Endothelin-1 inhibits prolyl hydroxylase domain 2 to activate hypoxia-inducible factor-1alpha in melanoma cells

Endothelin-1 increases Na+-K+-2Cl- cotransporter-1 expression in cultured astrocytes and in traumatic brain injury model: An involvement of HIF1α activation

Na+-K+-2Cl- cotransporter-1 (NKCC1) is present in brain cells, including astrocytes. The expression of astrocytic NKCC1 increases in the acute phase of traumatic brain injury (TBI), which induces brain edema. Endothelin-1 (ET-1) is a factor that induces brain edema and regulates the expression of several pathology-related genes in astrocytes. In the present study, we investigated the effect of ET-1 on NKCC1 expression in astrocytes. ET-1 (100 nM)-treated cultured astrocytes showed increased NKCC1 mRNA and protein levels. The effect of ET-1 on NKCC1 expression in cultured astrocytes was reduced by BQ788 (1 μM), an ETB antagonist, but not by FR139317 (1 μM), an ETA antagonist. The involvement of ET-1 in NKCC1 expression in TBI was examined using a fluid percussion injury (FPI) mouse model that replicates the pathology of TBI with high reproducibility. Administration of BQ788 (15 nmol/day) decreased FPI-induced expressions of NKCC1 mRNA and protein, accompanied with a reduction of astrocytic activation. FPI-induced brain edema was attenuated by BQ788 and NKCC1 inhibitors (azosemide and bumetanide). ET-1-treated cultured astrocytes showed increased mRNA and protein expression of hypoxia-inducible factor-1α (HIF1α). Immunohistochemical observations of mouse cerebrum after FPI showed co-localization of HIF1α with GFAP-positive astrocytes. Increased HIF1α expression in the TBI model was reversed by BQ788. FM19G11 (an HIF inhibitor, 1 μM) and HIF1α siRNA suppressed ET-induced increase in NKCC1 expression in cultured astrocytes. These results indicate that ET-1 increases NKCC1 expression in astrocytes through the activation of HIF1α.

Metabolic disruption exacerbates intestinal damage during sleep deprivation by abolishing HIF1α-mediated repair

Sleep deprivation (SD) has been reported to induce intestinal damage by several mechanisms, yet its role in modulating epithelial repair remains unclear. In this study, we find that chronic SD leads to colonic damage through continuous hypoxia. However, HIF1α, which generally responds to hypoxia to modulate barrier integrity, was paradoxically dysregulated in the colon. Further investigation revealed that a metabolic disruption during SD causes accumulation of α-ketoglutarate in the colon. The excessive α-ketoglutarate degrades HIF1α protein through PHD2 (prolyl hydroxylase 2) to abolish the intestinal repair functions of HIF1α. Collectively, these findings provide insights into how SD can exacerbate intestinal damage by fine-tuning metabolism to abolish HIF1α-mediated repair.

Endothelin and the tumor microenvironment: a finger in every pie

The tumor microenvironment (TME) plays a central role in the development of cancer. Within this complex milieu, the endothelin (ET) system plays a key role by triggering epithelial-to-mesenchymal transition, causing degradation of the extracellular matrix and modulating hypoxia response, cell proliferation, composition, and activation. These multiple effects of the ET system on cancer progression have prompted numerous preclinical studies targeting the ET system with promising results, leading to considerable optimism for subsequent clinical trials. However, these clinical trials have not lived up to the high expectations; in fact, the clinical trials have failed to demonstrate any substantiated benefit of targeting the ET system in cancer patients. This review discusses the major and recent advances of the ET system with respect to TME and comments on past and ongoing clinical trials of the ET system.

Bacterial Lysate from the Multi-Strain Probiotic SLAB51 Triggers Adaptative Responses to Hypoxia in Human Caco-2 Intestinal Epithelial Cells under Normoxic Conditions and Attenuates LPS-Induced Inflammatory Response

Hypoxia-inducible factor-1α (HIF-1α), a central player in maintaining gut-microbiota homeostasis, plays a pivotal role in inducing adaptive mechanisms to hypoxia and is negatively regulated by prolyl hydroxylase 2 (PHD2). HIF-1α is stabilized through PI3K/AKT signaling regardless of oxygen levels. Considering the crucial role of the HIF pathway in intestinal mucosal physiology and its relationships with gut microbiota, this study aimed to evaluate the ability of the lysate from the multi-strain probiotic formulation SLAB51 to affect the HIF pathway in a model of in vitro human intestinal epithelium (intestinal epithelial cells, IECs) and to protect from lipopolysaccharide (LPS) challenge. The exposure of IECs to SLAB51 lysate under normoxic conditions led to a dose-dependent increase in HIF-1α protein levels, which was associated with higher glycolytic metabolism and L-lactate production. Probiotic lysate significantly reduced PHD2 levels and HIF-1α hydroxylation, thus leading to HIF-1α stabilization. The ability of SLAB51 lysate to increase HIF-1α levels was also associated with the activation of the PI3K/AKT pathway and with the inhibition of NF-κB, nitric oxide synthase 2 (NOS2), and IL-1β increase elicited by LPS treatment. Our results suggest that the probiotic treatment, by stabilizing HIF-1α, can protect from an LPS-induced inflammatory response through a mechanism involving PI3K/AKT signaling.

Mechanisms of resistance to immune checkpoint inhibitors in melanoma: What we have to overcome?

Marching into the second decade after the approval of ipilimumab, it is clear that immune checkpoint inhibitors (ICIs) have dramatically improved the prognosis of melanoma. Although the current edge is already high, with a 4-year OS% of 77.9% for adjuvant nivolumab and a 6.5-year OS% of 49% for nivolumab/ipilimumab combination in the metastatic setting, a high proportion of patients with advanced melanoma have no benefit from immunotherapy, or experience an early disease relapse/progression in the first few months of treatment, surviving much less. Reasonably, the primary and acquired resistance to ICIs has entered into the focus of clinical research with positive (e.g., nivolumab and relatlimab combination) and negative feedbacks (e.g., nivolumab with pegylated-IL2, pembrolizumab with T-VEC, nivolumab with epacadostat, and combinatorial triplets of BRAF/MEK inhibitors with immunotherapy). Many intrinsic (intracellular or intra-tumoral) but also extrinsic (systematic) events are considered to be involved in the development of this resistance to ICIs: i) melanoma cell immunogenicity (e.g., tumor mutational burden, antigen-processing machinery and immunogenic cell death, neoantigen affinity and heterogeneity, genomic instability, melanoma dedifferentiation and phenotypic plasticity), ii) immune cell trafficking, T-cell priming, and cell death evasion, iii) melanoma neovascularization, cellular TME components(e.g., T_regs, CAFs) and extracellular matrix modulation, iv) metabolic antagonism in the TME(highly glycolytic status, upregulated CD39/CD73/adenosine pathway, iDO-dependent tryptophan catabolism), v) T-cell exhaustion and negative immune checkpoints, and vi) gut microbiota. In the present overview, we discuss how these parameters compromise the efficacy of ICIs, with an emphasis on the lessons learned by the latest melanoma studies; and in parallel, we describe the main ongoing approaches to overcome the resistance to immunotherapy. Summarizing this information will improve the understanding of how these complicated dynamics contribute to immune escape and will help to develop more effective strategies on how anti-tumor immunity can surpass existing barriers of ICI-refractory melanoma.

