YBX1 integration of oncogenic PI3K/mTOR signalling regulates the fitness of malignant epithelial cells

In heterogeneous head and neck cancer (HNC), subtype-specific treatment regimens are currently missing. An integrated analysis of patient HNC subtypes using single-cell sequencing and proteome profiles reveals an epithelial-mesenchymal transition (EMT) signature within the epithelial cancer-cell population. The EMT signature coincides with PI3K/mTOR inactivation in the mesenchymal subtype. Conversely, the signature is suppressed in epithelial cells of the basal subtype which exhibits hyperactive PI3K/mTOR signalling. We further identify YBX1 phosphorylation, downstream of the PI3K/mTOR pathway, restraining basal-like cancer cell proliferation. In contrast, YBX1 acts as a safeguard against the proliferation-to-invasion switch in mesenchymal-like epithelial cancer cells, and its loss accentuates partial-EMT and in vivo invasion. Interestingly, phospho-YBX1 that is mutually exclusive to partial-EMT, emerges as a prognostic marker for overall patient outcomes. These findings create a unique opportunity to sensitise mesenchymal cancer cells to PI3K/mTOR inhibitors by shifting them towards a basal-like subtype as a promising therapeutic approach against HNC.

Radiation therapy attenuates lymphatic vessel repair by reducing VEGFR-3 signalling

Introduction: Surgery and radiotherapy are key cancer treatments and the leading causes of damage to the lymphatics, a vascular network critical to fluid homeostasis and immunity. The clinical manifestation of this damage constitutes a devastating side-effect of cancer treatment, known as lymphoedema. Lymphoedema is a chronic condition evolving from the accumulation of interstitial fluid due to impaired drainage via the lymphatics and is recognised to contribute significant morbidity to patients who survive their cancer. Nevertheless, the molecular mechanisms underlying the damage inflicted on lymphatic vessels, and particularly the lymphatic endothelial cells (LEC) that constitute them, by these treatment modalities, remain poorly understood. Methods: We used a combination of cell based assays, biochemistry and animal models of lymphatic injury to examine the molecular mechanisms behind LEC injury and the subsequent effects on lymphatic vessels, particularly the role of the VEGF-C/VEGF-D/VEGFR-3 lymphangiogenic signalling pathway, in lymphatic injury underpinning the development of lymphoedema. Results: We demonstrate that radiotherapy selectively impairs key LEC functions needed for new lymphatic vessel growth (lymphangiogenesis). This effect is mediated by attenuation of VEGFR-3 signalling and downstream signalling cascades. VEGFR-3 protein levels were downregulated in LEC that were exposed to radiation, and LEC were therefore selectively less responsive to VEGF-C and VEGF-D. These findings were validated in our animal models of radiation and surgical injury. Discussion: Our data provide mechanistic insight into injury sustained by LEC and lymphatics during surgical and radiotherapy cancer treatments and underscore the need for alternative non-VEGF-C/VEGFR-3-based therapies to treat lymphoedema.

The cellular and molecular mediators of metastasis to the lung

Organ-specific metastasis to secondary organs is dependent on the formation of a supportive pre-metastatic niche. This tissue-specific microenvironmental response is thought to be mediated by mutational and epigenetic changes to primary tumour cells resulting in altered cross-talk between cell types. This response is augmented through the release of tumour and stromal signalling mediators including cytokines, chemokines, exosomes and growth factors. Although researchers have elucidated some of the cancer-promoting features that are bespoke to organotropic metastasis to the lungs, it remains unclear if these are organ-specific or generic between organs. Understanding the mechanisms that mediate the metastasis-promoting synergy between the host microenvironment, immunity, and pulmonary structures may elucidate predictive, prognostic and therapeutic markers that could be targeted to reduce the metastatic burden of disease. Herein, we give an updated summary of the known cellular and molecular mechanisms that contribute to the formation of the lung pre-metastatic niche and tissue-specific metastasis.

Brain Vascular Microenvironments in Cancer Metastasis

Primary tumours, particularly from major solid organs, are able to disseminate into the blood and lymphatic system and spread to distant sites. These secondary metastases to other major organs are the most lethal aspect of cancer, accounting for the majority of cancer deaths. The brain is a frequent site of metastasis, and brain metastases are often fatal due to the critical role of the nervous system and the limited options for treatment, including surgery. This creates a need to further understand the complex cell and molecular biology associated with the establishment of brain metastasis, including the changes to the environment of the brain to enable the arrival and growth of tumour cells. Local changes in the vascular network, immune system and stromal components all have the potential to recruit and foster metastatic tumour cells. This review summarises our current understanding of brain vascular microenvironments, fluid circulation and drainage in the context of brain metastases, as well as commenting on current cutting-edge experimental approaches used to investigate changes in vascular environments and alterations in specialised subsets of blood and lymphatic vessel cells during cancer spread to the brain.

Three-dimensional CRISPR screening reveals epigenetic interaction with anti-angiogenic therapy

Angiogenesis underlies development, physiology and pathogenesis of cancer, eye and cardiovascular diseases. Inhibiting aberrant angiogenesis using anti-angiogenic therapy (AAT) has been successful in the clinical treatment of cancer and eye diseases. However, resistance to AAT inevitably occurs and its molecular basis remains poorly understood. Here, we uncover molecular modifiers of the blood endothelial cell (EC) response to a widely used AAT bevacizumab by performing a pooled genetic screen using three-dimensional microcarrier-based cell culture and CRISPR–Cas9. Functional inhibition of the epigenetic reader BET family of proteins BRD2/3/4 shows unexpected mitigating effects on EC survival and/or proliferation upon VEGFA blockade. Moreover, transcriptomic and pathway analyses reveal an interaction between epigenetic regulation and anti-angiogenesis, which may affect chromosomal structure and activity in ECs via the cell cycle regulator CDC25B phosphatase. Collectively, our findings provide insight into epigenetic regulation of the EC response to VEGFA blockade and may facilitate development of quality biomarkers and strategies for overcoming resistance to AAT.

Through three-dimensional CRISPR screening, He et al. report that functional inhibition of BET family of proteins BRD2/3/4 shows mitigating effects on blood endothelial cell (EC) survival and/or proliferation upon VEGFA blockade. An interaction between epigenetic regulation and anti-angiogenesis, which may affect chromosomal structure and activity in ECs through CDC25B phosphatase, is potentially involved with EC resistance to anti-angiogenic therapy.

Pkd1 and Wnt5a genetically interact to control lymphatic vascular morphogenesis in mice

BACKGROUND

Lymphatic vascular development is regulated by well-characterized signaling and transcriptional pathways. These pathways regulate lymphatic endothelial cell (LEC) migration, motility, polarity, and morphogenesis. Canonical and non-canonical WNT signaling pathways are known to control LEC polarity and development of lymphatic vessels and valves. PKD1, encoding Polycystin-1, is the most commonly mutated gene in polycystic kidney disease but has also been shown to be essential in lymphatic vascular morphogenesis. The mechanism by which Pkd1 acts during lymphangiogenesis remains unclear.

