Heterozygous deficiency of PHD2 restores tumor oxygenation and inhibits metastasis via endothelial normalization

Angiogenesis and vascular stability in eicosanoids and cancer

Angiogenesis and inflammation are hallmarks of cancer. Arachidonic acid and other polyunsaturated fatty acids (PUFAs) are primarily metabolized by three distinct enzymatic systems initiated by cyclooxygenases, lipoxygenases, and cytochrome P450 enzymes (CYP) to generate bioactive eicosanoids, including prostanoids, leukotrienes, hydroxyeicosatetraenoic acids, and epoxyeicosatrienoic acids. As some of the PUFA metabolites playing essential roles in inflammatory processes, these pathways have been widely studied as therapeutic targets of inflammation. Because of their anti-inflammatory effects, these pathways were also proposed as anti-cancer targets. However, although the eicosanoids were linked to endothelial cell proliferation and angiogenesis almost two decades ago, it is only recently PUFA metabolites, especially those generated by CYP enzymes and the soluble epoxide hydrolase (sEH), have been recognized as important signaling mediators in physiological and pathological angiogenesis. Despite the fact that tumor growth and invasion are heavily dependent on inner-tumor angiogenesis and influenced by vascular stability, the role played by PUFA metabolites in tumor angiogenesis and vessel integrity has been largely overlooked. This review highlights current knowledge on the function of PUFA metabolites generated by the CYP/sEH pathway in angiogenesis and vascular stability as well as their potential involvement in cancer development.

Vascular white matter lesions negatively correlate with brain metastases in malignant melanoma-Results from a retrospective comparative analysis

OBJECTIVES

Brain metastasis (BM) is a major complication of different cancers. There is increasing evidence for influence of vascular factors on BM in patients with non-small cell lung cancer (NSCLC). It is not known if the same is true for other tumors that might rely on different forms of vasculogenesis. The objective of this retrospective study was to evaluate a possible negative association of vascular white matter lesions and vascular risk factors (vasRF) with brain metastases in patients with melanoma.

PATIENTS AND METHODS

3D-brain magnetic resonance imaging (MRI) of 30 patients with BM from malignant melanoma and screening MRI of 31 BM negative patients were analysed. Number of metastases was calculated and T2 hyperintensive white matter lesions (WML) were classified according to Fazekas-Score (grade I-III) per patient and compared between BM+ and BM- patients.

RESULTS

Patients without BM showed more pronounced WML (median = WML 1, mean = 1.3; SD = 1.04,) than patients with BM (median = WML 0, mean = 0.6; SD = 0.8, p = 0.017). With respect to vascular risk factors, BM were more likely (p^x2 = 0.019) in patients without vasRF.

CONCLUSIONS

WML and possibly vasRF may reduce the risk of BM in different malignant tumors including melanoma. Presence of WML in patients with BM could potentially influence treatment choice regarding local or whole brain treatment after further multicentric prospective validation.

Metabolic regulation of exercise-induced angiogenesis

Skeletal muscle relies on an ingenious network of blood vessels, which ensures optimal oxygen and nutrient supply. An increase in muscle vascularization is an early adaptive event to exercise training, but the cellular and molecular mechanisms underlying exercise-induced blood vessel formation are not completely clear. In this review, we provide a concise overview on how exercise-induced alterations in muscle metabolism can evoke metabolic changes in endothelial cells (ECs) that drive muscle angiogenesis. In skeletal muscle, angiogenesis can occur via sprouting and splitting angiogenesis and is dependent on vascular endothelial growth factor (VEGF) signaling. In the resting muscle, VEGF levels are controlled by the estrogen-related receptor γ (ERRγ). Upon exercise, the transcriptional coactivator peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC1α) orchestrates several adaptations to endurance exercise within muscle fibers and simultaneously promotes transcriptional activation of Vegf expression and increased muscle capillary density. While ECs are highly glycolytic and change their metabolism during sprouting angiogenesis in development and disease, a similar role for EC metabolism in exercise-induced angiogenesis in skeletal muscle remains to be elucidated. Nonetheless, recent studies have illustrated the importance of endothelial hydrogen sulfide and sirtuin 1 (SIRT1) activity for exercise-induced angiogenesis, suggesting that EC metabolic reprogramming may be fundamental in this process. We hypothesize that the exercise-induced angiogenic response can also be modulated by metabolic crosstalk between muscle and the endothelium. Defining the underlying molecular mechanisms responsible for skeletal muscle angiogenesis in response to exercise will yield valuable insight into metabolic regulation as well as the determinants of exercise performance.

The roles and signaling pathways of prolyl-4-hydroxylase 2 in the tumor microenvironment

Tumor hypoxia is a well-known microenvironmental factor that causes cancer progression and resistance to cancer treatment. Proline hydroxylases (PHDs), a small protein family, belong to an evolutionarily conserved superfamily of dioxygenases, considered the central regulator of the molecular hypoxia response. Prolyl-4-hydroxylase 2 (PHD2), one member of PHDs family, regulates the stability of the hypoxia-inducible factor-1 alpha (HIF-1α) in response to oxygen availability. During hypoxia, the inhibition of PHD2 permits the accumulation of HIF-1α, allowing the cellular adaptation to oxygen limitation, causing activation of numerous genes, which enhances the angiogenesis, metastasis and invasiveness. Accurate regulation of oxygen homeostasis is essential, and which implies PHD2 may have a regulatory role in the pathogenesis of cancer. Although ample evidence exists for a positive correlation between HIFs and tumor formation, metastasis and poor prognosis, the function of the PHD2 in carcinogenesis is less well understood. Despite their original role as the oxygen sensors of the cell and many of the its functions are clearly conveyed through the HIF system, PHD2 is currently known to display HIF-independent and hydroxylase-independent functions in cancer cells and stroma in the control of different cellular pathways. In this review, we summarize the recent advances in the structure, regulation and functions of PHD2 in cancer microenvironment.

Regulation of Blood and Lymphatic Vessels by Immune Cells in Tumors and Metastasis

Research over the last decades has provided strong evidence for the pivotal role of the tumor-associated blood and lymphatic vasculature in supporting immunoevasion and in subverting T cell-mediated immunosurveillance. Conversely, tumor blood and lymphatic vessel growth is in part regulated by the immune system, with infiltrating innate as well as adaptive immune cells providing both immunosuppressive and various angiogenic signals. Thus, tumor angiogenesis and escape of immunosurveillance are two cancer hallmarks that are tightly linked and interregulated by cell constituents from compartments secreting both chemokines and cytokines. In this review, we discuss the implication and regulation of innate and adaptive immune cells in regulating blood and lymphatic angiogenesis in tumor progression and metastases. Moreover, we also highlight novel therapeutic approaches that target the tumor vasculature as well as the immune compartment to sustain and improve therapeutic efficacy in cancer.

