The interaction between HIF-1 and AP-1 transcription factors in response to low oxygen

The transcriptomic and biochemical responses of blood clams (Tegillarca granosa) to prolonged intermittent hypoxia

The blood clam (Tegillarca granosa), a marine bivalve of ecological and economic significance, often encounters intermittent hypoxia in mudflats and aquatic environments. To study the response of blood clam foot to prolonged intermittent hypoxia, the clams were exposed to intermittent hypoxia conditions (0.5 mg/L dissolved oxygen, with a 12-h interval) for 31 days. Initially, transcriptomic analysis was performed, uncovering a total of 698 differentially expressed genes (DEGs), with 236 upregulated and 462 downregulated. These genes show enrichments in signaling pathways related to glucose metabolism, sugar synthesis and responses to oxidative stress. Furthermore, the activity of the enzyme glutathione peroxidase (GPx) and the levels of gpx1 mRNA showed gradual increases, reaching their peak on the 13th day of intermittent hypoxia exposure. This observation suggests an indirect protective role of GPx against oxidative stress. The results of this study make a significantly contribute to our broader comprehensive of the physiological, biochemical responses, and molecular reactions governing the organization of foot muscle tissue in marine bivalves exposed to prolonged intermittent hypoxic conditions.

New roles for AP-1/JUNB in cell cycle control and tumorigenic cell invasion via regulation of cyclin E1 and TGF-β2

BACKGROUND

JUNB transcription factor contributes to the formation of the ubiquitous transcriptional complex AP-1 involved in the control of many physiological and disease-associated functions. The roles of JUNB in the control of cell division and tumorigenic processes are acknowledged but still unclear.

RESULTS

Here, we report the results of combined transcriptomic, genomic, and functional studies showing that JUNB promotes cell cycle progression via induction of cyclin E1 and repression of transforming growth factor (TGF)-β2 genes. We also show that high levels of JUNB switch the response of TGF-β2 stimulation from an antiproliferative to a pro-invasive one, induce endogenous TGF-β2 production by promoting TGF-β2 mRNA translation, and enhance tumor growth and metastasis in mice. Moreover, tumor genomic data indicate that JUNB amplification associates with poor prognosis in breast and ovarian cancer patients.

CONCLUSIONS

Our results reveal novel functions for JUNB in cell proliferation and tumor aggressiveness through regulation of cyclin E1 and TGF-β2 expression, which might be exploited for cancer prognosis and therapy.

A systematic study of HIF1A cofactors in hypoxic cancer cells

Hypoxia inducible factor 1 alpha (HIF1A) is a transcription factor (TF) that forms highly structural and functional protein-protein interactions with other TFs to promote gene expression in hypoxic cancer cells. However, despite the importance of these TF-TF interactions, we still lack a comprehensive view of many of the TF cofactors involved and how they cooperate. In this study, we systematically studied HIF1A cofactors in eight cancer cell lines using the computational motif mining tool, SIOMICS, and discovered 201 potential HIF1A cofactors, which included 21 of the 29 known HIF1A cofactors in public databases. These 201 cofactors were statistically and biologically significant, with 19 of the top 37 cofactors in our study directly validated in the literature. The remaining 18 were novel cofactors. These discovered cofactors can be essential to HIF1A's regulatory functions and may lead to the discovery of new therapeutic targets in cancer treatment.

Transcriptomic analysis of the chorioallantois in equine premature placental separation

BACKGROUND

Equine premature placental separation (PPS) is poorly understood and represents an important risk factor for fetal/neonatal hypoxia.

OBJECTIVES

To examine transcriptomic changes in the chorioallantois (CA) from mares with clinical PPS compared to the CA from normal foaling mares. Differential gene expression was determined and gene ontology as well as molecular pathways related to PPS were characterised.

STUDY DESIGN

Retrospective case: control study.

METHODS

CA were collected from Thoroughbred mares with a clinical history of PPS (n=33) and from control Thoroughbred mares (n=4) with normal parturition for examination of transcriptional changes in the placenta associated with PPS. Transcriptomic changes in the villous CA near the cervical star were determined by Illumina® sequencing and subsequent bioinformatic analysis. PPS samples were divided by k-means clustering, and differentially expressed genes (DEGs) in each PPS cluster were identified by comparing to controls. Shared DEGs between PPS clusters were used for gene ontology analysis and pathway analysis.

RESULTS

A total of 1204 DEGs were identified between PPS and control. Gene ontology revealed extracellular matrix (ECM) and cell adhesion, and pathway analysis revealed fatty acid, p-53, hypoxia, and inflammation. Eleven key regulator genes of PPS including growth factors (IGF1, TGFB2, TGFB3), transcription factors (HIF1A, JUNB, SMAD3), and transmembrane receptors (FGFR1, TNFRSF1A, TYROBP) were also identified.

MAIN LIMITATIONS

The use of clinical history of PPS, in the absence of other criteria, may have led to misidentification of some cases as PPS.

CONCLUSIONS

Transcriptomic analysis indicated that changes in ECM and cell adhesion were important factors in equine PPS. Key predicted upstream events include genes associated with hypoxia, inflammation and growth factors related to the pathogenesis of equine PPS.

Role of Oxidative Stress in Reperfusion following Myocardial Ischemia and Its Treatments

Myocardial ischemia is a disease with high morbidity and mortality, for which reperfusion is currently the standard intervention. However, the reperfusion may lead to further myocardial damage, known as myocardial ischemia/reperfusion injury (MI/RI). Oxidative stress is one of the most important pathological mechanisms in reperfusion injury, which causes apoptosis, autophagy, inflammation, and some other damage in cardiomyocytes through multiple pathways, thus causing irreversible cardiomyocyte damage and cardiac dysfunction. This article reviews the pathological mechanisms of oxidative stress involved in reperfusion injury and the interventions for different pathways and targets, so as to form systematic treatments for oxidative stress-induced myocardial reperfusion injury and make up for the lack of monotherapy.

Defining Physiological Normoxia for Improved Translation of Cell Physiology to Animal Models and Humans

The extensive oxygen gradient between the air we breathe (Po₂ ~21 kPa) and its ultimate distribution within mitochondria (as low as ~0.5-1 kPa) is testament to the efforts expended in limiting its inherent toxicity. It has long been recognized that cell culture undertaken under room air conditions falls short of replicating this protection in vitro. Despite this, difficulty in accurately determining the appropriate O₂ levels in which to culture cells, coupled with a lack of the technology to replicate and maintain a physiological O₂ environment in vitro, has hindered addressing this issue thus far. In this review, we aim to address the current understanding of tissue Po₂ distribution in vivo and summarize the attempts made to replicate these conditions in vitro. The state-of-the-art techniques employed to accurately determine O₂ levels, as well as the issues associated with reproducing physiological O₂ levels in vitro, are also critically reviewed. We aim to provide the framework for researchers to undertake cell culture under O₂ levels relevant to specific tissues and organs. We envisage that this review will facilitate a paradigm shift, enabling translation of findings under physiological conditions in vitro to disease pathology and the design of novel therapeutics.

