Novel HIF-2α interaction with Reptin52 impairs HIF-2 transcriptional activity and EPO secretion

Hypoxia-inducible factor 2 (HIF-2), is essential for cellular response to hypoxia and holds an important role in erythropoiesis, angiogenesis, tissue invasion and metastasis, thus, constituting an important therapeutic target. Maximal HIF-2 transcriptional activation requires HIF-2α phosphorylation by ERK1/2 that impairs its CRM1-mediated nuclear export. Herein, we reveal a novel interaction of HIF-2α with Reptin52, a multifunctional protein involved in cellular functions orchestrated both in the nucleus and the cytoplasm. HIF-2α and Reptin52 interact both in nuclear and cytoplasmic fractions, however, ERK1/2 pathway inactivation seems to favour their association in the cytoplasm. Notably, we demonstrate that Reptin52 reduces HIF-2 transcriptional activity, which results in decreased EPO secretion under hypoxia, by impairing HIF-2α stability via a non-canonical PHD-VHL-proteasome independent mechanism. This interaction represents a novel HIF-2 fine tuning mechanism that allows for distinct HIF1/2 isoforms regulation.

FGF-2 and HGF reverse abiraterone's effect οn intracellular levels of DHT in androgen-dependent and androgen independent prostate cancer cell lines

PURPOSE

Growth factors such as fibroblast growth factor 2 (FGF-2) and hepatocyte growth factor (HGF) appear at high levels in prostate cancer (PC). Abiraterone is an androgen biosynthesis inhibitor which is currently in use as a standard treatment in clinics to impair tumor growth. Development of resistance to anticancer therapies is unfortunately a very common feature of cancer cells that threatens the patient lives. This study aimed to investigate whether FGF-2 and HGF act as a possible resistant mechanism to the abiraterone activity on the androgen synthesis pathway in PC.

METHODS

The intracellular levels of 17-OH progesterone and dihydrotestosterone (DHT) were determined by enzyme immunoassays in cell lysates of LNCaP and PC3 PC cells upon co-treatment of cells with abiraterone and FGF-2 or HGF.

RESULTS

Abiraterone treatment resulted in significant reduction in the intracellular levels of 17-OH progesterone and DHT in both LnCap and PC3 cells. FGF-2 and HGF were found to decrease the intracellular levels of 17-OH progesterone in both cell lines, whereas HGF alone was found to increase the intracellular levels of DHT only in PC3 cells. However, the simultaneous exposure of cells to abiraterone and FGF-2 or HGF was found to result in an increase in the intracellular levels of DHT, while it did not result in changes in the intracellular levels of 17-OH progesterone.

CONCLUSION

These findings suggest that FGF-2 and HGF may act as an escape mechanism, aiding the development of resistance to abiraterone by restoring intra-tumoral androgen synthesis that may contribute to disease progression.

High-Tidal-Volume Mechanical Ventilation and Lung Inflammation in Intensive Care Patients With Normal Lungs

BACKGROUND

This study was conducted to investigate whether high-tidal-volume mechanical ventilation is associated with increased lung inflammation compared with low-tidal-volume mechanical ventilation in critically ill patients with no evidence of lung injury.

METHODS

In this prospective, single-blind, randomized (1:1), parallel-group study, 18 critically ill patients with normal lungs were randomly assigned to receive mechanical ventilation with a tidal volume of either 6 mL/kg (low tidal volume) or 12 mL/kg (high tidal volume) during the first 4 days in the intensive care unit.

RESULTS

At baseline and at 24, 48, and 96 hours, exhaled breath condensate was collected to measure interleukin 1β, interleukin 10, tumor necrosis factor α, and total nitric oxide metabolites. Interleukin 1β levels in exhaled breath condensate were significantly increased at 24 hours compared with baseline in the high-tidal-volume group but not in the low-tidal-volume group. The interleukin 1β increase in the high-tidal-volume group was transient. Exhaled breath condensate levels of interleukin 1β, interleukin 10, tumor necrosis factor α, and total nitric oxide metabolites did not differ significantly between the high-tidal-volume and low-tidal-volume groups at any time point.