Inhibition of the Oxygen Sensor PHD2 Enhances Tissue-Engineered Endochondral Bone Formation

Tissue engineering holds great promise for bone regenerative medicine, but clinical translation remains challenging. An important factor is the low cell survival after implantation, primarily caused by the lack of functional vasculature at the bone defect. Interestingly, bone development and repair initiate predominantly via an avascular cartilage template, indicating that chondrocytes are adapted to limited vascularization. Given these advantageous properties of chondrocytes, we questioned whether tissue-engineered cartilage intermediates implanted ectopically in mice are able to form bone, even when the volume size increases. Here, we show that endochondral ossification proceeds efficiently when implant size is limited (≤30 mm³ ), but chondrogenesis and matrix synthesis are impaired in the center of larger implants, leading to a fibrotic core. Increasing the level of angiogenic growth factors does not improve this outcome, because this strategy enhances peripheral bone formation, but disrupts the conversion of cartilage into bone in the center, resulting in a fibrotic core, even in small implants. On the other hand, activation of hypoxia signaling in cells before implantation stimulates chondrogenesis and matrix production, which culminates in enhanced bone formation throughout the entire implant. Together, our results show that induction of angiogenesis alone may lead to adverse effects during endochondral bone repair, whereas activation of hypoxia signaling represents a superior therapeutic strategy to improve endochondral bone regeneration in large tissue-engineered implants. © 2018 American Society for Bone and Mineral Research.

HIF-1α metabolically controls collagen synthesis and modification in chondrocytes

Endochondral ossification, an important process in vertebrate bone formation, is highly dependent on correct functioning of growth plate chondrocytes1. Proliferation of these cells determines longitudinal bone growth and the matrix deposited provides a scaffold for future bone formation. However, these two energy-dependent anabolic processes occur in an avascular environment1,2. In addition, the centre of the expanding growth plate becomes hypoxic, and local activation of the hypoxia-inducible transcription factor HIF-1α is necessary for chondrocyte survival by unidentified cell-intrinsic mechanisms3-6. It is unknown whether there is a requirement for restriction of HIF-1α signalling in the other regions of the growth plate and whether chondrocyte metabolism controls cell function. Here we show that prolonged HIF-1α signalling in chondrocytes leads to skeletal dysplasia by interfering with cellular bioenergetics and biosynthesis. Decreased glucose oxidation results in an energy deficit, which limits proliferation, activates the unfolded protein response and reduces collagen synthesis. However, enhanced glutamine flux increases α-ketoglutarate levels, which in turn increases proline and lysine hydroxylation on collagen. This metabolically regulated collagen modification renders the cartilaginous matrix more resistant to protease-mediated degradation and thereby increases bone mass. Thus, inappropriate HIF-1α signalling results in skeletal dysplasia caused by collagen overmodification, an effect that may also contribute to other diseases involving the extracellular matrix such as cancer and fibrosis.

Loss of Phd2 cooperates with BRAFV600E to drive melanomagenesis

Prolyl hydroxylase domain protein 2 (PHD2) is a well-known master oxygen sensor. However, the role of PHD2 in tumor initiation remains controversial. We find that during the transition of human nevi to melanoma, the expression of PHD2 protein is significantly decreased and lower expression PHD2 in melanoma is associated with worse clinical outcome. Knockdown of PHD2 leads to elevated Akt phosphorylation in human melanocytes. Mice with conditional melanocyte-specific expression of Phd2^lox/lox (Tyr::CreER;Phd2^lox/lox) fail to develop pigmented lesions. However, deletion of Phd2 in combination with expression of BRaf^V600E in melanocytes (Tyr::CreER;Phd2^lox/lox;BRaf^CA) leads to the development of melanoma with 100% penetrance and frequent lymph node metastasis. Analysis of tumor tissues using reverse phase protein arrays demonstrates that Phd2 deletion activates the AKT-mTOR-S6 signaling axis in the recovered tumors. These data indicate that PHD2 is capable of suppressing tumor initiation largely mediated through inhibiting of the Akt-mTOR signaling pathway in the melanocyte lineage.

Prolyl hydroxylase domain protein 2 (PHD2) regulates cellular response to hypoxia. Here the authors show that PHD2 is downregulated in melanoma and that PHD2 depletion, in a mouse model, promotes the progression of benign melanocytic lesions into melanoma, via activation of the Akt/mTOR signaling cascade.

Discovery of a Vascular Endothelial Stem Cell (VESC) Population Required for Vascular Regeneration and Tissue Maintenance

The roles that blood vessels play in the maintenance of organs and tissues in addition to the delivery of oxygen and nutrients are being gradually clarified. The maintenance of tissue-specific organ stem cells, such as hematopoietic and neuronal stem cells, is supported by endothelial cells (ECs), which represent an important component of the stem cell niche. The maintenance of organogenesis, for example, osteogenesis and liver generation/regeneration, is supported by molecules referred to as "angiocrine signals" secreted by EC. The mechanisms responsible for the well-known functions of blood vessels, such as thermoregulation and metabolism, especially removal of local metabolites, have now been determined at the molecular level. Following the development of single-cell genetic analysis, blood cell heterogeneity, especially of mural cell populations, has been established and tissue-specific blood vessel formation and function are now also understood at the molecular level. Among the heterogeneous populations of ECs, it seems that a stem cell population with the ability to maintain the production of ECs long-term is present in pre-existing blood vessels. Neovascularization by therapeutic angiogenesis yields benefits in many diseases, not only ischemic disease but also metabolic disease and other vascular diseases. Therefore, vascular endothelial stem cells should be considered to use in vascular regeneration therapy.

Immune regulation of metastasis: mechanistic insights and therapeutic opportunities

Metastatic disease is the leading cause of death in cancer patients. Metastasis formation involves a cascade of events for which the underlying mechanisms are still poorly understood. During the metastatic cascade, cancer cells tightly interact with the immune system and they influence each other, both in the tumor microenvironment and systemically. The crosstalk between cancer and immune cells adds another layer of complexity to our understanding of metastasis formation, but at the same time opens new therapeutic opportunities for cancer patients. The intensifying development of immunotherapeutic strategies calls for a better understanding of immune regulation of metastasis in order to maximize the therapeutic benefit for patients with metastatic disease. In this Review and accompanying poster, we describe the main mechanisms of immune regulation of metastasis that have been reported to date, and present promising immunotherapeutic options that are currently available, or may become so in the near future, to tackle metastasis.

