Identification of Pur alpha as a new hypoxia response factor responsible for coordinated induction of the beta 2 integrin family

Genome-wide CRISPR/Cas9 screening identifies a targetable MEST-PURA interaction in cancer metastasis

BACKGROUND

Metastasis is one of the most lethal hallmarks of esophageal squamous cell carcinoma (ESCC), yet the mechanisms remain unclear due to a lack of reliable experimental models and systematic identification of key drivers. There is urgent need to develop useful therapies for this lethal disease.

METHODS

A genome-wide CRISPR/Cas9 screening, in combination with gene profiling of highly invasive and metastatic ESCC sublines, as well as PDX models, was performed to identify key regulators of cancer metastasis. The Gain- and loss-of-function experiments were taken to examine gene function. Protein interactome, RNA-seq, and whole genome methylation sequencing were used to investigate gene regulation and molecular mechanisms. Clinical significance was analyzed in tumor tissue microarray and TCGA databases. Homology modeling, modified ELISA, surface plasmon resonance and functional assays were performed to identify lead compound which targets MEST to suppress cancer metastasis.

FINDINGS

High MEST expression was associated with poor patient survival and promoted cancer invasion and metastasis in ESCC. Mechanistically, MEST activates SRCIN1/RASAL1-ERK-snail signaling by interacting with PURA. miR-449a was identified as a direct regulator of MEST, and hypermethylation of its promoter led to MEST upregulation, whereas systemically delivered miR-449a mimic could suppress tumor metastasis without overt toxicity. Furthermore, molecular docking and computational screening in a small-molecule library of 1,500,000 compounds and functional assays showed that G699-0288 targets the MEST-PURA interaction and significantly inhibits cancer metastasis.

INTERPRETATION

We identified the MEST-PURA-SRCIN1/RASAL1-ERK-snail signaling cascade as an important mechanism underlying cancer metastasis. Blockade of MEST-PURA interaction has therapeutic potential in management of cancer metastasis.

FUNDING

This work was supported by National Key Research and Development Program of China (2021YFC2501000, 2021YFC2501900, 2017YFA0505100); National Natural Science Foundation of China (31961160727, 82073196, 81973339, 81803551); NSFC/RGC Joint Research Scheme (N_HKU727/19); Natural Science Foundation of Guangdong Province (2021A1515011158, 2021A0505030035); Key Laboratory of Guangdong Higher Education Institutes of China (2021KSYS009).

PURα mediates epithelial-mesenchymal transition to promote esophageal squamous cell carcinoma progression by regulating Snail2

Esophageal squamous cell carcinoma (ESCC) is one of the most common lethal cancers in the world. Dysregulation of purine-rich element binding protein alpha (PURα), which contributes to the initiation of PURΑ syndrome, is reportedly involved in the progression of multiple cancers, but its function and underlying mechanisms in ESCC progression remain unclear. Here, we first demonstrated that PURα promoted cell growth, migration and invasion in ESCC both in vitro and in vivo. An immunohistochemistry assay was then performed on 225 ESCC tissues, showing that high PURα expression was positively associated with lymph node metastasis and the AJCC stage, and the ESCC patients with positive PURα expression had worse survival. In addition, RNA sequencing implied that PURα induced epithelial-mesenchymal transition (EMT) in ESCC, which was further confirmed by qPCR, Western blotting and immunofluorescence analyses. Mechanistically, PURα enhanced the transcription of Snail2 by binding to its promoter region. Knockdown of Snail2 reversed PURα-induced EMT and inhibited the migration and invasion of ESCC cells. In conclusion, this study indicated that PURα promotes Snail2 transcriptional activity to induce EMT during ESCC progression.

