Accumulation and nuclear import of HIF1 alpha during high and low oxygen concentration in skeletal muscle cells in primary culture

HIF-1α/MMP-9 Axis Is Required in the Early Phases of Skeletal Myoblast Differentiation under Normoxia Condition In Vitro

Hypoxia-inducible factor (HIF)-1α represents an oxygen-sensitive subunit of HIF transcriptional factor, which is usually degraded in normoxia and stabilized in hypoxia to regulate several target gene expressions. Nevertheless, in the skeletal muscle satellite stem cells (SCs), an oxygen level-independent regulation of HIF-1α has been observed. Although HIF-1α has been highlighted as a SC function regulator, its spatio-temporal expression and role during myogenic progression remain controversial. Herein, using biomolecular, biochemical, morphological and electrophysiological analyses, we analyzed HIF-1α expression, localization and role in differentiating murine C2C12 myoblasts and SCs under normoxia. In addition, we evaluated the role of matrix metalloproteinase (MMP)-9 as an HIF-1α effector, considering that MMP-9 is involved in myogenesis and is an HIF-1α target in different cell types. HIF-1α expression increased after 24/48 h of differentiating culture and tended to decline after 72 h/5 days. Committed and proliferating mononuclear myoblasts exhibited nuclear HIF-1α expression. Differently, the more differentiated elongated and parallel-aligned cells, which are likely ready to fuse with each other, show a mainly cytoplasmic localization of the factor. Multinucleated myotubes displayed both nuclear and cytoplasmic HIF-1α expression. The MMP-9 and MyoD (myogenic activation marker) expression synchronized with that of HIF-1α, increasing after 24 h of differentiation. By means of silencing HIF-1α and MMP-9 by short-interfering RNA and MMP-9 pharmacological inhibition, this study unraveled MMP-9's role as an HIF-1α downstream effector and the fact that the HIF-1α/MMP-9 axis is essential in morpho-functional cell myogenic commitment.

Sex-specific metabolic adaptations in transgenic mice overexpressing cytochrome b5 reductase-3

Cytochrome b5 reductase 3 (CYB5R3) activates respiratory metabolism in cellular systems and exerts a prolongevity action in transgenic mice overexpressing this enzyme, mimicking some of the beneficial effects of calorie restriction. The aim of our study was to investigate the role of sex on metabolic adaptations elicited by CYB5R3 overexpression, and how key markers related with mitochondrial function are modulated in skeletal muscle, one of the major contributors to resting energy expenditure. Young CYB5R3 transgenic mice did not exhibit the striking adaptations in carbon metabolism previously detected in older animals. CYB5R3 was efficiently overexpressed and targeted to mitochondria in skeletal muscle from transgenic mice regardless sex. Overexpression significantly elevated NADH in both sexes, although differences were not statistically significant for NAD+, and increased the abundance of cytochrome c and the fission protein DRP-1 in females but not in males. Moreover, while mitochondrial biogenesis and function markers (as TFAM, NRF-1 and cleaved SIRT3) were markedly upregulated by CYB5R3 overexpression in females, a downregulation was observed in males. Ultrastructural changes were also highlighted, with an increase in the number of mitochondria per surface unit, and in the size of intermyofibrillar mitochondria in transgenic females compared with their wild-type controls. Our results support that CYB5R3 overexpression upregulates markers consistent with enhanced mitochondrial biogenesis and function, and increases mitochondrial abundance in skeletal muscle, producing most of these potentially beneficial actions in females.

Fumonisin B1 disrupts mitochondrial function in oxidatively poised HepG2 liver cells by disrupting oxidative phosphorylation complexes and potential participation of lincRNA-p21

Fumonisin B₁ (FB₁) is etiologically linked to cancer, yet the underlying mechanisms remain largely unclear. It is also not known if mitochondrial dysfunction is involved as a contributor to FB₁-induced metabolic toxicity. This study investigated the effects of FB₁ on mitochondrial toxicity and its implications in cultured human liver (HepG2) cells. HepG2 cells poised to undergo oxidative and glycolytic metabolism were exposed to FB₁ for 6 h. We determined mitochondrial toxicity, reducing equivalent levels and mitochondrial sirtuin activity using luminometric, fluorometric and spectrophotometric methods. Molecular pathways involved were determined using western blots and PCR. Our data confirm that FB₁ is a mitochondrial toxin capable of disrupting the stability of complexes I and V of the mitochondrial electron transport and decreasing the NAD:NADH ratio in galactose supplemented HepG2 cells. We further showed that in cells treated with FB₁, p53 acts as a metabolic stress-responsive transcription factor that induces the expression of lincRNA-p21, which plays a crucial role in stabilising HIF-1α. The findings provide novel insights into the impact of this mycotoxin in the dysregulation of energy metabolism and may contribute to the growing body of evidence of its tumor promoting effects.

Hypoxia and HIFs in Ewing sarcoma: new perspectives on a multi-facetted relationship

Hypoxia develops during the growth of solid tumors and influences tumoral activity in multiple ways. Low oxygen tension is also present in the bone microenvironment where Ewing sarcoma (EwS) - a highly aggressive pediatric cancer - mainly arises. Hypoxia inducible factor 1 subunit alpha (HIF-1-a) is the principal molecular mediator of the hypoxic response in cancer whereas EWSR1::FLI1 constitutes the oncogenic driver of EwS. Interaction of the two proteins has been shown in EwS. Although a growing body of studies investigated hypoxia and HIFs in EwS, their precise role for EwS pathophysiology is not clarified to date. This review summarizes and structures recent findings demonstrating that hypoxia and HIFs play a role in EwS at multiple levels. We propose to view hypoxia and HIFs as independent protagonists in the story of EwS and give a perspective on their potential clinical relevance as prognostic markers and therapeutic targets in EwS treatment.

Oxygen Gradient Induced in Microfluidic Chips Can Be Used as a Model for Liver Zonation

Availability of oxygen plays an important role in tissue organization and cell-type specific metabolism. It is, however, difficult to analyze hypoxia-related adaptations in vitro because of inherent limitations of experimental model systems. In this study, we establish a microfluidic tissue culture protocol to generate hypoxic gradients in vitro, mimicking the conditions found in the liver acinus. To accomplish this, four microfluidic chips, each containing two chambers, were serially connected to obtain eight interconnected chambers. HepG2 hepatocytes were uniformly seeded in each chamber and cultivated under a constant media flow of 50 µL/h for 72 h. HepG2 oxygen consumption under flowing media conditions established a normoxia to hypoxia gradient within the chambers, which was confirmed by oxygen sensors located at the inlet and outlet of the connected microfluidic chips. Expression of Hif1α mRNA and protein was used to indicate hypoxic conditions in the cells and albumin mRNA and protein expression served as a marker for liver acinus-like zonation. Oxygen measurements performed over 72 h showed a change from 17.5% to 15.9% of atmospheric oxygen, which corresponded with a 9.2% oxygen reduction in the medium between chamber1 (inlet) and 8 (outlet) in the connected microfluidic chips after 72 h. Analysis of Hif1α expression and nuclear translocation in HepG2 cells additionally confirmed the hypoxic gradient from chamber1 to chamber8. Moreover, albumin mRNA and protein levels were significantly reduced from chamber1 to chamber8, indicating liver acinus zonation along the oxygen gradient. Taken together, microfluidic cultivation in interconnected chambers provides a new model for analyzing cells in a normoxic to hypoxic gradient in vitro. By using a well-characterized cancer cell line as a homogenous hepatocyte population, we also demonstrate that an approximate 10% reduction in oxygen triggers translocation of Hif1α to the nucleus and reduces albumin production.