Microglia Induce PDGFRB Expression in Glioma Cells to Enhance Their Migratory Capacity

High-grade gliomas (HGGs) are the most aggressive and invasive primary brain tumors. The platelet-derived growth factor (PDGF) signaling pathway drives HGG progression, and enhanced expression of PDGF receptors (PDGFRs) is a well-established aberration in a subset of glioblastomas (GBMs). PDGFRA is expressed in glioma cells, whereas PDGFRB is mostly restricted to the glioma-associated stroma. Here we show that the spatial location of TAMMs correlates with the expansion of a subset of tumor cells that have acquired expression of PDGFRB in both mouse and human low-grade glioma and HCGs. Furthermore, M2-polarized microglia but not bone marrow (BM)-derived macrophages (BMDMs) induced PDGFRB expression in glioma cells and stimulated their migratory capacity. These findings illustrate a heterotypic cross-talk between microglia and glioma cells that may enhance the migratory and invasive capacity of the latter by inducing PDGFRB.

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PDGFRB⁺ glioma cells are in physical contact with IBA1⁺ TAMMs in mouse and human glioma

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Aggregation of PDGFRB⁺ glioma cells correlated with the accumulation of IBA1⁺ TAMMs

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Microglia but not bone marrow-derived macrophages induced PDGFRB expression in vitro

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M2-polarized microglia stimulated glioma cell migration dependent on PDGFRB

Cellular and Molecular Heterogeneity Associated with Vessel Formation Processes

The microvasculature heterogeneity is a complex subject in vascular biology. The difficulty of building a dynamic and interactive view among the microenvironments, the cellular and molecular heterogeneities, and the basic aspects of the vessel formation processes make the available knowledge largely fragmented. The neovascularisation processes, termed vasculogenesis, angiogenesis, arteriogenesis, and lymphangiogenesis, are important to the formation and proper functioning of organs and tissues both in the embryo and the postnatal period. These processes are intrinsically related to microvascular cells, such as endothelial and mural cells. These cells are able to adjust their activities in response to the metabolic and physiological requirements of the tissues, by displaying a broad plasticity that results in a significant cellular and molecular heterogeneity. In this review, we intend to approach the microvasculature heterogeneity in an integrated view considering the diversity of neovascularisation processes and the cellular and molecular heterogeneity that contribute to microcirculatory homeostasis. For that, we will cover their interactions in the different blood-organ barriers and discuss how they cooperate in an integrated regulatory network that is controlled by specific molecular signatures.

The Warburg Effect in Endothelial Cells and its Potential as an Anti-angiogenic Target in Cancer

Endothelial cells (ECs) make up the lining of our blood vessels and they ensure optimal nutrient and oxygen delivery to the parenchymal tissue. In response to oxygen and/or nutrient deprivation, ECs become activated and sprout into hypo-vascularized tissues forming new vascular networks in a process termed angiogenesis. New sprouts are led by migratory tip cells and extended through the proliferation of trailing stalk cells. Activated ECs rewire their metabolism to cope with the increased energetic and biosynthetic demands associated with migration and proliferation. Moreover, metabolic signaling pathways interact and integrate with angiogenic signaling events. These metabolic adaptations play essential roles in determining EC fate and function, and are perturbed during pathological angiogenesis, as occurs in cancer. The angiogenic switch, or the growth of new blood vessels into an expanding tumor, increases tumor growth and malignancy. Limiting tumor angiogenesis has therefore long been a goal for anticancer therapy but the traditional growth factor targeted anti-angiogenic treatments have met with limited success. In recent years however, it has become increasingly recognized that focusing on altered tumor EC metabolism provides an attractive alternative anti-angiogenic strategy. In this review, we will describe the EC metabolic signature and how changes in EC metabolism affect EC fate during physiological sprouting, as well as in the cancer setting. Then, we will discuss the potential of targeting EC metabolism as a promising approach to develop new anti-cancer therapies.

Two-stage oxygen delivery for enhanced radiotherapy by perfluorocarbon nanoparticles

Tumors are usually hypoxic, which limits the efficacy of current tumor therapies, especially radiotherapy in which oxygen is essential to promote radiation-induced cell damage. Herein, by taking advantage of the ability of perfluorocarbon (PFC) to promote red blood cell penetration, we developed a simple but effective two-stage oxygen delivery strategy to modulate the hypoxic tumor microenvironment using PFC nanoparticles. Methods: We first examined the two-stage oxygen delivery ability of PFC nanoparticles on relieving tumor hypoxia through platelet inhibition. To evaluate the effect of PFC nanoparticles on radiation sensitization, CT26 tumor and SUM49PT tumor model were used. Results: In this study, PFC was encapsulated into albumin and intravenously injected into tumor-bearing mice without hyperoxic breathing. After accumulation in the tumor, PFC nanoparticles rapidly released the oxygen that was physically dissolved in PFC as the first-stage of oxygen delivery. Then, PFC subsequently promoted red blood cell infiltration, which further released O2 as the second-stage of oxygen delivery. Conclusion: The hypoxic tumor microenvironment was rapidly relieved via two-stage oxygen delivery, effectively increasing radiotherapy efficacy. The safety of all substances used in this study has been clinically demonstrated, ensuring that this simple strategy could be rapidly and easily translated into clinical applications to solve the clinical problems associated with tumor hypoxia.

Inhibition of prolyl hydroxylase domain proteins selectively enhances venous thrombus neovascularisation

BACKGROUND

Hypoxia within acute venous thrombi is thought to drive resolution through stabilisation of hypoxia inducible factor 1 alpha (HIF1α). Prolyl hydroxylase domain (PHD) isoforms are critical regulators of HIF1α stability. Non-selective inhibition of PHD isoforms with l-mimosine has been shown to increase HIF1α stabilisation and promote thrombus resolution.

OBJECTIVE

The aim of this study was to investigate the therapeutic potential of PHD inhibition in venous thrombus resolution.

METHODS

Thrombosis was induced in the inferior vena cava of mice using a combination of flow restriction and endothelial activation. Gene and protein expression of PHD isoforms in the resolving thrombus was measured by RT-PCR and immunohistochemistry. Thrombus resolution was quantified in mice treated with pan PHD inhibitors AKB-4924 and JNJ-42041935 or inducible all-cell Phd2 knockouts by micro-computed tomography, 3D high frequency ultrasound or endpoint histology.

RESULTS

Resolving venous thrombi demonstrated significant temporal gene expression profiles for PHD2 and PHD3 (P < 0.05), but not for PHD1. PHD isoform protein expression was localised to early and late inflammatory cell infiltrates. Treatment with selective pan PHD inhibitors, AKB-4924 and JNJ-42041935, enhanced thrombus neovascularisation (P < 0.05), but had no significant effect on overall thrombus resolution. Thrombus resolution or its markers, macrophage accumulation and neovascularisation, did not differ significantly in inducible all-cell homozygous Phd2 knockouts compared with littermate controls (P > 0.05).