Functional cooperation between HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR

OBJECTIVE

Hypoxia-inducible factor 1 (HIF-1) and activator protein 1 (AP-1) are important transcription factors regulating expression of genes involved in cell survival. HIF-1α and c-Jun are key components of HIF-1 and AP-1, respectively, and are regulated by epidermal growth factor receptor (EGFR)-mediated cell signaling and tumor microenvironmental cues. The roles of HIF-1α and c-Jun in development of resistance to EGFR tyrosine kinase inhibitor (TKI) in non-small cell lung cancer (NSCLC) with activating mutation of EGFR have not been explored. In this study, we investigated the roles of HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR.

MATERIALS AND METHODS

Changes in HIF-1α protein and in total and phosphorylated c-Jun levels in relation to changes in total and phosphorylated EGFR levels before and after gefitinib treatment were measured using Western blot analysis in NSCLC cells sensitive or resistant to gefitinib. The impact of overexpression of a constitutively expressed HIF-1α (HIF-1α/ΔODD) or a constitutively active c-Jun upstream regulator (SEK1 S220E/T224D mutant) on cell response to gefitinib was also examined. The effect of pharmacological inhibition of SEK1-JNK-c-Jun pathway on cell response to gefitinib was evaluated.

RESULTS

Downregulation of HIF-1α and total and phosphorylated c-Jun levels correlated with cell inhibitory response to gefitinib better than decrease in phosphorylated EGFR did in NSCLC cells with intrinsic or acquired resistance to gefitinib. Overexpression of HIF-1α/ΔODD or SEK1 S220E/T224D mutant conferred resistance to gefitinib. There exists a positive feed-forward regulation loop between HIF-1 and c-Jun. The JNK inhibitor SP600125 sensitized gefitinib-resistant NSCLC cells to gefitinib.

CONCLUSIONS

HIF-1α and c-Jun functionally cooperate in development of resistance to gefitinib in NSCLC cells. The translational value of inhibiting HIF-1α/c-Jun cooperation in overcoming resistance to EGFR TKI treatment of NSCLC cells with activating mutation of EGFR deserves further investigation.

The Role of Activator Protein-1 (AP-1) Family Members in CD30-Positive Lymphomas

The Activator Protein-1 (AP-1) transcription factor (TF) family, composed of a variety of members including c-JUN, c-FOS and ATF, is involved in mediating many biological processes such as proliferation, differentiation and cell death. Since their discovery, the role of AP-1 TFs in cancer development has been extensively analysed. Multiple in vitro and in vivo studies have highlighted the complexity of these TFs, mainly due to their cell-type specific homo- or hetero-dimerization resulting in diverse transcriptional response profiles. However, as a result of the increasing knowledge of the role of AP-1 TFs in disease, these TFs are being recognized as promising therapeutic targets for various malignancies. In this review, we focus on the impact of deregulated expression of AP-1 TFs in CD30-positive lymphomas including Classical Hodgkin Lymphoma and Anaplastic Large Cell Lymphoma.

Administration of FTY720 during Tourniquet-Induced Limb Ischemia Reperfusion Injury Attenuates Systemic Inflammation

Acute ischemia-reperfusion injury (IRI) of the extremities leads to local and systemic inflammatory changes which can hinder limb function and can be life threatening. This study examined whether the administration of the T-cell sequestration agent, FTY720, following hind limb tourniquet-induced skeletal muscle IRI in a rat model would attenuate systemic inflammation and multiple end organ injury. Sprague-Dawley rats were subjected to 1 hr of ischemia via application of a rubber band tourniquet. Animals were randomized to receive an intravenous bolus of either vehicle control or FTY720 15 min after band placement. Rats (n = 10/time point) were euthanized at 6, 24, and 72 hr post-IRI. Peripheral blood as well as lung, liver, kidney, and ischemic muscle tissue was analyzed and compared between groups. FTY720 treatment markedly decreased the number of peripheral blood T cells (p < 0.05) resulting in a decreased systemic inflammatory response and lower serum creatinine levels and had a modest but significant effect in decreasing the transcription of injury-associated target genes in multiple end organs. These findings suggest that early intervention with FTY720 may benefit the treatment of IRI of the limb. Further preclinical studies are necessary to characterize the short-term and long-term beneficial effects of FTY720 following tourniquet-induced IRI.

Lactate stimulates CA IX expression in normoxic cancer cells

Besides hypoxia, other factors and molecules such as lactate, succinate, and reactive oxygen species activate transcription factor hypoxia-inducible factor-1 (HIF-1) even in normoxia. One of the main target gene products of HIF-1 is carbonic anhydrase IX (CA IX). CA IX is overexpressed in many tumors and serves as prognostic factor for hypoxic, aggressive and malignant cancers. CA IX is also induced in normoxia in high cell density. In this study, we observed that lactate induces CA IX expression in normoxic cancer cells in vitro and in vivo. We further evidenced that participation of both HIF-1 and specificity protein 1 (SP1) transcription factors is crucial for lactate-driven normoxic induction of the CA9 gene. By inducing CA IX, lactate can facilitate the maintenance of cancer cell aggressive behavior in normoxia.

Different Oxygen Stresses on the Responses of Branchial Morphology and Protein Expression in the Gills and Labyrinth Organ in the Aquatic Air-breathing Fish, Trichogaster microlepis

Chun-Yen Huang and Hui-Chen Lin (2016) Organisms face direct challenges from a variety of abiotic factors in the environment. Changes in dissolved oxygen are one of the most common types of these challenges. The gills of some fish species can compensate for ambient oxygen changes by exhibiting morphological and functional plasticity that give the gill the ability to modify its structure. In the previous studies of aquatic air- breathing fish with an accessory air-breathing organ (the labyrinth organ), we found morphological and functional specializations between the 1st and 4th gills in the genus Trichogaster. This study investigated morphological and functional changes in the gills and labyrinth organ of the aquatic air-breathing fish T. microlepis over a 28- day period of oxygen uptake stresses. The experimental design was as follows: (1) a control group (held under normoxia with air-breathing respiration (ABR) allowed); (2) a hypoxic group (held under hypoxia with ABR); and (3) a restricted group (held under normoxia without ABR). We recorded the cumulative mortality of the fish and the frequency of ABR between the control and hypoxic groups, conducted morphological examinations of the lengths of gill filaments and lamellae of gills and determined the relative abundance of carbonic anhydrase II (CAII) and Na+/K+-ATPase (NKA). Mortality in the restricted group was higher than those in the control and the hypoxic groups. The frequency of ABR in the hypoxic condition was higher than that in the control. The lengths of the lamellae in the 1st, 3rd and 4th gills in the restricted group were significantly longer than those in the control group after 14 and 28 days. In addition, the relative abundance of CAII was significantly increased only in the labyrinth organ in the hypoxic group compared to the control group on day 3. The relative abundance of proliferating cell nuclear antigen also was significantly increased in the 1st gill, 4th gill and the labyrinth organ in the restricted group compared to the control group on day 14. This study showed, for the first time, that the 4th gill in T. microlepis, which is generally much-reduced compared to the other gills, can have elongated lamellae when fish are subjected to the restricted group for 28 day. The relative abundance of CAII in the labyrinth organ was significantly higher under hypoxic group than under control group on day 3.