Hypoxic Signaling in Skeletal Muscle Maintenance and Regeneration: A Systematic Review

In skeletal muscle tissue, oxygen (O₂) plays a pivotal role in both metabolism and the regulation of several intercellular pathways, which can modify proliferation, differentiation and survival of cells within the myogenic lineage. The concentration of oxygen in muscle tissue is reduced during embryogenesis and pathological conditions. Myogenic progenitor cells, namely satellite cells, are necessary for muscular regeneration in adults and are localized in a hypoxic microenvironment under the basal lamina, suggesting that the O₂ level could affect their function. This review presents the effects of reduced oxygen levels (hypoxia) on satellite cell survival, myoblast regeneration and differentiation in vertebrates. Further investigations and understanding of the pathways involved in adult muscle regeneration during hypoxic conditions are maybe clinically relevant to seek for novel drug treatments for patients with severe muscle damage. We especially outlined the effect of hypoxia-inducible factor 1-alpha (HIF1A), the most studied transcriptional regulator of cellular and developmental response to hypoxia, whose investigation has recently been awarded with the Nobel price.

Long-Term Deleterious Effects of Short-term Hyperoxia on Cancer Progression-Is Brain-Derived Neurotrophic Factor an Important Mediator? An Experimental Study

Perioperative factors promoting cancer recurrence and metastasis are under scrutiny. While oxygen toxicity is documented in several acute circumstances, its implication in tumor evolution is poorly understood. We investigated hyperoxia long-term effects on cancer progression and some underlying mechanisms using both in vitro and in vivo models of triple negative breast cancer (TNBC). We hypothesized that high oxygen exposure, even of short duration, may have long-term effects on cancer growth. Considering that hyperoxic exposure results in reactive oxygen species (ROS) formation, increased oxidative stress and increased Brain-Derived Neurotrophic Factor (BDNF) expression, BDNF may mediate hyperoxia effects offering cancer cells a survival advantage by increased angiogenesis and epithelial mesenchymal transition (EMT). Human breast epithelial MCF10A, human MDA-MB-231 and murine 4T1 TNBC were investigated in 2D in vitro system. Cells were exposed to normoxia or hyperoxia (40%, 60%, 80% O₂) for 6 h. We evaluated ROS levels, cell viability and the expression of BDNF, HIF-1α, VEGF-R2, Vimentin and E-Cadherin by immunofluorescence. The in vivo model consisted of 4T1 inoculation in Balb/c mice and tumor resection 2 weeks after and 6 h exposure to normoxia or hyperoxia (40%, 80% O₂). We measured lung metastases and the same molecular markers, immediately and 4 weeks after surgery. The in vitro study showed that short-term hyperoxia exposure (80% O₂) of TNBC cells increases ROS, increases BDNF expression and that promotes EMT and angiogenesis. The in vivo data indicates that perioperative hyperoxia enhances metastatic disease and this effect could be BDNF mediated.

Early redox activities modulate Xenopus tail regeneration

Redox state sustained by reactive oxygen species (ROS) is crucial for regeneration; however, the interplay between oxygen (O2), ROS and hypoxia-inducible factors (HIF) remains elusive. Here we observe, using an optic-based probe (optrode), an elevated and steady O2 influx immediately upon amputation. The spatiotemporal O2 influx profile correlates with the regeneration of Xenopus laevis tadpole tails. Inhibition of ROS production but not ROS scavenging decreases O2 influx. Inhibition of HIF-1α impairs regeneration and stabilization of HIF-1α induces regeneration in the refractory period. In the regeneration bud, hypoxia correlates with O2 influx, ROS production, and HIF-1α stabilization that modulate regeneration. Further analyses reveal that heat shock protein 90 is a putative downstream target of HIF-1α while electric current reversal is a de facto downstream target of HIF-1α. Collectively, the results show a mechanism for regeneration via the orchestration of O2 influx, ROS production, and HIF-1α stabilization.

Intrauterine Exposure to Cadmium Reduces HIF-1 DNA-Binding Ability in Rat Fetal Kidneys

During embryonic development, some hypoxia occurs due to incipient vascularization. Under hypoxic conditions, gene expression is mainly controlled by hypoxia-inducible factor 1 (HIF-1). The activity of this transcription factor can be altered by the exposure to a variety of compounds; among them is cadmium (Cd), a nephrotoxic heavy metal capable of crossing the placenta and reaching fetal kidneys. The goal of the study was to determine Cd effects on HIF-1 on embryonic kidneys. Pregnant Wistar rats were exposed to a mist of isotonic saline solution or CdCl₂ (D_Del = 1.48 mg Cd/kg/day), from gestational day (GD) 8 to 20. Embryonic kidneys were obtained on GD 21 for RNA and protein extraction. Results show that Cd exposure had no effect on HIF-1α and prolyl hydroxylase 2 protein levels, but it reduced HIF-1 DNA-binding ability, which was confirmed by a decrease in vascular endothelial growth factor (VEGF) mRNA levels. In contrast, the protein levels of VEGF were not changed, which suggests the activation of additional regulatory mechanisms of VEGF protein expression to ensure proper kidney development. In conclusion, Cd exposure decreases HIF-1-binding activity, posing a risk on renal fetal development.

Long-Term Chronic Intermittent Hypobaric Hypoxia Induces Glucose Transporter (GLUT4) Translocation Through AMP-Activated Protein Kinase (AMPK) in the Soleus Muscle in Lean Rats

Background: In chronic hypoxia (CH) and short-term chronic intermittent hypoxia (CIH) exposure, glycemia and insulin levels decrease and insulin sensitivity increases, which can be explained by changes in glucose transport at skeletal muscles involving GLUT1, GLUT4, Akt, and AMPK, as well as GLUT4 translocation to cell membranes. However, during long-term CIH, there is no information regarding whether these changes occur similarly or differently than in other types of hypoxia exposure. This study evaluated the levels of AMPK and Akt and the location of GLUT4 in the soleus muscles of lean rats exposed to long-term CIH, CH, and normoxia (NX) and compared the findings.

Methods: Thirty male adult rats were randomly assigned to three groups: a NX (760 Torr) group (n = 10), a CIH group (2 days hypoxia/2 days NX; n = 10) and a CH group (n = 10). Rats were exposed to hypoxia for 30 days in a hypobaric chamber set at 428 Torr (4,600 m). Feeding (10 g daily) and fasting times were accurately controlled. Measurements included food intake (every 4 days), weight, hematocrit, hemoglobin, glycemia, serum insulin (by ELISA), and insulin sensitivity at days 0 and 30. GLUT1, GLUT4, AMPK levels and Akt activation in rat soleus muscles were determined by western blot. GLUT4 translocation was measured with confocal microscopy at day 30.

Results: (1) Weight loss and increases in hematocrit and hemoglobin were found in both hypoxic groups (p < 0.05). (2) A moderate decrease in glycemia and plasma insulin was found. (3) Insulin sensitivity was greater in the CIH group (p < 0.05). (4) There were no changes in GLUT1, GLUT4 levels or in Akt activation. (5) The level of activated AMPK was increased only in the CIH group (p < 0.05). (6) Increased GLUT4 translocation to the plasma membrane of soleus muscle cells was observed in the CIH group (p < 0.05).