CONCLUSIONS

This data suggests that PHD-mediated thrombus neovascularisation has a limited role in the resolution of venous thrombi. Directly targeting angiogenesis alone may not be a viable therapeutic strategy to enhance venous thrombus resolution.

New Directions in the Study and Treatment of Metastatic Cancer

Traditional cancer therapy has relied on a strictly cytotoxic approach that views non-metastatic and metastatic tumor cells as identical in terms of molecular biology and sensitivity to therapeutic intervention. Mounting evidence suggests that, in fact, non-metastatic and metastatic tumor cells differ in key characteristics that could explain the capacity of the metastatic cells to not only escape the primary organ but also to survive while in the circulation and to colonize a distant organ. Here, we lay out a framework for a new multi-pronged therapeutic approach. This approach involves modifying the local microenvironment of the primary tumor to inhibit the formation and release of metastatic cells; normalizing the microenvironment of the metastatic organ to limit the capacity of metastatic tumor cells to invade and colonize the organ; remediating the immune response to tumor neoantigens; and targeting metastatic tumor cells on a systemic level by restoring critical and unique aspects of the cell’s phenotype, such as anchorage dependence. Given the limited progress against metastatic cancer using traditional therapeutic strategies, the outlined paradigm could provide a more rational alternative to patients with metastatic cancer.

Phenotype molding of stromal cells in the lung tumor microenvironment

Cancer cells are embedded in the tumor microenvironment (TME), a complex ecosystem of stromal cells. Here, we present a 52,698-cell catalog of the TME transcriptome in human lung tumors at single-cell resolution, validated in independent samples where 40,250 additional cells were sequenced. By comparing with matching non-malignant lung samples, we reveal a highly complex TME that profoundly molds stromal cells. We identify 52 stromal cell subtypes, including novel subpopulations in cell types hitherto considered to be homogeneous, as well as transcription factors underlying their heterogeneity. For instance, we discover fibroblasts expressing different collagen sets, endothelial cells downregulating immune cell homing and genes coregulated with established immune checkpoint transcripts and correlating with T-cell activity. By assessing marker genes for these cell subtypes in bulk RNA-sequencing data from 1,572 patients, we illustrate how these correlate with survival, while immunohistochemistry for selected markers validates them as separate cellular entities in an independent series of lung tumors. Hence, in providing a comprehensive catalog of stromal cells types and by characterizing their phenotype and co-optive behavior, this resource provides deeper insights into lung cancer biology that will be helpful in advancing lung cancer diagnosis and therapy.

The metabolic axis of macrophage and immune cell polarization

The extracellular space of solid tumors ranges from being well-nurtured to being completely ischemic and can serve as a source of intratumoral heterogeneity, determining the behavior and molecular profiles of malignant and stromal cells. Here, we discuss how the metabolic tumor microenvironment modulates the phenotypes of the immune cells that infiltrate tumors, with an emphasis on tumor-associated macrophages. These cells constitute a diverse population that has pro-tumoral and anti-inflammatory properties, and are likened to anti-inflammatory ‘M2’ macrophages. Recent findings show how different metabolic microenvironments specify an array of phenotypic changes in macrophages. In tumors, extracellular metabolite levels vary predictably according to proximity to the vasculature, and phenotypic changes in tumor-associated macrophages and in other immune cells are also predictable. We speculate that this ‘metabolic axis’ of macrophage polarization modulates – and is modulated by – the response to inflammatory cues, creating a wide variety of possible phenotypic states. Understanding how extracellular metabolites influence cell phenotypes allows us to predict how tumor-associated macrophages and other tumor cells might change, with the aim of harnessing this predictability for therapy. Overall, we describe an emerging picture in which chemokines, growth factors and the metabolic tumor microenvironment act together to determine the phenotypes of tumor-infiltrating immune cells.

Summary: Extracellular metabolites can mediate cell communication and change transcriptional and functional aspects of tumor and normal cells. This Review focuses on how these metabolic cues affect the immune system with a special focus on tumor-associated macrophages.

Osteocytic oxygen sensing controls bone mass through epigenetic regulation of sclerostin

Preservation of bone mass is crucial for healthy ageing and largely depends on adequate responses of matrix-embedded osteocytes. These cells control bone formation and resorption concurrently by secreting the WNT/β-catenin antagonist sclerostin (SOST). Osteocytes reside within a low oxygen microenvironment, but whether and how oxygen sensing regulates their function remains elusive. Here, we show that conditional deletion of the oxygen sensor prolyl hydroxylase (PHD) 2 in osteocytes results in a high bone mass phenotype, which is caused by increased bone formation and decreased resorption. Mechanistically, enhanced HIF-1α signalling increases Sirtuin 1-dependent deacetylation of the Sost promoter, resulting in decreased sclerostin expression and enhanced WNT/β-catenin signalling. Additionally, genetic ablation of PHD2 in osteocytes blunts osteoporotic bone loss induced by oestrogen deficiency or mechanical unloading. Thus, oxygen sensing by PHD2 in osteocytes negatively regulates bone mass through epigenetic regulation of sclerostin and targeting PHD2 elicits an osteo-anabolic response in osteoporotic models.

Osteocytes reside in a low oxygen environment, but it is not clear if oxygen sensing regulates their function. Here, the authors show that deletion of the oxygen sensor prolyl hydroxylase 2 in osteocytes leads to increased bone mass via regulation of sclerostin, and reduces bone loss in mouse models of osteoporosis.

Normalizing Tumor Microenvironment Based on Photosynthetic Abiotic/Biotic Nanoparticles

Tumor hypoxia has attained the status of a core hallmark of cancer that globally affects the entire tumor phenotype. Reversing tumor hypoxia might offer alternative therapeutic opportunities for current anticancer therapies. In this research, a photosynthetic leaf-inspired abiotic/biotic nano-thylakoid (PLANT) system was designed by fusing the thylakoid membrane with synthetic nanoparticles for efficient O₂ generation in vivo. Under 660 nm laser irradiation, the PLANT system exhibited intracellular O₂ generation and the anaerobic respiration of the multicellular tumor spheroid was suppressed by PLANT as well. In vivo, it was found that PLANT could not only normalize the entire metabolic network but also adjust the abnormal structure and function of the tumor vasculature. It was demonstrated that PLANT could significantly enhance the efficacy of phototherapy or antiangiogenesis therapy. This facile approach for normalizing the tumor microenvironment will find great potential in tumor therapy.

