least in part can be attributed to the occurrence of glutamate excitotoxicity. Although this excitotoxic damage is often related to increased NMDA receptor activation and subsequent calcium-mediated free radical generation, the mechanisms involving the transcriptional regulation of NMDA receptor subunit expression by hypoxic stress remains to be explored. Our study reveals a novel mechanism for the regulation of expression of the NR1 subunit of NMDA receptors by the Sp family of transcription factors through an oxidative-stress-mediated mechanism that also involves the molecular chaperone Hsp90. The findings not only show the occurrence of lipid peroxidation and DNA damage in hippocampal cells exposed to hypoxia but also reveal a calcium-independent mechanism of selective oxidation and degradation of Sp3 by the 20S proteasome. This along with increased DNA binding activity of Sp1 leads to NR1 upregulation in the hippocampus during hypoxic stress. The study therefore provides evidence for free radical-mediated regulation of gene expression in hypoxia and the scope of the use of antioxidants in preventing excitotoxic neuronal damage during hypoxia.

Hypoxia inducible factor-1 alpha activation of the JCV promoter: role in the pathogenesis of progressive multifocal leukoencephalopathy

Activation of viral promoter transcription is a crucial event in the life cycle of several viruses. Hypoxia inducible factor-1 alpha (HIF-1alpha) is an inducible transcription factor whose activity is dependent on environmental conditions, most notably oxygen levels and cellular stress. HIF-1alpha has been implicated in the pathogenesis of several viruses, including HIV-1, HHV-8 and RSV. Under hypoxic conditions or oxidative stress, HIF-1alpha becomes stable and translocates to the nucleus, where it modulates gene transcription. The objective of the present study was to investigate a possible role for HIF-1alpha in the activation of JCV. Glial cell cultures infected with JCV demonstrated a significant increase in the levels of HIF-1alpha, in where it is located to the nucleus. Immunohistochemical studies corroborated upregulation of HIF-1alpha in JCV infected oligodendrocytes and astrocytes in clinical samples of PML compared with normal glial cells from the same samples in which HIF-1alpha expression is weak. CAT assays performed in co-transfected glial cells demonstrated activation of the JCV early promoter in the presence of HIF-1alpha. This activation was potentiated in the presence of Smad3 and Smad4. Finally, chromatin immunoprecipitation assays demonstrated the binding of HIF-1alpha to the JCV control region. These results suggest a role for HIF-1alpha in the activation of JCV; understanding of this pathway may lead to the development of more effective therapies for PML, thus far an incurable disease.

Metal transcription factor-1 is involved in hypoxia-dependent regulation of placenta growth factor in trophoblast-derived cells

Placenta growth factor (PlGF) is a placental angiogenic factor. Metal-responsive transcription factor (MTF)-1 was reported to take part in the hypoxic induction of PlGF in RAS-transformed mouse fibroblasts. We contrarily showed that PlGF mRNA and protein levels decreased under hypoxia in a choriocarcinoma BeWo cell line derived from trophoblast. In this report, we examined whether hypoxia-dependent regulation of the PlGF gene in these cells also depends on MTF-1. We analyzed the effect of hypoxia on MTF-1 expression, and it was revealed to be decreased. Moreover, MTF-1 small interfering RNA treatment decreased PlGF mRNA level. To investigate the transcription of PlGF under hypoxia, we cloned promoter region of the human PlGF. Promoter deletion analysis suggested that triple repeats of metal-responsive element located between -511 and -468 bp in the promoter are important for the hypoxic regulation of PlGF. Treatment with MTF-1 small interfering RNA resulted in the significant decreased luciferase activity in PlGF reporter constructs. Chromatin immunoprecipitation showed the binding of the MTF-1 protein to the promoter region. We examined MTF-1 immunoreactivity in trophoblasts of term placental tissue from patients with normal pregnancies and preeclampsia, which represents a condition of placental hypoxia. Immunoreactivity of the MTF-1 protein was decreased in placentas from pregnant women with preeclampsia when compared with those from normal pregnant women. Taken together, these findings suggest that MTF-1 is involved in hypoxia-dependent regulation of PlGF in trophoblast-derived cells.