CONCLUSION

Short-term mechanical ventilation with a tidal volume of 12 mL/kg may trigger inflammatory responses in the lungs of intensive care unit patients without preexisting lung injury.

17-β estradiol attenuates the pro-oxidant activity of corticotropin-releasing hormone in macroendothelial cells

Corticotropin-releasing hormone, which is the predominant regulator of neuroendocrine responses to stress, attenuates inflammation through stimulation of glucocorticoid release. Enhanced corticotropin-releasing hormone expression has been detected in inflammatory cells of the vascular endothelium, where it acts as a local regulator of endothelial redox homeostasis. Estrogens have beneficial effects on endothelial integrity and function, though the mechanism underlying their antioxidative effect remains as yet largely unknown. We therefore investigated the effect of 17β-estradiol on pro-oxidant action of corticotropin-releasing hormone in vitro in macroendothelial cells, and, more specifically, the role of 17β-estradiol on corticotropin-releasing hormone-induced activities/release of the antioxidant enzymes namely, endothelial nitric oxide synthase, superoxide dismutase, catalase, and glutathione. We observed that 17β-estradiol abolished the stimulatory effect of corticotropin-releasing hormone on intracellular reactive oxygen species levels and counteracted its inhibitory effect on endothelial nitric oxide synthase activity and nitric oxide release. In addition, 17β-estradiol significantly induced superoxide dismutase and catalase activity, an effect that was not significantly influenced by corticotropin-releasing hormone. Finally, 17β-estradiol significantly increased glutathione levels and the glutathione/glutathione + glutathione disulfide ratio, an action that was partially blocked by corticotropin-releasing hormone. Our results reveal that 17β-estradiol counterbalances corticotropin-releasing hormone-mediated pro-inflammatory action and thereby maintains the physiological threshold of the endothelial cell redox environment. These observations may be of importance, considering the protective role of estrogen in the development of atherosclerosis.

ERK1/2 phosphorylates HIF-2α and regulates its activity by controlling its CRM1-dependent nuclear shuttling

Hypoxia-inducible factor 2 (HIF-2) is a principal component of the cellular response to oxygen deprivation (hypoxia). Its inducible subunit, HIF-2α (also known as EPAS1), is controlled by oxygen-dependent as well as oxygen-independent mechanisms, such as phosphorylation. We show here that HIF-2α is phosphorylated under hypoxia (1% O2) by extracellular signal-regulated protein kinases 1 and 2 (ERK1/2; also known as MAPK3 and MAPK1, respectively) at serine residue 672, as identified by in vitro phosphorylation assays. Mutation of this site to an alanine residue or inhibition of the ERK1/2 pathway decreases HIF-2 transcriptional activity and causes HIF-2α to mislocalize to the cytoplasm without changing its protein expression levels. Localization, reporter gene and immunoprecipitation experiments further show that HIF-2α associates with the exportin chromosomal maintenance 1 (CRM1, also known as XPO1) in a phosphorylation-sensitive manner and identify two critical leucine residues as part of an atypical CRM1-dependent nuclear export signal (NES) neighboring serine 672. Inhibition of CRM1 or mutation of these residues restores nuclear accumulation and activity of HIF-2α lacking the ERK1/2-mediated modification. In summary, we reveal a novel regulatory mechanism of HIF-2, involving ERK1/2-dependent phosphorylation of HIF-2α, which controls its nucleocytoplasmic shuttling and the HIF-2 transcriptional activity.This article has an associated First Person interview with the first author of the paper.