Conclusion: In lean rats experiencing long-term CIH, glycemia and insulin levels decrease and insulin sensitivity increases. Interestingly, there is no increase of GLUT1 or GLUT4 levels or in Akt activation. Therefore, cellular regulation of glucose seems to primarily involve GLUT4 translocation to the cell membrane in response to hypoxia-mediated AMPK activation.

Analysis of various potential prognostic markers and survival data in clear cell renal cell carcinoma

PURPOSE

Clear cell renal cell cancers frequently harbor Von Hippel-Lindau gene mutations, leading to stabilization of the hypoxia-inducible factors (HIFs) and their target genes. In this study, we investigated the relationship between vascular endotelial growth factor (VEGF), HIF-1α, HIF-2α, p53 positivity, microvessel density, and Ki-67 rates with prognostic histopathologic factors (Fuhrman nuclear grade, stage, and sarcomatoid differentiation) and survival in clear cell renal cell carcinomas.

MATERIAL AND METHODS

Seventy-two nephrectomy specimens diagnosed as clear cell renal cell carcinoma between 2000 and 2012 were reevaluated. Immunohistochemically VEGF, HIF-1α, HIF-2α, p53, CD34 (for microvessel density evaluation), and Ki-67 antibodies were applied to the tumor areas. The relationships of these antibodies with prognostic factors and survival rates were evaluated with statistical analyses.

RESULTS

Mean survival time was 105.6 months in patients with ccRCC. Patients with high expression of VEGF, HIF-1α and HIF-2α positivity, a high Ki-67 proliferation index, and a high microvessel density evaluation score had a shorter survival time (p < 0.05).

CONCLUSIONS

Our findings supported that with the use of these immunohistochemical markers, prognosis of renal cell carcinoma may be predicted at the first step of patient management. New treatment modalities targeted to HIF-1α and HIF-2α might be planned as well as VEGF-targeted therapies in the management of clear cell renal cell carcinomas.

Cold Inducible RNA Binding Protein Is Involved in Chronic Hypoxia Induced Neuron Apoptosis by Down-Regulating HIF-1α Expression and Regulated By microRNA-23a

Background: Neuron apoptosis mediated by hypoxia inducible factor 1α (HIF-1α) in hippocampus is one of the most important factors accounting for the chronic hypobaric hypoxia induced cognitive impairment. As a neuroprotective molecule that is up-regulated in response to various environmental stress, CIRBP was reported to crosstalk with HIF-1α under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. Objective: In this study, we tried to identify the role of CIRBP in HIF-1α mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. Methods: We established a chronic hypobaric hypoxia rat model as well as a tissue culture model where SH-SY5Y cells were exposed to 1% hypoxia. Based on these models, we measured the expressions of HIF-1α and CIRBP under hypoxia exposure and examined the apoptosis of neurons by TUNEL immunofluorescence staining and western blot analysis of apoptosis related proteins. In addition, by establishing HIF-1α shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1α in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1α and neuron apoptosis in the process of exposure. Furthermore, we measured the expression of the reported hypoxia related miRNAs in both models and the influence of miRNAs' over-expression/knock-down upon CIRBP in the process of HIF-1α mediated neuron apoptosis. Results: HIF-1α expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both in vivo and in vitro. CIRBP was induced in the early stage of exposure (3d/7d); however as the exposure was prolonged (21d), CIRBP level of the hypoxia group became significantly lower than that of control. In addition, HIF-1α knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1α may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1α up-regulation in hypoxia and inhibited HIF-1α mediated neuron apoptosis. Interestingly, miR-23a was also induced by hypoxia exposure and showed the same changing tendency with CIRBP (increasing in 3d/7d, decreasing in 21d). In addition, over-expressing miR-23a up-regulated CIRBP, down-regulated HIF-1α and attenuated neuron apoptosis. Conclusion: Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1α expression, and MiR-23a may be an important tool to maintain CIRBP level and function.

The hypoxia-inducible factors HIF1α and HIF2α are dispensable for embryonic muscle development but essential for postnatal muscle regeneration

Muscle satellite cells are myogenic stem cells whose quiescence, activation, self-renewal, and differentiation are influenced by oxygen supply, an environmental regulator of stem cell activity. Accordingly, stem cell-specific oxygen signaling pathways precisely control the balance between muscle growth and regeneration in response to oxygen fluctuations, and hypoxia-inducible factors (HIFs) are central mediators of these cellular responses. However, the in vivo roles of HIFs in quiescent satellite cells and activated satellite cells (myoblasts) are poorly understood. Using transgenic mouse models for cell-specific HIF expression, we show here that HIF1α and HIF2α are preferentially expressed in pre- and post-differentiation myoblasts, respectively. Interestingly, double knockouts of HIF1α and HIF2α (HIF1α/2α dKO) generated with the MyoD^Cre system in embryonic myoblasts resulted in apparently normal muscle development and growth. However, HIF1α/2α dKO produced with the tamoxifen-inducible, satellite cell-specific Pax7^CreER system in postnatal satellite cells delayed injury-induced muscle repair due to a reduced number of myoblasts during regeneration. Analysis of satellite cell dynamics on myofibers confirmed that HIF1α/2α dKO myoblasts exhibit reduced self-renewal but more pronounced differentiation under hypoxic conditions. Mechanistically, the HIF1α/2α dKO blunted hypoxia-induced activation of Notch signaling, a key determinant of satellite cell self-renewal. We conclude that HIF1α and HIF2α are dispensable for muscle stem cell function under normoxia but are required for maintaining satellite cell self-renewal in hypoxic environments. Our insights into a critical mechanism in satellite cell homeostasis during muscle regeneration could help inform research efforts to treat muscle diseases or improve muscle function.

Prolyl Hydroxylase Domain-2 Inhibition Improves Skeletal Muscle Regeneration in a Male Murine Model of Obesity

Obesity leads to a loss of muscle mass and impaired muscle regeneration. In obese individuals, pathologically elevated levels of prolyl hydroxylase domain enzyme 2 (PHD2) limit skeletal muscle hypoxia-inducible factor-1 alpha and vascular endothelial growth factor (VEGF) expression. Loss of local VEGF may further impair skeletal muscle regeneration. We hypothesized that PHD2 inhibition would restore vigorous muscle regeneration in a murine model of obesity. Adult (22-week-old) male mice were fed either a high-fat diet (HFD), with 60% of calories derived from fat, or a regular diet (RD), with 10% of calories derived from fat, for 16 weeks. On day 5 following cryoinjury to the tibialis anterior muscle, newly regenerated muscle fiber cross-sectional areas were significantly smaller in mice fed an HFD as compared to RD, indicating an impaired regenerative response. Cryoinjured gastrocnemius muscles of HFD mice also showed elevated PHD2 levels (twofold higher) and reduced VEGF levels (twofold lower) as compared to RD. Dimethyloxalylglycine, a cell permeable competitive inhibitor of PHD2, restored VEGF levels and significantly improved regenerating myofiber size in cryoinjured mice fed an HFD. We conclude that pathologically increased PHD2 in the obese state drives impairments in muscle regeneration, in part by blunting VEGF production. Inhibition of PHD2 over activity in the obese state normalizes VEGF levels and restores muscle regenerative potential.

