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Supplementary Data from Angiopoietin-2 Interferes with Anti-VEGFR2–Induced Vessel Normalization and Survival Benefit in Mice Bearing Gliomas

Purpose: In brain tumors, cerebral edema is a significant source of morbidity and mortality. Recent studies have shown that inhibition of vascular endothelial growth factor (VEGF) signaling induces transient vascular normalization and reduces cerebral edema, resulting in a modest survival benefit in glioblastoma patients. During anti-VEGF treatment, circulating levels of angiopoietin (Ang)-2 remained high after an initial minor reduction. It is not known, however, whether Ang-2 can modulate anti-VEGF treatment of glioblastoma. Here, we used an orthotopic glioma model to test the hypothesis that Ang-2 is an additional target for improving the efficacy of current anti-VEGF therapies in glioma patients.Experimental Design: To recapitulate high levels of Ang-2 in glioblastoma patients during anti-VEGF treatment, Ang-2 was ectopically expressed in U87 glioma cells. Animal survival and tumor growth were assessed to determine the effects of Ang-2 and anti–VEGF receptor 2 (VEGFR2) treatment. We also monitored morphologic and functional vascular changes using multiphoton laser scanning microscopy and immunohistochemistry.Results: Ectopic expression of Ang-2 had no effect on vascular permeability, tumor growth, or survival, although it resulted in higher vascular density, with dilated vessels and reduced mural cell coverage. On the other hand, when combined with anti-VEGFR2 treatment, Ang-2 destabilized vessels without affecting vessel regression and compromised the survival benefit of VEGFR2 inhibition by increasing vascular permeability. VEGFR2 inhibition normalized tumor vasculature whereas ectopic expression of Ang-2 diminished the beneficial effects of VEGFR2 blockade by inhibiting vessel normalization.Conclusion: Cancer treatment regimens combining anti-VEGF and anti-Ang-2 agents may be an effective strategy to improve the efficacy of current anti-VEGF therapies. Clin Cancer Res; 16(14); 3618–27. ©2010 AACR.

Advanced prostate cancer initially responds to hormonal treatment, but ultimately becomes resistant and requires more potent therapies. One mechanism of resistance observed in ∼10% of these patients is through lineage plasticity, which manifests in a partial or complete small cell or neuroendocrine prostate cancer (NEPC) phenotype. Here, we investigate the role of the mammalian SWI/SNF (mSWI/SNF) chromatin remodeling complex in NEPC. Using large patient datasets, patient-derived organoids and cancer cell lines, we identify mSWI/SNF subunits that are deregulated in NEPC and demonstrate that SMARCA4 (BRG1) overexpression is associated with aggressive disease. We also show that SWI/SNF complexes interact with different lineage-specific factors in NEPC compared to prostate adenocarcinoma. These data suggest a role for mSWI/SNF complexes in therapy-related lineage plasticity, which may be relevant for other solid tumors.

Background Speckle-type POZ protein (SPOP) is an E3 ubiquitin ligase adaptor protein that functions as a potential tumor suppressor, and SPOP mutations have been identified in ~10% of human prostate cancers. However, it remains unclear if mutant SPOP proteins can be utilized as biomarkers for early detection, diagnosis, prognosis or targeted therapy of prostate cancer. Moreover, the SPOP mutation sites are distributed in a relatively short region with multiple lysine residues, posing significant challenges for bottom-up proteomics analysis of the SPOP mutations. Methods To address this issue, PRISM (high-pressure, high-resolution separations coupled with intelligent selection and multiplexing)-SRM (selected reaction monitoring) mass spectrometry assays have been developed for quantifying wild-type SPOP protein and 11 prostate cancer-derived SPOP mutations. Results Despite inherent limitations due to amino acid sequence constraints, all the PRISM-SRM assays developed using Arg-C digestion showed a linear dynamic range of at least two orders of magnitude, with limits of quantification ranged from 0.1 to 1 fmol/μg of total protein in the cell lysate. Applying these SRM assays to analyze HEK293T cells with and without expression of the three most frequent SPOP mutations in prostate cancer (Y87N, F102C or F133V) led to confident detection of all three SPOP mutations in corresponding positive cell lines but not in the negative cell lines. Expression of the F133V mutation and wild-type SPOP was at much lower levels compared to that of F102C and Y87N mutations; however, at present, it is unknown if this also affects the biological activity of the SPOP protein. Conclusions In summary, PRISM-SRM enables multiplexed, isoform-specific detection of mutant SPOP proteins in cell lysates, providing significant potential in biomarker development for prostate cancer. Electronic supplementary material The online version of this article (doi:10.1186/s12967-017-1276-7) contains supplementary material, which is available to authorized users.