Subthreshold nitric oxide synthase inhibition improves synergistic effects of subthreshold MMP-2/MLCK-mediated cardiomyocyte protection from hypoxic injury

Injury of myocardium during ischaemia/reperfusion (I/R) is a complex and multifactorial process involving uncontrolled protein phosphorylation, nitration/nitrosylation by increased production of nitric oxide and accelerated contractile protein degradation by matrix metalloproteinase‐2 (MMP‐2). It has been shown that simultaneous inhibition of MMP‐2 with doxycycline (Doxy) and myosin light chain kinase (MLCK) with ML‐7 at subthreshold concentrations protects the heart from contractile dysfunction triggered by I/R in a synergistic manner. In this study, we showed that additional co‐administration of nitric oxide synthase (NOS) inhibitor (1400W or L‐NAME) in subthreshold concentrations improves this synergistic protection in the model of hypoxia–reoxygenation (H‐R)‐induced contractile dysfunction of cardiomyocytes. Isolated cardiomyocytes were subjected to 3 min. of hypoxia and 20 min. of reoxygenation in the presence or absence of the inhibitor cocktails. Contractility of cardiomyocytes was expressed as myocyte peak shortening. Inhibition of MMP‐2 by Doxy (25–100 μM), MLCK by ML‐7 (0.5–5 μM) and NOS by L‐NAME (25–100 μM) or 1400W (25–100 μM) protected myocyte contractility after H‐R in a concentration‐dependent manner. Inhibition of these activities resulted in full recovery of cardiomyocyte contractility after H‐R at the level of highest single‐drug concentration. The combination of subthreshold concentrations of NOS, MMP‐2 and MLCK inhibitors fully protected cardiomyocyte contractility and MLC1 from degradation by MMP‐2. The observed protection with addition of L‐NAME or 1400W was better than previously reported combination of ML‐7 and Doxy. The results of this study suggest that addition of NOS inhibitor to the mixture of inhibitors is better strategy for protecting cardiomyocyte contractility.

Protective effect of allicin on high glucose/hypoxia-induced aortic endothelial cells via reduction of oxidative stress

This study was designed to explore the protective effect of allicin on aortic endothelial cell injury induced by high glucose/hypoxia and to investigate the corresponding mechanisms. The primary-cultured murine aortic endothelial cells were subcultured. The third passage of cells was adopted and randomly divided into five groups: The normal group (NG), the mannitol group (MG), the high-glucose/hypoxia group (HG), the allicin group (AG) and the protein kinase C (PKC) inhibitor group (GG). The general morphology was observed under an inverted phase-contrast microscope and cell viability was assessed using the MTT assay. Intracellular reactive oxygen species (ROS) levels in the endothelial cells were quantified using dihydroethidium staining. The levels of 8-hydroxydeoxyguanosine (8-OHdG), nuclear factor-κB (NF-κB), NADPH oxidase 4 (Nox4) and hypoxia-inducible factor-1α (HIF-1α) and the activity of PKC were measured using ELISA. A quantitative polymerase chain reaction (qPCR) was adopted to evaluate the mRNA expression of Nox4, HIF-1α and NF-κB. The altered cell morphology observed in HG was notably ameliorated in the AG and GG. The protein levels of 8-OHdG, NF-κB, Nox4, HIF-1α and PKC in the HG were higher than those in the other groups. Furthermore, the cell viability in the AG was significantly increased and the protein levels of 8-OHdG, NF-κB, Nox4, HIF-1α and PKC were significantly decreased compared with those in the HG. The ROS production was found to be increased in the HG cells, while there was a significant decrease in the AG cells. These data indicate that allicin exerts a protective effect against high glucose/hypoxia-induced injury in aortic endothelial cells through its antioxidative action, which may involve the inhibition of the PKC pathway and regulation of HIF-1α.

Heterogeneous Effects of Direct Hypoxia Pathway Activation in Kidney Cancer

General activation of hypoxia-inducible factor (HIF) pathways is classically associated with adverse prognosis in cancer and has been proposed to contribute to oncogenic drive. In clear cell renal carcinoma (CCRC) HIF pathways are upregulated by inactivation of the von-Hippel-Lindau tumor suppressor. However HIF-1α and HIF-2α have contrasting effects on experimental tumor progression. To better understand this paradox we examined pan-genomic patterns of HIF DNA binding and associated gene expression in response to manipulation of HIF-1α and HIF-2α and related the findings to CCRC prognosis. Our findings reveal distinct pan-genomic organization of canonical and non-canonical HIF isoform-specific DNA binding at thousands of sites. Overall associations were observed between HIF-1α-specific binding, and genes associated with favorable prognosis and between HIF-2α-specific binding and adverse prognosis. However within each isoform-specific set, individual gene associations were heterogeneous in sign and magnitude, suggesting that activation of each HIF-α isoform contributes a highly complex mix of pro- and anti-tumorigenic effects.

Potential role of hypoxia in early stages of Hodgkin lymphoma pathogenesis

A unique feature of the germinal center B cell-derived Hodgkin and Reed/Sternberg cells of classical Hodgkin lymphoma is their lost B cell phenotype and the aberrant expression of factors of other hematopoietic cell types, including ID2 and NOTCH1. As cellular dedifferentiation and upregulation of ID2 and NOTCH1 are typical consequences of a hypoxic response, we wondered whether hypoxia may impose an HRS cell-like phenotype in B cells. Culturing normal B cells or cell lines of germinal center-type diffuse large B-cell lymphoma under hypoxic conditions caused partial downregulation of several B cell markers, ID2 upregulation, and increased NOTCH1 activity. The hypoxic cells acquired further features of Hodgkin and Reed/Sternberg cells, including increased JUN expression, and enhanced NFκB activity. The Hodgkin and Reed/Sternberg cell-expressed epigenetic regulators KDM4C and PCGF2, as well as the phosphatase DUSP1 were partially induced in hypoxic B cells. Inhibition of DUSP1 was toxic for classical Hodgkin lymphoma cell lines. Thus, hypoxia induces key Hodgkin and Reed/Sternberg cell characteristics in mature B cells. We speculate that hypoxic conditions in the germinal center may impose phenotypic changes in germinal center B cells, promoting their survival and initiating their differentiation towards a Hodgkin and Reed/Sternberg cell-like phenotype. These may then be stabilized by transforming events in the Hodgkin and Reed/Sternberg precursor cells.