CGG Repeat Expansion, and Elevated Fmr1 Transcription and Mitochondrial Copy Number in a New Fragile X PM Mouse Embryonic Stem Cell Model

The Fragile-X related disorders (FXDs) are Repeat Expansion Diseases (REDs) that result from expansion of a CGG-repeat tract located at the 5′ end of the FMR1 gene. While expansion affects transmission risk and can also affect disease risk and severity, the underlying molecular mechanism responsible is unknown. Despite the fact that expanded alleles can be seen both in humans and mouse models in vivo, existing patient-derived cells do not show significant repeat expansions even after extended periods in culture. In order to develop a good tissue culture model for studying expansions we tested whether mouse embryonic stem cells (mESCs) carrying an expanded CGG repeat tract in the endogenous Fmr1 gene are permissive for expansion. We show here that these mESCs have a very high frequency of expansion that allows changes in the repeat number to be seen within a matter of days. CRISPR-Cas9 gene editing of these cells suggests that this may be due in part to the fact that non-homologous end-joining (NHEJ), which is able to protect against expansions in some cell types, is not effective in mESCs. CRISPR-Cas9 gene editing also shows that these expansions are MSH2-dependent, consistent with those seen in vivo. While comparable human Genome Wide Association (GWA) studies are not available for the FXDs, such studies have implicated MSH2 in expansion in other REDs. The shared unusual requirement for MSH2 for this type of microsatellite instability suggests that this new cell-based system is relevant for understanding the mechanism responsible for this peculiar type of mutation in humans. The high frequency of expansions and the ease of gene editing these cells should expedite the identification of factors that affect expansion risk. Additionally, we found that, as with cells from human premutation (PM) carriers, these cell lines have elevated mitochondrial copy numbers and Fmr1 hyperexpression, that we show here is O₂-sensitive. Thus, this new stem cell model should facilitate studies of both repeat expansion and the consequences of expansion during early embryonic development.

Metabolic Factors that Contribute to Lupus Pathogenesis

Systemic lupus erythematosus (SLE) is an autoimmune disease in which organ damage is mediated by pathogenic autoantibodies directed against nucleic acids and protein complexes. Studies in SLE patients and in mouse models of lupus have implicated virtually every cell type in the immune system in the induction or amplification of the autoimmune response as well as the promotion of an inflammatory environment that aggravates tissue injury. Here, we review the contribution of CD4+ T cells, B cells, and myeloid cells to lupus pathogenesis and then discuss alterations in the metabolism of these cells that may contribute to disease, given the recent advances in the field of immunometabolism.

Characterization of purine-rich element binding protein B as a novel biomarker in acute myelogenous leukemia prognostication

Acute myelogenous leukemia (AML) is an aggressive hematologic cancer characterized by infiltration of proliferative, clonal, abnormally differentiated cells of myeloid lineage in the bone marrow and blood. Malignant cells in AML often exhibit chromosomal and other genetic or epigenetic abnormalities that are useful in prognostic risk assessment. In this study, the relative expression and novel single-stranded DNA (ssDNA) binding function of purine-rich element binding proteins A and B (Purα and Purβ) were systematically evaluated in established leukemia cell lines and in lineage committed myeloid cells isolated from patients diagnosed with a hematologic malignancy. Western blotting revealed that Purα and Purβ are markedly elevated in CD33⁺ /CD66b⁺ cells from AML patients compared to healthy subjects and to patients with other types of myeloid cell disorders. Results of in silico database analysis of PURA and PURB mRNA expression during hematopoiesis in conjunction with the quantitative immunoassay of the ssDNA-binding activities of Purα and Purβ in transformed leukocyte cell lines pointed to Purβ as the more distinguishing biomarker of myeloid cell differentiation status. Purβ ssDNA-binding activity was significantly increased in myeloid cells from AML patients but not from individuals with other myeloid-related diseases. The highest levels of Purβ activity were detected in myeloid cells from primary AML patients and from AML patients displaying other risk factors forecasting a poor prognosis. Collectively, these findings suggest that the enhanced ssDNA-binding activity of Purβ in transformed myeloid cells may serve as a unique and measurable phenotypic trait for improving prognostic risk stratification in AML.