Spatiotemporal endothelial cell - pericyte association in tumors as shown by high resolution 4D intravital imaging

Endothelial cells and pericytes are integral cellular components of the vasculature with distinct interactive functionalities. To study dynamic interactions between these two cells we created two transgenic animal lines. A truncated eNOS (endothelial nitric oxide synthase) construct was used as a GFP tag for endothelial cell evaluation and an inducible Cre-lox recombination, under control of the Pdgfrb (platelet derived growth factor receptor beta) promoter, was created for pericyte assessment. Also, eNOStag-GFP animals were crossed with the already established Cspg4-DsRed mice expressing DsRed fluorescent protein in pericytes. For intravital imaging we used tumors implanted in the dorsal skinfold of these transgenic animals. This setup allowed us to study time and space dependent complexities, such as distribution, morphology, motility, and association between both vascular cell types in all angiogenetic stages, without the need for additional labeling. Moreover, as fluorescence was still clearly detectable after fixation, it is possible to perform comparative histology following intravital evaluation. These transgenic mouse lines form an excellent model to capture collective and individual cellular and subcellular endothelial cell – pericyte dynamics and will help answer key questions on the cellular and molecular relationship between these two cells.

Chloroquine and nanoparticle drug delivery: A promising combination

Clinically approved cancer therapies include small molecules, antibodies, and nanoparticles. There has been major progress in the treatment of several cancer types over recent decades. However, many challenges remain for optimal use of conventional and nanoparticle-based therapies in oncology including poor drug delivery, rapid clearance, and drug resistance. The antimalarial agent chloroquine has been found to mitigate some of these challenges by modulating cancer cells and the tissue microenvironment. Particularly, chloroquine was recently found to reduce immunological clearance of nanoparticles by resident macrophages in the liver, leading to increased tumor accumulation of nanodrugs. Additionally, chloroquine has been shown to improve drug delivery and efficacy through normalization of tumor vasculature and suppression of several oncogenic and stress-tolerance pathways, such as autophagy, that protect cancer cells from cytotoxic agents. This review will discuss the use of chloroquine as combination therapy to improve cancer treatment.

PHD2 inactivation in Type I cells drives HIF-2α-dependent multilineage hyperplasia and the formation of paraganglioma-like carotid bodies

KEY POINTS

The carotid body is a peripheral arterial chemoreceptor that regulates ventilation in response to both acute and sustained hypoxia. Type I cells in this organ respond to low oxygen both acutely by depolarization and dense core vesicle secretion and, over the longer term, via cellular proliferation and enhanced ventilatory responses. Using lineage analysis, the present study shows that the Type I cell lineage itself proliferates and expands in response to sustained hypoxia. Inactivation of HIF-2α in Type I cells impairs the ventilatory, proliferative and cell intrinsic (dense core vesicle) responses to hypoxia. Inactivation of PHD2 in Type I cells induces multilineage hyperplasia and ultrastructural changes in dense core vesicles to form paraganglioma-like carotid bodies. These changes, similar to those observed in hypoxia, are dependent on HIF-2α. Taken together, these findings demonstrate a key role for the PHD2-HIF-2α couple in Type I cells with respect to the oxygen sensing functions of the carotid body.

ABSTRACT

The carotid body is a peripheral chemoreceptor that plays a central role in mammalian oxygen homeostasis. In response to sustained hypoxia, it manifests a rapid cellular proliferation and an associated increase in responsiveness to hypoxia. Understanding the cellular and molecular mechanisms underlying these processes is of interest both to specialized chemoreceptive functions of that organ and, potentially, to the general physiology and pathophysiology of cellular hypoxia. We have combined cell lineage tracing technology and conditionally inactivated alleles in recombinant mice to examine the role of components of the HIF hydroxylase pathway in specific cell types within the carotid body. We show that exposure to sustained hypoxia (10% oxygen) drives rapid expansion of the Type I, tyrosine hydroxylase expressing cell lineage, with little transdifferentiation to (or from) that lineage. Inactivation of a specific HIF isoform, HIF-2α, in the Type I cells was associated with a greatly reduced proliferation of Type I cells and hypoxic ventilatory responses, with ultrastructural evidence of an abnormality in the action of hypoxia on dense core secretory vesicles. We also show that inactivation of the principal HIF prolyl hydroxylase PHD2 within the Type I cell lineage is sufficient to cause multilineage expansion of the carotid body, with characteristics resembling paragangliomas. These morphological changes were dependent on the integrity of HIF-2α. These findings implicate specific components of the HIF hydroxylase pathway (PHD2 and HIF-2α) within Type I cells of the carotid body with respect to the oxygen sensing and adaptive functions of that organ.

Hypoxic Signalling in Tumour Stroma

Hypoxia is a common feature in solid tumors and is associated with cancer progression. The main regulators of the hypoxic response are hypoxia-inducible transcription factors (HIFs) that guide the cellular adaptation to hypoxia by gene activation. The actual oxygen sensing is performed by HIF prolyl hydroxylases (PHDs) that under normoxic conditions mark the HIF-α subunit for degradation. Cancer progression is not regulated only by the cancer cells themselves but also by the whole tumor microenvironment, which consists of cellular and extracellular components. Hypoxic conditions also affect the stromal compartment, where stromal cells are in close contact with the cancer cells. The important function of HIF in cancer cells has been shown by many animal models and described in hundreds of reviews, but less in known about PHDs and even less PHDs in stromal cells. Here, we review hypoxic signaling in tumors, mainly in the tumor stroma, with a focus on HIFs and PHDs.

Lysophosphatidic Acid Receptor 4 Activation Augments Drug Delivery in Tumors by Tightening Endothelial Cell-Cell Contact

Vascular normalization in tumors may improve drug delivery and anti-tumor immunity. Angiogenesis inhibitors induce hypoxia, which may facilitate malignant progression; therefore, we investigated other methods to promote vascular maturation. Here, we show that lysophosphatidic acid (LPA) enhances blood flow by promoting fine vascular networks, thereby improving vascular permeability and suppressing tumor growth when combined with anti-cancer drug treatment. Six different G protein-coupled receptors have been identified as LPA receptors (LPA1-6). In studies using mutant mice, we found that LPA4 is involved in vascular network formation. LPA4 activation induces circumferential actin bundling beneath the cell membrane and enhances linear adherens junction formation by VE-cadherin in endothelial cells. Therefore, we conclude that activation of LPA4 is a promising approach for vascular regulation.