Additional file 5: Figure S3. XICs of SPOP peptide VNPKGLDEESKDYLSLYLLLVSCPKSEVR and its mutant variants VNPKGLDEESKDYLSLCLLLVSCPKSEVR and VNPKGLDEESKDYLSLNLLLVSCPKSEVR without (A) and with (B) protective matrix in the pure peptide stocks in LC-SRM analysis.

Neuroendocrine prostate cancer (NEPC) is an aggressive subtype of prostate cancer that most commonly evolves from preexisting prostate adenocarcinoma (PCA). Using next-generation RNA sequencing and oligonucleotide arrays, we profiled 7 NEPC, 30 PCA, and 5 benign prostate tissue (BEN) samples and validated findings in tumors from a large cohort of patients (37 with NEPC, 169 with PCA, and 22 with BEN) using immunohistochemistry and FISH. We discovered significant overexpression and gene amplification of AURKA and MYCN in 40% of NEPC and 5% of PCA tumors, respectively, and evidence that they cooperate to induce a neuroendocrine phenotype in prostate cells. There was dramatic and enhanced sensitivity of NEPC (and MYCN overexpressing PCA) to Aurora kinase inhibitor therapy both in vitro and in vivo, with complete suppression of neuroendocrine marker expression following treatment. We propose that alterations in Aurora kinase A and N-myc are involved in the development of NEPC and that future clinical trials will help determine the efficacy of Aurora kinase inhibitor therapy. Significance: We report on the largest in-depth molecular analysis of NEPC and provide new insight into molecular events involved in the progression of prostate cancer. Cancer Discovery; 1(6); 487–95. ©2011 AACR. Read the Commentary on this article by Aparicio et al., p. 466 This article is highlighted in the In This Issue feature, p. 457

Prostate cancer (PCa) is the most commonly diagnosed cancer and the third highest cause of cancer-related death in men in Europe, where it is responsible for over 90,000 deaths a year. The mainstay of treatment for metastatic PCa is androgen-deprivation therapy (ADT). Although initially effective, the treatment ultimately fails and progression to castration-resistant prostate cancer (CRPC) occurs. Given that CRPC is still driven by hormonal signaling through aberrant activation of the androgen receptor (AR), improved, more potent AR-targeting therapies have been developed for CRPC patients. However, resistance to these therapies ultimately occurs as well. One form of resistance identified by my group results in a phenotypic switch leading to androgen receptor indifference and progression to neuroendocrine prostate cancer (NEPC), which shows a distinct histomorphology and expresses neural-like markers. Unlike more commonly recognized mechanisms of ADT resistance due to AR mutations or amplification, NEPC no longer responds to AR-targeting therapy and has a mean survival of 7 months. There is mounting evidence supporting the role of epigenetic events as a mechanism for transdifferentiation of PCa to an androgen signaling-indifferent state under specific genomic conditions, involving but not limited to TP53, RB1, and PTEN loss. However, the epigenetic regulators at work and the specific changes in the epigenetic landscape are unknown. The SWI/SNF complex is a major epigenetic player, both in regulating normal cell differentiation and in cancer biology. This presentation will focus on novel data supporting the role of alterations in this complex that could contribute to PCa phenotype plasticity. Citation Format: Joanna Cyrta, David Wilkes, Sung Suk Chae, Matteo Benelli, Rohan Bareja, Davide Prandi, Paola Maria Giovanna Cavaliere, Himisha Beltran, Andrea Sboner, Francesca Demichelis, Mark A. Rubin. Phenotype plasticity—a novel mechanism of targeted therapy resistance [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr IA19.

