NF-kappaB plays a key role in hypoxia-inducible factor-1-regulated erythropoietin gene expression

The Janus face of HIF-1α in ischemic stroke and the possible associated pathways

Stroke is the most devastating disease, causing paralysis and eventually death. Many clinical and experimental trials have been done in search of a new safe and efficient medicine; nevertheless, scientists have yet to discover successful remedies that are also free of adverse effects. This is owing to the variability in intensity, localization, medication routes, and each patient's immune system reaction. HIF-1α represents the modern tool employed to treat stroke diseases due to its functions: downstream genes such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. Its role can be achieved via two downstream EPO and VEGF strongly related to apoptosis and antioxidant processes. Recently, scientists paid more attention to drugs dealing with the HIF-1 pathway. This review focuses on medicines used for ischemia treatment and their potential HIF-1α pathways. Furthermore, we discussed the interaction between HIF-1α and other biological pathways such as oxidative stress; however, a spotlight has been focused on certain potential signalling contributed to the HIF-1α pathway. HIF-1α is an essential regulator of oxygen balance within cells which affects and controls the expression of thousands of genes related to sustaining homeostasis as oxygen levels fluctuate. HIF-1α's role in ischemic stroke strongly depends on the duration and severity of brain damage after onset. HIF-1α remains difficult to investigate, particularly in ischemic stroke, due to alterations in the acute and chronic phases of the disease, as well as discrepancies between the penumbra and ischemic core. This review emphasizes these contrasts and analyzes the future of this intriguing and demanding field.

Targeting HIF-1α by Natural and Synthetic Compounds: A Promising Approach for Anti-Cancer Therapeutics Development

Advancement in novel target detection using improved molecular cancer biology has opened up new avenues for promising anti-cancer drug development. In the past two decades, the mechanism of tumor hypoxia has become more understandable with the discovery of hypoxia-inducible factor-1α (HIF-1α). It is a major transcriptional regulator that coordinates the activity of various transcription factors and their downstream molecules involved in tumorigenesis. HIF-1α not only plays a crucial role in the adaptation of tumor cells to hypoxia but also regulates different biological processes, including cell proliferation, survival, cellular metabolism, angiogenesis, metastasis, cancer stem cell maintenance, and propagation. Therefore, HIF-1α overexpression is strongly associated with poor prognosis in patients with different solid cancers. Hence, pharmacological targeting of HIF-1α has been considered to be a novel cancer therapeutic strategy in recent years. In this review, we provide brief descriptions of natural and synthetic compounds as HIF-1α inhibitors that have the potential to accelerate anticancer drug discovery. This review also introduces the mode of action of these compounds for a better understanding of the chemical leads, which could be useful as cancer therapeutics in the future.

Inhibition of the HIF-1 Survival Pathway as a Strategy to Augment Photodynamic Therapy Efficacy

Photodynamic therapy (PDT) is a non-to-minimally invasive treatment modality that utilizes photoactivatable drugs called photosensitizers to disrupt tumors with locally photoproduced reactive oxygen species (ROS). Photosensitizer activation by light results in hyperoxidative stress and subsequent tumor cell death, vascular shutdown and hypoxia, and an antitumor immune response. However, sublethally afflicted tumor cells initiate several survival mechanisms that account for decreased PDT efficacy. The hypoxia inducible factor 1 (HIF-1) pathway is one of the most effective cell survival pathways that contributes to cell recovery from PDT-induced damage. Several hundred target genes of the HIF-1 heterodimeric complex collectively mediate processes that are involved in tumor cell survival directly and indirectly (e.g., vascularization, glucose metabolism, proliferation, and metastasis). The broad spectrum of biological ramifications culminating from the activation of HIF-1 target genes reflects the importance of HIF-1 in the context of therapeutic recalcitrance. This chapter elaborates on the involvement of HIF-1 in cancer biology, the hypoxic response mechanisms, and the role of HIF-1 in PDT. An overview of inhibitors that either directly or indirectly impede HIF-1-mediated survival signaling is provided. The inhibitors may be used as pharmacological adjuvants in combination with PDT to augment therapeutic efficacy.

Molecular Insights into the Oxygen-Sensing Pathway and Erythropoietin Expression Regulation in Erythropoiesis

Erythropoiesis is regulated by several factors, including the oxygen-sensing pathway as the main regulator of erythropoietin (EPO) synthesis in the kidney. The release of EPO from the kidney and its binding to the EPO receptor (EPOR) on erythrocyte progenitor cells in the bone marrow results in increased erythropoiesis. Any imbalance in these homeostatic mechanisms can lead to dysregulated erythropoiesis and hematological disorders. For example, mutations in genes encoding key players of oxygen-sensing pathway and regulation of EPO production (HIF-EPO pathway), namely VHL, EGLN, EPAS1 and EPO, are well known causative factors that contribute to the development of erythrocytosis. We aimed to investigate additional molecular mechanisms involved in the HIF-EPO pathway that correlate with erythropoiesis. To this end, we conducted an extensive literature search and used several in silico tools. We identified genes encoding transcription factors and proteins that control transcriptional activation or repression; genes encoding kinases, deacetylases, methyltransferases, conjugating enzymes, protein ligases, and proteases involved in post-translational modifications; and genes encoding nuclear transport receptors that regulate nuclear transport. All these genes may modulate the stability or activity of HIF2α and its partners in the HIF-EPO pathway, thus affecting EPO synthesis. The theoretical information we provide in this work can be a valuable tool for a better understanding of one of the most important regulatory pathways in the process of erythropoiesis. This knowledge is necessary to discover the causative factors that may contribute to the development of hematological diseases and improve current diagnostic and treatment solutions in this regard.

Hypoxia and Inflammation: Insights From High-Altitude Physiology

The key regulators of the transcriptional response to hypoxia and inflammation (hypoxia inducible factor, HIF, and nuclear factor-kappa B, NF-κB, respectively) are evolutionarily conserved and share significant crosstalk. Tissues often experience hypoxia and inflammation concurrently at the site of infection or injury due to fluid retention and immune cell recruitment that ultimately reduces the rate of oxygen delivery to tissues. Inflammation can induce activity of HIF-pathway genes, and hypoxia may modulate inflammatory signaling. While it is clear that these molecular pathways function in concert, the physiological consequences of hypoxia-induced inflammation and how hypoxia modulates inflammatory signaling and immune function are not well established. In this review, we summarize known mechanisms of HIF and NF-κB crosstalk and highlight the physiological consequences that can arise from maladaptive hypoxia-induced inflammation. Finally, we discuss what can be learned about adaptive regulation of inflammation under chronic hypoxia by examining adaptive and maladaptive inflammatory phenotypes observed in human populations at high altitude. We aim to provide insight into the time domains of hypoxia-induced inflammation and highlight the importance of hypoxia-induced inflammatory sensitization in immune function, pathologies, and environmental adaptation.

Phloroglucinol Strengthens the Antioxidant Barrier and Reduces Oxidative/Nitrosative Stress in Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) is one of the most commonly occurring diseases within western dietary patterns. Usually untreated, it may lead to type 2 diabetes mellitus (T2DM), steatohepatitis (NASH), and hepatocellular carcinoma (HCC). Besides its severe aftermath, up to now, there is no known therapeutic approach to this disease in everyday clinical practice. Most NAFLD patients are encouraged to do physical activities or diet change and remain without pharmacological treatment. In this study, we present phloroglucinol (PHG) as a novel and promising compound in NAFLD treatment. PHG significantly increased the level of enzymatic and nonenzymatic antioxidants both in palmitate and hydrogen peroxide-induced oxidative stress models. Strengthened antioxidative defense reduced the oxidative/nitrosative damage to cell proteins, lipids, and carbohydrates. Furthermore, PHG treatment reduced hepatic steatosis; lowered inflammatory markers, such as NF-κB or HIF-1α; and inhibited cell apoptosis. Moreover, PHG had a more comprehensive effect than other commonly used antioxidants: N-acetylcysteine (NAC) and α-lipoic acid (ALA), suggesting its clinical usability. Therefore, our paper supports the benefits of natural compounds as a therapeutical approach to NAFLD.

Influence of Zinc on the Acute Changes in Erythropoietin and Proinflammatory Cytokines with Hypoxia

Baranauskas, Marissa N., Joseph Powell, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, Hunter L. Paris, and Robert F. Chapman. Influence of zinc on the acute changes in erythropoietin and proinflammatory cytokines with hypoxia. High Alt Med Biol. 22: 148-156, 2021. Background: Considerable, unexplained, interindividual variability characterizes the erythropoietin (EPO) response to hypoxia, which can impact hematological acclimatization for individuals sojourning to altitude. Zinc supplementation has the potential to alter EPO by attenuating increases in inflammation and oxidative stress. Yet, the application of such an intervention has not been evaluated in humans. In this proof-of-concept study, we aimed to evaluate the EPO and inflammatory responses to acute hypoxia in human participants following chronic zinc supplementation. Methods: Nine physically active participants (men n = 5, women n = 4, age 28 ± 4 years, height 176 ± 11 cm, mass 77 ± 21 kg) were exposed to 12 hours of normobaric hypoxia simulating an altitude of 3,000 m (F_iO₂ = 0.14) before and after 8 weeks of supplementation with 40 mg/day of elemental zinc from picolinate. Blood samples for subsequent analysis of serum zinc, EPO, superoxide dismutase (extracellular superoxide dismutase [EC-SOD]), C-reactive protein (CRP), and proinflammatory cytokines were obtained pre- and postsupplementation and exposure to hypoxia. Results: After zinc supplementation, EPO increased by 64.9 ± 36.0% (mean ± standard deviation) following 12 hours of hypoxia, but this response was not different from presupplementation (70.8 ± 46.1%). Considerable interindividual (range: -1% to +208%) variability was apparent in the acute EPO response. While most markers of inflammation did not change with hypoxia, interleukin-6 concentrations increased from 1.17 ± 0.05 to 1.97 ± 0.32 pg/ml during the final 6 hours. The acute EPO response at 12 hours was not related to changes in serum zinc, EC-SOD, CRP, or proinflammatory cytokines. Conclusions: Zinc supplementation does not influence the acute EPO or inflammatory response with short-term exposure to moderate levels of normobaric hypoxia (3,000 m) in apparently healthy young adults.