The hematopoietic cell-specific transcription factor PU.1 is critical for expression of CD11c

PU.1 is a hematopoietic cell-specific transcription factor belonging to the Ets family, which plays an important role in the development of dendritic cells (DCs). CD11c (encoded by Itgax) is well established as a characteristic marker of hematopoietic lineages including DCs. In the present study, we analyzed the role of PU.1 (encoded by Spi-1) in the expression of CD11c. When small interfering RNA (siRNA) for Spi-1 was introduced into bone marrow-derived DCs (BMDCs), the mRNA level and cell surface expression of CD11c were dramatically reduced. Using reporter assays, the TTCC sequence at -56/-53 was identified to be critical for PU.1-mediated activation of the promoter. An EMSA showed that PU.1 directly bound to this region. ChIP assays demonstrated that a significant amount of PU.1 bound to this region on chromosomal DNA in BMDCs, which was decreased in LPS-stimulated BMDCs in accordance with the reduced levels of mRNAs of Itgax and Spi-1, and the histone acetylation degree. Enforced expression of exogenous PU.1 induced the expression of the CD11c protein on the cell surface of mast cells, whereas control transfectants rarely expressed CD11c. Quantitative RT-PCR also showed that the expression of a transcription factor Irf4, which is a partner molecule of PU.1, was reduced in PU.1-knocked down BMDCs. IRF4 transactivated the Itgax gene in a synergistic manner with PU.1. Taken together, these results indicate that PU.1 functions as a positive regulator of CD11c gene expression by directly binding to the Itgax promoter and through transactivation of the Irf4 gene.

Hypoxia Selectively Enhances Integrin α5β1 Receptor Expression in Breast Cancer to Promote Metastasis

Metastasis is the leading cause of breast cancer mortality. Previous studies have implicated hypoxia-induced changes in the composition and stiffness of the extracellular matrix (ECM) in the metastatic process. Therefore, the contribution of potential ECM-binding receptors in this process was explored. Using a bioinformatics approach, the expression of all integrin receptor subunits, in two independent breast cancer patient datasets, were analyzed to determine whether integrin status correlates with a validated hypoxia-inducible gene signature. Subsequently, a large panel of breast cancer cell lines was used to validate that hypoxia induces the expression of integrins that bind to collagen (ITGA1, ITGA11, ITGB1) and fibronectin (ITGA5, ITGB1). Hypoxia-inducible factors (HIF-1 and HIF-2) are directly required for ITGA5 induction under hypoxic conditions, which leads to enhanced migration and invasion of single cells within a multicellular 3D tumor spheroid but did not affect migration in a 2D microenvironment. ITGB1 expression requires HIF-1α, but not HIF-2α, for hypoxic induction in breast cancer cells. ITGA5 (α₅ subunit) is required for metastasis to lymph nodes and lungs in breast cancer models, and high ITGA5 expression in clinical biopsies is associated with an increased risk of mortality.Implications: These results reveal that targeting ITGA5 using inhibitors that are currently under consideration in clinical trials may be beneficial for patients with hypoxic tumors. Mol Cancer Res; 15(6); 723-34. ©2017 AACR.

Mutually Supportive Mechanisms of Inflammation and Vascular Remodeling

Chronic inflammation is often accompanied by angiogenesis, the development of new blood vessels from existing ones. This vascular response is a response to chronic hypoxia and/or ischemia, but is also contributory to the progression of disorders including atherosclerosis, arthritis, and tumor growth. Proinflammatory and proangiogenic mediators and signaling pathways form a complex and interrelated network in these conditions, and many factors exert multiple effects. Inflammation drives angiogenesis by direct and indirect mechanisms, promoting endothelial proliferation, migration, and vessel sprouting, but also by mediating extracellular matrix remodeling and release of sequestered growth factors, and recruitment of proangiogenic leukocyte subsets. The role of inflammation in promoting angiogenesis is well documented, but by facilitating greater infiltration of leukocytes and plasma proteins into inflamed tissues, angiogenesis can also propagate chronic inflammation. This review examines the mutually supportive relationship between angiogenesis and inflammation, and considers how these interactions might be exploited to promote resolution of chronic inflammatory or angiogenic disorders.