Regulation of myogenesis and skeletal muscle regeneration: effects of oxygen levels on satellite cell activity

Reduced oxygen (O₂) levels (hypoxia) are present during embryogenesis and exposure to altitude and in pathologic conditions. During embryogenesis, myogenic progenitor cells reside in a hypoxic microenvironment, which may regulate their activity. Satellite cells are myogenic progenitor cells localized in a local environment, suggesting that the O₂ level could affect their activity during muscle regeneration. In this review, we present the idea that O₂ levels regulate myogenesis and muscle regeneration, we elucidate the molecular mechanisms underlying myogenesis and muscle regeneration in hypoxia and depict therapeutic strategies using changes in O₂ levels to promote muscle regeneration. Severe hypoxia (≤1% O₂) appears detrimental for myogenic differentiation in vitro, whereas a 3-6% O₂ level could promote myogenesis. Hypoxia impairs the regenerative capacity of injured muscles. Although it remains to be explored, hypoxia may contribute to the muscle damage observed in patients with pathologies associated with hypoxia (chronic obstructive pulmonary disease, and peripheral arterial disease). Hypoxia affects satellite cell activity and myogenesis through mechanisms dependent and independent of hypoxia-inducible factor-1α. Finally, hyperbaric oxygen therapy and transplantation of hypoxia-conditioned myoblasts are beneficial procedures to enhance muscle regeneration in animals. These therapies may be clinically relevant to treatment of patients with severe muscle damage.-Chaillou, T. Lanner, J. T. Regulation of myogenesis and skeletal muscle regeneration: effects of oxygen levels on satellite cell activity.

The association between let-7, RAS and HIF-1α in Ewing Sarcoma tumor growth

Ewing Sarcoma (ES) is the second most common primary malignant bone tumor in children and adolescents. microRNAs (miRNAs) are involved in cancer as tumor suppressors or oncogenes. We studied the involvement of miRNAs located on chromosomes 11q and 22q that participate in the most common translocation in ES. Of these, we focused on 3 that belong to the let-7 family.

We studied the expression levels of let-7a, and let-7b and detected a significant correlation between low expression of let-7b and increased risk of relapse. let-7 is known to be a negative regulator of the RAS oncogene. Indeed, we detected an inverse association between the expression of let-7 and RAS protein levels and its downstream target p-ERK, following transfection of let-7 mimics and inhibitors. Furthermore, we identified let-7 as a negative regulator of HIF-1α and EWS-FLI-1. Moreover, we were able to show that HIF-1α directly binds to the EWS-FLI-1 promoter. Salirasib treatment in-vitro resulted in the reduction of cell viability, migration ability, and in the decrease of cells in S-phase. A significant reduction in tumor burden and in the expression levels of both HIF-1α and EWS-FLI-1 proteins were observed in mice after treatment.

Our results support the hypothesis that let-7 is a tumor suppressor that negatively regulates RAS, also in ES, and that HIF-1α may contribute to the aggressive metastatic behavior of ES. Moreover, the reduction in the tumor burden in a mouse model of ES following Salirasib treatment, suggests therapeutic potential for this RAS inhibitor in ES.

Establishment of a colorectal cancer nude mouse visualization model of HIF-1α overexpression

The aim of the present study was to establish a model of tumor cell growth and visualize HIF-1α overexpression in a nude mouse xenograft model of colorectal cancer (CRC). In the study, HIF-1α lentiviral vector and helper plasmid were co-transfected into 293T packaging cells using a liposome method, and the virus was collected following transfection and used to infect CRC SW480, SW620, LoVo and HCT116 cells. Puromycin was used for the selection and large-scale amplification of the stable HIF-1α expression of green fluorescent protein (GFP)-positive cells. HIF-1α-expressing cells were injected intraperitoneally into a nude mouse xenograft model, and resulting tumor nodules was separated and confirmed using an inverted fluorescence microscope. The results demonstrated that HIF-1α was not expressed in CRC cells in normoxic conditions. When treated with CoCl₂, the expression of HIF-1α could be induced in all the cancer cell lines, except SW480. HIF-1α was highly expressed following infection with lentiviral particles. Stable expression of HIF-1α promoted migration in the SW480 cells. Following intraperitoneal injection of nude mice with SW480-HIF-1α, a significant number of tumor nodules formed in the intestinal wall compared with the controls (P<0.05). The successful construction of the dual expression HIF-1α and GFP visualization xenograft model provides a good foundation for the screening of HIF-1α-related functions and for investigating the therapeutic potential of drugs that target HIF-1α.

The ETS Factor Myeloid Elf-1-Like Factor (MEF)/Elf4 Is Transcriptionally and Functionally Activated by Hypoxia

Hypoxia-inducible factor (HIF)-1α is a transcription factor belonging to the HIF family that is activated in mammalian cells during conditions of low oxygen tension or hypoxia to induce an adaptive response and promote cell survival. Some of the genes targeted by HIF-1α are important for angiogenesis and proliferation. Here, we found that the E26 transformation-specific (ETS) transcription factor myeloid elf-1-like factor (MEF)/Elf4 is activated by HIF-1α. MEF induces genes such as human beta-defensin 2 (HβD2) and perforin (PRF1), and is known to affect the cell cycle. Treatment with hypoxia mimetic CoCl2 or low O2 incubation up-regulated MEF mRNA and protein levels in various cell lines. HIF-1α overexpression in HEK293 cells also increased MEF mRNA and protein levels. In contrast, HIF-1α knockdown by small interfering RNA (siRNA) suppressed the induction of MEF in response to hypoxia. HIF-1α binds to the hypoxia response element in the MEF promoter region (-200 bp) and activates MEF promoter under hypoxia condition. The induction of MEF by hypoxia/HIF-1α correlated with the increase of MEF target genes HβD2 and PRF1. Intriguingly, the hypoxia-induced expression of HIF-1α target gene vascular endothelial growth factor (VEGF) was enhanced by the exogenous addition of MEF. Overall, these data indicate that hypoxia or HIF-1α positively regulates MEF expression and function.

HIF-1-driven skeletal muscle adaptations to chronic hypoxia: molecular insights into muscle physiology

Skeletal muscle is a metabolically active tissue and the major body protein reservoir. Drop in ambient oxygen pressure likely results in a decrease in muscle cells oxygenation, reactive oxygen species (ROS) overproduction and stabilization of the oxygen-sensitive hypoxia-inducible factor (HIF)-1α. However, skeletal muscle seems to be quite resistant to hypoxia compared to other organs, probably because it is accustomed to hypoxic episodes during physical exercise. Few studies have observed HIF-1α accumulation in skeletal muscle during ambient hypoxia probably because of its transient stabilization. Nevertheless, skeletal muscle presents adaptations to hypoxia that fit with HIF-1 activation, although the exact contribution of HIF-2, I kappa B kinase and activating transcription factors, all potentially activated by hypoxia, needs to be determined. Metabolic alterations result in the inhibition of fatty acid oxidation, while activation of anaerobic glycolysis is less evident. Hypoxia causes mitochondrial remodeling and enhanced mitophagy that ultimately lead to a decrease in ROS production, and this acclimatization in turn contributes to HIF-1α destabilization. Likewise, hypoxia has structural consequences with muscle fiber atrophy due to mTOR-dependent inhibition of protein synthesis and transient activation of proteolysis. The decrease in muscle fiber area improves oxygen diffusion into muscle cells, while inhibition of protein synthesis, an ATP-consuming process, and reduction in muscle mass decreases energy demand. Amino acids released from muscle cells may also have protective and metabolic effects. Collectively, these results demonstrate that skeletal muscle copes with the energetic challenge imposed by O2 rarefaction via metabolic optimization.