Sphingosine-1-phosphate controls endothelial sphingolipid homeostasis via ORMDL

Disruption of sphingolipid homeostasis and signaling has been implicated in diabetes, cancer, cardiometabolic, and neurodegenerative disorders. Yet, mechanisms governing cellular sensing and regulation of sphingolipid homeostasis remain largely unknown. In yeast, serine palmitoyltransferase, catalyzing the first and rate-limiting step of sphingolipid de novo biosynthesis, is negatively regulated by Orm1 and 2. Lowering sphingolipids triggers Orms phosphorylation, upregulation of serine palmitoyltransferase activity and sphingolipid de novo biosynthesis. However, mammalian orthologs ORMDLs lack the N-terminus hosting the phosphosites. Thus, which sphingolipid(s) are sensed by the cells, and mechanisms of homeostasis remain largely unknown. Here, we identify sphingosine-1-phosphate (S1P) as key sphingolipid sensed by cells via S1PRs to maintain homeostasis. The increase in S1P-S1PR signaling stabilizes ORMDLs, restraining SPT activity. Mechanistically, the hydroxylation of ORMDLs at Pro137 allows a constitutive degradation of ORMDLs via ubiquitin-proteasome pathway, preserving SPT activity. Disrupting S1PR/ORMDL axis results in ceramide accrual, mitochondrial dysfunction, impaired signal transduction, all underlying endothelial dysfunction, early event in the onset of cardio- and cerebrovascular diseases. Our discovery may provide the molecular basis for therapeutic intervention restoring sphingolipid homeostasis.

Metformin and simvastatin synergistically suppress endothelin 1-induced hypoxia and angiogenesis in multiple cancer types

Multiple cancers have been reported to be associated with angiogenesis and are sensitive to anti-angiogenic therapies. Vascular normalization, by restoring proper tumor perfusion and oxygenation, could limit tumor cell invasiveness and improve the effectiveness of anticancer treatments. However, the underlying anticancer mechanisms of antiangiogenic drugs are still unknown. Metformin (MET) and simvastatin (SVA), two metabolic-related drugs, have been shown to play important roles in modulating the hypoxic tumor microenvironment and angiogenesis. Whether the combination of MET and SVA could exert a more effective antitumor effect than individual treatments has not been examined. The antitumor effect of the synergism of SVA and MET was detected in mouse models, breast cancer patient-derived organoids, and multiple tumor cell lines compared with untreated, SVA, or MET alone. RNA sequencing revealed that the combination of MET and SVA (but not MET or SVA alone) inhibited the expression of endothelin 1 (ET-1), an important regulator of angiogenesis and the hypoxia-related pathway. We demonstrate that the MET and SVA combination showed synergistic effects on inhibiting tumor cell proliferation, promoting apoptosis, alleviating hypoxia, decreasing angiogenesis, and increasing vessel normalization compared with the use of a single agent alone. The MET and SVA combination suppressed ET-1-induced hypoxia-inducible factor 1α expression by increasing prolyl hydroxylase 2 (PHD2) expression. Furthermore, the MET and SVA combination showed a more potent anticancer effect compared with bosentan. Together, our findings suggest the potential application of the MET and SVA combination in antitumor therapy.

HIF-1α plays an essential role in BMP9-mediated osteoblast differentiation through the induction of a glycolytic enzyme, PDK1

Bone homeostasis is regulated by bone morphogenic proteins (BMPs), among which BMP9 is one of the most osteogenic. Here, we have found that BMP9 rapidly increases the protein expression of hypoxia-inducible factor-1α (HIF-1α) in osteoblasts under normoxic conditions more efficiently than BMP2 or BMP4. A combination of BMP9 and hypoxia further increased HIF-1α protein expression. HIF-1α protein induction by BMP9 is not accompanied by messenger RNA (mRNA) increase and is inhibited by the activation of prolyl hydroxylase domain (PHD)-containing protein, indicating that BMP9 induces HIF-1α protein expression by inhibiting PHD-mediated protein degradation. BMP9-induced HIF-1α protein increase was abrogated by inhibitors of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT) kinase, indicating that it is mediated by PI3K-AKT signaling pathway. BMP9 increased mRNA expression of pyruvate dehydrogenase kinase 1 (PDK1), a glycolytic enzyme, and vascular endothelial growth factor-A (VEGF-A), an angiogenic factor, in osteoblasts. Notably, BMP9-induced mRNA expression of PDK1, but not that of VEGF-A, was significantly inhibited by small interference RNA-mediated knockdown of Hif-1α. BMP9-induced matrix mineralization and osteogenic marker gene expressions were significantly inhibited by chemical inhibition and gene knockdown of either Hif-1α or Pdk-1, respectively. Since increased glycolysis is an essential feature of differentiated osteoblasts, our findings indicate that HIF-1α expression is important in BMP9-mediated osteoblast differentiation through the induction of PDK1.

Targeting the Endothelin-1 Receptors Curtails Tumor Growth and Angiogenesis in Multiple Myeloma

The endothelin-1 (ET-1) receptors were recently found to mediate pro-survival functions in multiple myeloma (MM) cells in response to autocrine ET-1. This study investigated the effectiveness of macitentan, a dual ET-1 receptor antagonist, in MM treatment, and the mechanisms underlying its activities. Macitentan affected significantly MM cell (RPMI-8226, U266, KMS-12-PE) survival and pro-angiogenic cytokine release by down-modulating ET-1-activated MAPK/ERK and HIF-1α pathways, respectively. HIF-1α silencing abrogated the ET-1 mediated induction of genes encoding for pro-angiogenic cytokines such as VEGF-A, IL-8, Adrenomedullin, and ET-1 itself. Upon exposure to macitentan, MM cells cultured in the presence of the hypoxia-mimetic agent CoCl₂, exogenous ET-1, or CoCl₂ plus ET-1, down-regulated HIF-1α and the transcription and release of downstream pro-angiogenic cytokines. Consistently, macitentan limited significantly the basal pro-angiogenic activity of RPMI-8226 cells in chorioallantoic membrane assay. In xenograft mouse models, established by injecting NOG mice either via intra-caudal vein with U266 or subcutaneously with RPMI-8226 cells, macitentan reduced effectively the number of MM cells infiltrating bone marrow, and the size and microvascular density of subcutaneous MM tumors. ET-1 receptors targeting by macitentan represents an effective anti-proliferative and anti-angiogenic therapeutic approach in preclinical settings of MM.

Ambrisentan, an endothelin receptor type A-selective antagonist, inhibits cancer cell migration, invasion, and metastasis

Several studies reported a central role of the endothelin type A receptor (ETAR) in tumor progression leading to the formation of metastasis. Here, we investigated the in vitro and in vivo anti-tumor effects of the FDA-approved ETAR antagonist, Ambrisentan, which is currently used to treat patients with pulmonary arterial hypertension. In vitro, Ambrisentan inhibited both spontaneous and induced migration/invasion capacity of different tumor cells (COLO-357 metastatic pancreatic adenocarcinoma, OvCar3 ovarian carcinoma, MDA-MB-231 breast adenocarcinoma, and HL-60 promyelocytic leukemia). Whole transcriptome analysis using RNAseq indicated Ambrisentan's inhibitory effects on the whole transcriptome of resting and PAR2-activated COLO-357 cells, which tended to normalize to an unstimulated profile. Finally, in a pre-clinical murine model of metastatic breast cancer, treatment with Ambrisentan was effective in decreasing metastasis into the lungs and liver. Importantly, this was associated with a significant enhancement in animal survival. Taken together, our work suggests a new therapeutic application for Ambrisentan in the treatment of cancer metastasis.

Pharmacologic inhibition of hypoxia-inducible factor (HIF)-hydroxylases ameliorates allergic contact dermatitis

BACKGROUND

When an immune cell migrates from the bloodstream to a site of chronic inflammation, it experiences a profound decrease in microenvironmental oxygen levels leading to a state of cellular hypoxia. The hypoxia-inducible factor-1α (HIF-1α) promotes an adaptive transcriptional response to hypoxia and as such is a major regulator of immune cell survival and function. HIF hydroxylases are the family of oxygen-sensing enzymes primarily responsible for conferring oxygen dependence upon the HIF pathway.