Upregulation of endogenous erythropoietin expression by DLBS6747, a bioactive fraction of Ipomoea batatas L. leaves, via increasing HIF1α transcription factor in HEK293 kidney cells

ETHNOPHARMACOLOGICAL RELEVANCE

Ipomoea batatas L., locally known as ubi jalar, is widely used in Indonesia and other countries as a folk remedy for various chronic diseases, including anemia-associated chronic kidney disease by increasing hematological parameters such as packed cell volume, white blood cells and platelet counts.

AIM OF THE STUDY

The aim of this study is to evaluate the effect of DLBS6747, a bioactive fraction of I. batatas L. leaves, on increasing EPO expression through the upregulation of HIF1α.

MATERIALS AND METHODS

Effect of DLBS6747 on EPO expression and its transcription factor, HIFs, was evaluated in normoxia and hypoxia conditions. Effect of DLBS6747 on several genes involved in EPO expression were evaluated in a time-course manner using conventional and real-time PCR, while the protein level were revealed using western blot and ELISA. The involvement of HIF1α was also confirmed by HIF1α siRNA.

RESULTS

Administration of DLBS6747 increased transcriptional activity of EPO through the regulation of its transcriptional factors, which include HIF1α, HIF2α and NFᴋB. The effect was found to be dependent on oxygen availability, wherein DLBS6747-increased EPO expression was found to be more significant in hypoxic condition. In normoxia and hypoxia, 40 μg/mL DLBS6747 increased HIF1α and HIF2α expressions at mRNA level, wherein the peak appeared in 12 h treatment (up to 7.9- and 8.6-folds, respectively). On the other hand, increased protein level was only found in hypoxia, where the highest HIF1α expression was observed at 6 h (7.5-folds increase) and started to decrease after the hours, while HIF2α was found to be increased time-dependently (up to 13.8-folds in 24 h). The mechanism of action of DLBS6747 as erythropoietin stimulating agent is more likely to affect the regulation of HIF1α, as confirmed by HIF1α siRNA which showed that DLBS6747 failed to increase EPO expression during co-incubation with HIF1α siRNA. DLBS6747 treatment also decreased NFᴋB time-dependently in normoxia, while no NFᴋB was detected in hypoxia, which revealed mimicking hypoxia activity of DLBS6747 to increase EPO expression.

CONCLUSION

These findings showed convincing evidences that DLBS6747 increases endogenous EPO production primarily via upregulation of its transcription factors, especially HIF1α, in human embryonic kidney HEK293 cells. This is the first molecular report that reveals the mechanism of action of natural-based erythropenia drug in different oxygen availability.

Cell Type-Specific Roles of NF-κB Linking Inflammation and Thrombosis

The transcription factor NF-κB is a central mediator of inflammation with multiple links to thrombotic processes. In this review, we focus on the role of NF-κB signaling in cell types within the vasculature and the circulation that are involved in thrombo-inflammatory processes. All these cells express NF-κB, which mediates important functions in cellular interactions, cell survival and differentiation, as well as expression of cytokines, chemokines, and coagulation factors. Even platelets, as anucleated cells, contain NF-κB family members and their corresponding signaling molecules, which are involved in platelet activation, as well as secondary feedback circuits. The response of endothelial cells to inflammation and NF-κB activation is characterized by the induction of adhesion molecules promoting binding and transmigration of leukocytes, while simultaneously increasing their thrombogenic potential. Paracrine signaling from endothelial cells activates NF-κB in vascular smooth muscle cells and causes a phenotypic switch to a “synthetic” state associated with a decrease in contractile proteins. Monocytes react to inflammatory situations with enforced expression of tissue factor and after differentiation to macrophages with altered polarization. Neutrophils respond with an extension of their life span—and upon full activation they can expel their DNA thereby forming so-called neutrophil extracellular traps (NETs), which exert antibacterial functions, but also induce a strong coagulatory response. This may cause formation of microthrombi that are important for the immobilization of pathogens, a process designated as immunothrombosis. However, deregulation of the complex cellular links between inflammation and thrombosis by unrestrained NET formation or the loss of the endothelial layer due to mechanical rupture or erosion can result in rapid activation and aggregation of platelets and the manifestation of thrombo-inflammatory diseases. Sepsis is an important example of such a disorder caused by a dysregulated host response to infection finally leading to severe coagulopathies. NF-κB is critically involved in these pathophysiological processes as it induces both inflammatory and thrombotic responses.

Erythropoietin in traumatic brain injury associated acute kidney injury: A randomized controlled trial

BACKGROUND

Acute kidney injury (AKI) in traumatic brain injury (TBI) is poorly understood and it is unknown if it can be attenuated using erythropoietin (EPO).

METHODS

Pre-planned analysis of patients included in the EPO-TBI (ClinicalTrials.gov NCT00987454) trial who were randomized to weekly EPO (40 000 units) or placebo (0.9% sodium chloride) subcutaneously up to three doses or until intensive care unit (ICU) discharge. Creatinine levels and urinary output (up to 7 days) were categorized according to the Kidney Disease Improving Global Outcome (KDIGO) classification. Severity of TBI was categorized with the International Mission for Prognosis and Analysis of Clinical Trials in TBI.

RESULTS

Of 3348 screened patients, 606 were randomized and 603 were analyzed. Of these, 82 (14%) patients developed AKI according to KDIGO (60 [10%] with KDIGO 1, 11 [2%] patients with KDIGO 2, and 11 [2%] patients with KDIGO 3). Male gender (hazard ratio [HR] 4.0 95% confidence interval [CI] 1.4-11.2, P = 0.008) and severity of TBI (HR 1.3 95% CI 1.1-1.4, P < 0.001 for each 10% increase in risk of poor 6 month outcome) predicted time to AKI. KDIGO stage 1 (HR 8.8 95% CI 4.5-17, P < 0.001), KDIGO stage 2 (HR 13.2 95% CI 3.9-45.2, P < 0.001) and KDIGO stage 3 (HR 11.7 95% CI 3.5-39.7, P < 0.005) predicted time to mortality. EPO did not influence time to AKI (HR 1.08 95% CI 0.7-1.67, P = 0.73) or creatinine levels during ICU stay (P = 0.09).

CONCLUSIONS

Acute kidney injury is more common in male patients and those with severe compared to moderate TBI and appears associated with worse outcome. EPO does not prevent AKI after TBI.

An Apparent Correlation Between Central Nervous System and Kidney's Erythropoietin and TNF Alpha Expression at Peak Experimental Autoimmune Encephalomyelitis Disease

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelination disease associated with inflammatory reactions and attenuation of antioxidant capacity. Several lines of evidence show that organs such as the liver and kidneys can share their antioxidant activity to protect the central nervous system (CNS) against neurodegenerative diseases. The aim of this study was to examine the possible interplay of the kidneys and CNS in pathogenesis of EAE. For this purpose, EAE model was induced in C57BL/6 mice, and expression of erythropoietin (EPO), TNF-α, and NFκB-1 was determined in the kidney and CNS at early and peak stages of the disease. Besides, changes in serum level of EPO and total antioxidant capacity (TAC) were measured by different clinical scores. Real-time PCR (qPCR) results showed a substantial increase in TNF-α and NFκB-1 expression in mice at EAE peak stage compared to sham (control). There was a positive correlation between kidney-EPO and CNS-inflammatory factor expression in EAE-induced mice. In general, EPO expression was relatively higher in the kidneys compared to CNS tissue in sham group. There was a significant upregulation in expression of EPO in the brain, spinal cord, and kidneys particularly at peak stage. Accordingly, changes in serum TAC were consistent with serum EPO concentration. This data may suggest that there is an EPO-mediated cross-talk between the kidney and CNS during EAE pathogenesis.

Selective IKK2 inhibitor IMD0354 disrupts NF-κB signaling to suppress corneal inflammation and angiogenesis

Corneal neovascularization is a sight-threatening condition caused by angiogenesis in the normally avascular cornea. Neovascularization of the cornea is often associated with an inflammatory response, thus targeting VEGF-A alone yields only a limited efficacy. The NF-κB signaling pathway plays important roles in inflammation and angiogenesis. Here, we study consequences of the inhibition of NF-κB activation through selective blockade of the IKK complex IκB kinase β (IKK2) using the compound IMD0354, focusing on the effects of inflammation and pathological angiogenesis in the cornea. In vitro, IMD0354 treatment diminished HUVEC migration and tube formation without an increase in cell death and arrested rat aortic ring sprouting. In HUVEC, the IMD0354 treatment caused a dose-dependent reduction in VEGF-A expression, suppressed TNFα-stimulated expression of chemokines CCL2 and CXCL5, and diminished actin filament fibers and cell filopodia formation. In developing zebrafish embryos, IMD0354 treatment reduced expression of Vegf-a and disrupted retinal angiogenesis. In inflammation-induced angiogenesis in the rat cornea, systemic selective IKK2 inhibition decreased inflammatory cell invasion, suppressed CCL2, CXCL5, Cxcr2, and TNF-α expression and exhibited anti-angiogenic effects such as reduced limbal vessel dilation, reduced VEGF-A expression and reduced angiogenic sprouting, without noticeable toxic effect. In summary, targeting NF-κB by selective IKK2 inhibition dampened the inflammatory and angiogenic responses in vivo by modulating the endothelial cell expression profile and motility, thus indicating an important role of NF-κB signaling in the development of pathologic corneal neovascularization.