RESULTS

Here we find that loss of non-canonical WNT signaling components Wnt5a and Ryk phenocopy lymphatic defects seen in Pkd1 knockout mice. To investigate genetic interaction, we generated Pkd1;Wnt5a double knockout mice. Loss of Wnt5a suppressed phenotypes seen in the lymphatic vasculature of Pkd1^-/- mice and Pkd1 deletion suppressed phenotypes observed in Wnt5a^-/- mice. Thus, we report mutually suppressive roles for Pkd1 and Wnt5a, with developing lymphatic networks restored to a more wild type state in double mutant mice. This genetic interaction between Pkd1 and the non-canonical WNT signaling pathway ultimately controls LEC polarity and the morphogenesis of developing vessel networks.

CONCLUSION

Our work suggests that Pkd1 acts at least in part by regulating non-canonical WNT signaling during the formation of lymphatic vascular networks.

Control of Gene Expression by Exosome-Derived Non-Coding RNAs in Cancer Angiogenesis and Lymphangiogenesis

Abstract: Tumour angiogenesis and lymphangiogenesis are hallmarks of cancer and have been associated with tumour progression, tumour metastasis and poor patient prognosis. Many factors regulate angiogenesis and lymphangiogenesis in cancer including non-coding RNAs which are a category of RNAs that do not encode proteins and have important regulatory functions at transcriptional and post-transcriptional levels. Non-coding RNAs can be encapsulated in extracellular vesicles called exosomes which are secreted by tumour cells or other cells in the tumour microenvironment and can then be taken up by the endothelial cells of blood vessels and lymphatic vessels. The "delivery" of these non-coding RNAs to endothelial cells in tumours can facilitate tumour angiogenesis and lymphangiogenesis. Here we review recent findings about exosomal non-coding RNAs, specifically microRNAs and long non-coding RNAs, which regulate tumour angiogenesis and lymphangiogenesis in cancer. We then focus on the potential use of these molecules as cancer biomarkers and opportunities for exploiting ncRNAs for the treatment of cancer.

RYK-mediated filopodial pathfinding facilitates midgut elongation

Between embryonic days 10.5 and 14.5, active proliferation drives rapid elongation of the murine midgut epithelial tube. Within this pseudostratified epithelium, nuclei synthesize DNA near the basal surface and move apically to divide. After mitosis, the majority of daughter cells extend a long, basally oriented filopodial protrusion, building a de novo path along which their nuclei can return to the basal side. WNT5A, which is secreted by surrounding mesenchymal cells, acts as a guidance cue to orchestrate this epithelial pathfinding behavior, but how this signal is received by epithelial cells is unknown. Here, we have investigated two known WNT5A receptors: ROR2 and RYK. We found that epithelial ROR2 is dispensable for midgut elongation. However, loss of Ryk phenocopies the Wnt5a ^-/- phenotype, perturbing post-mitotic pathfinding and leading to apoptosis. These studies reveal that the ligand-receptor pair WNT5A-RYK acts as a navigation system to instruct filopodial pathfinding, a process that is crucial for continuous cell cycling to fuel rapid midgut elongation.

Evolutionary Differences in the Vegf/Vegfr Code Reveal Organotypic Roles for the Endothelial Cell Receptor Kdr in Developmental Lymphangiogenesis

Lymphatic vascular development establishes embryonic and adult tissue fluid balance and is integral in disease. In diverse vertebrate organs, lymphatic vessels display organotypic function and develop in an organ-specific manner. In all settings, developmental lymphangiogenesis is considered driven by vascular endothelial growth factor (VEGF) receptor-3 (VEGFR3), whereas a role for VEGFR2 remains to be fully explored. Here, we define the zebrafish Vegf/Vegfr code in receptor binding studies. We find that while Vegfd directs craniofacial lymphangiogenesis, it binds Kdr (a VEGFR2 homolog) but surprisingly, unlike in mammals, does not bind Flt4 (VEGFR3). Epistatic analyses and characterization of a kdr mutant confirm receptor-binding analyses, demonstrating that Kdr is indispensible for rostral craniofacial lymphangiogenesis, but not caudal trunk lymphangiogenesis, in which Flt4 is central. We further demonstrate an unexpected yet essential role for Kdr in inducing lymphatic endothelial cell fate. This work reveals evolutionary divergence in the Vegf/Vegfr code that uncovers spatially restricted mechanisms of developmental lymphangiogenesis.

Non-canonical Wnt Signaling through Ryk Regulates the Generation of Somatostatin- and Parvalbumin-Expressing Cortical Interneurons

GABAergic interneurons have many important functions in cortical circuitry, a reflection of their cell diversity. The developmental origins of this diversity are poorly understood. Here, we identify rostral-caudal regionality in Wnt exposure within the interneuron progenitor zone delineating the specification of the two main interneuron subclasses. Caudally situated medial ganglionic eminence (MGE) progenitors receive high levels of Wnt signaling and give rise to somatostatin (SST)-expressing cortical interneurons. By contrast, parvalbumin (PV)-expressing basket cells originate mostly from the rostral MGE, where Wnt signaling is attenuated. Interestingly, rather than canonical signaling through β-catenin, signaling via the non-canonical Wnt receptor Ryk regulates interneuron cell-fate specification in vivo and in vitro. Indeed, gain of function of Ryk intracellular domain signaling regulates SST and PV fate in a dose-dependent manner, suggesting that Ryk signaling acts in a graded fashion. These data reveal an important role for non-canonical Wnt-Ryk signaling in establishing the correct ratios of cortical interneuron subtypes.

The Interplay Between Lymphatic Vessels and Chemokines

Chemokines are a family of small protein cytokines that act as chemoattractants to migrating cells, in particular those of the immune system. They are categorized functionally as either homeostatic, constitutively produced by tissues for basal levels of cell migration, or inflammatory, where they are generated in association with a pathological inflammatory response. While the extravasation of leukocytes via blood vessels is a key step in cells entering the tissues, the lymphatic vessels also serve as a conduit for cells that are recruited and localized through chemoattractant gradients. Furthermore, the growth and remodeling of lymphatic vessels in pathologies is influenced by chemokines and their receptors expressed by lymphatic endothelial cells (LECs) in and around the pathological tissue. In this review we summarize the diverse role played by specific chemokines and their receptors in shaping the interaction of lymphatic vessels, immune cells, and other pathological cell types in physiology and disease.