METHODS

Using a mouse model of allergic contact dermatitis (ACD), we tested the effects of treatment with the pharmacologic hydroxylase inhibitor DMOG, which mimics hypoxia, on disease development.

RESULTS

Re-exposure of sensitized mice to 2,4-dinitrofluorobenzene (DNFB) elicited inflammation, edema, chemokine synthesis (including CXCL1 and CCL5) and the recruitment of neutrophils and eosinophils. Intraperitoneal or topical application of the pharmacologic hydroxylase inhibitors dymethyloxalylglycine (DMOG) or JNJ1935 attenuated this inflammatory response. Reduced inflammation was associated with diminished recruitment of neutrophils and eosinophils but not lymphocytes. Finally, hydroxylase inhibition reduced cytokine-induced chemokine production in cultured primary keratinocytes through attenuation of the JNK pathway.

CONCLUSION

These data demonstrate that hydroxylase inhibition attenuates the recruitment of neutrophils to inflamed skin through reduction of chemokine production and increased neutrophilic apoptosis. Thus, pharmacologic inhibition of HIF hydroxylases may be an effective new therapeutic approach in allergic skin inflammation.

Endothelin-1 differentially directs lineage specification of adipose- and bone marrow-derived mesenchymal stem cells

Blood vessels composed of endothelial cells (ECs) contact with mesenchymal stem cells (MSCs) in different tissues, suggesting possible interaction between these 2 types of cells. We hypothesized that endothelin-1 (ET1), a secreted paracrine factor of ECs, can differentially direct the lineages of adipose-derived stem cells (ASCs) and bone marrow-derived MSCs (BMSCs). Predifferentiated ASCs and BMSCs were treated with ET1 for 2 cell passages and then induced for multilineage differentiation. Our results showed that adipogenesis of ET1-pretreated ASCs and osteogenesis of ET1-pretreated BMSCs were increased compared to those of control cells. The effect of ET1 on enhancing adipogenesis of ASCs and osteogenesis of BMSCs was attenuated by blocking endothelin receptor type A (ETAR) and/or endothelin receptor type B (ETBR). Western blot analysis indicated that regulation by ET1 was mediated through activation of the protein kinase B and ERK1/2 signaling pathways. We analyzed subpopulations of ASCs and BMSCs with or without ETAR and/or ETBR, and we found that ETAR⁺/ETBR^- and ETAR^-/ETBR⁺ subpopulations of ASCs and those of BMSCs pretreated with ET1 were prone to turning into adipocytes and osteoblasts, respectively, after differentiation induction. Our findings provide insight into the differential regulation of MSC specification by ET1, which may help develop viable approaches for tissue regeneration.-Lee, M.-S., Wang, J., Yuan, H., Jiao, H., Tsai, T.-L., Squire, M. W., Li, W.-J. Endothelin-1 differentially directs lineage specification of adipose- and bone marrow-derived mesenchymal stem cells.

Intravitreal administration of endothelin type A receptor or endothelin type B receptor antagonists attenuates hypertensive and diabetic retinopathy in rats

Hypertension is an independent risk factor for diabetic retinopathy, yet anti-hypertensive medications such as blockade of angiotensin II do not completely protect against vision-threatening vascular disease. We hypothesized that the potent vasoactive factor, endothelin (ET), is up-regulated in diabetic retinopathy and antagonism of the ET type A receptor (ETRA) or ET type B receptor (ETRB) ameliorates retinal vascular leakage independently of any blood pressure lowering effects. Spontaneously hypertensive rats (SHR) and their normotensive and genetic controls, Wistar Kyoto rats, were randomized to become diabetic or non-diabetic and studied for 8 weeks. Rats were further randomized to receive by intravitreal injection the ETRA antagonist, BQ123, the ETRB antagonist, BQ788, or vehicle, 5 days after the induction of streptozotocin diabetes and 4 weeks later. The treatments had no effect on systolic blood pressure which remained elevated in SHR. ET-1, ET-2, ETRA and ETRB were expressed in retina and retinal pigment epithelium (RPE)/choroid and increased by hypertension or diabetes. BQ123 reduced ET-1 and ET-2 expression in retina and RPE/choroid, while BQ788 had a similar effect but did not influence the mRNA levels of ET-1 in retina. Retinal vascular leakage and Müller cell stress as well as vascular endothelial growth factor (VEGF) expression in retina and RPE/choroid, were increased by hypertension or diabetes and there was an additive effect of these conditions. Treatment with BQ123 or BQ788 effectively reduced these events as well as the elevated levels of inflammatory factors in the retina. Our findings indicate that local ET systems exist in the retina and RPE/choroid that are up-regulated by hypertension and diabetes. The ability of locally delivered ET receptor antagonists to supress these overactive ET systems and reduce retinal vascular leakage and VEGF in the presence of hypertension indicate the potential of these approaches for the treatment of diabetic retinopathy.

Macitentan, a double antagonist of endothelin receptors, efficiently impairs migration and microenvironmental survival signals in chronic lymphocytic leukemia

The crosstalk between chronic lymphocytic leukemia (CLL) cells and tumor microenvironment is essential for leukemic clone maintenance, supporting CLL cells survival, proliferation and protection from drug-induced apoptosis. Over the past years, the role of several soluble factors involved in these processes has been studied. CLL cells express higher levels of endothelin 1 (ET-1) and ET_A receptor as compared to normal B cells. Upon ET-1 stimulation, CLL cells improve their survival and proliferation and reduce their sensitivity to the phosphoinositide-3-kinase δ inhibitor idelalisib and to fludarabine. Here, we demonstrate that CLL cells express not only ET_A receptor but also ET_B receptor. ET-1 acts as a homing factor supporting CLL cells migration and adhesion to microenvironmental cells. In addition, ET-1 stimulates a pro-angiogenic profile of CLL cells increasing VEGF expression through hypoxia-inducible factor-1 (HIF-1α) accumulation in CLL cells. Macitentan, a specific dual inhibitor of ET_A and ET_B receptors, targets CLL cells affecting leukemic cells migration and adhesion and overcoming the pro-survival and proliferation signals mediated by microenvironment. Furthermore, macitentan cooperates with ibrutinib inhibiting the BCR pathway and with ABT-199 disrupting BCL2 pathway. Our data describe the biological effects of a new drug, macitentan, able to counteract essential processes in CLL pathobiology as survival, migration, trafficking and drug resistance. These findings envision the possibility to interfere with ET receptors activity using macitentan as a possible novel therapeutic strategy for CLL patients.

Effects of Estrogen and Phytoestrogen Treatment on an In Vitro Model of Recurrent Stroke on HT22 Neuronal Cell Line

An increase of stroke incidence occurs in women with the decline of estrogen levels following menopause. This ischemic damage may recur, especially soon after the first insult has occurred. We evaluated the effects of estrogen and phytoestrogen treatment on an in vitro recurrent stroke model using the HT22 neuronal cell line. HT22 cells were treated with 17β-estradiol or genistein 1 h after the beginning of the first of two oxygen and glucose deprivation/reoxygenation (OGD/R) cycles. During the second OGD, there was a deterioration of some components of the electron transport chain, such as cytochrome c oxidase subunit 1 with a subsequent increase of reactive oxygen species (ROS) production. Accordingly, there was also an increase of apoptotic phenomena demonstrated by poly(ADP-ribose) polymerase 1 cleavage, Caspase-3 activity, and Annexin V levels. The recurrent ischemic injury also raised the hypoxia-inducible factor 1α and glucose transporter 1 levels, as well as the ratio between the lipidated and cytosolic forms of microtubule-associated protein 1A/1B-light chain 3 (LC3-II/LC3-I). We found a positive effect of estradiol and genistein treatment by partially preserving the impaired cell viability after the recurrent ischemic injury; however, this positive effect does not seem to be mediated neither by blocking apoptosis processes nor by decreasing ROS production. This work contribute to the better understanding of the molecular mechanisms triggered by recurrent ischemic damage in neuronal cells and, therefore, could help with the development of an effective treatment to minimize the consequences of this pathology.