Purpose: In brain tumors, cerebral edema is a significant source of morbidity and mortality. Recent studies have shown that inhibition of vascular endothelial growth factor (VEGF) signaling induces transient vascular normalization and reduces cerebral edema, resulting in a modest survival benefit in glioblastoma patients. During anti-VEGF treatment, circulating levels of angiopoietin (Ang)-2 remained high after an initial minor reduction. It is not known, however, whether Ang-2 can modulate anti-VEGF treatment of glioblastoma. Here, we used an orthotopic glioma model to test the hypothesis that Ang-2 is an additional target for improving the efficacy of current anti-VEGF therapies in glioma patients. Experimental Design: To recapitulate high levels of Ang-2 in glioblastoma patients during anti-VEGF treatment, Ang-2 was ectopically expressed in U87 glioma cells. Animal survival and tumor growth were assessed to determine the effects of Ang-2 and anti–VEGF receptor 2 (VEGFR2) treatment. We also monitored morphologic and functional vascular changes using multiphoton laser scanning microscopy and immunohistochemistry. Results: Ectopic expression of Ang-2 had no effect on vascular permeability, tumor growth, or survival, although it resulted in higher vascular density, with dilated vessels and reduced mural cell coverage. On the other hand, when combined with anti-VEGFR2 treatment, Ang-2 destabilized vessels without affecting vessel regression and compromised the survival benefit of VEGFR2 inhibition by increasing vascular permeability. VEGFR2 inhibition normalized tumor vasculature whereas ectopic expression of Ang-2 diminished the beneficial effects of VEGFR2 blockade by inhibiting vessel normalization. Conclusion: Cancer treatment regimens combining anti-VEGF and anti-Ang-2 agents may be an effective strategy to improve the efficacy of current anti-VEGF therapies. Clin Cancer Res; 16(14); 3618–27. ©2010 AACR.

Not all tumor vessels are equal. Tumor-associated vasculature includes immature vessels, regressing vessels, transport vessels undergoing arteriogenesis and peritumor vessels influenced by tumor growth factors. Current techniques for analyzing tumor blood flow do not discriminate between vessel subtypes and only measure average changes from a population of dissimilar vessels. We developed methodologies for simultaneously quantifying blood flow (velocity, flux, hematocrit and shear rate) in extended networks at single-capillary resolution in vivo. Our approach relies on deconvolution of signals produced by labeled red blood cells as they move relative to the scanning laser of a confocal or multiphoton microscope and provides fully resolved three-dimensional flow profiles within vessel networks. Using this methodology, we show that blood velocity profiles are asymmetric near intussusceptive tissue structures in tumors in mice. Furthermore, we show that subpopulations of vessels, classified by functional parameters, exist in and around a tumor and in normal brain tissue.

SummaryThe PI3K-AKT-FoxO pathway is integral to lifespan regulation in lower organisms and essential for the stability of long-lived cells in mammals. Here, we report the impact of combined FoxO1, 3, and 4 deficiencies on mammalian brain physiology with a particular emphasis on the study of the neural stem/progenitor cell (NSC) pool. We show that the FoxO family plays a prominent role in NSC proliferation and renewal. FoxO-deficient mice show initial increased brain size and proliferation of neural progenitor cells during early postnatal life, followed by precocious significant decline in the NSC pool and accompanying neurogenesis in adult brains. Mechanistically, integrated transcriptomic, promoter, and functional analyses of FoxO-deficient NSC cultures identified direct gene targets with known links to the regulation of human brain size and the control of cellular proliferation, differentiation, and oxidative defense. Thus, the FoxO family coordinately regulates diverse genes and pathways to govern key aspects of NSC homeostasis in the mammalian brain.