CCL27/CCL28-CCR10 Chemokine Signaling Mediates Migration of Lymphatic Endothelial Cells

Metastasis via the lymphatic vasculature is an important step in cancer progression. The formation of new lymphatic vessels (lymphangiogenesis), or remodeling of existing lymphatics, is thought to facilitate the entry and transport of tumor cells into lymphatic vessels and on to distant organs. The migration of lymphatic endothelial cells (LEC) toward guidance cues is critical for lymphangiogenesis. While chemokines are known to provide directional navigation for migrating immune cells, their role in mediating LEC migration during tumor-associated lymphangiogenesis is not well defined. Here, we undertook gene profiling studies to identify chemokine-chemokine receptor pairs that are involved in tumor lymphangiogenesis associated with lymph node metastasis. CCL27 and CCL28 were expressed in tumor cells with metastatic potential, while their cognate receptor, CCR10, was expressed by LECs and upregulated by the lymphangiogenic growth factor VEGFD and the proinflammatory cytokine TNFα. Migration assays demonstrated that LECs are attracted to both CCL27 and CCL28 in a CCR10-dependent manner, while abnormal lymphatic vessel patterning in CCR10-deficient mice confirmed the significant role of CCR10 in lymphatic patterning. In vivo analyses showed that LECs are recruited to a CCL27 or CCL28 source, while VEGFD was required in combination with these chemokines to enable formation of coherent lymphatic vessels. Moreover, tumor xenograft experiments demonstrated that even though CCL27 expression by tumors enhanced LEC recruitment, the ability to metastasize was dependent on the expression of VEGFD. These studies demonstrate that CCL27 and CCL28 signaling through CCR10 may cooperate with inflammatory mediators and VEGFD during tumor lymphangiogenesis. SIGNIFICANCE: The study shows that the remodeling of lymphatic vessels in cancer is influenced by CCL27 and CCL28 chemokines, which may provide a future target to modulate metastatic spread.

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

Abstract 1: A kinome-wide CRISPR screen reveals BET inhibition-associated endothelial cell resistance to anti-angiogenic therapy

Angiogenesis inhibition is a useful strategy for treating cancer. However, the efficacy of anti-angiogenic therapy (AAT) in clinical oncology has been limited largely by highly variable patient response and the inevitable occurrence of resistance. The modest patient benefits have underscored a pressing need for qualified biomarkers and better knowledge of resistance mechanisms. Blood endothelial cells (ECs) are one of the main targets of AAT in the tumor microenvironment. Hence, understanding the EC response to AAT will provide insight into tumor response. To identify molecular modifiers of the EC response to AAT (in this study, bevacizumab, a humanized neutralizing anti-VEGF-A monoclonal antibody), we developed a high-throughput genetic screening platform. This involved a three-dimensional microcarrier-based culture system, CRISPR-Cas9-driven gene loss-of-function (LOF) and VEGF-A-dependent serum-free culture conditions for response modifiers. A pooled kinome-wide CRISPR-Cas9-based screen of 763 genes (with four single guide RNAs/sgRNAs targeting each gene) identified 18 candidate genes that upon LOF (represented by sgRNAs) were significantly enriched or depleted in the bevacizumab versus control treatment arm (P ≤ 0.005, FDR ≤ 0.3). Further candidate evaluation using siRNAs validated six genes whose knockdown conferred EC resistance or sensitization to bevacizumab (P < 0.05). Of these, knockdown of BRD2 or BRD3, which encode the epigenetic reader bromodomain-containing protein 2 or 3 (BRD2 or BRD3), respectively, conferred EC resistance to bevacizumab. The bromodomain and extraterminal domain (BET) inhibitors JQ1 and I-BET762, which selectively target the BET family of proteins (BRD2, BRD3, BRD4 and BRDT), reproduced the results of BRD2 or BRD3 LOF, with a more prominent phenotype (P < 0.05). Drug dose-response assessment indicated an anti-angiogenic effect of BET inhibitors regardless of the presence of bevacizumab. This inhibitory effect was unexpectedly attenuated when cells were co-treated with bevacizumab under VEGF-A-dependent conditions. Experiments to investigate the mechanistic basis for this phenotype of resistance are ongoing and include differential gene expression analysis using RNA-Seq and in vivo evaluation. Applying a non-biased approach to identify molecular modifiers of the EC response to AAT, we demonstrate in this study that BET inhibition is unexpectedly associated with resistance to bevacizumab, despite BET inhibition alone having an anti-angiogenic effect. These observations prompt further evaluation of epigenetic regulation in tumor angiogenesis, particularly in the context of interaction between BET inhibition and VEGF blockade. Clinically, these findings may facilitate development of potential predictive and/or response biomarkers and strategies to overcome resistance to AAT and/or BET inhibitors.

Citation Format: Michael Y. He, Michael M. Halford, Marc G. Achen, Steven A. Stacker. A kinome-wide CRISPR screen reveals BET inhibition-associated endothelial cell resistance to anti-angiogenic therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1.

Exit Stage Left: A Tumor Cell's Journey from Lymph Node to Beyond

Even though we have known for over 250 years that cancers spread to regional lymph nodes (LNs) and distant organs, the fundamental question of which anatomical routes are taken by tumor cells has remained a mystery. Two recently published papers in Science, by Pereira et al. and Brown et al., directly address this important issue in tumor biology by assessing the capacity of tumor cells in LNs to spread to distant sites.

Deficiency of the Wnt receptor Ryk causes multiple cardiac and outflow tract defects

Ryk is a member of the receptor tyrosine kinase (RTK) family of proteins that control and regulate cellular processes. It is distinguished by binding Wnt ligands and having no detectable intrinsic protein tyrosine kinase activity suggesting Ryk is a pseudokinase. Here, we show an essential role for Ryk in directing morphogenetic events required for normal cardiac development through the examination of Ryk-deficient mice. We employed vascular corrosion casting, vascular perfusion with contrast dye, and immunohistochemistry to characterize cardiovascular and pharyngeal defects in Ryk^-/- embryos. Ryk^-/- mice exhibit a variety of malformations of the heart and outflow tract that resemble human congenital heart defects. This included stenosis and interruption of the aortic arch, ventriculoarterial malalignment, ventricular septal defects and abnormal pharyngeal arch artery remodelling. This study therefore defines a key intersection between a subset of growth factor receptors involved in planar cell polarity signalling, the Wnt family and mammalian cardiovascular development.

The biochemistry, signalling and disease relevance of RYK and other WNT-binding receptor tyrosine kinases

The receptor tyrosine kinases (RTKs) are a well-characterized family of growth factor receptors that have central roles in human disease and are frequently therapeutically targeted. The RYK, ROR, PTK7 and MuSK subfamilies make up an understudied subset of WNT-binding RTKs. Numerous developmental, stem cell and pathological roles of WNTs, in particular WNT5A, involve signalling via these WNT receptors. The WNT-binding RTKs have highly context-dependent signalling outputs and stimulate the β-catenin-dependent, planar cell polarity and/or WNT/Ca²⁺ pathways. RYK, ROR and PTK7 members have a pseudokinase domain in their intracellular regions. Alternative signalling mechanisms, including proteolytic cleavage and protein scaffolding functions, have been identified for these receptors. This review explores the structure, signalling, physiological and pathological roles of RYK, with particular attention paid to cancer and the possibility of therapeutically targeting RYK. The other WNT-binding RTKs are compared with RYK throughout to highlight the similarities and differences within this subset of WNT receptors.