Nuclear β-arrestin1 is a critical cofactor of hypoxia-inducible factor-1α signaling in endothelin-1-induced ovarian tumor progression

Hypoxia-inducible factor-1α (HIF-1α) mediates the response to hypoxia or other stimuli, such as growth factors, including endothelin-1 (ET-1), to promote malignant progression in numerous tumors. The importance of cofactors that regulate HIF-1α signalling within tumor is not well understood. Here we elucidate that ET-1/ET(A) receptor (ET(A)R)-induced pathway physically and functionally couples the scaffold protein β-arrestin1 (β-arr1) to HIF-1α signalling. In epithelial ovarian cancer (EOC) cells, ET-1/ET(A)R axis induced vascular-endothelial growth factor (VEGF) expression through HIF-1α nuclear accumulation. In these cells, activation of ET(A)R by ET-1, by mimicking hypoxia, promoted the nuclear interaction between β-arr1 and HIF-1α and the recruitment of p300 acetyltransferase to hypoxia response elements on the target gene promoters, resulting in enhanced histone acetylation, and HIF-1α target gene transcription. Indeed, β-arr1-HIF-1α interaction regulated the enhanced expression and release of downstream targets, such as ET-1 and VEGF, required for tumor cell invasion and pro-angiogenic effects in endothelial cells. These effects were abrogated by β-arr1 or HIF-1α silencing or by pharmacological treatment with the dual ET-1 receptor antagonist macitentan. Interestingly, ET(A)R/β-arr1 promoted the self-amplifying HIF-1α-mediated transcription of ET-1 that sustained a regulatory circuit involved in invasive and angiogenic behaviors. In a murine orthotopic model of metastatic human EOC, treatment with macitentan, or silencing of β-arr1, inhibits intravasation and metastasis formation. Collectively, these findings reveal the interplay of β-arr1 with HIF-1α in the complexity of ET-1/ET(A)R signalling, mediating epigenetic modifications directly involved in the metastatic process, and suggest that targeting ET-1-dependent β-arr1/HIF-1α pathway by using macitentan may impair EOC progression.

Targeting brain microvascular endothelial cells: a therapeutic approach to neuroprotection against stroke

Brain microvascular endothelial cells form the interface between nervous tissue and circulating blood, and regulate central nervous system homeostasis. Brain microvascular endothelial cells differ from peripheral endothelial cells with regards expression of specific ion transporters and receptors, and contain fewer fenestrations and pinocytotic vesicles. Brain microvascular endothelial cells also synthesize several factors that influence blood vessel function. This review describes the morphological characteristics and functions of brain microvascular endothelial cells, and summarizes current knowledge regarding changes in brain microvascular endothelial cells during stroke progression and therapies. Future studies should focus on identifying mechanisms underlying such changes and developing possible neuroprotective therapeutic interventions.

Evidence for proangiogenic cellular and humoral systemic response in patients with acute onset of spinal cord injury

CONTEXT/OBJECTIVE

Traumatic spinal cord injury (SCI) leads to disruption of local vasculature inducing secondary damage of neural tissue. Circulating endothelial progenitor cells (EPCs) play an important role in post-injury regeneration of vasculature, whereas endothelial cells (ECs) reflect endothelial damage.

METHODS

Twenty patients with SCI were assessed during the first 24 hours, at day 3, and day 7 post-injury and compared to 25 healthy subjects. We herein investigated EPC and EC counts by flow cytometry as well as the levels of soluble factors (SDF-1, HGF, VEGF, Ang2, EGF, endoglin, PLGF, FGF-2, ET-1, BDNF, IGF-1) regulating their migration and proangiogenic function. To better characterize peripheral blood (PB) cells, global gene expression profiles of PB-derived cells were determined using genome-wide RNA microarray technology.

RESULTS

We found significantly higher EPC (CD34(+)/CD133(+)/VEGFR2(+)) as well as EC (VEGFR2(+)) count in PB of patients with SCI within 7 days post-injury and the increased HGF, ET-1, Ang2, EGF, and PLGF plasma levels. Global gene expression analysis revealed considerably lower expression of genes associated with both innate and adaptive immune response in PB cells in patients.

CONCLUSION

Collectively, our findings demonstrate that SCI triggers bone marrow-derived EPC mobilization accompanied by increased circulating EC numbers. Significant changes in both chemoattractive and proangiogenic cytokines plasma levels occurring rapidly after SCI suggest their role in SCI-related regenerative responses to injury. Broadened knowledge concerning the mechanisms governing of human organism response to the SCI might be helpful in developing effective therapeutic strategies.

Hypoxia-independent drivers of melanoma angiogenesis

Tumor angiogenesis is a process which is traditionally regarded as the tumor’s response to low nutrient supply occurring under hypoxic conditions. However, hypoxia is not a pre-requisite for angiogenesis. The fact that even single tumor cells or small tumor cell aggregates are capable of attracting blood vessels reveals the early metastatic capability of tumor cells. This review sheds light on the hypoxia-independent mechanisms of tumor angiogenesis in melanoma.

Macitentan: An important addition to the treatment of pulmonary arterial hypertension

Macitentan is an orphan drug for the treatment of pulmonary arterial hypertension (PAH). Endothelin-1 (ET-1) plays a critical role of pathophysiology of PAH. Macitentan, a new dual endothelin receptor antagonist, has reportedly improved prognosis of PAH patients by delaying the progression of disease. It prevents the binding of ET-1 to both endothelin A (ET_A) and endothelin B (ET_B) receptors. Macitentan displays higher efficacy, lesser adverse effects and drug interactions. It has completed phase III trials in 2012 for treatment of PAH and has been tried for ischemic digital ulcers in systemic sclerosis, recurrent glioblastoma and combination with chemotherapeutic agents against various cancers. Safety data for macitentan were obtained primarily from a placebo-controlled clinical study in 742 patients with PAH. The Food and Drug Administration (FDA) approved the drug on 13 October 2013. It is an important addition to long-term treatment of PAH.

Endothelin-converting enzyme is a plausible target gene for hypoxia-inducible factor

Renal endothelin-converting enzyme (ECE)-1 is induced in experimental diabetes and following radiocontrast administration, conditions characterized by renal hypoxia, hypoxia-inducible factor (HIF) stabilization, and enhanced endothelin synthesis. Here we tested whether ECE-1 might be a HIF-target gene in vitro and in vivo. ECE-1 transcription and expression increased in cultured vascular endothelial and proximal tubular cell lines, subject to hypoxia, to mimosine or cobalt chloride. These interventions are known to stabilize HIF signaling by inhibition of HIF-prolyl hydroxylases. In rats, HIF-prolyl-hydroxylase inhibition by mimosine or FG-4497 increased HIF-1α immunostaining in renal tubules, principally in distal nephron segments. This was associated with markedly enhanced ECE-1 protein expression, predominantly in the renal medulla. A progressive and dramatic increase in ECE-1 immunostaining over time, in parallel with enhanced HIF expression, was also noted in conditional von Hippel-Lindau knockout mice. Since HIF and STAT3 are cross-stimulated, we triggered HIF expression by STAT3 activation in mice, transfected by or injected with a chimeric IL-6/IL-6-receptor protein, and found a similar pattern of enhanced ECE-1 expression. Chromatin immunoprecipitation sequence (ChIP-seq) and PCR analysis in hypoxic endothelial cells identified HIF binding at the ECE-1 promoter and intron regions. Thus, our findings suggest that ECE-1 may be a novel HIF-target gene.