A haplotype variant of the human chromogranin A gene (CHGA) promoter increases CHGA expression and the risk for cardiometabolic disorders

The acidic glycoprotein chromogranin A (CHGA) is co-stored/co-secreted with catecholamines and crucial for secretory vesicle biogenesis in neuronal/neuroendocrine cells. CHGA is dysregulated in several cardiovascular diseases, but the underlying mechanisms are not well established. Here, we sought to identify common polymorphisms in the CHGA promoter and to explore the mechanistic basis of their plausible contribution to regulating CHGA protein levels in circulation. Resequencing of the CHGA promoter in an Indian population (n = 769) yielded nine single-nucleotide polymorphisms (SNPs): G-1106A, A-1018T, T-1014C, T-988G, G-513A, G-462A, T-415C, C-89A, and C-57T. Linkage disequilibrium (LD) analysis indicated strong LD among SNPs at the -1014, -988, -462, and -89 bp positions and between the -1018 and -57 bp positions. Haplotype analysis predicted five major promoter haplotypes that displayed differential promoter activities in neuronal cells; specifically, haplotype 2 (containing variant T alleles at -1018 and -57 bp) exhibited the highest promoter activity. Systematic computational and experimental analyses revealed that transcription factor c-Rel has a role in activating the CHGA promoter haplotype 2 under basal and pathophysiological conditions (viz. inflammation and hypoxia). Consistent with the higher in vitro CHGA promoter activity of haplotype 2, individuals carrying this haplotype had higher plasma CHGA levels, plasma glucose levels, diastolic blood pressure, and body mass index. In conclusion, these results suggest a functional role of the CHGA promoter haplotype 2 (occurring in a large proportion of the world population) in enhancing CHGA expression in haplotype 2 carriers who may be at higher risk for cardiovascular/metabolic disorders.

Palmitic Acid-BSA enhances Amyloid-β production through GPR40-mediated dual pathways in neuronal cells: Involvement of the Akt/mTOR/HIF-1α and Akt/NF-κB pathways

The pathophysiological actions of fatty acids (FAs) on Alzheimer’s disease (AD), which are possibly mediated by genomic effects, are widely known; however, their non-genomic actions remain elusive. The aim of this study was to investigate the non-genomic mechanism of extra-cellular palmitic acid (PA) regulating beta-amyloid peptide (Aβ) production, which may provide a link between obesity and the occurrence of AD. In an obese mouse model, a high-fat diet (HFD) significantly increased the expression levels of APP and BACE1 as well as the AD pathology in the mouse brain. We further found that PA conjugated with bovine serum albumin (PA-BSA) increased the expression of APP and BACE1 and the production of Aβ through the G protein-coupled receptor 40 (GPR40) in SK-N-MC cells. PA-BSA coupling with GPR40 significantly induced Akt activation which is required for mTOR/p70S6K1-mediated HIF-1α expression and NF-κB phosphorylation facilitating the transcriptional activity of the APP and BACE1 genes. In addition, silencing of APP and BACE1 expression significantly decreased the production of Aβ in SK-N-MC cells treated with PA-BSA. In conclusion, these results show that extra-cellular PA coupled with GPR40 induces the expression of APP and BACE1 to facilitate Aβ production via the Akt-mTOR-HIF-1α and Akt-NF-κB pathways in SK-N-MC cells.

Erythropoietin Pathway: A Potential Target for the Treatment of Depression

During the past decade, accumulating evidence from both clinical and experimental studies has indicated that erythropoietin may have antidepressant effects. In addition to the kidney and liver, many organs have been identified as secretory tissues for erythropoietin, including the brain. Its receptor is expressed in cerebral and spinal cord neurons, the hypothalamus, hippocampus, neocortex, dorsal root ganglia, nerve axons, and Schwann cells. These findings may highlight new functions for erythropoietin, which was originally considered to play a crucial role in the progress of erythroid differentiation. Erythropoietin and its receptor signaling through JAK2 activate multiple downstream signaling pathways including STAT5, PI3K/Akt, NF-κB, and MAPK. These factors may play an important role in inflammation and neuroprogression in the nervous system. This is particularly true for the hippocampus, which is possibly related to learning, memory, neurocognitive deficits and mood alterations. Thus, the influence of erythropoietin on the downstream pathways known to be involved in the treatment of depression makes the erythropoietin-related pathway an attractive target for the development of new therapeutic approaches. Focusing on erythropoietin may help us understand the pathogenic mechanisms of depression and the molecular basis of its treatment.

Understanding complexity in the HIF signaling pathway using systems biology and mathematical modeling

Hypoxia is a common micro-environmental stress which is experienced by cells during a range of physiologic and pathophysiologic processes. The identification of the hypoxia-inducible factor (HIF) as the master regulator of the transcriptional response to hypoxia transformed our understanding of the mechanism underpinning the hypoxic response at the molecular level and identified HIF as a potentially important new therapeutic target. It has recently become clear that multiple levels of regulatory control exert influence on the HIF pathway giving the response a complex and dynamic activity profile. These include positive and negative feedback loops within the HIF pathway as well as multiple levels of crosstalk with other signaling pathways. The emerging model reflects a multi-level regulatory network that affects multiple aspects of the physiologic response to hypoxia including proliferation, apoptosis, and differentiation. Understanding the interplay between the molecular mechanisms involved in the dynamic regulation of the HIF pathway at a systems level is critically important in defining new appropriate therapeutic targets for human diseases including ischemia, cancer, and chronic inflammation. Here, we review our current knowledge of the regulatory circuits which exert influence over the HIF response and give examples of in silico model-based predictions of the dynamic behaviour of this system.

c-Kit Receptor Signaling Regulates Islet Vasculature, β-Cell Survival, and Function In Vivo

The receptor tyrosine kinase c-Kit plays an integral role in maintaining β-cell mass and function. Although c-Kit receptor signaling promotes angiogenesis in multiple cell types, its role in islet vasculature is unknown. This study examines the effects of c-Kit-mediated vascular endothelial growth factor isoform A (VEGF-A) and islet vascularization on β-cell function and survival using in vitro cell culture and in vivo mouse models. In cultured INS-1 cells and primary islets, c-Kit regulates VEGF-A expression via the Akt/mammalian target of rapamycin (mTOR) signaling pathway. Juvenile mice with mutated c-Kit (c-Kit(Wv/+)) showed impaired islet vasculature and β-cell dysfunction, while restoring c-Kit expression in β-cells of c-Kit(Wv/+) mice rescued islet vascular defects through modulation of the Akt/mTOR/VEGF-A pathway, indicating that c-Kit signaling in β-cells is a required regulator for maintaining normal islet vasculature. Furthermore, β-cell-specific c-Kit overexpression (c-KitβTg) in aged mice showed significantly increased islet vasculature and β-cell function, but, when exposed to a long-term high-fat diet, c-Kit signaling in c-KitβTg mice induced substantial vascular remodeling, which resulted in increased islet inflammatory responses and β-cell apoptosis. These results suggest that c-Kit-mediated VEGF-A action in β-cells plays a pivotal role in maintaining islet vascularization and function.

[Endogenous erythropoietin, acute kidney injury, and prognosis in patients with acute coronary syndrome]

AIM

To investigate the prognostic value of serum endogenous erythropoietin (EPO) in patients with acute coronary syndrome (ACS), including that in the development of acute kidney injury (AKI).

SUBJECTS AND METHODS

Eighty-four patients (46 men, 38 women; mean age 63 ± 11 years) with ACS were examined. Twenty-one (25%) patents were diagnosed with ECG ST-segment elevation acute myocardial infarction (STSEAMI), 12 (14%) had ECG non-STSEAMI, and 51 (61%) had unstable angina. Thrombolytic therapy was performed in 10 (48%) patients with STSEAMI. The patients whom had not undergone coronarography were included in the investigation to exclude the nephrotoxic effect of X-ray contrast agents.

RESULTS

AKI was observed in 7 of the patients with acute myocardial infarction and in only 1 of those with unstable angina. Four (5%) patients died during hospitalization. The EPO level of > 10.5 IU/ml predicted the development of AKI in the ACS patients with a sensitivity of 71% and a specificity of 67%. That of > 13.7 IU/ml was associated with hospital death in the ACS patients with a sensitivity of 100% and a specificity of 75% (AUC = 0.93%).

CONCLUSION

High serum EPO levels in an ACS patent during his hospital stay may serve as a biomarker for a high risk for AKI and high death rates.