The fibrinolysis inhibitor α2-antiplasmin restricts lymphatic remodelling and metastasis in a mouse model of cancer

Remodelling of lymphatic vessels in tumours facilitates metastasis to lymph nodes. The growth factors VEGF-C and VEGF-D are well known inducers of lymphatic remodelling and metastasis in cancer. They are initially produced as full-length proteins requiring proteolytic processing in order to bind VEGF receptors with high affinity and thereby promote lymphatic remodelling. The fibrinolytic protease plasmin promotes processing of VEGF-C and VEGF-D in vitro, but its role in processing them in cancer was unknown. Here we explore plasmin's role in proteolytically activating VEGF-D in vivo, and promoting lymphatic remodelling and metastasis in cancer, by co-expressing the plasmin inhibitor α₂-antiplasmin with VEGF-D in a mouse tumour model. We show that α₂-antiplasmin restricts activation of VEGF-D, enlargement of intra-tumoural lymphatics and occurrence of lymph node metastasis. Our findings indicate that the fibrinolytic system influences lymphatic remodelling in tumours which is consistent with previous clinicopathological observations correlating fibrinolytic components with cancer metastasis.

Systematic high-content genome-wide RNAi screens of endothelial cell migration and morphology

Many cell types undergo migration during embryogenesis and disease. Endothelial cells line blood vessels and lymphatics, which migrate during development as part of angiogenesis, lymphangiogenesis and other types of vessel remodelling. These processes are also important in wound healing, cancer metastasis and cardiovascular conditions. However, the molecular control of endothelial cell migration is poorly understood. Here, we present a dataset containing siRNA screens that identify known and novel components of signalling pathways regulating migration of lymphatic endothelial cells. These components are compared to signalling in blood vascular endothelial cells. Further, using high-content microscopy, we captured a dataset of images of migrating cells following transfection with a genome-wide siRNA library. These datasets are suitable for the identification and analysis of genes involved in endothelial cell migration and morphology, and for computational approaches to identify signalling networks controlling the migratory response and integration of cell morphology, gene function and cell signaling. This may facilitate identification of protein targets for therapeutically modulating angiogenesis and lymphangiogenesis in the context of human disease.

Vegfd modulates both angiogenesis and lymphangiogenesis during zebrafish embryonic development

Vascular endothelial growth factors (VEGFs) control angiogenesis and lymphangiogenesis during development and in pathological conditions. In the zebrafish trunk, Vegfa controls the formation of intersegmental arteries by primary angiogenesis and Vegfc is essential for secondary angiogenesis, giving rise to veins and lymphatics. Vegfd has been largely thought of as dispensable for vascular development in vertebrates. Here, we generated a zebrafish vegfd mutant by genome editing. vegfd mutants display significant defects in facial lymphangiogenesis independent of vegfc function. Strikingly, we find that vegfc and vegfd cooperatively control lymphangiogenesis throughout the embryo, including during the formation of the trunk lymphatic vasculature. Interestingly, we find that vegfd and vegfc also redundantly drive artery hyperbranching phenotypes observed upon depletion of Flt1 or Dll4. Epistasis and biochemical binding assays suggest that, during primary angiogenesis, Vegfd influences these phenotypes through Kdr (Vegfr2) rather than Flt4 (Vegfr3). These data demonstrate that, rather than being dispensable during development, Vegfd plays context-specific indispensable and also compensatory roles during both blood vessel angiogenesis and lymphangiogenesis.

The Role of the Tumor Vasculature in the Host Immune Response: Implications for Therapeutic Strategies Targeting the Tumor Microenvironment

Recently developed cancer immunotherapy approaches including immune checkpoint inhibitors and chimeric antigen receptor T cell transfer are showing promising results both in trials and in clinical practice. These approaches reflect increasing recognition of the crucial role of the tumor microenvironment in cancer development and progression. Cancer cells do not act alone, but develop a complex relationship with the environment in which they reside. The host immune response to tumors is critical to the success of immunotherapy; however, the determinants of this response are incompletely understood. The immune cell infiltrate in tumors varies widely in density, composition, and clinical significance. The tumor vasculature is a key component of the microenvironment that can influence tumor behavior and treatment response and can be targeted through the use of antiangiogenic drugs. Blood vascular and lymphatic endothelial cells have important roles in the trafficking of immune cells, controlling the microenvironment, and modulating the immune response. Improving access to the tumor through vascular alteration with antiangiogenic drugs may prove an effective combinatorial strategy with immunotherapy approaches and might be applicable to many tumor types. In this review, we briefly discuss the host's immune response to cancer and the treatment strategies utilizing this response, before focusing on the pathological features of tumor blood and lymphatic vessels and the contribution these might make to tumor immune evasion.

Differential Receptor Binding and Regulatory Mechanisms for the Lymphangiogenic Growth Factors Vascular Endothelial Growth Factor (VEGF)-C and -D

VEGF-C and VEGF-D are secreted glycoproteins that induce angiogenesis and lymphangiogenesis in cancer, thereby promoting tumor growth and spread. They exhibit structural homology and activate VEGFR-2 and VEGFR-3, receptors on endothelial cells that signal for growth of blood vessels and lymphatics. VEGF-C and VEGF-D were thought to exhibit similar bioactivities, yet recent studies indicated distinct signaling mechanisms (e.g. tumor-derived VEGF-C promoted expression of the prostaglandin biosynthetic enzyme COX-2 in lymphatics, a response thought to facilitate metastasis via the lymphatic vasculature, whereas VEGF-D did not). Here we explore the basis of the distinct bioactivities of VEGF-D using a neutralizing antibody, peptide mapping, and mutagenesis to demonstrate that the N-terminal α-helix of mature VEGF-D (Phe⁹³–Arg¹⁰⁸) is critical for binding VEGFR-2 and VEGFR-3. Importantly, the N-terminal part of this α-helix, from Phe⁹³ to Thr⁹⁸, is required for binding VEGFR-3 but not VEGFR-2. Surprisingly, the corresponding part of the α-helix in mature VEGF-C did not influence binding to either VEGFR-2 or VEGFR-3, indicating distinct determinants of receptor binding by these growth factors. A variant of mature VEGF-D harboring a mutation in the N-terminal α-helix, D103A, exhibited enhanced potency for activating VEGFR-3, was able to promote increased COX-2 mRNA levels in lymphatic endothelial cells, and had enhanced capacity to induce lymphatic sprouting in vivo. This mutant may be useful for developing protein-based therapeutics to drive lymphangiogenesis in clinical settings, such as lymphedema. Our studies shed light on the VEGF-D structure/function relationship and provide a basis for understanding functional differences compared with VEGF-C.

VEGF-D promotes pulmonary oedema in hyperoxic acute lung injury

Leakage of fluid from blood vessels, leading to oedema, is a key feature of many diseases including hyperoxic acute lung injury (HALI), which can occur when patients are ventilated with high concentrations of oxygen (hyperoxia). The molecular mechanisms driving vascular leak and oedema in HALI are poorly understood. VEGF‐D is a protein that promotes blood vessel leak and oedema when overexpressed in tissues, but the role of endogenous VEGF‐D in pathological oedema was unknown. To address these issues, we exposed Vegfd‐deficient mice to hyperoxia. The resulting pulmonary oedema in Vegfd‐deficient mice was substantially reduced compared to wild‐type, as was the protein content of bronchoalveolar lavage fluid, consistent with reduced vascular leak. Vegf‐d and its receptor Vegfr‐3 were more highly expressed in lungs of hyperoxic, versus normoxic, wild‐type mice, indicating that components of the Vegf‐d signalling pathway are up‐regulated in hyperoxia. Importantly, VEGF‐D and its receptors were co‐localized on blood vessels in clinical samples of human lungs exposed to hyperoxia; hence, VEGF‐D may act directly on blood vessels to promote fluid leak. Our studies show that Vegf‐d promotes oedema in response to hyperoxia in mice and support the hypothesis that VEGF‐D signalling promotes vascular leak in human HALI. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