Chemical targeting of GAPDH moonlighting function in cancer cells reveals its role in tubulin regulation

Glycolytic enzymes are attractive anticancer targets. They also carry out numerous, nonglycolytic "moonlighting" functions in cells. In this study, we investigated the anticancer activity of the triazine small molecule, GAPDS, that targets the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH). GAPDS showed greater toxicity against cancer cells compared to a known GAPDH enzyme inhibitor. GAPDS also selectively inhibited cell migration and invasion. Our analysis showed that GAPDS treatment reduced GAPDH levels in the cytoplasm, which would modulate the secondary, moonlighting functions of this enzyme. We then used GAPDS as a probe to demonstrate that a moonlighting function of GAPDH is tubulin regulation, which may explain its anti-invasive properties. We also observed that GAPDS has potent anticancer activity in vivo. Our study indicates that strategies to target the secondary functions of anticancer candidates may yield potent therapeutics and useful chemical probes.

Altered gene products involved in the malignant reprogramming of cancer stem/progenitor cells and multitargeted therapies

Recent studies in the field of cancer stem cells have revealed that the alterations in key gene products involved in the epithelial-mesenchymal transition (EMT) program, altered metabolic pathways such as enhanced glycolysis, lipogenesis and/or autophagy and treatment resistance may occur in cancer stem/progenitor cells and their progenies during cancer progression. Particularly, the sustained activation of diverse developmental cascades such as hedgehog, epidermal growth factor receptor (EGFR), Wnt/β-catenin, Notch, transforming growth factor-β (TGF-β)/TGF-βR receptors and/or stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) can play critical functions for high self-renewal potential, survival, invasion and metastases of cancer stem/progenitor cells and their progenies. It has also been observed that cancer cells may be reprogrammed to re-express different pluripotency-associated stem cell-like markers such as Myc, Oct-3/4, Nanog and Sox-2 along the EMT process and under stressful and hypoxic conditions. Moreover, the enhanced expression and/or activities of some drug resistance-associated molecules such as Bcl-2, Akt/molecular target of rapamycin (mTOR), nuclear factor-kappaB (NF-κB), hypoxia-inducible factors (HIFs), macrophage inhibitory cytokine-1 (MIC-1) and ATP-binding cassette (ABC) multidrug transporters frequently occur in cancer cells during cancer progression and metastases. These molecular events may cooperate for the survival and acquisition of a more aggressive and migratory behavior by cancer stem/progenitor cells and their progenies during cancer transition to metastatic and recurrent disease states. Of therapeutic interest, these altered gene products may also be exploited as molecular biomarkers and therapeutic targets to develop novel multitargeted strategies for improving current cancer therapies and preventing disease relapse.

Mechanisms of tumour vascularization in cutaneous malignant melanoma: clinical implications

Malignant melanoma represents < 10% of all skin cancers but is responsible for the majority of skin-cancer-related deaths. Metastatic melanoma has historically been considered as one of the most therapeutically challenging malignancies. Fortunately, for the first time after decades of basic research and clinical investigation, new drugs have produced major clinical responses. Angiogenesis has been considered an important target for cancer treatment. Initial efforts have focused primarily on targeting endothelial and tumour-related vascular endothelial growth factor signalling. Here, we review different mechanisms of tumour vascularization described in melanoma and discuss the potential clinical implications.

The interplay between hypoxia, endothelial and melanoma cells regulates vascularization and cell motility through endothelin-1 and vascular endothelial growth factor

Reciprocal growth factor exchanges between endothelial and malignant cells within the hypoxic microenvironment determine tumor progression. However, the nature of these exchanges has not yet been fully explored. We studied the mutual regulation between endothelial cells (EC), melanoma cells and hypoxia that dictate tumor aggressiveness and angiogenic activity. Here, we investigated the presence of bidirectional autocrine/paracrine endothelin (ET)-1/ET receptor (ETBR) signaling in melanoma cells, blood and lymphatic EC. In all these cells, hypoxia enhanced ET-1 expression, which in turn induced vascular endothelial growth factor (VEGF)-A and VEGF-C secretion, through the hypoxia-inducible growth factor (HIF)-1α and HIF-2α. Autocrine/paracrine exchanges of ET-1, VEGF-A and VEGF-C promoted tumor aggressiveness and morphological changes in blood and lymphatic EC. Furthermore, conditioned media from EC enhanced melanoma cell migration and vessel-like channel formation. This regulation was inhibited by ETBR blockade, by using the selective ETBR antagonist, or ETBR small interfering RNA (siRNA), and by VEGFR-2/-3 antibodies, indicating that ET-1, VEGF-A/VEGF-C, produced by melanoma cells or EC mediated inter-regulation between these cells. Interestingly, HIF-1α/HIF-2α siRNA, impaired this reciprocal regulation, demonstrating the key role of these transcriptional factors in signaling exchanges. In melanoma xenografts, the ETBR antagonist reduced tumor growth and the number of blood and lymphatic vessels. These results reveal an interplay between melanoma cells and EC mediated by ET-1 and VEGF-A/-C and coordinated by the hypoxic microenvironment through HIF-1α/2α transcriptional programs. Thus, targeting ETBR may improve melanoma treatment for tumor and EC, by inhibiting autocrine/paracrine signaling that sustains melanoma progression.

Dual endothelin receptor antagonism with bosentan reverses established vascular remodeling and dysfunctional angiogenesis in diabetic rats: relevance to glycemic control

AIMS

We have shown that diabetes causes cerebrovascular remodeling in part by the activation of the endothelin (ET-1) system in a glucose-dependent manner. We also reported increased yet dysfunctional cerebral angiogenesis in diabetes. Here, we tested the hypothesis that dual ET-1 receptor antagonism or glycemic control can reverse already established diabetes-induced vascular remodeling and neovascularization.

MAIN METHODS

18-week non-obese type-2 diabetic Goto-Kakizaki (GK) were treated with vehicle, metformin (300 mg/kg/day) or bosentan (100 mg/kg/day) for 4 weeks by oral gavage and compared to 10 and 18-weeks GK rats. Isolated middle cerebral artery (MCA) lumen diameter (LD), media thickness (MT), media:lumen (M:L) ratio, and cross-sectional area (CSA) were measured using pressurized arteriograph. Assessment of remodeling and angiogenesis in the brain parenchyma was achieved by three-dimensional reconstruction of fluorescently labeled images of the vasculature acquired by confocal microscopy, and measurement of neovascularization indices including vascular volume and surface area, branch density and tortuosity.

KEY FINDINGS

MCA remodeling (increased M:L ratio and CSA, but decreased LD) occurred by 18 weeks and did not progress by 22 weeks in diabetic GK rats. Metformin and bosentan partially corrected large artery remodeling. Both treatments significantly reduced all indices of neovascularization compared to untreated diabetic rats.

SIGNIFICANCE

Glycemic control or ET-1 antagonism can partially reverse diabetes-induced cerebrovascular remodeling and neovascularization. These results strongly suggest that either approach offers a therapeutic benefit and combination treatments need to be tested.

Molecular networks in melanoma invasion and metastasis

Metastatic melanoma accounts for approximately 80% of skin cancer-related deaths. Up to now there has been no effective treatment for stage IV melanoma patients due to the complexity and dissemination potential of this disease. Melanomas are heterogeneous tumors in which conventional therapies fail to improve overall survival. Targeted therapies are being developed, but the final outcome can be hampered by the incomplete knowledge of the process of melanoma progression. Even if the intracellular pathways are similar, the interaction of the cells with the surrounding environment should be taken into consideration. This article seeks to highlight some of the advances in the understanding of the molecular mechanisms underlying melanoma dissemination.