Hypoxia-inducible factor-1 modulates the expression of vascular endothelial growth factor and endothelial nitric oxide synthase induced by eccentric exercise

The present study investigated the effects of acute and chronic eccentric exercise on the hypoxia-inducible factor (HIF)-1α activation response and the concomitant modulation of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS) expression in rat skeletal muscle. Twenty-four male Wistar rats were randomly assigned to three experimental groups: rested control group, acutely exercised group after an intermittent downhill protocol for 90 min, and acutely exercise group with a previous eccentric training of 8 wk. HIF-1α activation, VEGF and eNOS gene expression, protein content, and promoter activation were assessed in vastus lateralis muscle biopsies. Acute eccentric exercise induced a marked activation of HIF-1α and resulted in increased VEGF and eNOS mRNA level and protein concentration. The binding of HIF-1α to the VEGF and eNOS promoters, measured by a chromatin immunoprecipitation assay, was undetectable in rested rats, whereas it was evident in acutely exercised animals. Acute exercise also increased myeloperoxidase, toll-like receptor-4, tumor necrosis factor-α, and interleukin-1β protein content, suggesting a contribution of proinflammatory stimuli to HIF-1α activation and VEGF overexpression. All of these effects were partially abolished by training. Moreover, training resulted in an increased capillary density. In summary, our findings indicate that eccentric exercise prompts an HIF-1α response in untrained skeletal muscle that contributes to the upregulation of VEGF and eNOS gene expression and is attenuated after an eccentric training program.

Modulation of p75 neurotrophin receptor under hypoxic conditions induces migration and invasion of C6 glioma cells

p75 neurotrophin receptor (p75NTR) has been reported to play important roles in various cancer types. However, the exact mechanism of tumorigenesis involving p75NTR is unknown. In this study, we investigated the relationship between the expression of p75NTR in malignant glioma and the impact on tumor cell migration and invasion. p75NTR and hypoxia-inducible factor-1α (HIF-1α) expression was down-regulated by short-hairpin RNA and up-regulated with expression vectors. By immunohistochemical staining and Western blot analysis, we found that p75NTR was expressed in both human and rat malignant gliomas. Knockdown of p75NTR increased the expression of vimentin, vascular endothelial growth factor, Matrix metalloproteinase 9, and TWIST, and enhanced the invasion and migration abilities assessed by transwell assay in the C6 tumor cells. Inverse expressions of p75NTR and HIF-1α were detected in glioma cell lines under hypoxic conditions, while increased HIF-1α significantly downregulated the expression of p75NTR, suggesting a HIF-1α-p75NTR-EMT pathway that may regulate glioma cells invasion and migration. Downregulation of p75NTR increased phosphorylation of Src, focal adhesion kinase (FAK) and paxillin. Knockdown of p75NTR also dysregulated β-catenin-mediated cell junctions, and up-regulated the expressions of fibronectin and L1CAM in the cell-cell junctions, thus suggesting that p75NTR knockdown contributed to a more aggressive migration phenotype via FAK signaling pathway. Our studies suggested that modulation of p75NTR under hypoxic condition could enhance C6 cells migration and invasion by induction of EMT, and activation of the FAK pathway. The HIF-1α-p75NTR-EMT axis may play a central role in glioma tumorigenesis.

Role of compartmentalization on HiF-1α degradation dynamics during changing oxygen conditions: a computational approach

HiF-1α is the central protein driving the cellular response to hypoxia. Its accumulation in cancer cells is linked to the appearance of chemoresistant and aggressive tumor phenotypes. As a consequence, understanding the regulation of HiF-1α dynamics is a major issue to design new anti-cancer therapies. In this paper, we propose a model of the hypoxia pathway, involving HiF-1α and its inhibitor pVHL. Based on data from the literature, we made the hypothesis that the regulation of HiF-1α involves two compartments (nucleus and cytoplasm) and a constitutive shuttle of the pVHL protein between them. We first show that this model captures correctly the main features of HiF-1α dynamics, including the bi-exponential degradation profile in normoxia, the kinetics of induction in hypoxia, and the switch-like accumulation. Second, we simulated the effects of a hypoxia/reoxygenation event, and show that it generates a strong instability of HiF-1α. The protein concentration rapidly increases 3 hours after the reoxygenation, and exhibits an oscillating pattern. This effect vanishes if we do not consider compartmentalization of HiF-1α. This result can explain various counter-intuitive observations about the specific molecular and cellular response to the reoxygenation process. Third, we simulated the HiF-1α dynamics in the tumor case. We considered different types of mutations associated with tumorigenesis, and we compared their consequences on HiF-1α dynamics. Then, we tested different therapeutics strategies. We show that a therapeutic decrease of HiF-1α nuclear level is not always correlated with an attenuation of reoxygenation-induced instabilities. Thus, it appears that the design of anti-HiF-1α therapies have to take into account these two aspects to maximize their efficiency.

Poly-ADP-ribose-polymerase inhibition ameliorates hind limb ischemia reperfusion injury in a murine model of type 2 diabetes

INTRODUCTION

Diabetes is known to increase poly-ADP-ribose-polymerase (PARP) activity and posttranslational poly-ADP-ribosylation of several regulatory proteins involved in inflammation and energy metabolism. These experiments test the hypothesis that PARP inhibition will modulate hind limb ischemia reperfusion (IR) in a mouse model of type-II diabetes and ameliorate the ribosylation and the activity/transnuclear localization of the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

METHODS

db/db mice underwent 1.5 hours of hind limb ischemia followed by 1, 7, or 24 hours of reperfusion. The treatment group received the PARP inhibitor PJ34 (PJ34) over a 24-hour period; the untreated group received Lactated Ringer (LR) at the same time points. IR muscles were analyzed for indices of PARP activity, fiber injury, metabolic activity, inflammation, GAPDH activity/intracellular localization, and poly-ADP-ribosylation of GAPDH.

RESULTS

PARP activity was significantly lower in the PJ34-treated groups than in the Lactated Ringer group at 7 and 24 hours of reperfusion. There was significantly less muscle fiber injury in the PJ34-treated group than in the Lactated Ringer-treated mice at 24 hours of reperfusion. PJ34 lowered levels of select proinflammatory molecules at 7 hours and 24 hours of IR. There were significant increases in metabolic activity only at 24 hours of IR in the PJ34 group, which temporally correlated with increase in GAPDH activity, decreased GAPDH poly-ADP-ribosylation, and nuclear translocation of GAPDH.

CONCLUSIONS

PJ34 reduced PARP activity, GAPDH ribosylation, and GAPDH translocation; ameliorated muscle fiber injury; and increased metabolic activity after hind limb IR injury in a murine model of type-II diabetes. PARP inhibition might be a therapeutic strategy after IR in diabetic humans.