Hypoxia: The Force that Drives Chronic Kidney Disease

In the United States the prevalence of end-stage renal disease (ESRD) reached epidemic proportions in 2012 with over 600,000 patients being treated. The rates of ESRD among the elderly are disproportionally high. Consequently, as life expectancy increases and the baby-boom generation reaches retirement age, the already heavy burden imposed by ESRD on the US health care system is set to increase dramatically. ESRD represents the terminal stage of chronic kidney disease (CKD). A large body of evidence indicating that CKD is driven by renal tissue hypoxia has led to the development of therapeutic strategies that increase kidney oxygenation and the contention that chronic hypoxia is the final common pathway to end-stage renal failure. Numerous studies have demonstrated that one of the most potent means by which hypoxic conditions within the kidney produce CKD is by inducing a sustained inflammatory attack by infiltrating leukocytes. Indispensable to this attack is the acquisition by leukocytes of an adhesive phenotype. It was thought that this process resulted exclusively from leukocytes responding to cytokines released from ischemic renal endothelium. However, recently it has been demonstrated that leukocytes also become activated independent of the hypoxic response of endothelial cells. It was found that this endothelium-independent mechanism involves leukocytes directly sensing hypoxia and responding by transcriptional induction of the genes that encode the β2-integrin family of adhesion molecules. This induction likely maintains the long-term inflammation by which hypoxia drives the pathogenesis of CKD. Consequently, targeting these transcriptional mechanisms would appear to represent a promising new therapeutic strategy.

Collaterals: Implications in cerebral ischemic diseases and therapeutic interventions

Despite the tremendous progress made in the treatment of cerebrovascular occlusive diseases, many patients suffering from ischemic brain injury still experience dismal outcomes. Although rehabilitation contributes to post-stroke functional recovery, there is no doubt that interventions that promote the restoration of blood supply are proven to minimize ischemic injury and improve recovery. In response to the acutely decreased blood perfusion during arterial occlusion, arteriogenesis, the compensation of blood flow through the collateral circulation during arterial obstructive diseases can act not only in a timely fashion but also much more efficiently compared to angiogenesis, the sprouting of new capillaries, and a mechanism occurring in a delayed fashion while increases the total resistance of the vascular bed of the affected territory. Interestingly, despite the vast differences between the two vascular remodeling mechanisms, some crucial growth factors and cytokines involved in angiogenesis are also required for arteriogenesis. Understanding the mechanisms underlying vascular remodeling after ischemic brain injury is a critical step towards the development of effective therapies for ischemic stroke. The present article will discuss our current views in vascular remodeling acutely after brain ischemia, namely arteriogenesis, and some relevant clinical therapies available on the horizon in augmenting collateral flow that hold promise in treating ischemic brain injury. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Phagocyte-myocyte interactions and consequences during hypoxic wound healing

Myocardial infarction (MI), secondary to atherosclerotic plaque rupture and occlusive thrombi, triggers acute margination of inflammatory neutrophils and monocyte phagocyte subsets to the damaged heart, the latter of which may give rise briefly to differentiated macrophage-like or dendritic-like cells. Within the injured myocardium, a primary function of these phagocytic cells is to remove damaged extracellular matrix, necrotic and apoptotic cardiac cells, as well as immune cells that turn over. Recognition of dying cellular targets by phagocytes triggers intracellular signaling, particularly in macrophages, wherein cytokines and lipid mediators are generated to promote inflammation resolution, fibrotic scarring, angiogenesis, and compensatory organ remodeling. These actions cooperate in an effort to preserve myocardial contractility and prevent heart failure. Immune cell function is modulated by local tissue factors that include secreted protease activity, oxidative stress during clinical reperfusion, and hypoxia. Importantly, experimental evidence suggests that monocyte function and phagocytosis efficiency is compromised in the setting of MI risk factors, including hyperlipidemia and ageing, however underlying mechanisms remain unclear. Herein we review seminal phagocyte and cardiac molecular factors that lead to, and culminate in, the recognition and removal of dying injured myocardium, the effects of hypoxia, and their relationship to cardiac infarct size and heart healing.