Cytochalasin H, an active anti-angiogenic constituent of the ethanol extract of Gleditsia sinensis thorns

Angiogenesis, the process of new vessel formation from the pre-existing blood vasculature, is critical for continuous tumor growth and is considered to be a validated antitumor target. The results of our previous study demonstrate the anti-angiogenic potential of an extract of Gleditsia sinensis thorns, which has been traditionally used in Korean medicine to remedy diverse diseases, including tumors. In the present study, we attempted to identify the active anti-angiogenic constituents of the ethanol extract of G. sinensis thorns (EEGS). By virtue of in vitro activity-guided fractionation using human umbilical vein endothelial cells (HUVEC) primary endothelial cells, chromatographic separation, and NMR spectral analyses, we isolated and identified the potent active constituent, cytochalasin H, a biologically active secondary metabolite of fungi. This unexpected active constituent may have originated from the endophytic fungi, Chaetomium globosum, which naturally populate G. sinensis, the identity of which was determined by analysis of fungal community. Cytochalasin H isolated from the EEGS showed in vitro anti-angiogenic activities such as suppressed cell growth and mobility in HUVEC, and inhibited the pro-angiogenic protein-induced formation of new blood vessels in vivo. The anti-angiogenic effect of cytochalasin H was in part due to reduced expression of pro-angiogenic factor, such as endothelin-1. This is the first report regarding the isolation and identification of cytochalasin H, as an active anti-angiogenic constituent of G. sinensis thorns.

Endothelin 1 in cancer: biological implications and therapeutic opportunities

Activation of autocrine and paracrine signalling by endothelin 1 (ET1) binding to its receptors elicits pleiotropic effects on tumour cells and on the host microenvironment. This activation modulates cell proliferation, apoptosis, migration, epithelial-to-mesenchymal transition, chemoresistance and neovascularization, thus providing a strong rationale for targeting ET1 receptors in cancer. In this Review, we discuss the advances in our understanding of the diverse biological roles of ET1 in cancer and describe the latest preclinical and clinical progress that has been made using small-molecule antagonists of ET1 receptors that inhibit ET1-driven signalling.

The signaling pathway of hypoxia inducible factor and its role in renal diseases

It is well-documented that hypoxia inducible factor (HIF) is a key mediator of tissue and cellular adaptation to hypoxia. HIF-target genes are also involved in cellular apoptosis and profibrotic mechanisms. The role of HIF in diseases is not consistent. It is a risk factor for tumor progression, whereas it plays a protective role against ischemic hypofusion. For renal diseases, it is not always a risk or protective factor. Many factors are involved in the pathogenesis of renal diseases. It is reported that HIF not only increases hypoxia tolerance, but also regulates a lot of signaling pathways. In the past decades, a number of studies were also conducted to explore the association between HIF and the risk of renal diseases. However, the role of HIF in the development of renal diseases was not entirely clear. In this study, the signal transduction pathways of HIF and its role in the pathogenesis of renal diseases were reviewed.

Overexpression of the HIF hydroxylase PHD3 is a favorable prognosticator for gastric cancer

Hypoxia-induced factors (HIFs) play a central role in the adaptive mechanisms of cancer cells to survive under conditions of hypoxia. HIFs are regulated by prolyl hydroxylases (PHDs) among which PHD3 is implicated as a tumor suppressor. We aimed to correlate PHD3 expression with clinicopathologic parameters and to evaluate its prognostic significance in gastric cancer. The 101 tissue samples were collected from 83 resected stages I–IV gastric cancer patients, which were grouped as non-cancerous mucosa (n=18) and primary carcinoma (n=83). PHD3 expression was evaluated by immunohistochemistry. We adopted Pearson chi-square test, univariate analysis, multivariate analysis and Kaplan–Meier method. The positive frequency of PHD3 in cancer cells was 42.2%, whereas non-cancerous mucosa had no detectable PHD3. The expression of PHD3 increased significantly from non-cancerous mucosa to cancer. A significant difference was observed between PHD3 expression and tumor differentiation (P=0.007). The overexpression of PHD3 was associated with well differentiation. In univariate analyses, American Joint Committee on Cancer (AJCC) stage (P<0.0001), pT classification (P<0.0001), pN classification (P<0.0001), differentiation (P=0.0121), peritoneal metastasis (P=0.0006) and gross features (P=0.0104) were significantly associated with survival except PHD3 (P=0.2228) (Table 3). In multivariate analysis, AJCC stage was prognostically independent [hazard ratio (HR), 3.078; 95% confidence interval (CI), 2.228–4.252; P<0.0001]. Overexpression of PHD3 is a favorable prognosticator for gastric cancer. AJCC stage is an independent prognostic factor of gastric cancer.

Cell type-specific dependency on the PI3K/Akt signaling pathway for the endogenous Epo and VEGF induction by baicalein in neurons versus astrocytes

The neuroprotective effect of baicalein is generally attributed to inhibition of 12/15-lipoxygenase (12/15-LOX) and suppression of oxidative stress, but recent studies showed that baicalein also activates hypoxia-inducible factor-α (HIF1α) through inhibition of prolyl hydrolase 2 (PHD2) and activation of the phosphatidylinositide-3 kinase (PI3K)/Akt signaling pathway. Yet, the significance and regulation of prosurvival cytokines erythropoietin (Epo) and vascular endothelial growth factor (VEGF), two transcriptional targets of HIF1α, in baicalein-mediated neuroprotection in neurons and astrocytes remains unknown. Here we investigated the causal relationship between the PI3K/Akt signaling pathway and Epo/VEGF expression in baicalein-mediated neuroprotection in primary rat cortical neurons and astrocytes. Our results show that baicalein induced Epo and VEGF expression in a HIF1α- and PI3K/Akt-dependent manner in neurons. Baicalein also protected neurons against excitotoxicity in a PI3K- and Epo/VEGF-dependent manner without affecting neuronal excitability. In contrast, at least a 10-fold higher concentration of baicalein was needed to induce Epo/VEGF production and PI3K/Akt activity in astrocytes for protection of neurons. Moreover, only baicalein-induced astrocytic VEGF, but not Epo expression requires HIF1α, while PI3K/Akt signaling had little role in baicalein-induced astrocytic Epo/VEGF expression. These results suggest distinct mechanisms of baicalein-mediated Epo/VEGF production in neurons and astrocytes for neuroprotection, and provide new insights into the mechanisms and potential of baicalein in treating brain injury in vivo.

Activation of hypoxia-inducible factor-1 in pulmonary arterial smooth muscle cells by endothelin-1

Numerous cellular responses to hypoxia are mediated by the transcription factor hypoxia-inducible factor-1 (HIF-1). HIF-1 plays a central role in the pathogenesis of hypoxic pulmonary hypertension. Under certain conditions, HIF-1 may utilize feedforward mechanisms to amplify its activity. Since hypoxia increases endothelin-1 (ET-1) levels in the lung, we hypothesized that during moderate, prolonged hypoxia ET-1 might contribute to HIF-1 signaling in pulmonary arterial smooth muscle cells (PASMCs). Primary cultures of rat PASMCs were treated with ET-1 or exposed to moderate, prolonged hypoxia (4% O(2) for 60 h). Levels of the oxygen-sensitive HIF-1α subunit and expression of HIF target genes were increased in both hypoxic cells and cells treated with ET-1. Both hypoxia and ET-1 also increased HIF-1α mRNA expression and decreased mRNA and protein expression of prolyl hydroxylase 2 (PHD2), which is the protein responsible for targeting HIF-1α for O(2)-dependent degradation. The induction of HIF-1α by moderate, prolonged hypoxia was blocked by BQ-123, an antagonist of ET-1 receptor subtype A. The effects of ET-1 were mediated by increased intracellular calcium, generation of reactive oxygen species, and ERK1/2 activation. Neither ET-1 nor moderate hypoxia induced the expression of HIF-1α or HIF target genes in aortic smooth muscle cells. These results suggest that ET-1 induces a PASMC-specific increase in HIF-1α levels by upregulation of HIF-1α synthesis and downregulation of PHD2-mediated degradation, thereby amplifying the induction of HIF-1α in PASMCs during moderate, prolonged hypoxia.