A Simple Bioassay for the Evaluation of Vascular Endothelial Growth Factors

The analysis of receptor tyrosine kinases and their interacting ligands involved in vascular biology is often challenging due to the constitutive expression of families of related receptors, a broad range of related ligands and the difficulty of dealing with primary cultures of specialized endothelial cells. Here we describe a bioassay for the detection of ligands to the vascular endothelial growth factor receptor-2 (VEGFR-2), a key transducer of signals that promote angiogenesis and lymphangiogenesis. A cDNA encoding a fusion of the extracellular (ligand-binding) region of VEGFR-2 with the transmembrane and cytoplasmic regions of the erythropoietin receptor (EpoR) is expressed in the factor-dependent cell line Ba/F3. This cell line grows in the presence of interleukin-3 (IL-3) and withdrawal of this factor results in death of the cells within 24 hr. Expression of the VEGFR-2/EpoR receptor fusion provides an alternative mechanism to promote survival and potentially proliferation of stably transfected Ba/F3 cells in the presence of a ligand capable of binding and cross-linking the extracellular portion of the fusion protein (i.e., one that can cross-link the VEGFR-2 extracellular region). The assay can be performed in two ways: a semi-quantitative approach in which small volumes of ligand and cells permit a rapid result in 24 hr, and a quantitative approach involving surrogate markers of a viable cell number. The assay is relatively easy to perform, is highly responsive to known VEGFR-2 ligands and can accommodate extracellular inhibitors of VEGFR-2 signaling such as monoclonal antibodies to the receptor or ligands, and soluble ligand traps.

Intestinal-specific activatable Myb initiates colon tumorigenesis in mice

Transcription factor Myb is overexpressed in most colorectal cancers (CRC). Patients with CRC expressing the highest Myb are more likely to relapse. We previously showed that mono-allelic loss of Myb in an Adenomatous polyposis coli (APC)-driven CRC mouse model (Apc^Min/+) significantly improves survival. Here we directly investigated the association of Myb with poor prognosis and how Myb co-operates with tumor suppressor genes (TSGs) (Apc) and cell cycle regulator, p27. Here we generated the first intestinal-specific, inducible transgenic model; a MybER transgene encoding a tamoxifen-inducible fusion protein between Myb and the estrogen receptor-α ligand-binding domain driven by the intestinal-specific promoter, Gpa33. This was to mimic human CRC with constitutive Myb activity in a highly tractable mouse model. We confirmed that the transgene was faithfully expressed and inducible in intestinal stem cells (ISCs) before embarking on carcinogenesis studies. Activation of the MybER did not change colon homeostasis unless one p27 allele was lost. We then established that MybER activation during CRC initiation using a pro-carcinogen treatment, azoxymethane (AOM), augmented most measured aspects of ISC gene expression and function and accelerated tumorigenesis in mice. CRC-associated symptoms of patients including intestinal bleeding and anaemia were faithfully mimicked in AOM-treated MybER transgenic mice and implicated hypoxia and vessel leakage identifying an additional pathogenic role for Myb. Collectively, the results suggest that Myb expands the ISC pool within which CRC is initiated while co-operating with TSG loss. Myb further exacerbates CRC pathology partly explaining why high MYB is a predictor of worse patient outcome.

A phase Ib/II translational study of sunitinib with neoadjuvant radiotherapy in soft-tissue sarcoma

Background:

Preoperative radiotherapy (RT) is commonly used to treat localised soft-tissue sarcomas (STS). Hypoxia is an important determinant of radioresistance. Whether antiangiogenic therapy can ‘normalise' tumour vasculature, thereby improving oxygenation, remains unknown.

Methods:

Two cohorts were prospectively enrolled. Cohort A evaluated the implications of hypoxia in STS, using the hypoxic tracer ¹⁸F-azomycin arabinoside (FAZA-PET). In cohort B, sunitinib was added to preoperative RT in a dose-finding phase 1b/2 design.

Results:

In cohort A, 13 out of 23 tumours were hypoxic (FAZA-PET), correlating with metabolic activity (r²=0.85; P<0.001). Two-year progression-free (PFS) and overall (OS) survival were 61% (95% CI: 0.44–0.84) and 87% (95% CI: 0.74–1.00), respectively. Hypoxia was associated with radioresistance (P=0.012), higher local recurrence (Hazard ratio (HR): 10.2; P=0.02), PFS (HR: 8.4; P=0.02), and OS (HR: 41.4; P<0.04). In Cohort B, seven patients received sunitinib at dose level (DL): 0 (50 mg per day for 2 weeks before RT; 25 mg per day during RT) and two patients received DL: −1 (37.5 mg per day for entire period). Dose-limiting toxicities were observed in 4 out of 7 patients at DL 0 and 2 out of 2 patients at DL −1, resulting in premature study closure. Although there was no difference in PFS or OS, patients receiving sunitinib had higher local failure (HR: 8.1; P=0.004).

Conclusion:

In STS, hypoxia is associated with adverse outcomes. The combination of sunitinib with preoperative RT resulted in unacceptable toxicities, and higher local relapse rates.

Lymphangiogenesis and lymphatic vessel remodelling in cancer

The generation of new lymphatic vessels through lymphangiogenesis and the remodelling of existing lymphatics are thought to be important steps in cancer metastasis. The past decade has been exciting in terms of research into the molecular and cellular biology of lymphatic vessels in cancer, and it has been shown that the molecular control of tumour lymphangiogenesis has similarities to that of tumour angiogenesis. Nevertheless, there are significant mechanistic differences between these biological processes. We are now developing a greater understanding of the specific roles of distinct lymphatic vessel subtypes in cancer, and this provides opportunities to improve diagnostic and therapeutic approaches that aim to restrict the progression of cancer.

Ccbe1 regulates Vegfc-mediated induction of Vegfr3 signaling during embryonic lymphangiogenesis

The VEGFC/VEGFR3 signaling pathway is essential for lymphangiogenesis (the formation of lymphatic vessels from pre-existing vasculature) during embryonic development, tissue regeneration and tumor progression. The recently identified secreted protein CCBE1 is indispensible for lymphangiogenesis during development. The role of CCBE1 orthologs is highly conserved in zebrafish, mice and humans with mutations in CCBE1 causing generalized lymphatic dysplasia and lymphedema (Hennekam syndrome). To date, the mechanism by which CCBE1 acts remains unknown. Here, we find that ccbe1 genetically interacts with both vegfc and vegfr3 in zebrafish. In the embryo, phenotypes driven by increased Vegfc are suppressed in the absence of Ccbe1, and Vegfc-driven sprouting is enhanced by local Ccbe1 overexpression. Moreover, Vegfc- and Vegfr3-dependent Erk signaling is impaired in the absence of Ccbe1. Finally, CCBE1 is capable of upregulating the levels of fully processed, mature VEGFC in vitro and the overexpression of mature VEGFC rescues ccbe1 loss-of-function phenotypes in zebrafish. Taken together, these data identify Ccbe1 as a crucial component of the Vegfc/Vegfr3 pathway in the embryo.