Interferon-γ-induced intestinal epithelial barrier dysfunction by NF-κB/HIF-1α pathway

Interferon-γ (IFN-γ) plays an important role in intestinal barrier dysfunction. However, the mechanisms are not fully understood. As hypoxia-inducible factor-1 (HIF-1) is a critical determinant response to hypoxia and inflammation, which has been shown to be deleterious to intestinal barrier function, we hypothesized that IFN-γ induces loss of barrier function through the regulation of HIF-1α activation and function. In this study, we detected the expressions of HIF-1α and tight junction proteins in IFN-γ-treated T84 intestinal epithelial cell line. IFN-γ led to an increase of HIF-1α expression in time- and dose-dependent manners but did not change the expression of HIF-1β. The IFN-γ-induced increase in HIF-1α was associated with an activation of NF-κB. Treatment with the NF-κB inhibitor, pyrolidinedithiocarbamate (PDTC), significantly suppressed the activation of NF-κB and the expression of HIF-1α. In addition, IFN-γ also increased intestinal epithelial permeability and depletion of tight junction proteins; inhibition of NF-κB or HIF-1α prevented the increase in intestinal permeability and alteration in tight junction protein expressions. Interestingly, we demonstrated that a significant portion of IFN-γ activation NF-kB and modulation tight junction expression is mediated through HIF-1α. Taken together, this study suggested that IFN-γ induced the loss of epithelial barrier function and disruption of tight junction proteins, by upregulation of HIF-1α expression through NF-κB pathway.

STAT3 or USF2 contributes to HIF target gene specificity

The HIF1- and HIF2-mediated transcriptional responses play critical roles in solid tumor progression. Despite significant similarities, including their binding to promoters of both HIF1 and HIF2 target genes, HIF1 and HIF2 proteins activate unique subsets of target genes under hypoxia. The mechanism for HIF target gene specificity has remained unclear. Using siRNA or inhibitor, we previously reported that STAT3 or USF2 is specifically required for activation of endogenous HIF1 or HIF2 target genes. In this study, using reporter gene assays and chromatin immuno-precipitation, we find that STAT3 or USF2 exhibits specific binding to the promoters of HIF1 or HIF2 target genes respectively even when over-expressed. Functionally, HIF1α interacts with STAT3 to activate HIF1 target gene promoters in a HIF1α HLH/PAS and N-TAD dependent manner while HIF2α interacts with USF2 to activate HIF2 target gene promoters in a HIF2α N-TAD dependent manner. Physically, HIF1α HLH and PAS domains are required for its interaction with STAT3 while both N- and C-TADs of HIF2α are involved in physical interaction with USF2. Importantly, addition of functional USF2 binding sites into a HIF1 target gene promoter increases the basal activity of the promoter as well as its response to HIF2+USF2 activation while replacing HIF binding site with HBS from a HIF2 target gene does not change the specificity of the reporter gene. Importantly, RNA Pol II on HIF1 or HIF2 target genes is primarily associated with HIF1α or HIF2α in a STAT3 or USF2 dependent manner. Thus, we demonstrate here for the first time that HIF target gene specificity is achieved by HIF transcription partners that are required for HIF target gene activation, exhibit specific binding to the promoters of HIF1 or HIF2 target genes and selectively interact with HIF1α or HIF2α protein.

Hypoxia-induced inflammation in the lung: a potential therapeutic target in acute lung injury?

Acute lung injury (ALI) is a severe form of hypoxic lung disease responsible for a large number of deaths worldwide. Despite recent advances in supportive care, no reduction in mortality has been evident since the introduction of a standard consensus definition almost two decades ago. New strategies are urgently required to help design effective therapies for this condition. A key pathological feature of ALI involves regional alveolar hypoxia. Because alveolar hypoxia in isolation, such as that encountered at high altitude, causes an inflammatory pulmonary phenotype in the absence of any other pathogenic stimuli, these regions may not be passive bystanders but may actually contribute to the pathogenesis and progression of lung injury. Unique transcriptional responses to hypoxia in the lung apparently allow it to express an inflammatory phenotype at levels of hypoxia that would not produce such a response in other organs. We will review recent advances in our understanding of these unique transcriptional responses to moderate levels of alveolar hypoxia, which may provide new insights into the pathogenesis of ALI.

Upstream stimulatory factor 2 and hypoxia-inducible factor 2α (HIF2α) cooperatively activate HIF2 target genes during hypoxia

While the functions of hypoxia-inducible factor 1α (HIF1α)/aryl hydrocarbon receptor nuclear translocator (ARNT) and HIF2α/ARNT (HIF2) proteins in activating hypoxia-inducible genes are well established, the role of other transcription factors in the hypoxic transcriptional response is less clear. We report here for the first time that the basic helix-loop-helix-leucine-zip transcription factor upstream stimulatory factor 2 (USF2) is required for the hypoxic transcriptional response, specifically, for hypoxic activation of HIF2 target genes. We show that inhibiting USF2 activity greatly reduces hypoxic induction of HIF2 target genes in cell lines that have USF2 activity, while inducing USF2 activity in cells lacking USF2 activity restores hypoxic induction of HIF2 target genes. Mechanistically, USF2 activates HIF2 target genes by binding to HIF2 target gene promoters, interacting with HIF2α protein, and recruiting coactivators CBP and p300 to form enhanceosome complexes that contain HIF2α, USF2, CBP, p300, and RNA polymerase II on HIF2 target gene promoters. Functionally, the effect of USF2 knockdown on proliferation, motility, and clonogenic survival of HIF2-dependent tumor cells in vitro is phenocopied by HIF2α knockdown, indicating that USF2 works with HIF2 to activate HIF2 target genes and to drive HIF2-depedent tumorigenesis.

Erythropoietin as a novel brain and kidney protective agent

Erythropoietin is a 30.4 kDa glycoprotein produced by the kidney, which is mostly known for its physiological function in regulating red blood cell production in the bone marrow Accumulating evidence, however suggests that erythropoietin has additional organ protective effects, which may specifically be useful in protecting the brain and kidneys from injury. Experimental evidence suggests that these protective mechanisms are multi-factorial in nature and may include inhibition of apoptotic cell death, stimulation of cellular regeneration, inhibition of deleterious pathways and promotion of recovery. In this article we review the physiology of erythropoietin, assess previous work that supports the role of erythropoietin as a general tissue protective agent and explain the mechanisms by which it may achieve this tissue protective effect. We then focus on specific laboratory and clinical data that suggest that erythropoietin has a strong brain protective and kidney protective effect. In addition, we comment on the implications of these studies for clinicians at the bedside and for researchers designing controlled trials to further elucidate the true clinical utility of erythropoietin as a neuroprotective and nephroprotective agent. Finally, we describe EPO-TBI, a double-blinded multi-centre randomised controlled trial involving the authors that is being conducted to investigate the organ protective effects of erythropoietin on the brain, and also assesses its effect on the kidneys.

Erythropoietin (EPO) in acute kidney injury

Erythropoietin (EPO) is a 30.4 kDa glycoprotein produced by the kidney, and is mostly well-known for its physiological function in regulating red blood cell production in the bone marrow. Accumulating evidence, however, suggests that EPO has additional organ protective effects, which may be useful in the prevention or treatment of acute kidney injury. These protective mechanisms are multifactorial in nature and include inhibition of apoptotic cell death, stimulation of cellular regeneration, inhibition of deleterious pathways, and promotion of recovery.

In this article, we review the physiology of EPO, assess previous work that supports the role of EPO as a general tissue protective agent, and explain the mechanisms by which it may achieve this tissue protective effect. We then focus on experimental and clinical data that suggest that EPO has a kidney protective effect.

Impaired synthesis of erythropoietin, glutamine synthetase and metallothionein in the skin of NOD/SCID/gamma(c)(null) and Foxn1 nu/nu mice with misbalanced production of MHC class II complex

Most skin pathologies are characterized by unbalanced synthesis of major histocompatability complex II (MHC-II) proteins. Healthy skin keratinocytes simultaneously produce large amounts of MHC-II and regeneration-supporting proteins, e.g. erythropoietin (EPO), EPO receptor (EPOR), glutamine synthetase (GS) and metallothionein (MT). To investigate the level of regeneration-supporting proteins in the skin during misbalanced production of MHC-II, skin sections from nonobese diabetic/severe combined immunodeficient (NOD/SCID)/gamma (c) (null) and or Foxn1 nu/nu mice which are a priory known to under- and over-express MHC II, respectively, were used. Double immunofluorescence analysis of NOD/SCID/gamma (c) (null) skin sections showed striking decrease in expression of MHC-II, EPO, GS and MT. In Foxn1 nu/nu mouse skin, GS was strongly expressed in epidermis and in hair follicles (HF), which lacked EPO. In nude mouse skin EPO and MHC-II were over-expressed in dermal fibroblasts and they were completely absent from cortex, channel, medulla and keratinocytes surrounding the HF, suggest a role for EPO in health and pathology of hair follicle. The level of expression of EPO and GS in both mutant mice was confirmed by results of Western blot analyses. Strong immunoresponsiveness of EPOR in the hair channels of NOD/SCID/gamma (c) (null) mouse skin suggests increased requirements of skin cells for EPO and possible benefits of exogenous EPO application during disorders of immune system accompanied by loss MHC-II in skin cells.