Bosentan inhibits oxidative and nitrosative stress and rescues occlusive pulmonary hypertension

Pulmonary arterial hypertension (PH) is a fatal disease marked by excessive pulmonary vascular cell proliferation. Patients with idiopathic PH express endothelin-1 (ET-1) at high levels in their lungs. As the activation of both types of ET-1 receptor (ETA and ETB) leads to increased generation of superoxide and hydrogen peroxide, this may contribute to the severe oxidative stress found in PH patients. As a number of pathways may induce oxidative stress, the particular role of ET-1 remains unclear. The aim of this study was to determine whether inhibition of ET-1 signaling could reduce pulmonary oxidative stress and attenuate the progression of disease in rats with occlusive-angioproliferative PH induced by a single dose of SU5416 (200 mg/kg) and subsequent exposure to hypoxia for 21 days. Using this regimen, animals developed severe PH as evidenced by a progressive increase in right-ventricle (RV) peak systolic pressure (RVPSP), severe RV hypertrophy, and pulmonary endothelial and smooth muscle cell proliferation, resulting in plexiform vasculopathy. PH rats also had increased oxidative stress, correlating with endothelial nitric oxide synthase uncoupling and NADPH oxidase activation, leading to enhanced protein nitration and increases in markers of vascular remodeling. Treatment with the combined ET receptor antagonist bosentan (250 mg/kg/day; day 10 to 21) prevented further increase in RVPSP and RV hypertrophy, decreased ETA/ETB protein levels, reduced oxidative stress and protein nitration, and resulted in marked attenuation of pulmonary vascular cell proliferation. We conclude that inhibition of ET-1 signaling significantly attenuates the oxidative and nitrosative stress associated with PH and prevents its progression.

Endothelin-1 induces the transactivation of vascular endothelial growth factor receptor-3 and modulates cell migration and vasculogenic mimicry in melanoma cells

Endothelin receptor B (ET(B)R) is a G-protein-coupled receptor overexpressed in melanoma, blood, and lymphatic endothelial cells. Given that aberrant signal transduction can be mediated through cross talk between receptors, here, we explore the functional relationship between ET(B)R and the vascular endothelial growth factor receptor (VEGFR)-3 system and how this cross talk might influence the aggressive behavior of melanoma cells. The expression of VEGFR-3 and its ligands, VEGF-C and VEGF-D, significantly increased after activating ET(B)R by ET-1 in primary and metastatic melanoma cell lines. These effects, similarly to those induced by hypoxia, were mediated by hypoxia-inducible factor (HIF)-1α and HIF-2α. ET-1 caused the phosphorylation of VEGFR-3, which was accompanied by the activation of the downstream signaling molecules, such as MAPK and AKT. Inhibition of c-Src activity or silencing of the scaffold protein β-arrestin-1 reduced ET-1-induced VEGFR-3 phosphorylation, demonstrating that, upon ET-1 stimulus, β-arrestin-1 is involved with c-Src in the ET(B)R-mediated VEGFR-3 transactivation. Moreover, ET-1 in combination with VEGF-C further increased VEGFR-3, MAPK, and AKT phosphorylation and markedly promoted cell migration and vasculogenic mimicry. Dual inhibition of ET(B)R and VEGFR-3 was required for the effective inhibition of these effects, as well as for VEGFR-3 phosphorylation, demonstrating that ET(B)R cross talk with VEGFR-3 enhances cell plasticity and motility. Finally, in melanoma xenografts, ET(B)R antagonist inhibited tumor growth and the activation of the VEGF-C/VEGFR-3 axis, indicating that targeting ET(B)R may improve melanoma treatment acting directly or indirectly by impairing ET(B)R cross talk with VEGFR-3.

Hypoxia-inducing factors as master regulators of stemness properties and altered metabolism of cancer- and metastasis-initiating cells

Accumulating lines of experimental evidence have revealed that hypoxia-inducible factors, HIF-1α and HIF-2α, are key regulators of the adaptation of cancer- and metastasis-initiating cells and their differentiated progenies to oxygen and nutrient deprivation during cancer progression under normoxic and hypoxic conditions. Particularly, the sustained stimulation of epidermal growth factor receptor (EGFR), insulin-like growth factor-1 receptor (IGF-1R), stem cell factor (SCF) receptor KIT, transforming growth factor-β receptors (TGF-βRs) and Notch and their downstream signalling elements such as phosphatidylinositol 3′-kinase (PI3K)/Akt/molecular target of rapamycin (mTOR) may lead to an enhanced activity of HIFs. Moreover, the up-regulation of HIFs in cancer cells may also occur in the hypoxic intratumoral regions formed within primary and secondary neoplasms as well as in leukaemic cells and metastatic prostate and breast cancer cells homing in the hypoxic endosteal niche of bone marrow. The activated HIFs may induce the expression of numerous gene products such as induced pluripotency-associated transcription factors (Oct-3/4, Nanog and Sox-2), glycolysis- and epithelial-mesenchymal transition (EMT) programme-associated molecules, including CXC chemokine receptor 4 (CXCR4), snail and twist, microRNAs and angiogenic factors such as vascular endothelial growth factor (VEGF). These gene products in turn can play critical roles for high self-renewal ability, survival, altered energy metabolism, invasion and metastases of cancer cells, angiogenic switch and treatment resistance. Consequently, the targeting of HIF signalling network and altered metabolic pathways represents new promising strategies to eradicate the total mass of cancer cells and improve the efficacy of current therapies against aggressive and metastatic cancers and prevent disease relapse.

Increased circulating endothelial progenitor cells in patients with haemorrhagic and ischaemic stroke: the role of endothelin-1

Ischaemic stroke induces endothelial progenitor cell (EPC) mobilisation from bone marrow into peripheral blood. Circulating EPCs play an important role in post-injury regeneration of vasculature, whereas endothelial cells (ECs) have been shown to reflect endothelial damage and may be responsible for increased Endothelin-1 (ET-1) expression. We investigated herein the association between numbers of circulating ECs and EPCs, the levels of soluble factors regulating their migration and function, and the clinical outcome in patients with haemorrhagic (HS) or ischaemic stroke (IS). Sixteen patients with HS and eighteen with IS were assessed during the first 24h, day 3, and day 7 after stroke and compared them with twenty-three control subjects. We found elevated EPC and EC concentrations using flow cytometry and increase in VEGF, SDF-1, HGF, and ET-1 plasma levels by ELISA in the HS patients, while ET-1 mRNA expression in peripheral blood cells was elevated in the IS patients. Significant correlations were observed between EPCs or ECs and Big ET-1 protein or mRNA levels in HS but not in the IS patients. We suggest that ET-1 may play a role in pathophysiology of stroke and subsequent EPC mobilisation; however, further studies aimed at the precise elucidation of this issue are required.

Rapid vascular responses to anthrax lethal toxin in mice containing a segment of chromosome 11 from the CAST/Ei strain on a C57BL/6 genetic background

Host allelic variation controls the response to B. anthracis and the disease course of anthrax. Mouse strains with macrophages that are responsive to anthrax lethal toxin (LT) show resistance to infection while mouse strains with LT non-responsive macrophages succumb more readily. B6.CAST.11M mice have a region of chromosome 11 from the CAST/Ei strain (a LT responsive strain) introgressed onto a LT non-responsive C57BL/6J genetic background. Previously, B6.CAST.11M mice were found to exhibit a rapid inflammatory reaction to LT termed the early response phenotype (ERP), and displayed greater resistance to B. anthracis infection compared to C57BL/6J mice. Several ERP features (e.g., bloat, hypothermia, labored breathing, dilated pinnae vessels) suggested vascular involvement. To test this, Evan’s blue was used to assess vessel leakage and intravital microscopy was used to monitor microvascular blood flow. Increased vascular leakage was observed in lungs of B6.CAST.11M mice compared to C57BL/6J mice 1 hour after systemic administration of LT. Capillary blood flow was reduced in the small intestine mesentery without concomitant leukocyte emigration following systemic or topical application of LT, the latter suggesting a localized tissue mechanism in this response. Since LT activates the Nlrp1b inflammasome in B6.CAST.11M mice, the roles of inflammasome products, IL-1β and IL-18, were examined. Topical application to the mesentery of IL-1β but not IL-18 revealed pronounced slowing of blood flow in B6.CAST.11M mice that was not present in C57BL/6J mice. A neutralizing anti-IL-1β antibody suppressed the slowing of blood flow induced by LT, indicating a role for IL-1β in the response. Besides allelic differences controlling Nlrp1b inflammasome activation by LT observed previously, evidence presented here suggests that an additional genetic determinant(s) could regulate the vascular response to IL-1β. These results demonstrate that vessel leakage and alterations to blood flow are part of the rapid response in mice resistant to B. anthracis infection.