Postischemic revascularization: from cellular and molecular mechanisms to clinical applications

After the onset of ischemia, cardiac or skeletal muscle undergoes a continuum of molecular, cellular, and extracellular responses that determine the function and the remodeling of the ischemic tissue. Hypoxia-related pathways, immunoinflammatory balance, circulating or local vascular progenitor cells, as well as changes in hemodynamical forces within vascular wall trigger all the processes regulating vascular homeostasis, including vasculogenesis, angiogenesis, arteriogenesis, and collateral growth, which act in concert to establish a functional vascular network in ischemic zones. In patients with ischemic diseases, most of the cellular (mainly those involving bone marrow-derived cells and local stem/progenitor cells) and molecular mechanisms involved in the activation of vessel growth and vascular remodeling are markedly impaired by the deleterious microenvironment characterized by fibrosis, inflammation, hypoperfusion, and inhibition of endogenous angiogenic and regenerative programs. Furthermore, cardiovascular risk factors, including diabetes, hypercholesterolemia, hypertension, diabetes, and aging, constitute a deleterious macroenvironment that participates to the abrogation of postischemic revascularization and tissue regeneration observed in these patient populations. Thus stimulation of vessel growth and/or remodeling has emerged as a new therapeutic option in patients with ischemic diseases. Many strategies of therapeutic revascularization, based on the administration of growth factors or stem/progenitor cells from diverse sources, have been proposed and are currently tested in patients with peripheral arterial disease or cardiac diseases. This review provides an overview from our current knowledge regarding molecular and cellular mechanisms involved in postischemic revascularization, as well as advances in the clinical application of such strategies of therapeutic revascularization.

The inflammatory tissue microenvironment in IBD

A current view of the inflammatory bowel diseases (IBDs) includes the luminal triggering of innate immune disease in a genetically susceptible host. Given the unique anatomy and complex environment of the intestine, local microenvironmental cues likely contribute significantly to both disease progression and resolution in IBD. Compartmentalized tissue and microbe populations within the intestine result in significant metabolic shifts within these tissue microenvironments. During active inflammatory disease, metabolic demands often exceed supply, resulting in localized areas of metabolic stress and diminished oxygen delivery (hypoxia). There is much recent interest in harnessing these microenvironmental changes to the benefit of the tissue, including targeting these pathways for therapy of IBD. Here, we review the current understanding of metabolic microenvironments within the intestine in IBD, with discussion of the advantages and disadvantages of targeting these pathways to treat patients with IBD.

Hypoxia-inducible factor and target gene expression are decreased in patients with sepsis: prospective observational clinical and cellular studies

BACKGROUND

Hypoxia-inducible factor-1 (HIF-1) is a molecular key player in response to hypoxemic/inflammatory conditions prevailing in sepsis. In a prospective observational study, we tested the hypotheses that sepsis affects HIF-1α messenger ribonucleic acid (mRNA) expression (primary hypothesis) and also (secondary hypotheses) the expression of the HIF-1α target genes adrenomedullin and β2-integrins. Furthermore, we tested that lipopolysaccharide administration increases HIF-1α mRNA and protein in naive and endotoxin-tolerant monocytes.