Pharmacologic or Genetic Targeting of Glutamine Synthetase Skews Macrophages toward an M1-like Phenotype and Inhibits Tumor Metastasis

Glutamine-synthetase (GS), the glutamine-synthesizing enzyme from glutamate, controls important events, including the release of inflammatory mediators, mammalian target of rapamycin (mTOR) activation, and autophagy. However, its role in macrophages remains elusive. We report that pharmacologic inhibition of GS skews M2-polarized macrophages toward the M1-like phenotype, characterized by reduced intracellular glutamine and increased succinate with enhanced glucose flux through glycolysis, which could be partly related to HIF1α activation. As a result of these metabolic changes and HIF1α accumulation, GS-inhibited macrophages display an increased capacity to induce T cell recruitment, reduced T cell suppressive potential, and an impaired ability to foster endothelial cell branching or cancer cell motility. Genetic deletion of macrophagic GS in tumor-bearing mice promotes tumor vessel pruning, vascular normalization, accumulation of cytotoxic T cells, and metastasis inhibition. These data identify GS activity as mediator of the proangiogenic, immunosuppressive, and pro-metastatic function of M2-like macrophages and highlight the possibility of targeting this enzyme in the treatment of cancer metastasis.

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GS expression and activity are induced by M2 stimuli, especially under starvation

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Inhibition of GS activity skews M2 macrophages toward an M1-like phenotype

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Metabolic rewiring by GS loss favors immunostimulatory and antiangiogenic features

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GS ablation in macrophages blocks vessels, immunosuppression, and metastasis

Vascular targeting of LIGHT normalizes blood vessels in primary brain cancer and induces intratumoural high endothelial venules

High-grade brain cancer such as glioblastoma (GBM) remains an incurable disease. A common feature of GBM is the angiogenic vasculature, which can be targeted with selected peptides for payload delivery. We assessed the ability of micelle-tagged, vascular homing peptides RGR, CGKRK and NGR to specifically bind to blood vessels in syngeneic orthotopic GBM models. By using the peptide CGKRK to deliver the tumour necrosis factor (TNF) superfamily member LIGHT (also known as TNF superfamily member 14; TNFSF14) to angiogenic tumour vessels, we have generated a reagent that normalizes the brain cancer vasculature by inducing pericyte contractility and re-establishing endothelial barrier integrity. LIGHT-mediated vascular remodelling also activates endothelia and induces intratumoural high endothelial venules (HEVs), which are specialized blood vessels for lymphocyte infiltration. Combining CGKRK-LIGHT with anti-vascular endothelial growth factor and checkpoint blockade amplified HEV frequency and T-cell accumulation in GBM, which is often sparsely infiltrated by immune effector cells, and reduced tumour burden. Furthermore, CGKRK and RGR peptides strongly bound to blood vessels in freshly resected human GBM, demonstrating shared peptide-binding activities in mouse and human primary brain tumour vessels. Thus, peptide-mediated LIGHT targeting is a highly translatable approach in primary brain cancer to reduce vascular leakiness and enhance immunotherapy. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Regional differences in endothelial cell cytoskeleton, junctional proteins and phosphorylated tyrosine labeling in the porcine vortex vein system

We previously demonstrated endothelial phenotype heterogeneity in the vortex vein system. This study is to further determine whether regional differences are present in the cytoskeleton, junctional proteins and phosphorylated tyrosine labeling within the system. The vortex vein system of twenty porcine eyes was perfused with labels for f-actin, claudin-5, VE-Cadherin, phosphorylated tyrosine and nucleic acid. The endothelial cells of eight different regions (choroidal veins, pre-ampulla, anterior ampulla, mid-ampulla, posterior ampulla, post-ampulla, intra-scleral canal and the extra-ocular vortex vein) were studied using confocal microscopy. There were regional differences in the endothelial cell structures. Cytoskeleton labeling was relatively even in intensity throughout Regions 1 to 6. Overall VE-Cadherin had a non-uniform distribution and thicker width endothelial cell border staining than claudin-5. Progressing downstream there was an increased variation in thickness of VE-cadherin labeling. There was an overlap in phosphorylated tyrosine and VE-Cadherin labeling in the post-ampulla, intra-scleral canal and extra-ocular vortex vein. Intramural cells were observed that were immune-positive for VE-Cadherin and phosphorylated tyrosine. There were significant differences in the number of intramural cells in different regions. Significant regional differences with endothelial cell labeling of cytoskeleton, junction proteins, and phosphorylated tyrosine were found within the vortex vein system. These findings support existing data on endothelial cell phenotype heterogeneity, and may aid in the knowledge of venous pathologies by understanding regions of vulnerability to endothelial damage within the vortex vein system. It could be valuable to further investigate and characterize the VE-cadherin and phosphotyrosine immune-positive intramural cells.

The PHD1 oxygen sensor in health and disease

The hypoxia-inducible factor (HIF) co-ordinates the adaptive transcriptional response to hypoxia in metazoan cells. The hypoxic sensitivity of HIF is conferred by a family of oxygen-sensing enzymes termed HIF hydroxylases. This family consists of three prolyl hydroxylases (PHD1-3) and a single asparagine hydroxylase termed factor inhibiting HIF (FIH). It has recently become clear that HIF hydroxylases are functionally non-redundant and have discrete but overlapping physiological roles. Furthermore, altered abundance or activity of these enzymes is associated with a number of pathologies. Pharmacological HIF-hydroxylase inhibitors have recently proven to be both tolerated and therapeutically effective in patients. In this review, we focus on the physiology, pathophysiology and therapeutic potential of the PHD1 isoform, which has recently been implicated in diseases including inflammatory bowel disease, ischaemia and cancer.

Co-Emergence of Specialized Endothelial Cells from Embryonic Stem Cells

A well-formed and robust vasculature is critical to the health of most organ systems in the body. However, the endothelial cells (ECs) forming the vasculature can exhibit a number of distinct functional subphenotypes like arterial or venous ECs, as well as angiogenic tip and stalk ECs. In this study, we investigate the in vitro differentiation of EC subphenotypes from embryonic stem cells (ESCs). Using our staged induction methods and chemically defined mediums, highly angiogenic EC subpopulations, as well as less proliferative and less migratory EC subpopulations, are derived. Furthermore, the EC subphenotypes exhibit distinct surface markers, gene expression profiles, and positional affinities during sprouting. While both subpopulations contained greater than 80% VE-cad⁺/CD31⁺ cells, the tip/stalk-like EC contained predominantly Flt4⁺/Dll4⁺/CXCR4⁺/Flt-1^- cells, while the phalanx-like EC was composed of higher numbers of Flt-1⁺ cells. These studies suggest that the tip-specific EC can be derived in vitro from stem cells as a distinct and relatively stable EC subphenotype without the benefit of its morphological positioning in the sprouting vessel.