Adhesion Prevention to Polypropylene Meshes Using Combined Icodextrin Four Percent and Dimetindene Maleate

BACKGROUND

The use of surgical meshes in ventral hernia repair has significantly reduced hernia recurrence rates. However, when placed intraperitoneally prosthetic materials can trigger the development of peritoneal adhesions. The present experimental study evaluated the combined icodextrin 4% and dimetindene maleate treatment in preventing peritoneal adhesion formation to polypropylene and titanium-coated polypropylene meshes.

MATERIALS AND METHODS

Sixty female white rabbits were divided into four groups. A 2 × 2 cm piece of mesh was fixed to intact peritoneum in all animals through a midline laparotomy. A lightweight polypropylene mesh was implanted in groups 1 and 2 and a titanium-coated polypropylene mesh in groups 3 and 4. Groups 2 and 4 were treated, intraoperatively, with intravenous dimetindene maleate (0.1 mg/kg) and intraperitoneal solution of icodextrin 4% (20 mL/kg) and for the next 6 d with dimetindene maleate intramuscularly. The observation period lasted 15 d. Adhesion scores, percentage of mesh affected surface, tissue hydroxyproline levels, and tissue histopathology were examined.

RESULTS

All animals in group 1 and 57% of animals in group 3 presented postoperative adhesions. The combination of antiadhesives significantly reduced the extent and severity of adhesions as well as the hydroxyproline levels in groups 2 and 4 compared with groups 1 and 3. On microscopic evaluation, animals in group 1 exhibited higher inflammation scores compared with group 2, whereas animals in groups 2 and 4 had better mesotheliazation compared with groups 1 and 3.

CONCLUSIONS

The combined administration of icodextrin 4% and dimetindene maleate reduces the extent and severity of adhesions and may be successfully used to prevent adhesion formation after mesh intraperitoneal placement.

Hypoxia upregulates integrin gene expression in microvascular endothelial cells and promotes their migration and capillary-like tube formation

Tissue hypoxia affects gene expression through the hypoxia-inducible transcription factors, HIF-1 and HIF-2, in both physiological and pathological angiogenesis. Angiogenesis is a complex response of endothelial cells integrating cell proliferation, migration, tube formation, and their interaction with the extracellular matrix through integrin receptors. In this report, we studied the effect of hypoxia on the angiogenic functions of human microvascular endothelial cells (HMEC-1) as well as on expression of the angiogenic integrins α_ν β₃ , α_ν β₅ , and α₅ β₁ . Exposure of HMEC-1 to hypoxia (1% O₂ ) or to DMOG, a prolyl-4-hydroxylase inhibitor, caused significant reduction to their proliferation rate, whereas their migration ability toward laminin-1 or collagen IV and capillary-like tube formation were significantly enhanced. In addition, α_v , β₁ , β₃ , and β₅ integrins expression was increased under hypoxia in HMEC-1, while α₅ integrin was not affected. Both HIF-1 and HIF-2 protein expression and transcriptional activity were induced under hypoxia in HMEC-1. The knockdown of either HIF-1α or HIF-2α inhibited integrin β₃ hypoxic stimulation, suggesting a HIF-dependent induction of β₃ integrin in HMEC-1. Taken together, our results indicate that hypoxia transcriptionally up-regulates angiogenic integrins in microvascular endothelial cells along with promoting migration and tube formation of HMEC-1.

HIF-2α phosphorylation by CK1δ promotes erythropoietin secretion in liver cancer cells under hypoxia

Hypoxia inducible factor 2 (HIF-2) is a transcriptional activator implicated in the cellular response to hypoxia. Regulation of its inducible subunit, HIF-2α (also known as EPAS1), involves post-translational modifications. Here, we demonstrate that casein kinase 1δ (CK1δ; also known as CSNK1D) phosphorylates HIF-2α at Ser383 and Thr528 in vitro We found that disruption of these phosphorylation sites, and silencing or chemical inhibition of CK1δ, reduced the expression of HIF-2 target genes and the secretion of erythropoietin (EPO) in two hepatic cancer cell lines, Huh7 and HepG2, without affecting the levels of HIF-2α protein expression. Furthermore, when CK1δ-dependent phosphorylation of HIF-2α was inhibited, we observed substantial cytoplasmic mislocalization of HIF-2α, which was reversed upon the addition of the nuclear protein export inhibitor leptomycin B. Taken together, these data suggest that CK1δ enhances EPO secretion from liver cancer cells under hypoxia by modifying HIF-2α and promoting its nuclear accumulation. This modification represents a new mechanism of HIF-2 regulation that might allow HIF isoforms to undertake differing functions.