Effects of hypoxia on ionic regulation, glycogen utilization and antioxidative ability in the gills and liver of the aquatic air-breathing fish Trichogaster microlepis

We examined the hypothesis that Trichogaster microlepis, a fish with an accessory air-breathing organ, uses a compensatory strategy involving changes in both behavior and protein levels to enhance its gas exchange ability. This compensatory strategy enables the gill ion-regulatory metabolism to maintain homeostasis during exposure to hypoxia. The present study aimed to determine whether ionic regulation, glycogen utilization and antioxidant activity differ in terms of expression under hypoxic stresses; fish were sampled after being subjected to 3 or 12h of hypoxia and 12h of recovery under normoxia. The air-breathing behavior of the fish increased under hypoxia. No morphological modification of the gills was observed. The expression of carbonic anhydrase II did not vary among the treatments. The Na(+)/K(+)-ATPase enzyme activity did not decrease, but increases in Na(+)/K(+)-ATPase protein expression and ionocyte levels were observed. The glycogen utilization increased under hypoxia as measured by glycogen phosphorylase protein expression and blood glucose level, whereas the glycogen content decreased. The enzyme activity of several components of the antioxidant system in the gills, including catalase, glutathione peroxidase, and superoxidase dismutase, increased in enzyme activity. Based on the above data, we concluded that T. microlepis is a hypoxia-tolerant species that does not exhibit ion-regulatory suppression but uses glycogen to maintain energy utilization in the gills under hypoxic stress. Components of the antioxidant system showed increased expression under the applied experimental treatments.

Macrophages promote coal tar pitch extract-induced tumorigenesis of BEAS-2B cells and tumor metastasis in nude mice mediated by AP-1

BACKGROUND

We sought to evaluate the role of tumor associated macrophages (TAMs) on the promotion of coal tar pitch extract (CTPE)-induced tumorigenesis of human bronchial epithelial cells (BEAS-2B) and tumor metastasis in nude mice, and related mechanisms.

MATERIALS AND METHODS

BEAS-2B cells were first treated with 2.4 mg/mL CTPE for 72 hours. After removal of CTPE, the cells were continuously cultured and passaged using trypsin-EDTA. THP-1 cells were used as macrophage-like cells. BEAS-2B cells under different conditions (n=6/ group) were injected into the back necks of nude mice, and alterations of tumor xenograft growth, indicative of tumorigenicity, and tumor metastasis were determined. Pathological changes (tumor nests and microvascular lesions) of HE-stained tumor tissues were also evaluated. The expression of AP-1(c-Jun) in xenografts and metastatic tumors was determined using immunohistochemistry.

RESULTS

Tumor size and weight in nude mice transplanted with the mixture of CTPE-induced passage 30 BEAS-2B and THP-1 cells (2:1) were increased compared to those from the CTPE-treated BEAS-2B cells at passage 30 alone at different observation time points. Tumor metastasis to lymph nodes and liver was only detected after transplantation of a mixture the two kinds of cells. The numbers of tumor nests and microvascular lesions, and the expression levels of AP-1 (c-Jun) in tumors from the mixture of two kinds of cells were increased apparently in contrast to those in tumor from the CTPE-treated BEAS-2B cells of passage 30 alone. In addition, there was positive correlation between AP-1 (c-Jun) expression level and the number of microvascular lesions, or between AP-1 (c-Jun) expression level and tumor metastasis in these two groups.

CONCLUSIONS

TAMs not only facilitate tumorigenesis transformation of CTPE-induced BEAS-2B cells, but also promote tumor growth, angiogenesis and metastasis in nude mice in vivo, which may be mediated by AP-1.

A feedback regulatory loop between HIF-1α and miR-21 in response to hypoxia in cardiomyocytes

Accumulating evidence suggests that hypoxia-inducible factor 1α (HIF-1α) regulates numerous miRNAs and is crucial for cellular response to hypoxia. However, the relationship between HIF-1α and miR-21 in hypoxic cardiomyocytes is little known. We found that hypoxia induced HIF-1α and miR-21 expression. HIF-1α knockdown increased cell apoptosis and reduced miR-21 expression. Furthermore, we found that HIF-1α transcriptionally enhanced miR-21 promoter activity by binding to its promoter, which required the recruitment of CBP/p300. In addition, we found that miR-21 inhibition increased cell apoptosis and reduced HIF-1α expression, and modulated the PTEN/Akt pathway. Our results indicate that HIF-1α-miR-21 feedback contributes to the adaptation of cardiomyocytes to hypoxia, and has potential as therapeutic target for myocardial ischemia.

JunB/cyclin-D1 imbalance in placental mesenchymal stromal cells derived from preeclamptic pregnancies with fetal-placental compromise

INTRODUCTION

In the present study, we characterized the expression of Activating Protein 1 (AP-1) factors, key cell cycle regulators, in primary placental mesenchymal stromal cells (PDMSCs) derived from normal and preeclamptic (PE) pregnancies with fetal-placental compromise.

METHODS

PDMSCs were isolated from control (n = 20) and preeclamptic (n = 24) placentae. AP-1 expression was determined by semi-quantitative RT-PCR (sqRT-PCR), Real Time PCR and Western Blot assay. PDMSCs were plated and JunB siRNA was performed. JunB and Cyclin-D1 expression were assessed by Real Time and Western Blot analyses.

RESULTS

JunB expression was significantly increased while Cyclin-D1 expression was significantly down-regulated in PE relative to control PDMSCs. JunB siRNA was accompanied by JunB down-regulation and increased Cyclin-D1 in normal PDMSCs.

CONCLUSIONS

We described, for the first time, AP-1 expression in PDMSCs derived from physiological and PE placentae. Importantly, we demonstrated that JunB over-expression in PE-PDMSCs affects Cyclin-D1 regulation. Our data suggest a possible contribution of these pathological placental cells to the altered cell cycle regulation typical of preeclamptic placentae.

N-acetylcysteine and allopurinol confer synergy in attenuating myocardial ischemia injury via restoring HIF-1α/HO-1 signaling in diabetic rats

OBJECTIVES

To determine whether or not the antioxidants N-acetylcysteine (NAC) and allopurinol (ALP) confer synergistic cardioprotection against myocardial ischemia/reperfusion (MI/R) injury by stabilizing hypoxia inducible factor 1α (HIF-1α)/heme oxygenase 1 (HO-1) signaling in diabetic myocardium.

METHODS

Control or diabetic [streptozotocin (STZ)-induced] Sprague Dawley rats received vehicle or NAC, ALP or their combination for four weeks starting one week after STZ injection. The animals were then subjected to thirty minutes of coronary artery occlusion followed by two hours reperfusion in the absence or presence of the selective HO-1 inhibitor, tin protoporphyrin-IX (SnPP-IX) or the HIF-1α inhibitor 2-Methoxyestradiol (2ME2). Cardiomyocytes exposed to high glucose were subjected to hypoxia/re-oxygenation in the presence or absence of HIF-1α and HO-1 achieved by gene knock-down with related siRNAs.