The ablation of the matricellular protein EMILIN2 causes defective vascularization due to impaired EGFR-dependent IL-8 production affecting tumor growth

EMILIN2 is an extracellular matrix constituent playing an important role in angiogenesis; however, the underlying mechanism is unknown. Here we show that EMILIN2 promotes angiogenesis by directly binding epidermal growth factor receptor (EGFR), which enhances interleukin-8 (IL-8) production. In turn, IL-8 stimulates the proliferation and migration of vascular endothelial cells. Emilin2 null mice were generated and exhibited delayed retinal vascular development, which was rescued by the administration of the IL-8 murine ortholog MIP-2. Next, we assessed tumor growth and tumor-associated angiogenesis in these mice. Tumor cell growth in Emilin2 null mice was impaired as well as the expression of MIP-2. The vascular density of the tumors developed in Emilin2 null mice was prejudiced and vessels perfusion, as well as response to chemotherapy, decreased. Accordingly, human tumors expressing high levels of EMILIN2 were more responsive to chemotherapy. These results point at EMILIN2 as a key microenvironmental cue affecting vessel formation and unveil the possibility to develop new prognostic tools to predict chemotherapy efficacy.

Advantages and Disadvantages of Combined Chemotherapy with Carmustine Wafer and Bevacizumab in Patients with Newly Diagnosed Glioblastoma: A Single-Institutional Experience

OBJECTIVE

To retrospectively determine the safety and efficacy of combined chemotherapy with carmustine (BCNU) wafer, bevacizumab, and temozolomide plus radiotherapy in patients with newly diagnosed glioblastoma (GBM).

METHODS

A total of 54 consecutive newly diagnosed GBMs were resected at our institution between 2010 and 2016. Twenty-nine patients underwent BCNU wafer implantation into the resection cavity followed by standard radiochemotherapy with temozolomide (TMZ, Stupp regimen) plus additional bevacizumab treatment between 2013 and 2016. Twenty-five patients who underwent resection without BCNU implantation between 2010 and 2012 were enrolled as a control group; these patients were treated with the Stupp regimen and did not receive bevacizumab. This retrospective study included evaluation of progression-free survival and overall survival, plus comparisons between the combined therapy group and the control group.

RESULTS

There were no significant differences in age, sex, Karnofsky Performance Status on admission, isocitrate dehydrogenase 1/2 mutation ratio, or resection rate between the combined and standard therapy groups. The median overall survival in the combined therapy group and control group was 24.2 months and 15.30, respectively (P = 0.027). The median progression-free survival was 16.8 months and 7.30 months, respectively (P = 0.009). Overall, the incidence of adverse events leading to discontinuation of the study drug was similar between the treatment groups, except for infection, which was more common in the combined treatment group and required repeat surgery.

CONCLUSIONS

The combined therapy showed higher efficacy compared with standard therapy in patients with GBM. Therefore, combined therapy seems to be effective with an acceptable toxicity profile.

SOD3 improves the tumor response to chemotherapy by stabilizing endothelial HIF-2α

One drawback of chemotherapy is poor drug delivery to tumor cells, due in part to hyperpermeability of the tumor vasculature. Extracellular superoxide dismutase (SOD3) is an antioxidant enzyme usually repressed in the tumor milieu. Here we show that specific SOD3 re-expression in tumor-associated endothelial cells (ECs) increases doxorubicin (Doxo) delivery into and chemotherapeutic effect on tumors. Enhanced SOD3 activity fostered perivascular nitric oxide accumulation and reduced vessel leakage by inducing vascular endothelial cadherin (VEC) transcription. SOD3 reduced HIF prolyl hydroxylase domain protein activity, which increased hypoxia-inducible factor-2α (HIF-2α) stability and enhanced its binding to a specific VEC promoter region. EC-specific HIF-2α ablation prevented both the SOD3-mediated increase in VEC transcription and the enhanced Doxo effect. SOD3, VEC, and HIF-2α levels correlated positively in primary colorectal cancers, which suggests a similar interconnection of these proteins in human malignancy.

Tumour vasculature influences drug delivery. Here, the authors show that SOD3 re-expression enhances doxorubicin delivery and effects through normalization of tumour vasculature via the HIF-2a/VE-cadherin pathway.

Transient loss of venous integrity during developmental vascular remodeling leads to red blood cell extravasation and clearance by lymphatic vessels

Maintenance of blood vessel integrity is crucial for vascular homeostasis and is mainly controlled at the level of endothelial cell (EC) junctions. Regulation of endothelial integrity has largely been investigated in the mature quiescent vasculature. Less is known about how integrity is maintained during vascular growth and remodeling involving extensive junctional reorganization. Here, we show that embryonic mesenteric blood vascular remodeling is associated with a transient loss of venous integrity and concomitant extravasation of red blood cells (RBCs), followed by their clearance by the developing lymphatic vessels. In wild-type mouse embryos, we observed activated platelets extending filopodia at sites of inter-EC gaps. In contrast, embryos lacking the activatory C-type lectin domain family 1, member b (CLEC1B) showed extravascular platelets and an excessive number of RBCs associated with and engulfed by the first lymphatic EC clusters that subsequently form lumenized blood-filled vessels connecting to the lymphatic system. These results uncover novel functions of platelets in maintaining venous integrity and lymphatic vessels in clearing extravascular RBCs during developmental remodeling of the mesenteric vasculature. They further provide insight into how vascular abnormalities characterized by blood-filled lymphatic vessels arise.

CD157 Marks Tissue-Resident Endothelial Stem Cells with Homeostatic and Regenerative Properties

The generation of new blood vessels via angiogenesis is critical for meeting tissue oxygen demands. A role for adult stem cells in this process remains unclear. Here, we identified CD157 (bst1, bone marrow stromal antigen 1) as a marker of tissue-resident vascular endothelial stem cells (VESCs) in large arteries and veins of numerous mouse organs. Single CD157⁺ VESCs form colonies in vitro and generate donor-derived portal vein, sinusoids, and central vein endothelial cells upon transplantation in the liver. In response to injury, VESCs expand and regenerate entire vasculature structures, supporting the existence of an endothelial hierarchy within blood vessels. Genetic lineage tracing revealed that VESCs maintain large vessels and sinusoids in the normal liver for more than a year, and transplantation of VESCs rescued bleeding phenotypes in a mouse model of hemophilia. Our findings show that tissue-resident VESCs display self-renewal capacity and that vascular regeneration potential exists in peripheral blood vessels.

Hypoxia Pathway Proteins As Central Mediators of Metabolism in the Tumor Cells and Their Microenvironment

Low oxygen tension or hypoxia is a determining factor in the course of many different processes in animals, including when tissue expansion and cellular metabolism result in high oxygen demands that exceed its supply. This is mainly happening when cells actively proliferate and the proliferating mass becomes distant from the blood vessels, such as in growing tumors. Metabolic alterations in response to hypoxia can be triggered in a direct manner, such as the switch from oxidative phosphorylation to glycolysis or inhibition of fatty acid desaturation. However, as the modulated action of hypoxia-inducible factors or the oxygen sensors (prolyl hydroxylase domain-containing enzymes) can also lead to changes in enzyme expression, these metabolic changes can also be indirect. With this review, we want to summarize our current knowledge of the hypoxia-induced changes in metabolism during cancer development, how they are affected in the tumor cells and in the cells of the microenvironment, most prominently in immune cells.