Wnt5a induces Ryk-dependent and -independent effects on callosal axon and dendrite growth

The non-canonical Wnt receptor, Ryk, promotes chemorepulsive axon guidance in the developing mouse brain and spinal cord in response to Wnt5a. Ryk has also been identified as a major suppressor of axonal regrowth after spinal cord injury. Thus, a comprehensive understanding of how growing axons and dendrites respond to Wnt5a-mediated Ryk activation is required if we are to overcome this detrimental activity. Here we undertook a detailed analysis of the effect of Wnt5a/Ryk interactions on axonal and dendritic growth in dissociated embryonic mouse cortical neuron cultures, focusing on callosal neurons known to be responsive to Ryk-induced chemorepulsion. We show that Ryk inhibits axonal growth in response to Wnt5a. We also show that Wnt5a inhibits dendrite growth independently of Ryk. However, this inhibition is relieved when Ryk is present. Therefore, Wnt5a-mediated Ryk activation triggers divergent responses in callosal axons and dendrites in the in vitro context.

Abstract A113: Chronic stress promotes lymph node metastasis through beta-adrenergic regulation of lymphangiogenesis

Lymphangiogenesis drives breast cancer metastasis to lymph nodes. However, the physiological pathways that regulate lymphangiogenesis and lymph node metastasis are yet to be defined. We have previously shown that chronic stress increased metastasis of primary tumour cells to lymph nodes via beta-adrenergic receptor signaling. Consistent with a critical role for beta-adrenergic signaling in cancer progression, recent clinical studies found that blockade of beta-adrenergic activation protected women with triple negative breast cancer from distant metastasis.

To investigate if the beta-adrenergic pathway promotes metastasis by impacting lymphangiogenesis, we explored the effect of restraint stress or pharmacological activation of beta-adrenergic pathways in an orthotopic xenograft model of triple negative breast cancer. To physiologically activate beta-adrenergic signaling, mice were subjected to 2 hours of daily restraint for 7 days prior to tumor cell inoculation and 14 days thereafter. Serial bioluminescence imaging revealed chronic stress reduced time to lymph node metastasis and increased tumor cell load in draining lymph nodes. Stress increased the expression of lymphangiogenic factor VEGF-C and its receptor Vefgr-3 and increased lymphangiogenesis within primary tumors. Pharmacological activation of beta-adrenergic signaling with isoproterenol similarly increased lymphangiogenesis and metastasis.

Prostaglandin-mediated dilation of lymphatic collector vessels was recently linked to increased breast cancer metastasis. We found stress increased expression of COX-2, the rate limiting enzyme in prostaglandin production, and increased dilation of lymphatic vessels that link primary tumors to draining lymph nodes. Treatment with COX-2 inhibitor celecoxib reversed stress-induced lymph vessel dilation and similarly blocked stress-enhanced lymph node metastasis and tumor lymphangiogenesis.

Together, these data show that beta-adrenergic receptor signalling may be an important effector pathway of stress-enhanced lymphangiogenesis and LN metastasis and that beta-blockade of lymphangiogenesis may be an important mechanism in protecting women with breast cancer from the adverse effects of stress biology.

Citation Format: Caroline P. Le, Matthew A. Pimentel, Corina Kim, Cameron J. Nowell, Tara Karnezis, Ming G. Chai, Marco Herald, Steven A. Stacker, Erica K. Sloan. Chronic stress promotes lymph node metastasis through beta-adrenergic regulation of lymphangiogenesis. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A113.

A fully human inhibitory monoclonal antibody to the Wnt receptor RYK

RYK is an unusual member of the receptor tyrosine kinase (RTK) family that is classified as a putative pseudokinase. RYK regulates fundamental biological processes including cell differentiation, migration and target selection, axon outgrowth and pathfinding by transducing signals across the plasma membrane in response to the high affinity binding of Wnt family ligands to its extracellular Wnt inhibitory factor (WIF) domain. Here we report the generation and initial characterization of a fully human inhibitory monoclonal antibody to the human RYK WIF domain. From a naïve human single chain fragment variable (scFv) phage display library, we identified anti-RYK WIF domain–specific scFvs then screened for those that could compete with Wnt3a for binding. Production of a fully human IgG_1κ from an inhibitory scFv yielded a monoclonal antibody that inhibits Wnt5a-responsive RYK function in a neurite outgrowth assay. This antibody will have immediate applications for modulating RYK function in a range of settings including development and adult homeostasis, with significant potential for therapeutic use in human pathologies.

Ryk, a receptor regulating Wnt5a-mediated neurogenesis and axon morphogenesis of ventral midbrain dopaminergic neurons

Ryk is an atypical transmembrane receptor tyrosine kinase that has been shown to play multiple roles in development through the modulation of Wnt signaling. Within the developing ventral midbrain (VM), Wnts have been shown to contribute to the proliferation, differentiation, and connectivity of dopamine (DA) neurons; however, the Wnt-related receptors regulating these events remain less well described. In light of the established roles of Wnt5a in dopaminergic development (regulating DA differentiation as well as axonal growth and repulsion), and its interaction with Ryk elsewhere within the central nervous system, we investigated the potential role of Ryk in VM development. Here we show temporal and spatial expression of Ryk within the VM, suggestive of a role in DA neurogenesis and axonal plasticity. In VM primary cultures, we show that the effects of Wnt5a on VM progenitor proliferation, DA differentiation, and DA axonal connectivity can be inhibited using an Ryk-blocking antibody. In support, Ryk knockout mice showed reduced VM progenitors and DA precursor populations, resulting in a significant decrease in DA cells. However, Ryk(-/-) mice displayed no defects in DA axonal growth, guidance, or fasciculation of the MFB, suggesting other receptors may be involved and/or compensate for the loss of this receptor. These findings identify for the first time Ryk as an important receptor for midbrain DA development.

The VEGF signaling pathway in cancer: the road ahead

The vascular endothelial growth factor (VEGF) family of soluble protein growth factors consists of key mediators of angiogenesis and lymphangiogenesis in the context of tumor biology. The members of the family, VEGF-A (also known as VEGF), VEGF-B, VEGF-C, VEGF-D, and placenta growth factor (PIGF), play important roles in vascular biology in both normal physiology and pathology. The generation of a humanized neutralizing antibody to VEGF-A (bevacizumab, also known as Avastin) and the demonstration of its benefit in numerous human cancers have confirmed the merit of an anti-angiogenesis approach to cancer treatment and have validated the VEGF-A signaling pathway as a therapeutic target. Other members of the VEGF family are now being targeted, and their relevance to human cancer and the development of resistance to anti-VEGF-A treatment are being evaluated in the clinic. Here, we discuss the potential of targeting VEGF family members in the diagnosis and treatment of cancer.