Genomic instability is a fundamental feature of human cancer often resulting from impaired genome maintenance. In prostate cancer, structural genomic rearrangements are a common mechanism driving tumorigenesis. However, somatic alterations predisposing to chromosomal rearrangements in prostate cancer remain largely undefined. Here, we show that SPOP, the most commonly mutated gene in primary prostate cancer modulates DNA double strand break (DSB) repair, and that SPOP mutation is associated with genomic instability. In vivo, SPOP mutation results in a transcriptional response consistent with BRCA1 inactivation resulting in impaired homology-directed repair (HDR) of DSB. Furthermore, we found that SPOP mutation sensitizes to DNA damaging therapeutic agents such as PARP inhibitors. These results implicate SPOP as a novel participant in DSB repair, suggest that SPOP mutation drives prostate tumorigenesis in part through genomic instability, and indicate that mutant SPOP may increase response to DNA-damaging therapeutics. DOI: http://dx.doi.org/10.7554/eLife.09207.001, eLife digest Prostate cancer is the most common type of cancer in men in the UK and USA. Cancers develop when cells in the body acquire genetic mutations that allow the cells to grow rapidly and form a mass known as a tumor. Prostate cancer cells from different individuals can carry different genetic mutations, which affects whether the disease progresses and how the tumors respond to medical treatments. This genetic variety arises in cancer cells partly from a phenomenon known as genomic instability, in which DNA mutations accumulate due to defects in DNA repair. Genetic studies of biopsies taken from human prostate cancers have shown that genomic instability causes chromosomes—the structures in which the cell's DNA is organized—to break and then be stuck back together haphazardly. As a result, fragments of chromosomes can end up in the wrong position, be duplicated, or be lost altogether. All of these mutations could spur on the growth of the tumor. However, it is currently not clear why some prostate cancers are more genomically unstable than others, or what exactly causes this instability. Boysen, Barbieri et al. studied prostate cancer cells taken from patients before they started medical treatment. The experiments show that the cancer cells with high levels of genomic instability also often had mutations in a gene that encodes a protein called SPOP. These mutations occur in about 10 percent of men with prostate cancer and appear early in the development of the tumors. Next, they studied the SPOP protein in zebrafish (which is nearly identical to human SPOP), as well as in mouse and human cells. The experiments show that SPOP normally helps the cell to accurately repair DNA that has been damaged. Mutations in SPOP change the DNA repair process, which lead to genomic instability by increasing the likelihood that broken chromosomes will be stuck back together incorrectly. Further experiments tested drugs known as PARP inhibitors on mouse and human prostate cancer cells. The drugs, which have been recently tested successfully in patients with prostate cancer, block a different method of DNA repair that operates separately to the one that involves SPOP. When both of these pathways were inactivated—one by the SPOP mutation, the other by the drug—the cancer cells died more quickly. Therefore, men that are diagnosed with types of prostate cancer in which the gene that encodes SPOP is mutated might benefit from treatment with PARP inhibitors or other therapies that affect DNA repair. DOI: http://dx.doi.org/10.7554/eLife.09207.002

The bioactive lipid sphingosine-1-phosphate (SPP) is abundantly formed and released during the activation of platelets by thrombotic stimuli. Once exported, SPP interacts with the G-protein-coupled receptors (GPCR) of the EDG-1 family. SPP binds to EDG-1 with the dissociation constant of approximately 8 nM and induces signal transduction events such as mitogen-activated protein kinase (MAP kinase) activation, decrease of cAMP levels, remodeling of the actin cytoskeleton, among others. EDG-1 is a prototypical member of a large family of GPCRs that interact with glycero- and sphingolysolipid phosphates, namely, SPP and lysophosphatidic acid (LPA). Three other GPCRs, trivially termed EDG-3, EDG-5, and EDG-8, are also high-affinity receptors for SPP. The four SPP receptor subtypes regulate different intracellular signal transduction pathways. In vascular endothelial cells, cooperative signaling between EDG-1 and EDG-3 subtypes of SPP receptors results in adherens junction assembly, cell survival, morphogenesis into capillary-like networks, and angiogenesis. SPP acts distinctly, albeit cooperatively, with polypeptide angiogenic factors, resulting in the formation of mature neovessels. Thus SPP signaling as an extracellular mediator via the EDG-1 family of GPCRs may be a heretofore unrecognized mechanism for the regulation of angiogenesis and vascular endothelial cell function.

The recent landmark Phase III clinical trial with a VEGF-specific antibody suggests that antiangiogenic therapy must be combined with cytotoxic therapy for the treatment of solid tumors. However, there are no guidelines for optimal scheduling of these therapies. Here we show that VEGFR2 blockade creates a "normalization window"--a period during which combined radiation therapy gives the best outcome. This window is characterized by an increase in tumor oxygenation, which is known to enhance radiation response. During the normalization window, but not before or after it, VEGFR2 blockade increases pericyte coverage of brain tumor vessels via upregulation of Ang1 and degrades their pathologically thick basement membrane via MMP activation.