RESULTS

Myocardial and plasma levels of 15-F2t-isoprostane, an index of oxidative stress, were significantly increased in diabetic rats while cardiac HO-1 protein and activity were reduced; this was accompanied with reduced cardiac protein levels of HIF-1α, and increased post-ischemic myocardial infarct size and cellular injury. NAC and ALP given alone and in particular their combination normalized cardiac levels of HO-1 and HIF-1α protein expression and prevented the increase in 15-F2t-isoprostane, resulting in significantly attenuated post-ischemic myocardial infarction. NAC and ALP also attenuated high glucose-induced post-hypoxic cardiomyocyte death in vitro. However, all the above protective effects of NAC and ALP were cancelled either by inhibition of HO-1 or HIF-1α with SnPP-IX and 2ME2 in vivo or by HO-1 or HIF-1α gene knock-down in vitro.

CONCLUSION

NAC and ALP confer synergistic cardioprotection in diabetes via restoration of cardiac HIF-1α and HO-1 signaling.

Autocrine production of IL-11 mediates tumorigenicity in hypoxic cancer cells

IL-11 and its receptor, IL-11Ra, are expressed in human cancers; however, the functional role of IL-11 in tumor progression is not known. We found that IL11 is a hypoxia-inducible, VHL-regulated gene in human cancer cells and that expression of IL11 mRNA was dependent, at least in part, on HIF-1. A cooperative interaction between HIF-1 and AP-1 mediated transcriptional activation of the IL11 promoter. Additionally, we found that human cancer cells expressed a functional IL-11Ra subunit, which triggered signal transduction either by exogenous recombinant human IL-11 or by autocrine production of IL-11 in cells cultured under hypoxic conditions. Silencing of IL11 dramatically abrogated the ability of hypoxia to increase anchorage-independent growth and significantly reduced tumor growth in xenograft models. Notably, these results were phenocopied by partial knockdown of STAT1 in a human prostate cancer cell line (PC3), suggesting that this pathway may play an important role in mediating the effects of IL-11 under hypoxic conditions. In conclusion, these results identify IL11 as an oxygen- and VHL-regulated gene and provide evidence of a pathway "hijacked" by hypoxic cancer cells that may contribute to tumor progression.

Cooperativity of stress-responsive transcription factors in core hypoxia-inducible factor binding regions

The transcriptional response driven by Hypoxia-inducible factor (HIF) is central to the adaptation to oxygen restriction. Despite recent characterization of genome-wide HIF DNA binding locations and hypoxia-regulated transcripts in different cell types, the molecular bases of HIF target selection remain unresolved. Herein, we combined multi-level experimental data and computational predictions to identify sequence motifs that may contribute to HIF target selectivity. We obtained a core set of bona fide HIF binding regions by integrating multiple HIF1 DNA binding and hypoxia expression profiling datasets. This core set exhibits evolutionarily conserved binding regions and is enriched in functional responses to hypoxia. Computational prediction of enriched transcription factor binding sites identified sequence motifs corresponding to several stress-responsive transcription factors, such as activator protein 1 (AP1), cAMP response element-binding (CREB), or CCAAT-enhancer binding protein (CEBP). Experimental validations on HIF-regulated promoters suggest a functional role of the identified motifs in modulating HIF-mediated transcription. Accordingly, transcriptional targets of these factors are over-represented in a sorted list of hypoxia-regulated genes. Altogether, our results implicate cooperativity among stress-responsive transcription factors in fine-tuning the HIF transcriptional response.

HIF-VEGF pathways are critical for chronic otitis media in Junbo and Jeff mouse mutants

Otitis media with effusion (OME) is the commonest cause of hearing loss in children, yet the underlying genetic pathways and mechanisms involved are incompletely understood. Ventilation of the middle ear with tympanostomy tubes is the commonest surgical procedure in children and the best treatment for chronic OME, but the mechanism by which they work remains uncertain. As hypoxia is a common feature of inflamed microenvironments, moderation of hypoxia may be a significant contributory mechanism. We have investigated the occurrence of hypoxia and hypoxia-inducible factor (HIF) mediated responses in Junbo and Jeff mouse mutant models, which develop spontaneous chronic otitis media. We found that Jeff and Junbo mice labeled in vivo with pimonidazole showed cellular hypoxia in inflammatory cells in the bulla lumen, and in Junbo the middle ear mucosa was also hypoxic. The bulla fluid inflammatory cell numbers were greater and the upregulation of inflammatory gene networks were more pronounced in Junbo than Jeff. Hif-1α gene expression was elevated in bulla fluid inflammatory cells, and there was upregulation of its target genes including Vegfa in Junbo and Jeff. We therefore investigated the effects in Junbo of small-molecule inhibitors of VEGFR signaling (PTK787, SU-11248, and BAY 43-9006) and destabilizing HIF by inhibiting its chaperone HSP90 with 17-DMAG. We found that both classes of inhibitor significantly reduced hearing loss and the occurrence of bulla fluid and that VEGFR inhibitors moderated angiogenesis and lymphangiogenesis in the inflamed middle ear mucosa. The effectiveness of HSP90 and VEGFR signaling inhibitors in suppressing OM in the Junbo model implicates HIF–mediated VEGF as playing a pivotal role in OM pathogenesis. Our analysis of the Junbo and Jeff mutants highlights the role of hypoxia and HIF–mediated pathways, and we conclude that targeting molecules in HIF–VEGF signaling pathways has therapeutic potential in the treatment of chronic OM.

Otitis media with effusion (OME) is the commonest cause of hearing loss in children, and treatment using grommets remains the commonest surgical procedure in children. Chronic forms of OM are known from human population studies to have a significant genetic component, but little is known of the underlying genes or pathways involved. We have analyzed two chronic OM mouse models, the Junbo and Jeff mutants, and have found that both demonstrate hypoxia and hypoxia-inducible factor (HIF) mediated responses. There is upregulation of inflammatory pathways in the mutant middle ears and in Junbo elevation of cytokines that modulate Hif-1α. Hif-1α levels are raised in the middle ear as well as downstream targets of HIF such as Vegfa. We explored the effects of small-molecule inhibitors of HSP90 and VEGF receptor signaling in the Junbo mutant and found significant reductions in hearing loss, the occurrence of bulla fluid, and moderation of vascular changes in the inflamed middle ear mucosa with the VEGF receptor inhibitors. The study of the Junbo and Jeff mutants demonstrates the role of hypoxia and HIF mediated pathways in OM pathogenesis, and it indicates that targeting the HIF–VEGF pathway may represent a novel approach to therapeutic intervention in chronic OM.