Activation of phosphatidylinositol 3-kinase/protein kinase B by corticotropin-releasing factor in human monocytes

Corticotropin-releasing factor (CRF) exerts proinflammatory effects in peripheral tissues, whereas the intracellular pathways mediating these effects have not been completely characterized yet. We have previously shown that CRF induces nuclear factor-kappaB DNA-binding activity in mouse and human leukocytes. Here we demonstrate that in the human monocytic THP-1 cells, CRF activates the phosphatidylinositol 3-kinase (PI3K)/Akt and ERK1/2 pathways. These effects of CRF are mediated by corticotropin-releasing factor receptor 2 (CRF2), as suggested by their abolishment after treatment with the specific CRF2 antagonist, astressin 2B. The CRF-mediated PI3K/Akt activation induces cell survival as suggested by the stimulation of the antiapoptotic factor Bcl-2. ERK1/2 activation results in up-regulation of IL-8 expression, an effect inhibited by the CRF-induced activation of PI3K/Akt. These studies demonstrate novel effects of CRF in human monocytes mediated by the activation of PI3K/Akt. Moreover, they reveal pathway-specific effects of the CRF/CRF2 system in chemokine activation and cell survival that may be of importance for the development of novel therapeutics for inflammatory diseases.

Erythropoietin in patients with acute coronary syndrome and its cardioprotective action after percutaneous coronary intervention

BACKGROUND

Erythropoietin (EPO) has been shown to have effects beyond hematopoiesis, such as prevention of cardiac apoptosis. The purpose of the current study is to examine the influence of the time-course change in the serum concentration of endogenous EPO on cardiac functions in the chronic phase in patients with acute coronary syndrome, who successfully achieved reperfusion by primary percutaneous coronary intervention (PCI).

METHODS AND RESULTS

The prospective study included 34 patients with angiographically documented coronary artery disease, including 24 patients with acute myocardial infarction (AMI) and 10 patients with unstable angina pectoris (UAP) who underwent successful PCI within 24 h from the onset. Serum EPO concentration significantly increased at Day 3 and Day 7 compared with that at Day 1 in the AMI group, and the level at Day 3 was significantly higher in the AMI group than in the UAP group. There were significant correlations between DeltaEPO and Delta left ventricular ejection fraction (LVEF) or Delta left ventricular end-diastolic volume index and between peak EPO concentration and DeltaLVEF.

CONCLUSIONS

These data showed the time-dependent increase of serum EPO in AMI patients after primary PCI, indicating its possible contribution to cardioprotective effect in the chronic phase.

A novel hypoxia-response element in the lactate dehydrogenase-B gene of the killifish Fundulus heteroclitus

Previous studies have suggested that the lactate dehydrogenase-B gene (Ldh-B) of the Atlantic killifish, Fundulus heteroclitus, is a hypoxia-responsive gene. Here, we demonstrate that the F. heteroclitus Ldh-B promoter confers hypoxia-dependence upon reporter gene expression in transiently transfected mammalian (Hep3B) and fish (RTG-2 and RTH-149) cells in culture. Mutation and deletion analyses identified a putative hypoxia-response element (HRE) between 109 and 90 nucleotides upstream of the major start site. This HRE is characterized by the sequence 5'-GATGTG-3' spaced by 8 nucleotides from a perfect inverted repeat, and both sites are necessary for hypoxic induction of reporter gene expression in mammalian and fish cells. This HRE differs from the canonical sequence at one nucleotide position that is invariant among HREs from a wide range of hypoxia-sensitive genes. In fish cells, maximal induction of reporter gene expression driven by this HRE occurred at the lowest oxygen level tested (0.5%), took 48 h to 96 h, and was independent of glucose concentration (between 5.6 and 25 mM). Under all conditions tested, hypoxic induction of gene expression was lower in RTH-149 cells than in RTG-2, suggesting a potential defect in hypoxia signaling in RTH-149 cells. These results demonstrate that the F. heteroclitus Ldh-B promoter contains a novel HRE that is capable of driving reporter gene expression in a sequence-specific and oxygen-, time-, and cell line-dependent manner.

Hypoxia. Regulation of NFkappaB signalling during inflammation: the role of hydroxylases

NFκB is a master regulator of innate immunity and inflammatory signalling. Microenvironmental hypoxia has long been identified as being coincident with chronic inflammation. The contribution of microenvironmental hypoxia to NFκB-induced inflammation has more recently been appreciated. Identification of the co-regulation of NFκB and hypoxia inducible factor (HIF) pathways by 2-oxo-glutarate-dependent hydroxylase family members has highlighted an intimate relationship between NFκB inflammatory signalling and HIF-mediated hypoxic signalling pathways. Adding another layer of complexity to our understanding of the role of NFκB inflammatory signalling by hypoxia is the recent recognition of the contribution of basal NFκB activity to HIF-1α transcription. This observation implicates an important and previously unappreciated role for NFκB in inflammatory disease where HIF-1α is activated. The present review will discuss recent literature pertaining to the regulation of NFκB inflammatory signalling by hypoxia and some of the inflammatory diseases where this may play an important role. Furthermore, we will discuss the potential for prolylhydroxylase inhibitors in inflammatory disease.

Interdependent roles for hypoxia inducible factor and nuclear factor-kappaB in hypoxic inflammation

Decreased oxygen availability (hypoxia) is a hallmark feature of the microenvironment in a number of chronic inflammatory conditions including arthritis and inflammatory bowel disease (IBD). Recent advances in our understanding of oxygen-dependent cell signalling have uncovered several mechanisms by which hypoxia impacts upon the development of inflammation through the coordinated expression of adaptive, inflammatory and apoptotic genes. Two central transcription factors involved in the regulation of this response are hypoxia inducible factor (HIF) and nuclear factor-kappaB (NF-kappaB) which display different degrees of sensitivity to activation during hypoxia. Furthermore, HIF and NF-kappaB demonstrate an intimate interdependence at several mechanistic levels. Recent studies indicate that these pathways may represent important new therapeutic targets in diseases characterized by hypoxic inflammation.

LPS induces hypoxia-inducible factor 1 activation in macrophage-differentiated cells in a reactive oxygen species-dependent manner

A prominent feature of various inflamed and diseased tissue is the presence of low oxygen tension (hypoxia). Effector cells of the innate immune system must maintain their viability and physiologic functions in a hypoxic microenvironment. Monocytes circulating in the bloodstream differentiate into macrophages. During this process, cells acquire the ability to exert effects at hypoxic sites of inflammation. The transcription factor hypoxia-inducible factor 1 (HIF-1) mediates adaptive responses to reduced oxygen availability. In this study, we demonstrated that lipopolysaccharide (LPS) induces HIF-1 activation by enhancing both HIF-1alpha protein expression through a translation-dependent pathway and HIF-1alpha transcriptional activity in THP-1 human myeloid cells that have undergone macrophage differentiation but not in undifferentiated monocytic THP-1 cells. LPS-induced HIF-1 activation was blocked by treatment with antioxidant (N-acetylcysteine or thioredoxin-1), NADPH oxidase inhibitor (diphenyleneiodonium), indicating that reactive oxygen species generated in response to LPS are essential in this process. LPS-mediated activation of HIF-1 was independent of NF-kappaB activity. LPS-induced ROS generation and HIF-1 activation required the expression of Toll-like receptor 4 or myeloid differentiation factor (MyD) 88, thus providing a molecular basis for the selective activation of HIF-1 in differentiated THP-1 cells.

Differential gene expression of aldolase C (ALDOC) and hypoxic adaptation in chickens

Two sequence variants of the aldolase C (ALDOC) gene were discovered based on comparison of the sequences from an altiplano chicken breed (Tibetan chicken) and two lowland breeds (White Leghorn and ShouGuang). Gel-shift results indicated that one of these variants, L25375:c.310-258G>A, was able to bind hypoxia-induced factor-l (HIF1A), therefore, functioning as a hypoxia response element (HRE). The combined activity of the HRE and HIF1A could increase under the influence of a hypoxic stimulus. Hypoxia leads to increased death rates of chicken embryos, while the L25375:c.310-258G>A described herein is prevalent in healthy embryos grown under hypoxic conditions. Fluorescence quantitative real-time PCR results revealed that HIF1A upregulated the transcript level of the glycolytic enzyme ALDOC in the brain and skeletal muscle of animals subjected to hypoxia. Thus, a large amount of ATP is produced by increased glycolysis, allowing the organism to meet energy metabolism demands. As such, we believe this sequence variant is an adaptation to external anoxic environment.

Hypoxia transcriptionally induces macrophage-inflammatory protein-3alpha/CCL-20 in primary human mononuclear phagocytes through nuclear factor (NF)-kappaB

Hypoxia, a condition of low oxygen tension, occurring in many pathological processes, modifies the mononuclear phagocyte transcriptional profile. Here, we demonstrate hypoxic up-regulation of the CCL20 chemokine in primary human monocytes (Mn) and macrophages. mRNA induction was paralleled by protein secretion and dependent on gene transcription activation. Functional studies of the CCL20 promoter using a series of 5'-deleted and mutated reporter constructs demonstrated the requirement for the NF-kappaB-binding site located at position -92/-82 for gene transactivation by hypoxia, as 1) transcription was abrogated by a 3-bp mutation of the NF-kappaB motif; 2) three copies of the wild-type NF-kappaB-binding site conferred hypoxia responsiveness to a minimal heterologous promoter; and 3) hypoxia increased specific NF-kappaB binding to this sequence. Furthermore, we provide evidence of the specific role of a single NF-kappaB family member, p50, in mediating CCL20 gene transcription in hypoxic Mn. p50 homodimers were the only detectable NF-kappaB complexes binding the cognate kappaB site on the CCL20 promoter upon hypoxia exposure, and NF-kappaBp50 knockdown by lentiviral-mediated short hairpin RNA interference resulted in complete binding inhibition. NF-kappaBp50 overexpression in transient cotransfection studies promoted CCL20 gene transactivation, which was abrogated by mutation of the -92/-82 kappaB site. Moreover, nuclear expression of the other NF-kappaB family members was inhibited in hypoxic Mn. In conclusion, this study characterizes a previously unrecognized role for hypoxia as a transcriptional inducer of CCL20 in human mononuclear phagocytes and highlights the importance of the NF-kappaB pathway in mediating this response, with potential implications for inflammatory disease and cancer pathogenesis.