The propeptides of VEGF-D determine heparin binding, receptor heterodimerization, and effects on tumor biology

VEGF-D is an angiogenic and lymphangiogenic glycoprotein that can be proteolytically processed generating various forms differing in subunit composition due to the presence or absence of N- and C-terminal propeptides. These propeptides flank the central VEGF homology domain, that contains the binding sites for VEGF receptors (VEGFRs), but their biological functions were unclear. Characterization of propeptide function will be important to clarify which forms of VEGF-D are biologically active and therefore clinically relevant. Here we use VEGF-D mutants deficient in either propeptide, and in the capacity to process the remaining propeptide, to monitor the functions of these domains. We report for the first time that VEGF-D binds heparin, and that the C-terminal propeptide significantly enhances this interaction (removal of this propeptide from full-length VEGF-D completely prevents heparin binding). We also show that removal of either the N- or C-terminal propeptide is required for VEGF-D to drive formation of VEGFR-2/VEGFR-3 heterodimers which have recently been shown to positively regulate angiogenic sprouting. The mature form of VEGF-D, lacking both propeptides, can also promote formation of these receptor heterodimers. In a mouse tumor model, removal of only the C-terminal propeptide from full-length VEGF-D was sufficient to enhance angiogenesis and tumor growth. In contrast, removal of both propeptides is required for high rates of lymph node metastasis. The findings reported here show that the propeptides profoundly influence molecular interactions of VEGF-D with VEGF receptors, co-receptors, and heparin, and its effects on tumor biology.

The Wnt coreceptor Ryk regulates Wnt/planar cell polarity by modulating the degradation of the core planar cell polarity component Vangl2

The Wnt signaling pathways control many critical developmental and adult physiological processes. In vertebrates, one fundamentally important function of Wnts is to provide directional information by regulating the evolutionarily conserved planar cell polarity (PCP) pathway during embryonic morphogenesis. However, despite the critical roles of Wnts and PCP in vertebrate development and disease, little is known about the molecular mechanisms underlying Wnt regulation of PCP. Here, we have found that the receptor-like tyrosine kinase (Ryk), a Wnt5a-binding protein required in axon guidance, regulates PCP signaling. We show that Ryk interacts with Vangl2 genetically and biochemically, and such interaction is potentiated by Wnt5a. Loss of Ryk in a Vangl2(+/-) background results in classic PCP defects, including open neural tube, misalignment of sensory hair cells in the inner ear, and shortened long bones in the limbs. Complete loss of both Ryk and Vangl2 results in more severe phenotypes that resemble the Wnt5a(-/-) mutant in many aspects such as shortened anterior-posterior body axis, limb, and frontonasal process. Our data identify the Wnt5a-binding protein Ryk as a general regulator of the mammalian Wnt/PCP signaling pathway. We show that Ryk transduces Wnt5a signaling by forming a complex with Vangl2 and that Ryk regulates PCP by at least in part promoting Vangl2 stability. As human mutations in WNT5A and VANGL2 are found to cause Robinow syndrome and neural tube defects, respectively, our results further suggest that human mutations in RYK may also be involved in these diseases.

Remodeling of the lymphatic vasculature during mouse mammary gland morphogenesis is mediated via epithelial-derived lymphangiogenic stimuli

Despite the key roles of lymphatic vessels in homeostasis and disease, the cellular sources of signals that direct lymphatic vascular growth and patterning remain unknown. Using high-resolution imaging in two and three dimensions, we demonstrated that postnatal mouse mammary gland lymphatic vessels share an intimate spatial association with epithelial ducts and large blood vessels. We further demonstrated that the lymphatic vasculature is remodeled together with the mammary epithelial tree and blood vasculature during postnatal mouse mammary gland morphogenesis. Neither estrogen receptor α nor progesterone receptor were detected in lymphatic endothelial cells in the mouse mammary gland, suggesting that mammary gland lymphangiogenesis is not likely regulated directly by these steroid hormones. Epithelial cells, especially myoepithelial cells, were determined to be a rich source of prolymphangiogenic stimuli including VEGF-C and VEGF-D with temporally regulated expression levels during mammary gland morphogenesis. Blockade of VEGFR-3 signaling using a small-molecule inhibitor inhibited the proliferation of primary lymphatic endothelial cells promoted by mammary gland conditioned medium, suggesting that lymphangiogenesis in the mammary gland is likely driven by myoepithelial-derived VEGF-C and/or VEGF-D. These findings provide new insight into the architecture of the lymphatic vasculature in the mouse mammary gland and, by uncovering the proximity of lymphatic vessels to the epithelial tree, suggest a potential mechanism by which metastatic tumor cells access the lymphatic vasculature.

Vascular endothelial growth factor-D: signaling mechanisms, biology, and clinical relevance

Vascular endothelial growth factor-D (VEGF-D) is a secreted glycoprotein that promotes growth of blood vessels (angiogenesis) and lymphatic vessels (lymphangiogenesis), and can induce remodeling of large lymphatics. VEGF-D enhances solid tumor growth and metastatic spread in animal models of cancer, and in some human cancers VEGF-D correlates with metastatic spread, poor patient outcome, and, potentially, with resistance to anti-angiogenic drugs. Hence, VEGF-D signaling is a potential target for novel anti-cancer therapeutics designed to enhance anti-angiogenic approaches and to restrict metastasis. In the cardiovascular system, delivery of VEGF-D in animal models enhanced angiogenesis and tissue perfusion, findings which have led to a range of clinical trials testing this protein for therapeutic angiogenesis in cardiovascular diseases. Despite these experimental and clinical developments, our knowledge of the signaling mechanisms driven by VEGF-D is still evolving--here we explore the biology of VEGF-D, its signaling mechanisms, and the clinical relevance of this growth factor.

The connection between lymphangiogenic signalling and prostaglandin biology: a missing link in the metastatic pathway

Substantial evidence supports important independent roles for lymphangiogenic growth factor signaling and prostaglandins in the metastatic spread of cancer. The significance of the lymphangiogenic growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, is well established in animal models of metastasis, and a strong correlation exits between an increase in expression of VEGF-C and VEGF-D, and metastatic spread in various solid human cancers. Similarly, key enzymes that control the production of prostaglandins, cyclooxygenases (COX-1 and COX-2, prototypic targets of Non-steroidal anti-inflammatory drugs (NSAIDs)), are frequently over-expressed or de-regulated in the progression of cancer. Recent data have suggested an intersection of lymphangiogenic growth factor signaling and the prostaglandin pathways in the control of metastatic spread via the lymphatic vasculature. Furthermore, this correlates with current clinical data showing that some NSAIDs enhance the survival of cancer patients through reducing metastasis. Here, we discuss the potential biochemical and cellular basis for such anti-cancer effects of NSAIDs through the prostaglandin and VEGF signaling pathways.