Cobalt stimulates HIF-1-dependent but inhibits HIF-2-dependent gene expression in liver cancer cells

Hypoxia-inducible factors (HIFs) are transcriptional regulators that mediate the cellular response to low oxygen. Although HIF-1 is usually considered as the principal mediator of hypoxic adaptation, several tissues and different cell types express both HIF-1 and HIF-2 isoforms under hypoxia or when treated with hypoxia mimetic chemicals such as cobalt. However, the similarities or differences between HIF-1 and HIF-2, in terms of their tissue- and inducer-specific activation and function, are not adequately characterized. To address this issue, we investigated the effects of true hypoxia and hypoxia mimetics on HIF-1 and HIF-2 induction and specific gene transcriptional activity in two hepatic cancer cell lines, Huh7 and HepG2. Both hypoxia and cobalt caused rapid induction of both HIF-1α and HIF-2α proteins. Hypoxia induced erythropoietin (EPO) expression and secretion in a HIF-2-dependent way. Surprisingly, however, EPO expression was not induced when cells were treated with cobalt. In agreement, both HIF-1- and HIF-2-dependent promoters (of PGK and SOD2 genes, respectively) were activated by hypoxia while cobalt only activated the HIF-1-dependent PGK promoter. Unlike cobalt, other hypoxia mimetics such as DFO and DMOG activated both types of promoters. Furthermore, cobalt impaired the hypoxic stimulation of HIF-2, but not HIF-1, activity and cobalt-induced HIF-2α interacted poorly with USF-2, a HIF-2-specific co-activator. These data show that, despite similar induction of HIF-1α and HIF-2α protein expression, HIF-1 and HIF-2 specific gene activating functions respond differently to different stimuli and suggest the operation of oxygen-independent and gene- or tissue-specific regulatory mechanisms involving additional transcription factors or co-activators.

MgcRacGAP, a cytoskeleton regulator, inhibits HIF-1 transcriptional activity by blocking its dimerization

Hypoxia inducible factor-1 (HIF-1), a dimeric transcription factor of the bHLH-PAS family, is comprised of HIF-1α, which is inducible by hypoxia and ARNT or HIF-1β, which is constitutively expressed. HIF-1 is involved in cellular homeostasis under hypoxia, in development and in several diseases affected by oxygen availability, particularly cancer. Since its expression is positively correlated with poor outcome prognosis for cancer patients, HIF-1 is a target for pharmaceutical therapy. We have previously shown that male germ cell Rac GTPase activating protein (MgcRacGAP), a regulator of Rho proteins which are principally involved in cytoskeletal organization, binds to HIF-1α and inhibits its transcriptional activity. In this work, we have explored the mechanism of the MgcRacGAP-mediated HIF-1 inactivation. We show that the Myo domain of MgcRacGAP, which is both necessary and sufficient for HIF-1 repression, binds to the PAS-B domain of HIF-1α. Furthermore MgcRacGAP competes with ARNT for binding to the HIF-1α PAS-B domain, as shown by in vitro binding pull down assays. In mammalian cells, ARNT overexpression can overcome the MgcRacGAP-mediated inhibition and MgcRacGAP binding to HIF-1α in vivo inhibits its dimerization with ARNT. We additionally present results indicating that MgcRacGAP binding to HIF-1α is specific, since it does not affect the transcriptional activity of HIF-2, a close evolutionary relative of HIF-1 also involved in hypoxia regulation and cancer. Our results reveal a new mechanism for HIF-1 transcriptional activity regulation, suggest a novel hypoxia-cytoskeleton link and provide new tools for selective HIF-1 inhibition.