Hypoxia up-regulates hypoxia-inducible factor-1alpha transcription by involving phosphatidylinositol 3-kinase and nuclear factor kappaB in pulmonary artery smooth muscle cells

The oxygen sensitive alpha-subunit of the hypoxia-inducible factor-1 (HIF-1) is a major trigger of the cellular response to hypoxia. Although the posttranslational regulation of HIF-1alpha by hypoxia is well known, its transcriptional regulation by hypoxia is still under debate. We, therefore, investigated the regulation of HIF-1alpha mRNA in response to hypoxia in pulmonary artery smooth muscle cells. Hypoxia rapidly enhanced HIF-1alpha mRNA levels and HIF-1alpha promoter activity. Furthermore, inhibition of the phosphatidylinositol 3-kinase (PI3K)/AKT but not extracellular signal-regulated kinase 1/2 pathway blocked the hypoxia-dependent induction of HIF-1alpha mRNA and HIF-1alpha promoter activity, suggesting involvement of a PI3K/AKT-regulated transcription factor. Interestingly, hypoxia also induced nuclear factor-kappaB (NFkappaB) nuclear translocation and activity. In line, expression of the NFkappaB subunits p50 and p65 enhanced HIF-1alpha mRNA levels, whereas blocking of NFkappaB by an inhibitor of nuclear factor-kappaB attenuated HIF-1alpha mRNA induction by hypoxia. Reporter gene assays revealed the presence of an NFkappaB site within the HIF-1alpha promoter, and mutation of this site abolished induction by hypoxia. In line, gel shift analysis and chromatin immunoprecipitation confirmed binding of p50 and p65 NFkappaB subunits to the HIF-1alpha promoter under hypoxia. Together, these findings provide a novel mechanism in which hypoxia induces HIF-1alpha mRNA expression via the PI3K/AKT pathway and activation of NFkappaB.

Chronic hypoxia promotes an aggressive phenotype in rat prostate cancer cells

In general, tumors cells that are resistant to apoptosis and increase angiogenesis are a result of the hypoxic responses contributing to the malignant phenotype. In this study, we developed a chronic hypoxic cell model (HMLL), by incubating the prostate cancer MatLyLu cells in a hypoxic chamber (1% O(2)) over 3 weeks. Surviving cells were selected through each cell passage and were grown in the hypoxic condition up to 8 weeks. This strategy resulted in survival of only 5% of the cells. The surviving hypoxic cells displayed a greater stimulation on hypoxic adaptive response, including a greater expression of glucose transporter1 (Glut1) and VEGF secretion. In addition, higher invasion activity was observed in the chronic hypoxic HMLL cells as compared to MatLyLu cells exposed to acute hypoxia (1% O(2), 5 h) using the matrigel assay. To further examine the role of HIF-1alpha in tumor progression, both MatLyLu and HMLL cells were transfected with dominant-negative form of HIF-1alpha (DNHIF-1alpha). The Matrigel invasion activity induced by chronic hypoxia was significantly attenuated by DNHIF-1alpha. These results suggest that signaling pathways leading to hypoxic response may be differentially regulated in chronic hypoxic cells and acute hypoxic cells. Chronic hypoxia may play a greater role than acute hypoxia in promoting the aggressive phenotype of tumor cells. This observation mimics the clinical scenario where tumor cells following treatment with radiation are subjected to hypoxic conditions. The reemergence of tumor following treatment usually results in tumor cells that are more aggressive and metastatic.

FLIP(L) protects neurons against in vivo ischemia and in vitro glucose deprivation-induced cell death

Knowledge of the molecular mechanisms that underlie neuron death after stroke is important to allow the development of effective neuroprotective strategies. In this study, we investigated the contribution of death receptor signaling pathways to neuronal death after ischemia using in vitro and in vivo models of ischemic injury and transgenic mice that are deficient in tumor necrosis factor receptor I (TNFRI KO) or show neuron-specific overexpression of the long isoform of cellular Fas-associated death domain-like interleukin-1-beta-converting enzyme-inhibitory protein (FLIP(L)). Caspase 8 was activated in brain lesions after permanent middle cerebral artery occlusion (pMCAO) and in cortical neurons subjected to glucose deprivation (GD) and was necessary for GD-induced neuron death. Thus, neurons treated with zIETD-FMK peptide or overexpressing a dominant-negative caspase 8 mutant were fully protected against GD-induced death. The presence of the neuroprotective TNFRI was necessary for selectively sustaining p50/p65NF-kappaB activity and the expression of the p43 cleavage form of FLIP(L), FLIP(p43), an endogenous inhibitor of caspase 8, in pMCAO lesions and GD-treated neurons. Moreover, TNF pretreatment further upregulated p50/p65NF-kappaB activity and FLIP(p43) expression in neurons after GD. The knock-down of FLIP in wild-type (WT) neurons using a short hairpin RNA revealed that FLIP(L) is essential for TNF/TNFRI-mediated neuroprotection after GD. Furthermore, the overexpression of FLIP(L) was sufficient to rescue TNFRI KO neurons from GD-induced death and to enhance TNF neuroprotection in WT neurons, and neuron-specific expression of FLIP(L) in transgenic mice significantly reduced lesion volume after pMCAO. Our results identify a novel role for the TNFRI-NF-kappaB-FLIP(L) pathway in neuroprotection after ischemia and identify potential new targets for stroke therapy.

Hepatitis C virus stabilizes hypoxia-inducible factor 1alpha and stimulates the synthesis of vascular endothelial growth factor

Hepatitis C virus (HCV) infection is one of the major causes of chronic hepatitis, liver cirrhosis, which subsequently leads to hepatocellular carcinoma (HCC). The overexpression of the angiogenic factors has been demonstrated in HCC. In this study, we investigated the potential of HCV gene expression in inducing angiogenesis. Our results show that HCV infection leads to the stabilization of hypoxia-inducible factor 1alpha (HIF-1alpha). We further show that this stabilization was mediated via oxidative stress induced by HCV gene expression. The activation of NF-kappaB, STAT-3, PI3-K/AkT, and p42/44 mitogen-activated protein kinase was necessary for HIF-1alpha stabilization. HIF-1alpha induction in turn led to the stimulation of vascular endothelial growth factor. By using the chick chorioallantoic membrane assay, we show that HCV-infected cells released angiogenic cytokines, leading to neovascularization in vivo. These results indicate the potential of HCV gene expression in angiogenesis.

Tetrathiomolybdate promotes tumor necrosis and prevents distant metastases by suppressing angiogenesis in head and neck cancer

Angiogenesis is well recognized as an essential process that influences not only the growth of head and neck squamous cell carcinoma (HNSCC) but also promotes its invasive and metastatic behavior. The critical role of copper in multiple facets of angiogenesis makes it an important therapeutic target. Tetrathiomolybdate is a potent copper chelator, which has shown remarkable ability to suppress angiogenesis. Although this may involve multiple mechanisms, the effects on vascular endothelial growth factor (VEGF) are pivotal. In previous work, tetrathiomolybdate suppressed production of several proangiogenic cytokines by HNSCC cell lines. Given these results, we hypothesized that tetrathiomolybdate would impair tumor growth and metastasis by HNSCC. To test this concept, we evaluated the effects of long-term tetrathiomolybdate treatment on the growth and metastatic progression of HNSCC using a xenograft animal model. The results showed that tetrathiomolybdate treatment is able to maintain effective inhibition of angiogenesis. There was a significant reduction in the tumor size and vascularity with evident gross necrosis in the tetrathiomolybdate-treated animals. These effects were highly correlated with suppression of human VEGF expressed in the developing tumors as well as the mouse VEGF levels detected in the plasma. Moreover, tetrathiomolybdate treatment drastically suppressed the development of lung metastases. Taken together, these results show that tetrathiomolybdate can act long-term as a suppressor of vascularity and inhibit the growth of metastasis in this model of HNSCC.

The integration of lipid-sensing and anti-inflammatory effects: how the PPARs play a role in metabolic balance

The peroxisomal proliferating-activated receptors (PPARs) are lipid-sensing transcription factors that have a role in embryonic development, but are primarily known for modulating energy metabolism, lipid storage, and transport, as well as inflammation and wound healing. Currently, there is no consensus as to the overall combined function of PPARs and why they evolved. We hypothesize that the PPARs had to evolve to integrate lipid storage and burning with the ability to reduce oxidative stress, as energy storage is essential for survival and resistance to injury/infection, but the latter increases oxidative stress and may reduce median survival (functional longevity). In a sense, PPARs may be an evolutionary solution to something we call the 'hypoxia-lipid' conundrum, where the ability to store and burn fat is essential for survival, but is a 'double-edged sword', as fats are potentially highly toxic. Ways in which PPARs may reduce oxidative stress involve modulation of mitochondrial uncoupling protein (UCP) expression (thus reducing reactive oxygen species, ROS), optimising forkhead box class O factor (FOXO) activity (by improving whole body insulin sensitivity) and suppressing NFkB (at the transcriptional level). In light of this, we therefore postulate that inflammation-induced PPAR downregulation engenders many of the signs and symptoms of the metabolic syndrome, which shares many features with the acute phase response (APR) and is the opposite of the phenotype associated with calorie restriction and high FOXO activity. In genetically susceptible individuals (displaying the naturally mildly insulin resistant 'thrifty genotype'), suboptimal PPAR activity may follow an exaggerated but natural adipose tissue-related inflammatory signal induced by excessive calories and reduced physical activity, which normally couples energy storage with the ability to mount an immune response. This is further worsened when pancreatic decompensation occurs, resulting in gluco-oxidative stress and lipotoxicity, increased inflammatory insulin resistance and oxidative stress. Reactivating PPARs may restore a metabolic balance and help to adapt the phenotype to a modern lifestyle.