Vascular stabilization, a process by which nascent vessels are invested with mural cells, is important in angiogenesis. Here we describe the molecular basis of vascular stabilization regulated by sphingosine 1-phosphate (S1P), a platelet-derived lipid mediator. S1P1 receptor-dependent cell-surface trafficking and activation of the cell-cell adhesion molecule N-cadherin is essential for interactions between endothelial and mural cells. Endothelial cell S1P1/Gi/Rac pathway induces microtubule polymerization, resulting in trafficking of N-cadherin to polarized plasma membrane domains. S1P treatment modulated the phosphorylation of N-cadherin as well as p120-catenin and induced the formation of cadherin/catenin/actin complexes containing novel regulatory and trafficking factors. The net result of endothelial cell S1P1 receptor activation is the proper trafficking and strengthening of N-cadherin-dependent cell-cell adhesion with mural cells. Perturbation of N-cadherin expression with small interfering RNA profoundly attenuated vascular stabilization in vitro and in vivo. S1P-induced trafficking and activation of N-cadherin provides a novel mechanism for the stabilization of nascent blood vessels by mural cells and may be exploited to control angiogenesis and vascular diseases.

Angiogenesis, also known as new blood vessel formation, is regulated coordinately with other tissue differentiation events during limb development. Although vascular endothelial cell growth factor (VEGF) is important in the regulation of angiogenesis, chondrogenesis and osteogenesis during limb development, the role of other angiogenic factors is not well understood. Sphingosine 1-phosphate, a platelet-derived lipid mediator, regulates angiogenesis and vascular maturation via its action on the G-protein-coupled receptor S1P1 (also known as EDG-1). In addition to vascular defects, abnormal limb development was also observed in S1p1−/− mice. Here we show that strong induction of S1P1 expression is observed in the blood vessels and the interdigital mesenchymal cells during limb development. Deletion of S1P1 results in aberrant chondrocyte condensation and defective digit morphogenesis. Interestingly, the vasculature in the S1p1−/− limbs was hyperplastic and morphologically altered. In addition, the hypoxia inducible factor (HIF)-1α and its response gene VEGF were induced in S1p1−/− limbs. However, aberrant regulation of HIF-1α and VEGF were not observed in embryonic fibroblasts derived from S1p1−/− mice, suggesting a non-cell autonomous effect of S1P1 on VEGF expression. Indeed, similar limb defects were observed in endothelium-specific S1P1 null mice in vivo. These data suggest that the function of S1P1 in the developing vasculature is essential for proper limb development.

The enzyme sphingosine kinase (SK) catalyzes the formation of sphingosine 1-phosphate (S1P), a bioactive lipid that acts extracellularly on G protein-coupled receptors of the S1P1/EDG-1 subfamily. Although S1P is formed in the cytosol of various cells, S1P release is not understood and is controversial because this lipid mediator is also regarded as a second messenger. In this report, we describe the existence of an extracellular S1P-generating system in vascular endothelial cells. Endothelial cells release SK constitutively and form S1P in the range of receptor stimulation. Levels of sphingosine but not ATP in the extracellular environment are rate-limiting. Treatment of endothelial cells with small interfering RNA for SK-1 transcript specifically inhibited SK export, and SK-1-transfected human embryonic kidney 293 cells exhibited enhanced release of SK-1. The export of SK-1 is constitutive and is inhibited by cytochalasin D and treatment at 4 °C but not by brefeldin A or nocodazole, suggesting that a nonclassical secretory pathway that requires the actin cytoskeleton dynamics is involved. Because S1P regulates angiogenesis and vascular maturation, we overexpressed SK-1 using an adenoviral vector in vivo in the Matrigel system of angiogenesis. Overexpression of SK-1 resulted in enhanced release of SK activity and induced angiogenesis and vascular maturation. These findings suggest that S1P is made in the extracellular milieu and that extracellular export of SK contributes to the action of S1P in the vascular system.