Hypoxia and hypoxia inducible factor-1α are required for normal endometrial repair during menstruation

Heavy menstrual bleeding (HMB) is common and debilitating, and often requires surgery due to hormonal side effects from medical therapies. Here we show that transient, physiological hypoxia occurs in the menstrual endometrium to stabilise hypoxia inducible factor 1 (HIF-1) and drive repair of the denuded surface. We report that women with HMB have decreased endometrial HIF-1α during menstruation and prolonged menstrual bleeding. In a mouse model of simulated menses, physiological endometrial hypoxia occurs during bleeding. Maintenance of mice under hyperoxia during menses decreases HIF-1α induction and delays endometrial repair. The same effects are observed upon genetic or pharmacological reduction of endometrial HIF-1α. Conversely, artificial induction of hypoxia by pharmacological stabilisation of HIF-1α rescues the delayed endometrial repair in hypoxia-deficient mice. These data reveal a role for HIF-1 in the endometrium and suggest its pharmacological stabilisation during menses offers an effective, non-hormonal treatment for women with HMB.

Targeting tumor-associated macrophages to combat pancreatic cancer

The tumor microenvironment is replete with cells that evolve with and provide support to tumor cells during the transition to malignancy. The hijacking of the immune system in the pancreatic tumor microenvironment is suggested to contribute to the failure to date to produce significant improvements in pancreatic cancer survival by various chemotherapeutics. Regulatory T cells, myeloid derived suppressor cells, and fibroblasts, all of which constitute a complex ecology microenvironment, can suppress CD8+ T cells and NK cells, thus inhibiting effector immune responses. Tumor-associated macrophages (TAM) are versatile immune cells that can express different functional programs in response to stimuli in tumor microenvironment at different stages of pancreatic cancer development. TAM have been implicated in suppression of anti-tumorigenic immune responses, promotion of cancer cell proliferation, stimulation of tumor angiogenesis and extracellular matrix breakdown, and subsequent enhancement of tumor invasion and metastasis. Many emerging agents that have demonstrated efficacy in combating other types of tumors via modulation of macrophages in tumor microenvironments are, however, only marginally studied for pancreatic cancer prevention and treatment. A better understanding of the paradoxical roles of TAM in pancreatic cancer may pave the way to novel preventive and therapeutic approaches. Here we give an overview of the recruitment and differentiation of macrophages, TAM and pancreatic cancer progression and prognosis, as well as the potential preventive and therapeutic targets that interact with TAM for pancreatic cancer prevention and treatment.

VE-Cadherin-Mediated Epigenetic Regulation of Endothelial Gene Expression

RATIONALE

The mechanistic foundation of vascular maturation is still largely unknown. Several human pathologies are characterized by deregulated angiogenesis and unstable blood vessels. Solid tumors, for instance, get their nourishment from newly formed structurally abnormal vessels which present wide and irregular interendothelial junctions. Expression and clustering of the main endothelial-specific adherens junction protein, VEC (vascular endothelial cadherin), upregulate genes with key roles in endothelial differentiation and stability.

OBJECTIVE

We aim at understanding the molecular mechanisms through which VEC triggers the expression of a set of genes involved in endothelial differentiation and vascular stabilization.

METHODS AND RESULTS

We compared a VEC-null cell line with the same line reconstituted with VEC wild-type cDNA. VEC expression and clustering upregulated endothelial-specific genes with key roles in vascular stabilization including claudin-5, vascular endothelial-protein tyrosine phosphatase (VE-PTP), and von Willebrand factor (vWf). Mechanistically, VEC exerts this effect by inhibiting polycomb protein activity on the specific gene promoters. This is achieved by preventing nuclear translocation of FoxO1 (Forkhead box protein O1) and β-catenin, which contribute to PRC2 (polycomb repressive complex-2) binding to promoter regions of claudin-5, VE-PTP, and vWf. VEC/β-catenin complex also sequesters a core subunit of PRC2 (Ezh2 [enhancer of zeste homolog 2]) at the cell membrane, preventing its nuclear translocation. Inhibition of Ezh2/VEC association increases Ezh2 recruitment to claudin-5, VE-PTP, and vWf promoters, causing gene downregulation. RNA sequencing comparison of VEC-null and VEC-positive cells suggested a more general role of VEC in activating endothelial genes and triggering a vascular stability-related gene expression program. In pathological angiogenesis of human ovarian carcinomas, reduced VEC expression paralleled decreased levels of claudin-5 and VE-PTP.

CONCLUSIONS

These data extend the knowledge of polycomb-mediated regulation of gene expression to endothelial cell differentiation and vessel maturation. The identified mechanism opens novel therapeutic opportunities to modulate endothelial gene expression and induce vascular normalization through pharmacological inhibition of the polycomb-mediated repression system.

PHD3 Controls Lung Cancer Metastasis and Resistance to EGFR Inhibitors through TGFα

Lung cancer is the leading cause of cancer-related death worldwide, in large part due to its high propensity to metastasize and to develop therapy resistance. Adaptive responses to hypoxia and epithelial-mesenchymal transition (EMT) are linked to tumor metastasis and drug resistance, but little is known about how oxygen sensing and EMT intersect to control these hallmarks of cancer. Here, we show that the oxygen sensor PHD3 links hypoxic signaling and EMT regulation in the lung tumor microenvironment. PHD3 was repressed by signals that induce EMT and acted as a negative regulator of EMT, metastasis, and therapeutic resistance. PHD3 depletion in tumors, which can be caused by the EMT inducer TGFβ or by promoter methylation, enhanced EMT and spontaneous metastasis via HIF-dependent upregulation of the EGFR ligand TGFα. In turn, TGFα stimulated EGFR, which potentiated SMAD signaling, reinforcing EMT and metastasis. In clinical specimens of lung cancer, reduced PHD3 expression was linked to poor prognosis and to therapeutic resistance against EGFR inhibitors such as erlotinib. Reexpression of PHD3 in lung cancer cells suppressed EMT and metastasis and restored sensitivity to erlotinib. Taken together, our results establish a key function for PHD3 in metastasis and drug resistance and suggest opportunities to improve patient treatment by interfering with the feedforward signaling mechanisms activated by PHD3 silencing.Significance: This study links the oxygen sensor PHD3 to metastasis and drug resistance in cancer, with implications for therapeutic improvement by targeting this system. Cancer Res; 78(7); 1805-19. ©2018 AACR.