Hypoxia causes triglyceride accumulation by HIF-1-mediated stimulation of lipin 1 expression

Adaptation to hypoxia involves hypoxia-inducible transcription factors (HIFs) and requires reprogramming of cellular metabolism that is essential during both physiological and pathological processes. In contrast to the established role of HIF-1 in glucose metabolism, the involvement of HIFs and the molecular mechanisms concerning the effects of hypoxia on lipid metabolism are poorly characterized. Here, we report that exposure of human cells to hypoxia causes accumulation of triglycerides and lipid droplets. This is accompanied by induction of lipin 1, a phosphatidate phosphatase isoform that catalyzes the penultimate step in triglyceride biosynthesis, whereas lipin 2 remains unaffected. Hypoxic upregulation of lipin 1 expression involves predominantly HIF-1, which binds to a single distal hypoxia-responsive element in the lipin 1 gene promoter and causes its activation under low oxygen conditions. Accumulation of hypoxic triglycerides or lipid droplets can be blocked by siRNA-mediated silencing of lipin 1 expression or kaempferol-mediated inhibition of HIF-1. We conclude that direct control of lipin 1 transcription by HIF-1 is an important regulatory feature of lipid metabolism and its adaptation to hypoxia.

Oxidative stress and inflammatory markers in the exhaled breath condensate of children with OSA

INTRODUCTION

Obstructive sleep apnea (OSA) in children has been associated with systemic inflammation and oxidative stress. Limited evidence indicates that pediatric OSA is associated with oxidative stress and inflammation in the airway.

OBJECTIVE

The objective of this study is to assess the hypothesis that levels of oxidative stress and inflammatory markers in the exhaled breath condensate (EBC) of children with OSA are higher than those of control subjects.

METHODS

Participants were children with OSA and control subjects who underwent overnight polysomnography. Morning levels of hydrogen peroxide (H(2)O(2)) and sum of nitrite and nitrate (NO(x)) in EBC of participants were measured.

RESULTS

Twelve subjects with moderate-to-severe OSA (mean age ± standard deviation: 6.3 ± 1.7 years; apnea-hypopnea index--AHI, 13.6 ± 10.1 episodes/h), 22 subjects with mild OSA (6.7 ± 2.1 years; AHI, 2.8 ± 1 episodes/h) and 16 control participants (7.7 ± 2.4 years; AHI, 0.6 ± 0.3 episodes/h) were recruited. Children with moderate-to severe OSA had higher log-transformed H(2)O(2) concentrations in EBC compared to subjects with mild OSA, or to control participants: 0.4 ± 1.1 versus -0.9 ± 1.3 (p = 0.015), or versus -1.2 ± 1.2 (p = 0.003), respectively. AHI and % sleep time with oxygen saturation of hemoglobin <95% were significant predictors of log-transformed H(2)O(2) after adjustment by age and body mass index z score (p < 0.05). No significant differences were demonstrated between the three study groups in terms of EBC NO(x) levels.

CONCLUSIONS

Children with moderate-to-severe OSA have increased H(2)O(2) levels in morning EBC, an indirect index of altered redox status in the respiratory tract.

The C-terminal region of HPNAP activates neutrophils and promotes their adhesion to endothelial cells

Entire Helicobacter Pylori Neutrophil Activated Protein (HPNAP) and its truncated forms NH(2)-terminal region HPNAP(1-57) and C-terminal region HPNAP(58-144) after cloning into pET29c vector, purification and removal of LPS traces were subjected to human neutrophil activation. Our results revealed that the C-terminal region of HPNAP is indispensable for human neutrophil stimulation and their further adhesion to endothelial cells - a step necessary to H. pylori inflammation - in a ratio equal to that exhibited by the entire protein. In addition, experiments concerning the implication of Arabino-Galactan-Proteins (AGPs) derived from Chios Mastic Gum (CMG), the natural resin of the plant Pistacia lentiscus var. Chia revealed the inhibition of neutrophil activation and therefore their adhesion to endothelial cells, in vitro. Both, the involvement of HPNAP C-terminal region in stimulation-adhesion of neutrophils to endothelial cells as well as the inhibition of this process by AGPs have to be further investigated and may be exploited in a future anti-inflammatory therapy for H. pylori patients.