Augmentation of normal and glutamate-impaired neuronal respiratory capacity by exogenous alternative biofuels

Mitochondrial respiratory capacity is critical for responding to changes in neuronal energy demand. One approach toward neuroprotection is the administration of alternative energy substrates ("biofuels") to overcome brain injury-induced inhibition of glucose-based aerobic energy metabolism. This study tested the hypothesis that exogenous pyruvate, lactate, β-hydroxybutyrate, and acetyl-L-carnitine each increase neuronal respiratory capacity in vitro either in the absence of or following transient excitotoxic glutamate receptor stimulation. Compared to the presence of 5 mM glucose alone, the addition of pyruvate, lactate, or β-hydroxybutyrate (1.0-10.0 mM) to either day in vitro (DIV) 14 or 7 rat cortical neurons resulted in significant, dose-dependent stimulation of respiratory capacity, measured by cell respirometry as the maximal O2 consumption rate in the presence of the respiratory uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. A 30-min exposure to 100 μM glutamate impaired respiratory capacity for DIV 14, but not DIV 7, neurons. Glutamate reduced the respiratory capacity for DIV 14 neurons with glucose alone by 25 % and also reduced respiratory capacity with glucose plus pyruvate, lactate, or β-hydroxybutyrate. However, respiratory capacity in glutamate-exposed neurons following pyruvate or β-hydroxybutyrate addition was still, at least, as high as that obtained with glucose alone in the absence of glutamate exposure. These results support the interpretation that previously observed neuroprotection by exogenous pyruvate, lactate, or β-hydroxybutyrate is at least partially mediated by their preservation of neuronal respiratory capacity.

A combined proteomic and transcriptomic approach shows diverging molecular mechanisms in thoracic aortic aneurysm development in patients with tricuspid- and bicuspid aortic valve

Thoracic aortic aneurysm is a pathological local dilatation of the aorta, potentially leading to aortic rupture or dissection. The disease is a common complication of patients with bicuspid aortic valve, a congenital disorder present in 1-2% of the population. Using two dimensional fluorescence difference gel electrophoresis proteomics followed by mRNA expression, and alternative splicing analysis of the identified proteins, differences in dilated and nondilated aorta tissues between 44 patients with bicuspid and tricuspid valves was examined. The pattern of protein expression was successfully validated with LC-MS/MS. A multivariate analysis of protein expression data revealed diverging protein expression fingerprints in patients with tricuspid compared with the patients with bicuspid aortic valves. From 302 protein spots included in the analysis, 69 and 38 spots were differentially expressed between dilated and nondilated aorta specifically in patients with tricuspid and bicuspid aortic valve, respectively. 92 protein spots were differentially expressed between dilated and nondilated aorta in both phenotypes. Similarly, mRNA expression together with alternative splicing analysis of the identified proteins also showed diverging fingerprints in the two patient groups. Differential splicing was abundant but the expression levels of differentially spliced mRNA transcripts were low compared with the wild type transcript and there was no correlation between splicing and the number of spots. Therefore, the different spots are likely to represent post-translational modifications. The identification of differentially expressed proteins suggests that dilatation in patients with a tricuspid aortic valve involves inflammatory processes whereas aortic aneurysm in patients with BAV may be the consequence of impaired repair capacity. The results imply that aortic aneurysm formation in patients with bicuspid and tricuspid aortic valves involve different biological pathways leading to the same phenotype.

Hypoxia increases mouse satellite cell clone proliferation maintaining both in vitro and in vivo heterogeneity and myogenic potential

Satellite cells (SCs) are essential for postnatal muscle growth and regeneration, however, their expansion potential in vitro is limited. Recently, hypoxia has been used to enhance proliferative abilities in vitro of various primary cultures. Here, by isolating SCs from single mouse hindlimb skeletal myofibers, we were able to distinguish two subpopulations of clonally cultured SCs (Low Proliferative Clones - LPC - and High Proliferative Clones - HPC), which, as shown in rat skeletal muscle, were present at a fixed proportion. In addition, culturing LPC and HPC at a low level of oxygen we observed a two fold increased proliferation both for LPC and HPC. LPC showed higher myogenic regulatory factor (MRF) expression than HPC, particularly under the hypoxic condition. Notably, a different myogenic potential between LPC and HPC was retained in vivo: green fluorescent protein (GFP)+LPC transplantation in cardiotoxin-injured Tibialis Anterior led to a higher number of new GFP+muscle fibers per transplanted cell than GFP+HPC. Interestingly, the in vivo myogenic potential of a single cell from an LPC is similar if cultured both in normoxia and hypoxia. Therefore, starting from a single satellite cell, hypoxia allows a larger expansion of LPC than normal O₂ conditions, obtaining a consistent amount of cells for transplantation, but maintaining their myogenic regeneration potential.

Degradation of HIF-1alpha under hypoxia combined with induction of Hsp90 polyubiquitination in cancer cells by hypericin: a unique cancer therapy

The perihydroxylated perylene quinone hypericin has been reported to possess potent anti-metastatic and antiangiogenic activities, generated by targeting diverse crossroads of cancer-promoting processes via unique mechanisms. Hypericin is the only known exogenous reagent that can induce forced poly-ubiquitination and accelerated degradation of heat shock protein 90 (Hsp90) in cancer cells. Hsp90 client proteins are thereby destabilized and rapidly degraded. Hsp70 client proteins may potentially be also affected via preventing formation of hsp90-hsp70 intermediate complexes. We show here that hypericin also induces enhanced degradation of hypoxia-inducible factor 1α (HIF-1α) in two human tumor cell lines, U87-MG glioblastoma and RCC-C2VHL−/− renal cell carcinoma and in the non-malignant ARPE19 retinal pigment epithelial cell line. The hypericin-accelerated turnover of HIF-1α, the regulatory precursor of the HIF-1 transcription factor which promotes hypoxic stress and angiogenic responses, overcomes the physiologic HIF-1α protein stabilization which occurs in hypoxic cells. The hypericin effect also eliminates the high HIF-1α levels expressed constitutively in the von-Hippel Lindau protein (pVHL)-deficient RCC-C2VHL−/− renal cell carcinoma cell line. Unlike the normal ubiquitin-proteasome pathway-dependent turnover of HIF-α proteins which occurs in normoxia, the hypericin-induced HIF-1α catabolism can occur independently of cellular oxygen levels or pVHL-promoted ubiquitin ligation of HIF-1α. It is mediated by lysosomal cathepsin-B enzymes with cathepsin-B activity being optimized in the cells through hypericin-mediated reduction in intracellular pH. Our findings suggest that hypericin may potentially be useful in preventing growth of tumors in which HIF-1α plays pivotal roles, and in pVHL ablated tumor cells such as renal cell carcinoma through elimination of elevated HIF-1α contents in these cells, scaling down the excessive angiogenesis which characterizes these tumors.

Analysis of the single-nucleotide polymorphism in the 5'UTR and part of intron I of the sheep MSTN gene

The myostatin (MSTN) gene region encompassing the 5'UTR and part of intron I was sequenced in animals of two herds of Latvian Darkhead sheep to extend data on the ovine MSTN gene polymorphism and to provide information useful for local breed conservation. Two and four polymorphic loci were revealed in the 5'UTR and intron I. Four and five local haplotypes were constructed, respectively. The genotyping data obtained and that previously reported for the same genomic region were combined in one dataset for the haplotype analysis. Recombination events were detected between loci (c.-40, c.-37) in the 5'UTR and (c.373+18, c.373+101) and (c.373+101, c.373+241) in intron I. Single-nucleotide polymorphisms at c.373+249 and c.373+323 appear to be involved in the strong linkage (p < 0.01). Linkage blocks (c.373+241, c.373+243) and (c.373+241, c.373+259) were revealed at nominal (p < 0.05) level of probability. Haplotype-specific patterns of the transcription factor binding sites predicted in silico were constructed to evaluate a putative functional significance of the particular alleles and haplotypes. A nucleotide at c.373+18 was shown to influence the pre-mRNA secondary structure. DNA curvature predicted in silico for allele c.373+101C was proven experimentally. A possible impact of the particular polymorphisms on the transcription and/or splicing efficiency is discussed.