Molecular mechanisms regulating macrophage response to hypoxia

Monocytes and Macrophages (Mo/Mɸ) exhibit great plasticity, as they can shift between different modes of activation and, driven by their immediate microenvironment, perform divergent functions. These include, among others, patrolling their surroundings and maintaining homeostasis (resident Mo/Mɸ), combating invading pathogens and tumor cells (classically activated or M1 Mo/Mɸ), orchestrating wound healing (alternatively activated or M2 Mo/Mɸ), and restoring homeostasis after an inflammatory response (resolution Mɸ). Hypoxia is an important factor in the Mɸ microenvironment, is prevalent in many physiological and pathological conditions, and is interdependent with the inflammatory response. Although Mo/Mɸ have been studied in hypoxia, the mechanisms by which hypoxia influences the different modes of their activation, and how it regulates the shift between them, remain unclear. Here we review the current knowledge about the molecular mechanisms that mediate this hypoxic regulation of Mɸ activation. Much is known about the hypoxic transcriptional regulatory network, which includes the master regulators hypoxia-induced factor-1 and NF-κB, as well as other transcription factors (e.g., AP-1, Erg-1), but we also highlight the role of post-transcriptional and post-translational mechanisms. These mechanisms mediate hypoxic induction of Mɸ pro-angiogenic mediators, suppress M1 Mɸ by post-transcriptionally inhibiting pro-inflammatory mediators, and help shift the classically activated Mɸ into an activation state which approximate the alternatively activated or resolution Mɸ.

The kreisler mutation leads to the loss of intrinsically hypoxia-activated spots in the region of the retrotrapezoid nucleus/parafacial respiratory group

Acute hypoxia elicits a biphasic respiratory response characterized in the newborn by a transient hyperventilation followed by a severe decrease in respiratory drive known as hypoxic respiratory depression. Medullary O(2) chemosensitivity is known to contribute to respiratory depression induced by hypoxia, although precise involvement of cell populations remains to be determined. Having a thorough knowledge of these populations is of relevance because perturbations in the respiratory response to hypoxia may participate in respiratory diseases in newborns. We aimed to analyze the hypoxic response of ponto-medullary cell populations of kreisler mutant mice. These mice have defects in a gene expressed in two rhombomeres encompassing a part of the medulla oblongata implicated in hypoxic respiratory depression. Central responses to hypoxia were analyzed in newborn mice by measuring respiratory rhythm in ex vivo caudal pons-medullary-spinal cord preparations and c-fos expression in wild-type and kreisler mutants. The homozygous kreisler mutation, which eliminates most of rhombomere 5 and mis-specifies rhombomere 6, abolished (1) an early decrease in respiratory frequency within 10 min of hypoxia and (2) an intrinsic hypoxic activation, which is characterized by an increase in c-fos expression in the region of the ventral medullary surface encompassing the retrotrapezoid nucleus/parafacial respiratory group expressing Phox2b. This increase in c-fos expression persisted in wild-type Phox2b-negative and Phox2b-positive cells after blockade of synaptic transmission and rhythmogenesis by a low [Ca(2+)](0). Another central response was retained in homozygous kreisler mutant mice; it was distinguished by (1) a delayed (10-30 min) depression of respiratory frequency and (2) a downregulation of c-fos expression in the ventrolateral reticular nucleus of the medulla, the nucleus of the solitary tract, and the area of the A5 region. Thus, two types of ponto-medullary cell groups, with distinct anatomical locations, participate in central hypoxic respiratory depression in newborns.

Knockdown of cytoglobin expression sensitizes human glioma cells to radiation and oxidative stress

Cytoglobin is a recently identified vertebrate globin whose functions include scavenging reactive oxygen and nitrosative species. In tumor cells, CYGB may function as a tumor suppressor gene. Here we show that knockdown of cytoglobin expression can sensitize human glioma cells to oxidative stress induced by chemical inhibitors of the electron transport chain and as well can increase cellular radiosensitivity. When treated with antimycin A, an inhibitor of the mitochondrial electron transport chain, cytoglobin-deficient cells showed significantly higher H₂O₂ levels, whereas H₂O₂ levels were significantly reduced in cytoglobin-overexpressing cells. In addition, cytoglobin knockdown significantly decreased the doubling time of glioma cell lines, consistent with a putative tumor suppressor function. These finding suggest that modulating cytoglobin levels may be a promising treatment strategy for sensitizing human glioma cells to oxidative stress that is induced by ionizing radiation, certain chemotherapies and ischemia-reperfusion.

Oxidative stress and hypoxia-induced factor 1α expression in gastric ischemia

AIM: To investigate the relation of reactive oxygen species (ROS) to hypoxia induced factor 1α (HIF-1α) in gastric ischemia.

METHODS: The animal model of gastric ischemia reperfusion was established by placing an elastic rubber band on the proximal part of the bilateral lower limb for ligature for 3 h and reperfusion for 0, 1, 3, 6, 12 or 24 h. Ischemic post-conditioning, three cycles of 30-s reperfusion and 30-s femoral aortic reocclusion were conducted before reperfusion. Histological and immunohistochemical methods were used to assess the gastric oxidative damageand the expression of HIF1-α in gastric ischemia. The malondialdehyde (MDA) content and superoxide dismutase (SOD), xanthine oxidase (XOD) and myeloperoxidase (MPO) activities were determined by colorimetric assays.

RESULTS: Ischemic post-conditioning can reduce post-ischemic oxidativestressand the expression of HIF-1α of gastric tissue resulting from limb ischemia reperfusion injury. MDA, SOD, XOD and MPO were regarded as indexes for mucosal injuries from ROS, and ROS was found to affect the expression of HIF-1α under gastric ischemic conditions.

CONCLUSION: ROS affects HIF-1α expression under gastric ischemic conditions induced by limb ischemia reperfusion injury. Therefore, ROS can regulate HIF-1α expression in gastric ischemia.

Regulation of Cyr61/CCN1 expression by hypoxia through cooperation of c-Jun/AP-1 and HIF-1α in retinal vascular endothelial cells

Hypoxia is the most important factor in the pathogenesis of diabetic retinopathy. Cysteine-rich 61 (Cyr61) is one of the angiogenic factors involved in the development of proliferative diabetic retinopathy (PDR). The aim of this study was to investigate the mechanism of hypoxia-induced Cyr61 expression in retinal vascular endothelial cells. The hypoxia-induced expression of mRNA and protein of Cyr61 was studied in monkey choroidal retinal vascular endothelial (RF/6A) cells. Luciferase reporter assays and electrophoretic mobility shift assays were used to identify the hypoxia responsible region and transcription factors in the Cyr61 promoter. Chromatin immunoprecipitation and immunoprecipitation were performed to study the role of hypoxia-inducible factor (HIF)-1α and c-Jun/activator protein-1 (AP-1) in Cyr61 transcriptional regulation. The results showed that hypoxia significantly induced Cyr61 mRNA and protein expression in RF/6A cells. The effect was mediated through phosphorylation of c-Jun. Luciferase assays, electrophoretic mobility shift assays, chromatin immunoprecipitation and immunoprecipitation showed that HIF-1α interacted with c-Jun/AP-1 and their binding on the AP-1 binding motif within the Cyr61 promoter induced the expression of Cyr61. In conclusion, hypoxia controlled the transcriptional regulation of the Cyr61 gene in RF/6A cells by cooperation of HIF-1α and c-Jun/AP-1. Cyr61 might play an important role in ischemic retinal diseases, such as PDR.