Taxanes are the only chemotherapies used to treat patients with metastatic castration-resistant prostate cancer (CRPC). Despite the initial efficacy of taxanes in treating CRPC, all patients ultimately fail due to the development of drug resistance. In this study, we show that ERG overexpression in in vitro and in vivo models of CRPC is associated with decreased sensitivity to taxanes. ERG affects several parameters of microtubule dynamics and inhibits effective drug-target engagement of docetaxel or cabazitaxel with tubulin. Finally, analysis of a cohort of 34 men with metastatic CRPC treated with docetaxel chemotherapy reveals that ERG-overexpressing prostate cancers have twice the chance of docetaxel resistance than ERG-negative cancers. Our data suggest that ERG plays a role beyond regulating gene expression and functions outside the nucleus to cooperate with tubulin towards taxane insensitivity. Determining ERG rearrangement status may aid in patient selection for docetaxel or cabazitaxel therapy and/or influence co-targeting approaches., Metastatic castration-resistant prostate cancer is treated with the microtubule-stabilizing drugs taxanes, but resistance ultimately develops. Here Galletti et al. show that ERG, a transcription factor commonly overexpressed in prostate cancers, confers taxane resistance by binding to soluble tubulin.

Fusions between the transmembrane protease serine 2 (TMPRSS2) and ETS related gene (ERG) represent one of the most specific biomarkers that define a distinct molecular subtype of prostate cancer. Studies of TMPRSS2-ERG gene fusions have seldom been performed at the protein level, primarily due to the lack of high-quality antibodies suitable for quantitative studies. Herein, we applied a recently developed PRISM (high-pressure high-resolution separations with intelligent selection and multiplexing)-SRM (selected reaction monitoring) strategy for quantifying ERG protein in prostate cancer cell lines and tumors. The highly sensitive PRISM-SRM assays provided confident detection of 6 unique ERG peptides in both TMPRSS2-ERG positive cell lines and tissues, but not in cell lines or tissues lacking the TMPRSS2-ERG rearrangement, clearly indicating that ERG protein expression is significantly increased in the presence of the TMPRSS2-ERG gene fusion. Significantly, our results provide evidence that two distinct ERG protein isoforms are simultaneously expressed in TMPRSS2-ERG positive samples as evidenced by the concomitant detection of two mutually exclusive peptides in two patient tumors and in the VCaP prostate cancer cell line. Three peptides, shared across almost all fusion protein products, were determined to be the most abundant peptides, providing "signature" peptides for detection of ERG over-expression resulting from TMPRSS2-ERG gene fusion. The PRISM-SRM assays provide valuable tools for studying TMPRSS2-ERG gene fusion protein products in prostate cancer.

The role of the protein kinase Akt in cell migration is incompletely understood. Here we show that sphingosine-1-phosphate (S1P)-induced endothelial cell migration requires the Akt-mediated phosphorylation of the G protein-coupled receptor (GPCR) EDG-1. Activated Akt binds to EDG-1 and phosphorylates the third intracellular loop at the T 236 residue. Transactivation of EDG-1 by Akt is not required for G i -dependent signaling but is indispensable for Rac activation, cortical actin assembly, and chemotaxis. Indeed, T236AEDG-1 mutant sequestered Akt and acted as a dominant-negative GPCR to inhibit S1P-induced Rac activation, chemotaxis, and angiogenesis. Transactivation of GPCRs by Akt may constitute a specificity switch to integrate rapid G protein-dependent signals into long-term cellular phenomena such as cell migration.

Sphingosine 1-phosphate (SPP), a platelet-derived bioactive lysophospholipid, is a regulator of angiogenesis. However, molecular mechanisms involved in SPP-induced angiogenic responses are not fully defined. Here we report the molecular mechanisms involved in SPP-induced human umbilical vein endothelial cell (HUVEC) adhesion and migration. SPP-induced HUVEC migration is potently inhibited by antisense phosphothioate oligonucleotides against EDG-1 as well as EDG-3 receptors. In addition, C3 exotoxin blocked SPP-induced cell attachment, spreading and migration on fibronectin-, vitronectin- and Matrigel-coated surfaces, suggesting that endothelial differentiation gene receptor signaling via the Rho pathway is critical for SPP-induced cell migration. Indeed, SPP induced Rho activation in an adherence-independent manner, whereas Rac activation was dispensible for cell attachment and focal contact formation. Interestingly, both EDG-1 and -3 receptors were required for Rho activation. Since integrins are critical for cell adhesion, migration, and angiogenesis, we examined the effects of blocking antibodies against alpha(v)beta(3), beta(1), or beta(3) integrins. SPP induced Rho-dependent integrin clustering into focal contact sites, which was essential for cell adhesion, spreading and migration. Blockage of alpha(v)beta(3)- or beta(1)-containing integrins inhibited SPP-induced HUVEC migration. Together our results suggest that endothelial differentiation gene receptor-mediated Rho signaling is required for the activation of integrin alpha(v)beta(3) as well as beta(1)-containing integrins, leading to the formation of initial focal contacts and endothelial cell migration.