METHODS

In 99 patients with sepsis and 48 healthy volunteers, leukocyte HIF-1α mRNA expression (real-time polymerase chain reaction), cytokine concentrations (enzymelinked immunosorbent assay), and intracellular distribution of HIF-1α protein (immunofluorescence staining) were assessed. In vitro, HIF-1α mRNA expression and protein were measured in naive or endotoxin-tolerant (48 h; 0.05 ng/ml lipopolysaccharide) monocytes, with/without additional lipopolysaccharide (6h; 1 μg/ml).

RESULTS

In comparison to healthy volunteers, HIF-1α mRNA expression (-67%; P = 0.0001) and HIF-1α protein positive cells (-66.7%; P = 0.01) were decreased in sepsis. mRNA expression of adrenomedullin (-75%), CD11a (-85%), and CD11b (-86%; all P = 0.0001) was also decreased. In contrast, interleukin 6 (P = 0.0001), interleukin 10 (P = 0.0001), and tumor necrosis factor-α (P = 0.0002) concentrations were increased. Of note, HIF-1α mRNA expression was inversely associated with illness severity (Simplified Acute Physiology Score II; r = -0.29; P = 0.0001). In vitro, acute lipopolysaccharide administration of naive monocytic cells increased HIF-1α mRNA expression, whereas HIF-1α mRNA and protein (-60%; P = 0.001) were decreased in endotoxin-tolerant cells, which still up regulated cytokines.

CONCLUSIONS

In sepsis, HIF-1α mRNA expression was suppressed and inversely associated with illness severity. While acute lipopolysaccharide administration increased HIF-1α mRNA expression, prolonged stimulation suppressed HIF-1α expression. The clinical implications of decreased HIF-1α may include maladaption to tissue hypoxia or depressed immune function.

Bpur, the Lyme disease spirochete's PUR domain protein: identification as a transcriptional modulator and characterization of nucleic acid interactions

The PUR domain is a nucleic acid-binding motif found in critical regulatory proteins of higher eukaryotes and in certain species of bacteria. During investigations into mechanisms by which the Lyme disease spirochete controls synthesis of its Erp surface proteins, it was discovered that the borrelial PUR domain protein, Bpur, binds with high affinity to double-stranded DNA adjacent to the erp transcriptional promoter. Bpur was found to enhance the effects of the erp repressor protein, BpaB. Bpur also bound single-stranded DNA and RNA, with relative affinities RNA > double-stranded DNA > single-stranded DNA. Rational site-directed mutagenesis of Bpur identified amino acid residues and domains critical for interactions with nucleic acids, and it revealed that the PUR domain has a distinct mechanism of interaction with each type of nucleic acid ligand. These data shed light on both gene regulation in the Lyme spirochete and functional mechanisms of the widely distributed PUR domain.

Myeloid hypoxia-inducible factor-1α is essential for skeletal muscle regeneration in mice

The outstanding regeneration ability of skeletal muscle is based on stem cells that become activated and develop to myoblasts after myotrauma. Proliferation and growth of myoblasts result in self-renewal of skeletal muscle. In this article, we show that myotrauma causes a hypoxic microenvironment leading to accumulation of the transcription factor hypoxia-inducible factor-1 (HIF-1) in skeletal muscle cells, as well as invading myeloid cells. To evaluate the impact of HIF-1 in skeletal muscle injury and repair, we examined mice with a conditional HIF-1α knockout targeted to skeletal muscle or myeloid cells in a model of soft tissue trauma. No differences in acute trauma size were detected between control and HIF-1α knockout mice. However, muscles of myeloid HIF-1α knockout mice showed a significant delay in myoblast proliferation and growth of regenerating myofibers, in association with decreased expression of cyclooxygenase-2 in HIF-1α-deficient myeloid cells. Moreover, the removal of necrotic cell debris and the regeneration of endothelial cell structure were impaired in myeloid HIF-1α knockout mice that showed delayed invasion of macrophages to the injury site. Our findings for the first time, to our knowledge, demonstrate that myeloid HIF-1α is required for adequate skeletal muscle regeneration.