Suppression of hypoxia-inducible factor-1alpha and its downstream genes reduces acute hyperglycemia-enhanced hemorrhagic transformation in a rat model of cerebral ischemia

We evaluated a role of hypoxia-inducible factor-1alpha (HIF-1alpha) and its downstream genes in acute hyperglycemia-induced hemorrhagic transformation in a rat model of focal cerebral ischemia. Male Sprague-Dawley rats weighing 280-300 g (n = 105) were divided into sham, 90 min middle cerebral artery occlusion (MCAO), MCAO plus HIF-1alpha inhibitors, 2-methoxyestradiol (2ME2) or 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), groups. Rats received an injection of 50% dextrose (6 ml/kg intraperitoneally) at 15 min before MCAO. HIF-1alpha inhibitors were administered at the onset of reperfusion. The animals were examined for neurological deficits and sacrificed at 6, 12, 24, and 72 hr following MCAO. The cerebral tissues were collected for histology, zymography, and Western blot analysis. The expression of HIF-1alpha was increased in ischemic brain tissues after MCAO and reduced by HIF-1alpha inhibitors. In addition, 2ME2 reduced the expression of vascular endothelial growth factor (VEGF) and the elevation of active matrix metalloproteinase-2 and -9 (MMP-2/MMP-9) in the ipsilateral hemisphere. Both 2ME2 and YC-1 reduced infarct volume and ameliorated neurological deficits. However, only 2ME2 attenuated hemorrhagic transformation in the ischemic territory. In conclusion, the inhibition of HIF-1alpha and its downstream genes attenuates hemorrhagic conversion of cerebral infarction and ameliorates neurological deficits after focal cerebral ischemia.

AP-1--The Jun proteins: Oncogenes or tumor suppressors in disguise?

Since its discovery more than two decades ago the involvement of the Activating protein 1 (AP-1) in proliferation, inflammation, differentiation, apoptosis, cellular migration and wound healing has been intensively studied. A model based on the early studies suggested antagonistic roles for the Jun proteins in proliferation and transformation. c-Jun was suggested to enhance transformation whereas JunB suggested to inhibit it in an antagonistic manner. Surprisingly, despite accumulation of data obtained from animal models regarding the role of Jun proteins in cancer and identification of oncogenic pathways regulating them, their involvement in human cancer was not demonstrated until recently. Here, we will describe the current knowledge about the roles of Jun proteins in human neoplasia. We will focus on the pathological examples demonstrating that the initial dogma has to be reexamined. For example, like c-Jun, JunB seems to play an oncogenic role in lymphomas, particularly in Hodgkin's lympomas. Furthermore, unlike the antagonistic activities of c-Jun and JunB in the transcription of genes coding for major cell cycle regulators such as CyclinD or p16INK4A, the transcription of other cell cycle regulating genes is modified similarly by c-Jun or JunB. Interestingly, some of these genes such as the ones coding for CyclinA or p19(ARF) are important players in either positive or negative regulation of cellular proliferation and survival. Finally, we will also discuss results posing JNK, known so far as the major activator of c-Jun, as a negative regulator of c-Jun level and activity. These recent findings suggest that the role of each Jun protein in neoplasia as well as in cellular survival should be examined in a context-dependent manner.

Activating transcription factor 2 increases transactivation and protein stability of hypoxia-inducible factor 1alpha in hepatocytes

HIF-1 (hypoxia inducible factor 1) performs a crucial role in mediating the response to hypoxia. However, other transcription factors are also capable of regulating hypoxia-induced target-gene transcription. In a previous report, we demonstrated that the transcription factor ATF-2 (activating transcription factor 2) regulates hypoxia-induced gene transcription, along with HIF-1alpha. In the present study, we show that the protein stability of ATF-2 is induced by hypoxia and the hypoxia-mimic CoCl2 (cobalt chloride), and that ATF-2 induction enhances HIF-1alpha protein stability via direct protein interaction. The knockdown of ATF-2 using small interfering RNA and translation-inhibition experiments demonstrated that ATF-2 plays a key role in the maintenance of the expression level and transcriptional activity of HIF-1alpha. Furthermore, we determined that ATF-2 interacts directly with HIF-1alpha both in vivo and in vitro and competes with the tumour suppressor protein p53 for HIF-1alpha binding. Collectively, these results show that protein stabilization of ATF-2 under hypoxic conditions is required for the induction of the protein stability and transactivation activity of HIF-1alpha for efficient hypoxia-associated gene expression.

Calcineurin activates cytoglobin transcription in hypoxic myocytes

Cardiac hypertrophy develops in response to a variety of cardiovascular stresses and results in activation of numerous signaling cascades and proteins. In the present study, we demonstrate that cytoglobin is a stress-responsive hemoprotein in the hypoxia-induced hypertrophic myocardium and it is transcriptionally regulated by calcineurin-dependent transcription factors. The cytoglobin transcript level is abundantly expressed in the adult heart and in response to hypoxia cytoglobin expression is markedly up-regulated within the hypoxia-induced hypertrophic heart. To define the molecular mechanism resulting in the induction of cytoglobin, we undertook a transcriptional analysis of the 5' upstream regulatory region of the cytoglobin gene. Evolutionarily conserved binding elements for transcription factors HIF-1, AP-1, and NFAT are located within the upstream region of the cytoglobin gene. Transcriptional assays demonstrated that calcineurin activity modulates cytoglobin transcription. Increased calcineurin activity enhances the ability of NFAT and AP-1 to bind to the putative cytoglobin promoter, especially under hypoxic conditions. In addition, inhibition of calcineurin, NFAT, and/or AP-1 activities decreases endogenous cytoglobin transcript and protein levels. Thus, the regulation of cytoglobin transcription by calcineurin-dependent transcription factors suggests that cytoglobin may have a functional role in calcium-dependent events accompanying cardiac remodeling.

Transcriptional control of the tumor- and hypoxia-marker carbonic anhydrase 9: A one transcription factor (HIF-1) show?