Sphingolipid signaling pathways have been implicated in many critical cellular events. Sphingosine-1-phosphate (SPP), a sphingolipid metabolite found in high concentrations in platelets and blood, stimulates members of the endothelial differentiation gene (Edg) family of G protein-coupled receptors and triggers diverse effects, including cell growth, survival, migration, and morphogenesis. To determine the in vivo functions of the SPP/Edg signaling pathway, we disrupted the Edg1 gene in mice. Edg1(-/-) mice exhibited embryonic hemorrhage leading to intrauterine death between E12.5 and E14.5. Vasculogenesis and angiogenesis appeared normal in the mutant embryos. However, vascular maturation was incomplete due to a deficiency of vascular smooth muscle cells/pericytes. We also show that Edg-1 mediates an SPP-induced migration response that is defective in mutant cells due to an inability to activate the small GTPase, Rac. Our data reveal Edg-1 to be the first G protein-coupled receptor required for blood vessel formation and show that sphingolipid signaling is essential during mammalian development.

Speckle-type POZ protein (SPOP) is an E3 ubiquitin ligase adaptor protein that functions as a potential tumor suppressor, and SPOP mutations have been identified in ∼10% of human prostate cancers. However, it remains unclear if mutant SPOP proteins can be utilized as biomarkers for diagnosis, prognosis or targeted therapy of prostate cancer. To address this issue, selected reaction monitoring (SRM) and PRISM (high-pressure, high-resolution separations coupled with intelligent selection and multiplexing) -SRM mass spectrometry assays have been developed for quantifying mutant SPOP proteins. SRM assays for wild-type SPOP protein and 11 prostate cancer-derived mutations were developed. The presence of multiple lysine residues in the mutation regions precludes the use of conventional tryptic digestion. Arg-C was selected instead due to its superior performance in generating mutation site(s) containing SPOP peptides that are more suitable for SRM analysis comparing to other proteases (e.g., Asp-N). Although the resulting Arg-C peptides are longer and more hydrophobic than typical tryptic peptides, all the SRM assays showed a linear dynamic range of more than two orders of magnitude. The limits of quantification for the mutation site(s) containing peptides range from 10 to 100 fmol/μg of total protein in the cell lysate. Applying these SRM assays to analyze 293T cells with and without expression of the three most frequent SPOP mutations in prostate cancer (Y87N, F102C or F133V) led to confident detection of all three SPOP mutations in corresponding positive cell lines but not in the negative cell lines. Expression of the F133V mutation and wild-type SPOP was at much lower levels compared to that of F102C and Y87N mutations, which agrees with RT-PCR results. It is unknown if this is related to activity of the SPOP protein. PRISM-SRM assays have shown further improvement in sensitivity. SRM enables multiplexed, isoform-specific detection of mutant SPOP proteins in cell lysates, which holds great potential in biomarker development for prostate cancer. Citation Format: Hui Wang, Christopher Barbieri, Jintang He, Yuqian Gao, Chaochao Wu, Athena Schepmoes, Thomas Fillmore, Tujin Shi, Sung-Suk Chae, Dennis Huang, Juan Miguel Mosquera, Wei-Jun Qian, Richard Smith, Sudhir Srivastava, Jacob Kagan, David Camp, Karin Rodland, Mark Rubin, Tao Liu. Quantification of mutant SPOP proteins in prostate cancer using targeted proteomics. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3872.