Receptor of Advanced Glycation End Products (RAGE) Positively Regulates CD36 Expression and Reactive Oxygen Species Production in Human Monocytes in Diabetes

Introduction: Advanced glycation end products (AGEs) engagement of a monocyte surface receptor (RAGE) induces atherosclerosis. AGEs also act as CD36 ligands. We studied reactive oxygen species (ROS) and CD36 expression after siRNA inhibition of RAGE expression in human monocytes. Methods: We isolated monocytes from: a) 10 type 2 diabetics, and b) 5 age- and sex-matched healthy individuals. CD36 expression and ROS production were evaluated before and after RAGE knockdown. Results: After incubation of monocytes with AGE + bovine serum albumin (BSA), CD36 expression and intracellular ROS increased significantly in all groups. In RAGE-knockdown monocytes, AGE-induced CD36 expression and ROS generation were also significantly inhibited. Conclusions: Blocking RAGE expression using siRNA in human monocytes led to a significant inhibition of CD36 expression and ROS production, suggesting a positive interaction between RAGE, CD36 expression and ROS generation in monocytes.

A novel assay for the evaluation of the prooxidant–antioxidant balance, before and after antioxidant vitamin administration in type II diabetes patients

OBJECTIVES

The application of a novel assay for the direct measurement of prooxidant-antioxidant balance (PAB) in type II diabetes and the evaluation of antioxidant therapy.

DESIGN AND METHODS

The assay is based on 3,3',5,5'-tetramethylbenzidine and its cation, used as a redox indicator participating in two simultaneous reactions. PAB was determined in the sera of healthy volunteers and type II diabetes patients. The results were compared with clinical and biological parameters, protein oxidation markers, as well as the results of antioxidant and prooxidant assays. PAB, after administration of vitamins C and E for 1 day, 1 month and 2 months was also determined.

RESULTS

Increased PAB was found in the patients' group and correlated with parameters involved in diabetic complications, protein oxidation markers, antioxidant and prooxidant assays. One day after vitamin administration, a significant shift of PAB towards antioxidants was observed. PAB remained unchanged after 1 month and changed marginally in favor of prooxidants in the second month of the therapy.

CONCLUSIONS

These results indicate that the measurement of PAB may be useful to identify and follow-up patients who need antioxidant therapy.

Effect of Endothelin on Sodium/Hydrogen Exchanger Activity of Human Monocytes and Atherosclerosis-Related Functions

The objective of this article is to investigate the influence of endothelin-1 (ET-1) on human monocyte Na(+)/H(+) exchanger (NHE) activity and on the atherosclerosis-related monocyte functions. ET-1 caused an increase in pHi and in (22)Na influx of monocytes. A reversal of ET-1 effect on pHi was observed in the presence of the NHE1 inhibitor, cariporide. In addition, the activation of NHE1 by ET-1 was mediated via protein kinase C (PKC), mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), and NADPH oxidase. Also, a link between ET-1 and nitric oxide (NO) was observed. Furthermore, after ET-1 treatment, an increase of the adhesive capacity, the migration ability on laminin and CD36 expression of monocytes, was observed; using cariporide this increase was abolished. Our results showed that ET-1 induces a signaling pathway with the involvement of PKC, MAPK, PI3K, and NADPH oxidase where NHE1 plays a key role. ET-1 also plays a significant role in atherosclerosis-related functions of human monocytes, via NHE1 activation.