The Wnt receptor Ryk plays a role in mammalian planar cell polarity signaling

Wnts are essential for a wide range of developmental processes, including cell growth, division, and differentiation. Some of these processes signal via the planar cell polarity (PCP) pathway, which is a β-catenin-independent Wnt signaling pathway. Previous studies have shown that Ryk, a member of the receptor tyrosine kinase family, can bind to Wnts. Ryk is required for normal axon guidance and neuronal differentiation during development. Here, we demonstrate that mammalian Ryk interacts with the Wnt/PCP pathway. In vitro analysis showed that the Wnt inhibitory factor domain of Ryk was necessary for Wnt binding. Detailed analysis of two vertebrate model organisms showed Ryk phenotypes consistent with PCP signaling. In zebrafish, gene knockdown using morpholinos revealed a genetic interaction between Ryk and Wnt11 during the PCP pathway-regulated process of embryo convergent extension. Ryk-deficient mouse embryos displayed disrupted polarity of stereociliary hair cells in the cochlea, a characteristic of disturbed PCP signaling. This PCP defect was also observed in mouse embryos that were double heterozygotes for Ryk and Looptail (containing a mutation in the core Wnt/PCP pathway gene Vangl2) but not in either of the single heterozygotes, suggesting a genetic interaction between Ryk and Vangl2. Co-immunoprecipitation studies demonstrated that RYK and VANGL2 proteins form a complex, whereas RYK also activated RhoA, a downstream effector of PCP signaling. Overall, our data suggest an important role for Ryk in Wnt/planar cell polarity signaling during vertebrate development via the Vangl2 signaling pathway, as demonstrated in the mouse cochlea.

Towards the biomarker-guided rational use of antiangiogenic agents in the treatment of metastatic colorectal cancer

SUMMARY Clinical oncology experience with recently marketed antiangiogenic agents, which inhibit proteins important for tumor angiogenesis, has exposed significant limitations to their efficacy. Bevacizumab, a humanized neutralizing anti-VEGF-A monoclonal antibody, used in combination with cytotoxic chemotherapy for the treatment of metastatic colorectal cancer, represents the best-studied clinical example of targeted antiangiogenic therapy. In this context, bevacizumab provides modestly improved progression-free and overall survival in unselected patient populations via poorly understood mechanisms. Here we review concepts central to the identification and development of biomarkers in order to refine clinical use of bevacizumab in treating colorectal cancer and outline a phenotype-driven strategy for the discovery of high-value candidate biomarkers based on large-scale screening by molecular perturbation.

VEGF-D promotes tumor metastasis by regulating prostaglandins produced by the collecting lymphatic endothelium

Lymphatic metastasis is facilitated by lymphangiogenic growth factors VEGF-C and VEGF-D that are secreted by some primary tumors. We identified regulation of PGDH, the key enzyme in prostaglandin catabolism, in endothelial cells of collecting lymphatics, as a key molecular change during VEGF-D-driven tumor spread. The VEGF-D-dependent regulation of the prostaglandin pathway was supported by the finding that collecting lymphatic vessel dilation and subsequent metastasis were affected by nonsteroidal anti-inflammatory drugs (NSAIDs), known inhibitors of prostaglandin synthesis. Our data suggest a control point for cancer metastasis within the collecting lymphatic endothelium, which links VEGF-D/VEGFR-2/VEGFR-3 and the prostaglandin pathways. Collecting lymphatics therefore play an active and important role in metastasis and may provide a therapeutic target to restrict tumor spread.

A role for bone morphogenetic protein-4 in lymph node vascular remodeling and primary tumor growth

Lymph node metastasis, an early and prognostically important event in the progression of many human cancers, is associated with expression of VEGF-D. Changes to lymph node vasculature that occur during malignant progression may create a metastatic niche capable of attracting and supporting tumor cells. In this study, we sought to characterize molecules expressed in lymph node endothelium that could represent therapeutic or prognostic targets. Differential mRNA expression profiling of endothelial cells from lymph nodes that drained metastatic or nonmetastatic primary tumors revealed genes associated with tumor progression, in particular bone morphogenetic protein-4 (BMP-4). Metastasis driven by VEGF-D was associated with reduced BMP-4 expression in high endothelial venules, where BMP-4 loss could remodel the typical high-walled phenotype to thin-walled vessels. VEGF-D expression was sufficient to suppress proliferation of the more typical BMP-4-expressing high endothelial venules in favor of remodeled vessels, and mechanistic studies indicated that VEGF receptor-2 contributed to high endothelial venule proliferation and remodeling. BMP-4 could regulate high endothelial venule phenotype and cellular function, thereby determining morphology and proliferation responses. Notably, therapeutic administration of BMP-4 suppressed primary tumor growth, acting both at the level of tumor cells and tumor stromal cells. Together, our results show that VEGF-D-driven metastasis induces vascular remodeling in lymph nodes. Furthermore, they implicate BMP-4 as a negative regulator of this process, suggesting its potential utility as a prognostic marker or antitumor agent.

Proteolytic processing of vascular endothelial growth factor-D is essential for its capacity to promote the growth and spread of cancer

VEGF-D is a mitogen for endothelial cells that promotes tumor growth and metastatic spread in animal models, and expression of which correlates with lymph node metastasis in some human cancers. It is secreted from the cell as a full-length form with propeptides flanking a central region containing binding sites for VEGFR-2 and VEGFR-3, receptors that signal for angiogenesis and lymphangiogenesis. The propeptides can be cleaved from VEGF-D, enhancing affinity for VEGFR-2 and VEGFR-3 in vitro; however, the importance of this processing in cancer is unclear. To explore the necessity of processing for the effects of VEGF-D in cancer, we use a mutant full-length form that cannot be processed, and show that, in contrast to full-length VEGF-D that is processed, this mutant does not promote tumor growth and lymph node metastasis in a mouse tumor model. Processing of VEGF-D is required for tumor angiogenesis, lymphangiogenesis, and recruitment of tumor-associated macrophages. These observations may be explained by the requirement of processing for VEGF-D to bind neuropilin receptors and activate VEGFR-2. Our results indicate that proteolytic processing is necessary for VEGF-D to promote the growth and spread of cancer, and suggest that enzymes catalyzing this processing could be targets for antimetastatic therapeutics.

Wnt5a regulates midbrain dopaminergic axon growth and guidance

During development, precise temporal and spatial gradients are responsible for guiding axons to their appropriate targets. Within the developing ventral midbrain (VM) the cues that guide dopaminergic (DA) axons to their forebrain targets remain to be fully elucidated. Wnts are morphogens that have been identified as axon guidance molecules. Several Wnts are expressed in the VM where they regulate the birth of DA neurons. Here, we describe that a precise temporo-spatial expression of Wnt5a accompanies the development of nigrostriatal projections by VM DA neurons. In mice at E11.5, Wnt5a is expressed in the VM where it was found to promote DA neurite and axonal growth in VM primary cultures. By E14.5, when DA axons are approaching their striatal target, Wnt5a causes DA neurite retraction in primary cultures. Co-culture of VM explants with Wnt5a-overexpressing cell aggregates revealed that Wnt5a is capable of repelling DA neurites. Antagonism experiments revealed that the effects of Wnt5a are mediated by the Frizzled receptors and by the small GTPase, Rac1 (a component of the non-canonical Wnt planar cell polarity pathway). Moreover, the effects were specific as they could be blocked by Wnt5a antibody, sFRPs and RYK-Fc. The importance of Wnt5a in DA axon morphogenesis was further verified in Wnt5a^−/− mice, where fasciculation of the medial forebrain bundle (MFB) as well as the density of DA neurites in the MFB and striatal terminals were disrupted. Thus, our results identify a novel role of Wnt5a in DA axon growth and guidance.