Passive mechanical forces upregulate the fast myosin heavy chain IId/x via integrin and p38 MAP kinase activation in a primary muscle cell culture

We have studied the mechanism by which a previously described primary muscle culture growing on microcarriers predominantly expresses fast myosin heavy chain (MHC) IId/x. We have measured MHC IId/x mRNA and protein levels, mRNA of MHC I and markers of muscle metabolism, insulin-like growth factor (IGF)-1 and mechano-growth factor (MGF) transcripts, indicators of the activation of the Akt-mammalian target of rapamycin (mTOR) axis, the p38-, ERK1/2-, and JNK-mitogen-activated protein kinase (MAP) kinase pathways, and of protein phosphatase PP2A, and we have assessed the involvement of integrin. By placing the culture flasks on a rotary shaker, we induce a continuous motion of the culture medium in which the carrier-myotube aggregates are suspended. This motion exerts passive forces on the myotubes that are decisive for the predominance of MHC II expression. These forces act via integrin, which transduces the mechanical signal into activation of PP2A and of p38 MAP-Kinase. The latter presumably is directly responsible for a drastic upregulation of MHC IId/x, whereas MHC I and metabolic markers remain unaffected. At the same time, despite an elevated level of IGF-1 transcription under passive forces, the IGF-1 receptor-Akt-mTOR axis is switched off as evident from the lack of an effect of inhibition of the IGF-1 receptor and from the PP2A-mediated low degree of phosphorylation of Akt and 4E-BP1. Similarly, the ERK1/2- and JNK-MAP kinase pathways are repressed. We conclude that passive stretch exerted on the myotubes by the rotary fluid motion induces a rather selective upregulation of fast MHC II, which goes along with a mild muscle hypertrophy as judged from the amount of protein per cell and is caused by p38 MAP kinase activity elevated via integrin sensing. The direct link between passive stretch and MHC II expression constitutes a novel mechanism, which is expected to become effective physiologically under passive stretch and eccentric contractions of skeletal muscles.

The response of human skeletal muscle tissue to hypoxia

Hypoxia refers to environmental or clinical settings that potentially threaten tissue oxygen homeostasis. One unique aspect of skeletal muscle is that, in addition to hypoxia, oxygen balance in this tissue may be further compromised when exercise is superimposed on hypoxia. This review focuses on the cellular and molecular responses of human skeletal muscle to acute and chronic hypoxia, with emphasis on physical exercise and training. Based on published work, it is suggested that hypoxia does not appear to promote angiogenesis or to greatly alter oxidative enzymes in skeletal muscle at rest. Although the HIF-1 pathway in skeletal muscle is still poorly documented, emerging evidence suggests that muscle HIF-1 signaling is only activated to a minor degree by hypoxia. On the other hand, combining hypoxia with exercise appears to improve some aspects of muscle O(2) transport and/or metabolism.

Satellite cell-mediated angiogenesis in vitro coincides with a functional hypoxia-inducible factor pathway

Muscle regeneration involves the coordination of myogenesis and revascularization to restore proper muscle function. Myogenesis is driven by resident stem cells termed satellite cells (SC), whereas angiogenesis arises from endothelial cells and perivascular cells of preexisting vascular segments and the collateral vasculature. Communication between myogenic and angiogenic cells seems plausible, especially given the number of growth factors produced by SC. To characterize these interactions, we developed an in vitro coculture model composed of rat skeletal muscle SC and microvascular fragments (MVF). In this system, isolated epididymal MVF suspended in collagen gel are cultured over a rat SC monolayer culture. In the presence of SC, MVF exhibit greater indices of angiogenesis than MVF cultured alone. A positive dose-dependent effect of SC conditioned medium (CM) on MVF growth was observed, suggesting that SC secrete soluble-acting growth factor(s). Next, we specifically blocked VEGF action in SC CM, and this was sufficient to abolish satellite cell-induced angiogenesis. Finally, hypoxia-inducible factor-1alpha (HIF-1alpha), a transcriptional regulator of VEGF gene expression, was found to be expressed in cultured SC and in putative SC in sections of in vivo stretch-injured rat muscle. Hypoxic culture conditions increased SC HIF-1alpha activity, which was positively associated with SC VEGF gene expression and protein levels. Collectively, these initial observations suggest that a heretofore unexplored aspect of satellite cell physiology is the initiation of a proangiogenic program.

Hypoxia inducible factor-1alpha correlates with vascular endothelial growth factor A and C indicating worse prognosis in clear cell renal cell carcinoma

BACKGROUND

The role of angiogenesis in the pathogenesis of renal cell carcinoma is well recognized, however, the influence of tumor cells in this activity has not yet been fully clarified. The aim of this study was to analyze the expression of hypoxia inducible factor-1alpha (HIF-1alpha), a regulatory factor of angiogenic switch, in comparison to vascular endothelial growth factor A and C (VEGF-A and VEGF-C), recognized to be involved in blood and lymph vessel neoangiogenesis, with potential association in the prognosis of patients with renal cell carcinoma.

METHODS

Ninety-four patients with diagnosis of clear cell renal cell carcinomas (CCRCC), all clinicopathological characteristics and overall survival were unrolled in this study. Immunohistochemicaly VEGF-A, VEGF-C, HIF-1alpha and Ki67 were detected on tumor cells and the staining was performed on tissue microarrays (TMA). The staining was evaluated as a percentage of cytoplasmic or nuclear positive tumor cells.

RESULTS

Variable expression of all three proteins was confirmed. Both angiogenic factors demonstrated perimembranous or diffuse cytoplasmic staining, with diffuse pattern positively associated (p < 0.001). Nuclear HIF-1alpha expression (nHIF-1alpha) showed inverse correlation with diffuse cytoplasmic VEGF-A (p = 0.002) and VEGF-C (p = 0.053), while cytoplasmic HIF-1alpha expression (cHIF-1alpha) showed positive correlation with diffuse staining of both angiogenic factors (p < 0.001; p < 0.001, respectively). In comparison to clinicopathological characteristics, a higher nuclear grade (p = 0.006; p < 0.001, respectively), larger tumor size (p = 0.009; p = 0.015, respectively), higher stage (p = 0.023; p = 0.027, respectively) and shorter survival (p = 0.018; p = 0.024, respectively) were associated with overexpression of cHIF-1alpha and diffuse cytoplasmic VEGF-A expression. In contrary, overexpression of nHIF-1alpha was associated with better diagnostic parameters i.e. lower nuclear grade (p = 0.006), smaller tumor size (p = 0.057), and longer survival (p = 0.005).

CONCLUSION

Overexpression of VEGF-A and cHIF-1alpha in tumor cells highlights a more aggressive subtype of CCRCC that might have some clinical implications. The significance of nHIF-1alpha expression associated with better differentiated tumors should be further elucidated.