Transcriptional activation by hypoxia is mediated by the hypoxia-inducible factor (HIF) via binding to the hypoxia-responsive element (HRE). Hypoxia in solid tumors associates with poorer outcome of the disease and reliable cellular markers of tumor hypoxia would represent a valuable diagnostic marker and a potential therapeutic target. In this category, carbonic anhydrase IX (CAIX) is one of the most promising candidates. Here, we summarize the knowledge about transcriptional regulation of CA9. The HRE is the central regulatory element in the CA9 promoter, whereas other elements are limited to lesser roles of amplification of signals received at the HRE. The analysis of known mechanisms of activation of CA9 reveals the prominent role of the HIF-1 pathway. Experimental paradigms with uncoupled HIF-1alpha stability and transcriptional activity (pericellular hypoxia, proteasomal inhibitor) provide evidence that CA9 expression monitors transcriptional activity of HIF-1, rather than the abundance of HIF-1alpha. Furthermore, these paradigms could provide a corollary to some of the apparently discordant cases (CAIX+, HIF-1alpha-) or (CAIX-, HIF-1alpha+) observed in vivo. In conclusion, the existing data support the notion that CA9, due to the unique structure of its promoter, is one of the most sensitive endogenous sensors of HIF-1 activity.

Regulation of gene expression by hypoxia

Hypoxia induces profound changes in the cellular gene expression profile. The discovery of a major transcription factor family activated by hypoxia, HIF (hypoxia-inducible factor), and the factors that contribute to HIF regulation have greatly enhanced our knowledge of the molecular aspects of the hypoxic response. However, in addition to HIF, other transcription factors and cellular pathways are activated by exposure to reduced oxygen. In the present review, we summarize the current knowledge of how additional hypoxia-responsive transcription factors integrate with HIF and how other cellular pathways such as chromatin remodelling, translation regulation and microRNA induction, contribute to the co-ordinated cellular response observed following hypoxic stress.

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

Central to the process of inflammation are hypoxic conditions that lead to the binding of circulating leukocytes to the endothelium. We have previously shown that such binding is mediated by monocytes being able to directly sense hypoxic conditions and respond by inducing their surface expression of the beta(2) integrin family of adhesion molecules. In this study, we show that coordinated induction of the beta(2) integrins during direct hypoxia-sensing occurs through transcriptional activation of each of the genes by which they are encoded. Certain of the molecular mechanisms that mediate this activation in transcription are dependent upon hypoxia-inducible factor-1 (HIF-1), whereas others are HIF-1 independent. In search of these HIF-1-independent mechanisms, we identified Pur alpha as a new hypoxia-response factor. Binding of Pur alpha to the HIF-1-independent beta(2) integrin promoters is induced by hypoxia and mutagenesis of these Pur alpha-binding sites almost completely abolishes the ability of the promoters to respond to hypoxic conditions. Additional studies using siRNA directed against Pur alpha also revealed a loss in the hypoxic response of the beta(2) integrin promoters. Taken together, our findings demonstrate that hypoxia induces a coordinated up-regulation in beta(2) integrin expression that is dependent upon transcriptional mechanisms mediated by HIF-1 and Pur alpha.

c-Jun and JunB Are Essential for Hypoglycemia-MediatedVEGFInduction

Physiological conditions like hypoxia or hypoglycemia trigger expression of VEGF, a key regulator of angiogenesis. To elucidate the molecular mechanism underlying the VEGF regulation of hypoglycemia, we investigated the role of AP-1 transcription factor subunits c-Jun and JunB. Using c-jun(-/-) and junB(-/-) mouse embryonic fibroblasts, we demonstrate that both c-Jun and JunB are required for the hypoglycemia-mediated induction of VEGF expression. This process is independent of the master regulator of hypoxic stress HIF-1, as HIF expression and stabilization are not affected by the loss of AP-1 subunits. Analysis of signaling cascades regulating c-Jun and/or JunB activity and/or transcription upon hypoglycemia by application of specific inhibitors of protein kinase C (PKC) or extracellular signal-regulated kinase (ERK) signaling revealed that hypoglycemia-mediated induction of c-Jun is regulated via a PKCalpha-dependent signaling pathway. In contrast, JunB is activated by the MAP kinase ERK for the AP-1 subunits c-Jun and JunB to mediate VEGF regulaltion of hypoglycemia.

Evidence of HIF-1 functional binding activity to caspase-3 promoter after photothrombotic cerebral ischemia

Hypoxia-inducible factor 1 alpha (HIF-1alpha) is a transcription factor that was suggested in vitro to promote cell death by modulation of proapoptotic genes. In this report, we tested the hypothesis of an in vivo proapoptotic role of HIF-1alpha after an ischemic insult. For this purpose, HIF-1alpha and procaspase-3 mRNA and protein expressions were examined in rat brain subjected to 12- and 24-h permanent focal ischemia and the presence of an HIF-1 binding activity to the caspase-3 gene promoter was explored. The results showed that HIF-1alpha and procaspase-3 expressions increased with a similar pattern in response to ischemia. In addition, caspase-3 activation was observed in cells that express HIF-1alpha. Moreover, electrophoretic mobility assay revealed a specific HIF-1 binding activity to the caspase-3 gene promoter. Altogether the present data provide strong arguments for a causative relationship between HIF-1alpha and caspase-3 inductions through a functional binding activity to the caspase-3 gene promoter.

Activated protein C inhibits tissue plasminogen activator-induced brain hemorrhage

Brain hemorrhage is a serious complication of tissue plasminogen activator (tPA) therapy for ischemic stroke. Here we report that activated protein C (APC), a plasma serine protease with systemic anticoagulant, anti-inflammatory and antiapoptotic activities, and direct vasculoprotective and neuroprotective activities, blocks tPA-mediated brain hemorrhage after transient brain ischemia and embolic stroke in rodents. We show that APC inhibits a pro-hemorrhagic tPA-induced, NF-kappaB-dependent matrix metalloproteinase-9 pathway in ischemic brain endothelium in vivo and in vitro by acting through protease-activated receptor 1. The present findings suggest that APC may improve thrombolytic therapy for stroke, in part, by reducing tPA-mediated hemorrhage.

5'-AMP-activated protein kinase (AMPK) is induced by low-oxygen and glucose deprivation conditions found in solid-tumor microenvironments

Low oxygen gradients (hypoxia and anoxia) are important determinants of pathological conditions under which the tissue blood supply is deficient or defective, such as in solid tumors. We have been investigating the relationship between the activation of hypoxia-inducible factor 1 (HIF-1), the primary transcriptional regulator of the mammalian response to hypoxia, and 5'-AMP-activated protein kinase (AMPK), another regulatory system important for controlling cellular energy metabolism. In the present study, we used mouse embryo fibroblasts nullizygous for HIF-1alpha or AMPK expression to show that AMPK is rapidly activated in vitro by both physiological and pathophysiological low-oxygen conditions, independently of HIF-1 activity. These findings imply that HIF-1 and AMPK are components of a concerted cellular response to maintain energy homeostasis in low-oxygen or ischemic-tissue microenvironments. Finally, we used transformed derivatives of wild-type and HIF-1alpha- or AMPKalpha-null mouse embryo fibroblasts to determine whether AMPK is activated in vivo. We obtained evidence that AMPK is activated in authentic hypoxic tumor microenvironments and that this activity overlaps with regions of hypoxia detected by a chemical probe. We also showed that AMPK is important for the growth of this tumor model.