Effects of a single dose of erythropoietin on subsequent seizure susceptibility in rats exposed to acute hypoxia at P10

PURPOSE

To determine if posthypoxia treatment with erythropoietin (EPO) has protective effects against subsequent susceptibility to seizure related neuronal injury in rat pups subjected to acute hypoxia at P10.

METHODS

Four groups of rats were manipulated at P10, as described below, then all received kainic acid (KA) (10 mg/kg i.p.) at P29: Hypoxia-NS-KA group (n = 11): subjected to acute hypoxia (down to 4% O2), and then immediately received saline i.p. Hypoxia-EPO-KA group (n = 10): subjected to acute hypoxia and then immediately received EPO (1,000 U/Kg i.p.). Normoxia-NS-KA group (n = 11): sham manipulated and injected with saline. Normoxia-EPO-KA group (n = 10): sham manipulated then immediately injected with EPO (1000 U/Kg i.p.). After receiving KA at P29, all rats were monitored using videotape techniques, and were sacrificed at P31. TUNEL and Hoechst stains to assess for apoptosis, and regular histology for hippocampal cell counts were performed.

RESULTS

Administration of the single dose of erythropoietin directly after an acute hypoxic event at P10 resulted at P29 in increased latency to forelimb clonus seizures, reduced duration of these seizures, protection against hippocampal cell loss, and decreased hippocampal apoptosis in the Hypoxia-EPO-KA group as compared to the Hypoxia-NS-KA group.

CONCLUSION

These data support the presence of favorable protective effects of erythropoietin against the long-term consequences of acute hypoxia in the developing brain and raise the possibility of its investigation as a potential neuroprotective agent after human neonatal hypoxic encephalopathy.

YC-1 inhibits HIF-1 expression in prostate cancer cells: contribution of Akt/NF-kappaB signaling to HIF-1alpha accumulation during hypoxia

Hypoxia-inducible factor 1 (HIF-1), a transcription factor that is critical for tumor adaptation to microenvironmental stimuli, represents an attractive chemotherapeutic target. YC-1 is a novel antitumor agent that inhibits HIF-1 through previously unexplained mechanisms. In the present study, YC-1 was found to prevent HIF-1alpha and HIF-1beta accumulation in response to hypoxia or mitogen treatment in PC-3 prostate cancer cells. Neither HIF-1alpha protein half-life nor mRNA level was affected by YC-1. However, YC-1 was found to suppress the PI3K/Akt/mTOR/4E-BP pathway, which serves to regulate HIF-1alpha expression at the translational step. We demonstrated that YC-1 also inhibited hypoxia-induced activation of nuclear factor (NF)-kappaB, a downstream target of Akt. Two modulators of the Akt/NF-kappaB pathway, caffeic acid phenethyl ester and evodiamine, were observed to decrease HIF-1alpha expression. Additionally, overexpression of NF-kappaB partly reversed the ability of wortmannin to inhibit HIF-1alpha-dependent transcriptional activity, suggesting that NF-kappaB contributes to Akt-mediated HIF-1alpha accumulation during hypoxia. Overall, we identify a potential molecular mechanism whereby YC-1 serves to reduce HIF-1 expression.

Comparison of neuroprotective effects of erythropoietin (EPO) and carbamylerythropoietin (CEPO) against ischemia-like oxygen-glucose deprivation (OGD) and NMDA excitotoxicity in mouse hippocampal slice cultures

In addition to its well-known hematopoietic effects, erythropoietin (EPO) also has neuroprotective properties. However, hematopoietic side effects are unwanted for neuroprotection, underlining the need for EPO-like compounds with selective neuroprotective actions. One such compound, devoid of hematopoietic bioactivity, is the chemically modified, EPO-derivative carbamylerythropoietin (CEPO). For comparison of the neuroprotective effects of CEPO and EPO, we subjected organotypic hippocampal slice cultures to oxygen-glucose deprivation (OGD) or N-methyl-d-aspartate (NMDA) excitotoxicity. Hippocampal slice cultures were pretreated for 24 h with 100 IU/ml EPO (=26 nM) or 26 nM CEPO before OGD or NMDA lesioning. Exposure to EPO and CEPO continued during OGD and for the next 24 h until histology, as well as during the 24 h exposure to NMDA. Neuronal cell death was quantified by cellular uptake of propidium iodide (PI), recorded before the start of OGD and NMDA exposure and 24 h after. In cultures exposed to OGD or NMDA, CEPO reduced PI uptake by 49+/-3 or 35+/-8%, respectively, compared to lesion-only controls. EPO reduced PI uptake by 33+/-5 and 15+/-8%, respectively, in the OGD and NMDA exposed cultures. To elucidate a possible mechanism involved in EPO and CEPO neuroprotection against OGD, the integrity of alpha-II-spectrin cytoskeletal protein was studied. Both EPO and CEPO significantly reduced formation of spectrin cleavage products in the OGD model. We conclude that CEPO is at least as efficient neuroprotectant as EPO when excitotoxicity is modeled in mouse hippocampal slice cultures.

Erythropoietin and the cardiorenal syndrome: cellular mechanisms on the cardiorenal connectors

We have recently proposed severe cardiorenal syndrome (SCRS), in which cardiac and renal failure mutually amplify progressive failure of both organs. This frequent pathophysiological condition has an extremely poor prognosis. Interactions between inflammation, the renin-angiotensin system, the balance between the nitric oxide and reactive oxygen species and the sympathetic nervous system form the cardiorenal connectors and are cornerstones in the pathophysiology of SCRS. An absolute deficit of erythropoietin (Epo) and decreased sensitivity to Epo in this syndrome both contribute to the development of anemia, which is more pronounced than renal anemia in the absence of heart failure. Besides expression on erythroid progenitor cells, Epo receptors are present in the heart, kidney, and vascular system, in which activation results in antiapoptosis, proliferation, and possibly antioxidation and anti-inflammation. Interestingly, Epo can improve cardiac and renal function. We have therefore reviewed the literature with respect to Epo and the cardiorenal connectors. Indeed, there are indications that Epo can diminish inflammation, reduce renin-angiotensin system activity, and shift the nitric oxide and reactive oxygen species balance toward nitric oxide. Information about Epo and the sympathetic nervous system is scarce. This analysis underscores the relevance of a further understanding of clinical and cellular mechanisms underlying protective effects of Epo, because this will support better treatment of SCRS.

Tissue fibrosis and carcinogenesis: divergent or successive pathways dictate multiple molecular therapeutic targets for oligo decoy therapies

The extracellular matrix (ECM) is composed of several families of macromolecular components: fibrous proteins such as collagens, type I collagen (COL1), type III collagen (COL3), fibronectin, elastin, and glycoconjugates such as proteoglycans and matrix glycoproteins. Their receptors on the cell membrane, most of which in the case of the ECM belong to the integrins, which are heterodimeric proteins composed of alpha and beta chains. COL1 is the major fibrous collagen of bone, tendon, and skin; while COL3 is the more pliable collagen of organs like liver. Focus will not only be given to the regulation of synthesis of several fibrogenic parameters but also modulation of their degradation during growth factor-induced tissue fibrosis and cancer development. Evidence will be provided that certain tissues, which undergo fibrosis, also become cancerous. Why does there exist a divergency between tissues, which undergo frank fibrosis as an endpoint, and those tissues that undergo fibrosis and subsequently are susceptible to carcinogenicity; resulting from the etiological factor(s) causing the initial injury? For example, why does a polyvinyl alcohol (PVA) sponge implant become encapsulated and filled with fibrous tissue then fibrosis tissue growth stops? Why does the subcutaneous injection of a fibrogenic growth factor cause a benign growth and incisional wounding results in fibrosis and ultimately scarring? There are many examples of tissues, which undergo fibrosis as a prerequisite to carcinogenesis. Is there a cause-effect relationship? If you block tissue fibrosis in these precancerous tissues, would you block cancer formation? What are the molecular targets for blocking fibrosis and ultimately carcinogenesis? How can oligo decoys may be used to attenuate carcinogenesis and which oligo decoys specifically attenuate fibrogenesis as a prelude to carcinogenesis? What are other molecular targets for oligo decoy therapy in carcinogenesis?