Absence of GAPDH regulation in tumor-cells of different origin under hypoxic conditions in - vitro

Background

Gene expression studies related to cancer diagnosis and treatment are important. In order to conduct such experiment accurately, absolutely reliable housekeeping genes are essential to normalize cancer related gene expression. The most important characteristics of such genes are their presence in all cells and their expression levels remain relatively constant under different experimental conditions. However, no single gene of this group of genes manifests always stable expression levels under all experimental conditions. Incorrect choice of housekeeping genes leads to interpretation errors of experimental results including evaluation and quantification of pathological gene expression. Here, we examined (a) the degree of GAPDH expression regulation in Hep-1-6 mouse hepatoma and Hep-3-B and HepG2 human hepatocellular carcinoma cell lines as well as in human lung adenocarcinoma epithelial cell line (A-549) in addition to both HT-29, and HCT-116 colon cancer cell lines, under hypoxic conditions in vitro in comparison to other housekeeping genes like β-actin, serving as experimental loading controls, (b) the potential use of GAPDH as a target for tumor therapeutic approaches was comparatively examined in vitro on both protein and mRNA level, by western blot and semi quantitative RT-PCR, respectively.

Findings

No hypoxia-induced regulatory effect on GAPDH expression was observed in the cell lines studied in vitro that were; Hep-1-6 mouse hepatoma and Hep-3-B and HepG2 human hepatocellular carcinoma cell lines, Human lung adenocarcinoma epithelial cell line (A-549), both colon cancer cell lines HT-29, and HCT-116.

Conclusion

As it is the case for human hepatocellular carcinoma, mouse hepatoma, human colon cancer, and human lung adenocarcinoma, GAPDH represents an optimal choice of a housekeeping gene and/(or) loading control to determine the expression of hypoxia induced genes in tumors of different origin. The results confirm our previous findings in human glioblastoma that this gene is not an attractive target for tumor therapeutic approaches because of the lack of GAPDH regulation under hypoxia.

Atypical CRM1-dependent nuclear export signal mediates regulation of hypoxia-inducible factor-1alpha by MAPK

Hypoxia-inducible factor 1 (HIF-1) is the key transcriptional activator of hypoxia-inducible genes and an important anti-cancer target. Its regulated subunit, HIF-1alpha, is controlled by oxygen levels and major signaling pathways. We reported previously that phosphorylation of Ser(641/643) by p42/44 MAPK is essential for HIF-1alpha nuclear accumulation and activity. We now show that a fragment of HIF-1alpha (amino acids 616-658), termed MAPK target domain, contains a nuclear export signal (NES), which has atypical hydrophobic residue spacing. Localization, reporter gene, and co-immunoprecipitation assays demonstrate that the identified NES interacts with CRM1 in a phosphorylation-sensitive manner. Furthermore, disruption of the NES (I637A/L638A/I639A) restores nuclear localization and activity of nonphosphorylated HIF-1alpha and renders it largely resistant to inhibition of MAPK, an effect reproduced by a phosphomimetic mutation (S641E). As these data predict, overexpression of wild-type or mutant (S641A/S643A) MAPK target domain in HeLa cells modulates the activity and subcellular distribution of endogenous HIF-1alpha. We suggest that control of HIF-1alpha nuclear transport represents an important MAPK-dependent regulatory mechanism.

GAPDH is not regulated in human glioblastoma under hypoxic conditions

Background

Gene expression studies related to cancer diagnosis and treatment are becoming more important. Housekeeping genes that are absolutely reliable are essential for these studies to normalize gene expression. An incorrect choice of housekeeping genes leads to interpretation errors of experimental results including evaluation and quantification of pathological gene expression. Here, we examined (a) the degree of regulation of GAPDH expression in human glioblastoma cells under hypoxic conditions in vitro in comparison to other housekeeping genes like β-actin, serving as experimental loading controls, (b) the potential use of GAPDH as a target for tumor therapeutic approaches and (c) differences in GAPDH expression between low-grade astrocytomas and glioblastomas, for which modest and severe hypoxia, respectively, have been previously demonstrated. GAPDH and β-actin expression was comparatively examined in vivo in human low-grade astrocytoma and glioblastoma on both protein and mRNA level, by Western blot and semiquantitative RT-PCR, respectively. Furthermore, the same proteins were determined in vitro in U373, U251 and GaMG human glioblastoma cells using the same methods. HIF-1α protein regulation under hypoxia was also determined on mRNA level in vitro in GaMG and on protein level in U251, U373 and GaMG cells.

Results

We observed no hypoxia-induced regulatory effect on GAPDH expression in the three glioblastoma cell lines studied in vitro. In addition, GAPDH expression was similar in patient tumor samples of low-grade astrocytoma and glioblastoma, suggesting a lack of hypoxic regulation in vivo.

Conclusion

GAPDH represents an optimal choice of a housekeeping gene and/or loading control to determine the expression of hypoxia induced genes at least in glioblastoma. Because of the lack of GAPDH regulation under hypoxia, this gene is not an attractive target for tumor therapeutic approaches in human glioblastoma.

Effects of hypoxia on proliferation and differentiation of myoblasts

Oxygen is an environmental and developmental signal regulator, and its role is involved in energy homeostasis, development and process of differentiation. Myoblasts persist in skeletal muscle as satellite cells, which possess capability of self-renewing and differentiation into mature myofiber. Myoblasts play a critical role in postnatal muscle regeneration after injury as well as maintaining myofibers' function. Though oxygen is vital to nearly all forms of life, studies focused on investigating the effects of oxygen level on proliferation and differentiation of myoblasts are few. Lower oxygen concentration is more close to the level of oxygen in physiological and pathological environment in vivo. So physiological environment is actually optimum condition for myogenesis. It is significant for understanding repair and regeneration of skeletal muscle to study on effects of hypoxia on myogenesis. HIF-1 signaling pathway was involved in these processes as well as other signaling pathways would be, and accordingly, deep studying and further revealing the signaling pathways involved in mechanism will provide evidences or references for looking for novel targets for stem cells therapy and drug treatment.

Identification of MAPK phosphorylation sites and their role in the localization and activity of hypoxia-inducible factor-1alpha

Hypoxia-inducible factor 1 (HIF-1) controls the expression of most genes induced by hypoxic conditions. Regulation of expression and activity of its inducible subunit, HIF-1alpha, involves several post-translational modifications. To study HIF-1alpha phosphorylation, we have used human full-length recombinant HIF-1alpha as a substrate in kinase assays. We show that at least two different nuclear protein kinases, one of them identified as p42/p44 MAPK, can modify HIF-1alpha. Analysis of in vitro phosphorylated HIF-1alpha by mass spectroscopy revealed residues Ser-641 and Ser-643 as possible MAPK phosphorylation sites. Site-directed mutagenesis of these residues reduced significantly the phosphorylation of HIF-1alpha. When these mutant forms of HIF-1alpha were expressed in HeLa cells, they exhibited much lower transcriptional activity than the wild-type form. However, expression of the same mutants in yeast revealed that their capacity to stimulate transcription was not significantly compromised. Localization of the green fluorescent protein-tagged HIF-1alpha mutants in HeLa cells showed their exclusion from the nucleus in contrast to wild-type HIF-1alpha. Treatment of the cells with leptomycin B, an inhibitor of the major exportin CRM1, reversed this exclusion and led to nuclear accumulation and partial recovery of the activity of the HIF-1alpha mutants. Moreover, inhibition of the MAPK pathway by PD98059 impaired the phosphorylation, nuclear accumulation, and activity of wild-type GFP-HIF-1alpha. Overall, these data suggest that phosphorylation of Ser-641/643 by MAPK promotes the nuclear accumulation and transcriptional activity of HIF-1alpha by blocking its CRM1-dependent nuclear export.