Endothelin-1 cooperates with hypoxia to induce vascular-like structures through vascular endothelial growth factor-C, -D and -A in lymphatic endothelial cells

AIMS

Lymphangiogenesis refers to the formation of new lymphatic vessels and is thought to constitute conduits for the tumor cells to metastasize. We previously demonstrated that endothelin (ET)-1 through its binding with ETB receptor (ET(B)R) expressed on lymphatic endothelial cells (LEC), induced cell growth and invasiveness. Since vascular endothelial growth factor (VEGF)-A/-C/-D, and hypoxia play key role in lymphatic differentiation, in this study we investigated the involvement of these growth factors and hypoxia in ET-1-induced lymphangiogenesis.

MAIN METHODS

Real time PCR and ELISA were used to quantify VEGF-A/-C/-D. LEC morphological differentiation was analyzed by tube formation assay on Matrigel.

KEY FINDINGS

Hypoxia, as well as ET-1, induced an increase in VEGF-A/-C and -D expression that was reduced in the presence of a selective ET(B)R antagonist, BQ788, and enhanced when ET-1 was administered under hypoxic conditions. We analyzed the role of hypoxia on LEC morphological differentiation, and found that hypoxia increased the formation of vascular-like structures on Matrigel and that in combination with ET-1 this effect was markedly enhanced. The use of specific antibodies neutralizing VEGF-A, or recombinant VEGFR-3/(Flt-4)/Fc that block VEGF-C/-D, inhibited the effect of ET-1 as well that of hypoxia.

SIGNIFICANCE

These results demonstrated that ET-1 and hypoxia act, at list in part, through VEGF to induce lymphangiogenic events and that these two stimuli may cooperate to induce VEGF-A/-C/-D expression and lymphatic differentiation. These data further support the role of ET-1 as potent lymphangiogenic factor that relies on the interplay with hypoxic microenvironment and with VEGF family members.

HIF-1 and c-Src mediate increased glucose uptake induced by endothelin-1 and connexin43 in astrocytes

In previous work we showed that endothelin-1 (ET-1) increases the rate of glucose uptake in astrocytes, an important aspect of brain function since glucose taken up by astrocytes is used to supply the neurons with metabolic substrates. In the present work we sought to identify the signalling pathway responsible for this process in primary culture of rat astrocytes. Our results show that ET-1 promoted an increase in the transcription factor hypoxia-inducible factor-1α (HIF-1α) in astrocytes, as shown in other cell types. Furthermore, HIF-1α-siRNA experiments revealed that HIF-1α participates in the effects of ET-1 on glucose uptake and on the expression of GLUT-1, GLUT-3, type I and type II hexokinase. We previously reported that these effects of ET-1 are mediated by connexin43 (Cx43), the major gap junction protein in astrocytes. Indeed, our results show that silencing Cx43 increased HIF-1α and reduced the effect of ET-1 on HIF-1α, indicating that the effect of ET-1 on HIF-1α is mediated by Cx43. The activity of oncogenes such as c-Src can up-regulate HIF-1α. Since Cx43 interacts with c-Src, we investigated the participation of c-Src in this pathway. Interestingly, both the treatment with ET-1 and with Cx43-siRNA increased c-Src activity. In addition, when c-Src activity was inhibited neither ET-1 nor silencing Cx43 were able to up-regulate HIF-1α. In conclusion, our results suggest that ET-1 by down-regulating Cx43 activates c-Src, which in turn increases HIF-1α leading to the up-regulation of the machinery required to take up glucose in astrocytes. Cx43 expression can be reduced in response not only to ET-1 but also to various physiological and pathological stimuli. This study contributes to the identification of the signalling pathway evoked after Cx43 down-regulation that results in increased glucose uptake in astrocytes. Interestingly, this is the first evidence linking Cx43 to HIF-1, which is a master regulator of glucose metabolism.

Endothelins and their receptors in cancer: identification of therapeutic targets

Endothelins and their receptors are important in normal physiology, but have been implicated in various pathophysiological conditions. Members of the so-called "endothelin axis" are dysregulated in a wide range of human cancers, opening the door for novel anticancer therapies. Established cancer chemotherapeutic agents and drugs that target specific components of the endothelin axis have been combined with promising results, but more work is needed in this area. The endothelin axis affects numerous signaling pathways, including Ras, mitogen activated protein kinases, β-catenin/T-cell factor/lymphoid enhancer factor, nuclear factor-κB (NFκB), SNAIL, and mammalian target of rapamycin (mTOR). There is much still to learn about optimizing drug specificity in this area, while minimizing off-target effects. Selective agonists and antagonists of endothelins, their receptors, and upstream processing enzymes, as well as knockdown strategies in vitro, are providing valuable leads for testing in the clinical setting. The endothelin axis continues to be an attractive avenue of scientific endeavor, both in the cancer arena and in other important health-related disciplines.

The proliferation, apoptosis, invasion of endothelial-like epithelial ovarian cancer cells induced by hypoxia

BACKGROUND

Epithelial ovarian cancer is one of the most malignant cancers in women because metastasis occurs in the most of patients by the time of diagnosis. Cancer cells have strong capacity to form angiogenesis or vasculogenic mimicry, which plays the major role in its malignant phenotype. Vasculogenic mimicry might contribute to the failure of the angiogenesis-targeted therapy strategies. Under the microenvironment of the tumor, hypoxia is the most common phenomena because of the vast energy and oxygen consuming. In the present study, the endothelial-like cells induced by hypoxia from SKOV-3 and ES-2 ovarian cancer cells were harvested to investigate the changes in their biological behaviors.

METHODS

The endothelial-like cells from SKOV-3 and ES-2 cells were harvested by laser capture microdissection. The biological behaviors of the endothelial-like cells, including proliferation, cell cycle, apoptosis, invasion and telomerase activity were determined by MTT, FCM, Transwell chamber and TRAP-ELISA methods. HIF-1α is the most important factor for the behavior changes under hypoxic condition. Some other genes relative to biological behaviors are also changes following the changes of HIF-1α. In order to elucidate the underlying mechanisms for these changes by hypoxia, the relative genes expressions including HIF-1α, CyclinD1, Flk-1, VEGF, p53 and V-src were determined by real-time PCR.

RESULTS

SKOV-3 and ES-2 cells were resistant to hypoxia by adoption of proliferation, apoptosis, differentiation and invasion. Combined with other studies, the more poorly cancer cells differentiate, the more strongly cells are resistant to hypoxia, the more possible to form vasculogenic mimicry. The changes in the expression of HIF-1α, and HIF-1α-dependent VEGF, Flk-1, Cyclin D1, and HIF-1α-independent p53 have been involved in this process.

CONCLUSIONS

HIF-1α took an important role in the behavioral changes of SKOV-3 and ES-2 cells by hypoxia. At the same time, other mechanisms were also involved in this process.