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.

Hypoxia and metabolic factors that influence inflammatory bowel disease pathogenesis

The gastrointestinal epithelium is anatomically positioned to provide a selective barrier between the anaerobic lumen and lamina propria, which has a high rate of metabolism. Supported by a complex vasculature, this important barrier is affected by reduced blood flow and resultant tissue hypoxia, particularly during the severe metabolic shifts associated with active inflammation in individuals with inflammatory bowel disease. Activation of hypoxia-inducible factor (HIF) under these conditions promotes resolution of inflammation in mouse models of disease. Protective influences of HIF are attributed, in part, to the complex regulation of barrier protection with the intestinal mucosa. Reagents that activate HIF, via inhibition of the prolyl hydroxylase enzymes, might be developed to induce hypoxia-mediated resolution in patients with intestinal mucosal inflammatory disease.

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.

Metabolic shifts in immunity and inflammation

Sites of ongoing inflammation and triggered immune responses are characterized by significant changes in metabolic activity. Recent studies have indicated that such shifts in tissue metabolism result from a combination of profound recruitment of inflammatory cells (neutrophils and monocytes) and high proliferation rates among lymphocyte populations. The resultant shifts in energy supply and demand can result in metabolic acidosis and diminished delivery and/or availability of oxygen, leading to hypoxia extensive enough to trigger transcriptional and translation changes in tissue phenotype. Such phenotypic shifts can imprint fundamental changes to tissue metabolism. In this study, we review recent work addressing metabolic changes and metabolic control of inflammation and immunity.

Hypoxia: an alarm signal during intestinal inflammation

Intestinal epithelial cells that line the mucosal surface of the gastrointestinal tract are positioned between an anaerobic lumen and a highly metabolic lamina propria. As a result of this unique anatomy, intestinal epithelial cells function within a steep physiologic oxygen gradient relative to other cell types. Furthermore, during active inflammatory disease such as IBD, metabolic shifts towards hypoxia are severe. Studies in vitro and in vivo have shown that the activation of hypoxia-inducible factor (HIF) serves as an alarm signal to promote the resolution of inflammation in various mouse models of disease. Amelioration of disease occurs, at least in part, through transcriptional upregulation of nonclassic epithelial barrier genes. There is much interest in harnessing hypoxia-inducible pathways, including stabilizing HIF directly or via inhibition of prolyl hydroxylase enzymes, for therapy of IBD. In this Review, we discuss the signaling pathways involved in the regulation of hypoxia and discuss how hypoxia may serve as an endogenous alarm signal for the presence of mucosal inflammatory disease. We also discuss the pros and cons of targeting these pathways to treat patients with IBD.

Multiple roles for Puralpha in cellular and viral regulation

Pur-alpha is a ubiquitous multifunctional protein that is strongly conserved throughout evolution, binds to both DNA and RNA and functions in the initiation of DNA replication, control of transcription and mRNA translation. In addition, it binds to several cellular regulatory proteins including the retinoblastoma protein, E2F-1, Sp1, YB-1, cyclin T1/Cdk9 and cyclin A/Cdk2. These observations and functional studies provide evidence that Puralpha is a major player in the regulation of the cell cycle and oncogenic transformation. Puralpha also binds to viral proteins such as the large T-antigen of JC virus (JCV) and the Tat protein of human immunodeficiency virus-1 (HIV-1) and plays a role in the cross-communication of these viruses in the opportunistic polyomavirus JC (JCV) brain infection, progressive multifocal leukoencephalopathy (PML). The creation of transgenic mice with inactivation of the PURA gene that encodes Puralpha has revealed that Puralpha is critical for postnatal brain development and has unraveled an essential role of Puralpha in the transport of specific mRNAs to the dendrites and the establishment of the postsynaptic compartment in the developing neurons. Finally, the availability of cell cultures from the PURA knockout mice has allowed studies that have unraveled a role for Puralpha in DNA repair.