Novel renoprotective actions of erythropoietin: New uses for an old hormone (Review Article)

Erythropoietin (EPO) has been used widely for the treatment of anaemia associated with chronic kidney disease and cancer chemotherapy for nearly 20 years. More recently, EPO has been found to interact with its receptor (EPO-R) expressed in a large variety of non-haematopoietic tissues to induce a range of cytoprotective cellular responses, including mitogenesis, angiogenesis, inhibition of apoptosis and promotion of vascular repair through mobilization of endothelial progenitor cells from the bone marrow. Administration of EPO or its analogue, darbepoetin, promotes impressive renoprotection in experimental ischaemic and toxic acute renal failure, as evidenced by suppressed tubular epithelial apoptosis, enhanced tubular epithelial proliferation and hastened functional recovery. This effect is still apparent when administration is delayed up to 6 h after the onset of injury and can be dissociated from its haematological effects. Based on these highly encouraging results, at least one large randomized controlled trial of EPO therapy in ischaemic acute renal failure is currently underway. Preliminary experimental and clinical evidence also indicates that EPO may be renoprotective in chronic kidney disease. The purpose of the present article is to review the renoprotective benefits of different protocols of EPO therapy in the settings of acute and chronic kidney failure and the potential mechanisms underpinning these renoprotective actions. Gaining further insight into the pleiotropic actions of EPO will hopefully eventuate in much-needed, novel therapeutic strategies for patients with kidney disease.

Erythropoietin production: Molecular mechanisms of the antagonistic actions of cyclic adenosine monophosphate and interleukin-1

Erythropoietin (Epo) mRNA expression is suppressed by interleukin 1 (IL-1). Cyclic adenosine monophosphate (cAMP) can increase Epo mRNA and Epo protein levels in IL-1 treated HepG2 cells to some extent. To identify molecular mechanisms of this reaction we investigated three transcription factors (NF-kappaB, GATA-2 and HIF-1) that control the Epo gene. Western blot analyses and electrophoretic mobility shift assays (EMSAs) revealed that IL-1 strongly activated NF-kappaB, which is a likely suppressor of the Epo promoter. Treatment of the cells with dibutyryl-cAMP (Bt2-cAMP) inhibited the activation of NF-kappaB by IL-1. Bt2-cAMP increased GATA-2 DNA binding. Since GATA-2 is a suppressor of the Epo promoter, GATA-2 activation was unlikely to cause the increase of Epo mRNA expression in IL-1 treated cells. Furthermore, Western blots, EMSAs and reporter gene studies showed that Bt2-cAMP was without effect on the hypoxia-inducible transcription factor HIF-1. Thus, NF-kappaB is probably the primary transcription factor by which cAMP counteracts the inhibition of Epo gene expression by IL-1.

The HIV-1 Tat protein enhances megakaryocytic commitment of K562 cells by facilitating CREB transcription factor coactivation by CBP

The human immunodeficiency virus type 1 (HIV-1) Tat protein regulates transcription factor functions and alters cellular gene expression. Because hematopoietic progenitor cell (HPC) differentiation requires activation of lineage-specific transcription factors, Tat may affect hematopoiesis in HIV-1-infected micro-environments. We have monitored the molecular effects of Tat on megakaryocytic differentiation in the HPC line, K562. Flow cytometry analysis of CD61 indicated that phorbol myristate acetate (PMA) (16 nM) stimulated megakaryocytic commitment of K562 cells was increased (3- to 4-fold) following exposure to Tat (1-100 ng/ml). Activation of the megakaryocytic transcription factor cAMP regulatory element binding protein (CREB) and its coactivation by the CREB binding protein (CBP) was subsequently monitored. CREB phosphorylation and DNA binding were measured by Western immunodetection and electrophoretic mobility shift assays (EMSA), respectively. Within 2 hrs after stimulation, Tat increased both CREB phosphorylation and DNA binding by 7- to 10-fold. Transient cotransfection with CREB reporter and CBP expression plasmids demonstrated that Tat treatment increases (3- to 4-fold) both PMA-stimulated and CBP-mediated transcription via the cAMP regulatory element. Histone acetyl transferase (HAT) activity was increased (8- to 10-fold) in Tat-stimulated cells, which suggested increased chromosomal accessibility of transcription factors. Two-hybrid cotransfection assays using reporter plasmid containing the GAL4 DNA-binding domain and expression plasmid coding for the GAL4-CBP fusion protein, showed that Tat increases (2-fold) CBP-mediated coactivation of CREB. Both reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis showed that Tat treatment increases CBP gene expression (7- to 9-fold) and protein levels (5- to 7-fold) within 6-12 hrs after stimulation. Our findings indicated that Tat treatment increases both CREB function and CREB coactivation by CBP, which may facilitate megakaryocytic commitment of K562 cells. Induction of this molecular signaling by HIV-1 Tat protein may have relevance in understanding the HIV-induced hematologic manifestations and possibly in regulation of viral infectivity parameters in progenitor cell reservoirs.

Employing new cellular therapeutic targets for Alzheimer's disease: a change for the better?

Alzheimer's disease is a progressive disorder that results in the loss of cognitive function and memory. Although traditionally defined by the presence of extracellular plaques of amyloid-beta peptide aggregates and intracellular neurofibrillary tangles in the brain, more recent work has begun to focus on elucidating the complexities of Alzheimer's disease that involve the generation of reactive oxygen species and oxidative stress. Apoptotic processes that are incurred as a function of oxidative stress affect neuronal, vascular, and monocyte derived cell populations. In particular, it is the early apoptotic induction of cellular membrane asymmetry loss that drives inflammatory microglial activation and subsequent neuronal and vascular injury. In this article, we discuss the role of novel cellular pathways that are invoked during oxidative stress and may potentially mediate apoptotic injury in Alzheimer's disease. Ultimately, targeting new avenues for the development of therapeutic strategies linked to mechanisms that involve inflammatory microglial activation, cellular metabolism, cell-cycle regulation, G-protein regulated receptors, and cytokine modulation may provide fruitful gains for both the prevention and treatment of Alzheimer's disease.

Erythropoietin requires NF-kappaB and its nuclear translocation to prevent early and late apoptotic neuronal injury during beta-amyloid toxicity

No longer considered exclusive for the function of the hematopoietic system, erythropoietin (EPO) is now considered as a viable agent to address central nervous system injury in a variety of cellular systems that involve neuronal, vascular, and inflammatory cells. Yet, it remains unclear whether the protective capacity of EPO may be effective for chronic neurodegenerative disorders such as Alzheimer's disease (AD) that involve beta-amyloid (Abeta) apoptotic injury to hippocampal neurons. We therefore investigated whether EPO could prevent both early and late apoptotic injury during Abeta exposure in primary hippocampal neurons and assessed potential cellular pathways responsible for this protection. Primary hippocampal neuronal injury was evaluated by trypan blue dye exclusion, DNA fragmentation, membrane phosphatidylserine (PS) exposure, and nuclear factor-kappaB (NF-kappaB) expression with subcellular translocation. We show that EPO, in a concentration specific manner, is able to prevent the loss of both apoptotic genomic DNA integrity and cellular membrane asymmetry during Abeta exposure. This blockade of Abeta generated neuronal apoptosis by EPO is both necessary and sufficient, since protection by EPO is completely abolished by co-treatment with an anti-EPO neutralizing antibody. Furthermore, neuroprotection by EPO is closely linked to the expression of NF-kappaB p65 by preventing the degradation of this protein by Abeta and fostering the subcellular translocation of NF-kappaB p65 from the cytoplasm to the nucleus to allow the initiation of an anti-apoptotic program. In addition, EPO intimately relies upon NF-kappaB p65 to promote neuronal survival, since gene silencing of NF-kappaB p65 by RNA interference removes the protective capacity of EPO during Abeta exposure. Our work illustrates that EPO is an effective entity at the neuronal cellular level against Abeta toxicity and requires the close modulation of the NF-kappaB p65 pathway, suggesting that either EPO or NF-kappaB may be used as future potential therapeutic strategies for the management of chronic neurodegenerative disorders, such as AD.

YC-1 suppresses constitutive nuclear factor-κB activation and induces apoptosis in human prostate cancer cells

Although the indazole compound, YC-1, is reported to exert anticancer activities in several cancer cell types, its target and mechanism of action have not been well explored. The objectives of this study were to ascertain whether YC-1 directly induces apoptosis in prostate cancer cells and to explore the mechanism(s) whereby YC-1 causes cell death. Hormone-refractory metastatic human prostate cancer PC-3 cells were selected for this study. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay indicated that YC-1 suppresses growth of PC-3 cells in a concentration-dependent and time-dependent manner. Apoptosis was determined using 4',6-diamidino-2-phenylindole staining, and cell cycle progression was examined by FACScan flow cytometry. YC-1 treatment showed chromatin condensation and increased the percentage of PC-3 cells in the hypodiploid sub-G0-G1 phase, indicative of apoptosis. Additionally, exposure to YC-1 was found to induce activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase. Translocation and activation of nuclear factor-kappaB (NF-kappaB) were determined by immunofluorescent staining and ELISA, respectively. The results showed that YC-1 abolished constitutive nuclear translocation and activation of NF-kappaB/p65. Furthermore, inhibition of inhibitor of kappaBalpha (IkappaBalpha) phosphorylation and accumulation of IkappaBalpha were observed. The antitumor effects of YC-1 were evaluated by measuring the growth of tumor xenografts in YC-1-treated severe combined immunodeficient mice. The volumes of PC-3 tumors produced in severe combined immunodeficient mice were observed to decline significantly after treatment with YC-1 compared with vehicle controls. We concluded that the antitumor effects of YC-1 in PC-3 cells include the induction of apoptosis and the suppression of NF-kappaB activation. Given these unique actions, further investigations of the effects of YC-1 against hormone-refractory prostate cancer are warranted.