Prostate cancer is the second most common cancer in men worldwide and causes over 250,000 deaths each year. Overtreatment of indolent disease also results in significant morbidity. Common genetic alterations in prostate cancer include losses of NKX3.1 (8p21) and PTEN (10q23), gains of AR (the androgen receptor gene) and fusion of ETS family transcription factor genes with androgen-responsive promoters. Recurrent somatic base-pair substitutions are believed to be less contributory in prostate tumorigenesis but have not been systematically analyzed in large cohorts. Here, we sequenced the exomes of 112 prostate tumor and normal tissue pairs. New recurrent mutations were identified in multiple genes, including MED12 and FOXA1. SPOP was the most frequently mutated gene, with mutations involving the SPOP substrate-binding cleft in 6–15% of tumors across multiple independent cohorts. Prostate cancers with mutant SPOP lacked ETS family gene rearrangements and showed a distinct pattern of genomic alterations. Thus, SPOP mutations may define a new molecular subtype of prostate cancer., National Human Genome Research Institute (U.S.) (Large Scale Sequencing Program Grant U54 HG003067)

We sought to characterize the function of bone marrow stromal cell (BMSC) populations in tumor progression. Because this function may depend on the cell-lineage and mouse strain heterogeneity, we first characterized ex vivo the BMSCs harvested from C57BL/6 versus FVB mice and established their in vivo function in tumor growth and metastasis experiments. All plastic-adherent BMSCs expressed platelet-derived growth factor receptor beta (PDGFRβ) and stem cell antigen 1 (Sca1), consistent with a mesenchymal precursor phenotype, as well as CD80. Moreover, these BMSCs were capable of differentiation along mesenchymal lineage into adipocytes, osteoblasts, chondrocytes or myofibroblasts. However, further phenotypic analysis detected a distinct populations of myeloid (CD11b(+)) precursor cells amongst the ex vivo expanded BMSCs -with specific surface marker phenotypes and gene expression pattern. When co-implanted with metastatic cancer cells, all the BMSCs persisted and integrated into tumor stroma, but only myeloid BMSCs significantly promoted tumor growth and metastasis. These data demonstrate the differential effect of BMSCs sub-populations on tumor progression. These results may have important implications for anti-tumor therapy and for the use of mesenchymal BMSCs as cell-based therapies.

The role of vascular endothelial growth factor receptor 1 (VEGFR1/Flt1) in tumor metastasis remains incompletely characterized. Recent reports suggested that blocking VEGFR1 activity or the interaction with its ligands (VEGF and PlGF) has anti-tumor effects. Moreover, several studies showed that VEGFR1 mediates tumor progression to distant metastasis. All these effects may be exerted indirectly by recruitment of bone marrow-derived cells (BMDCs), such as myeloid cells. We investigated the role of VEGFR1 activity in BMDCs during the pre-metastatic phase, i.e., prior to metastatic nodule formation in mice after surgical removal of the primary tumor. Using pharmacologic blockade or genetic deletion of the tyrosine kinase domain of VEGFR1, we demonstrate that VEGFR1 activity is not required for the infiltration of de novo myeloid BMDCs in the pre-metastatic lungs in two tumor models and in two mouse models. Moreover, in line with emerging clinical observations, we show that blockade of VEGFR1 activity neither prevents nor changes the rate of spontaneous metastasis formation after primary tumor removal. Prevention of metastasis will require further identification and exploration of cellular and molecular pathways that mediate the priming of the metastatic soil.

Background: Genomic instability is a fundamental feature of human cancer, and DNA repair defects resulting in impaired genome maintenance promote pathogenesis of many types of cancers. In prostate cancer, structural genomic rearrangements, including translocations and copy number aberrations, are a key mechanism driving tumorigenesis. Recently, whole genome sequencing revealed a striking abundance, complexity, and heterogeneity of genomic rearrangements, potentially suggesting distinct mechanisms of instability in different molecular classes of prostate cancer. However, the somatic alterations underlying these phenomena remain largely undefined. Recurrent mutations in SPOP, the substrate-recognition component of an E3-ubiquitin ligase, represent the most common point mutations in primary prostate cancer, occurring in about 10% of tumors. SPOP mutations define a distinct molecular class of prostate cancer; they are mutually exclusive with TMPRSS2-ERG fusions, but harbor distinct patterns of copy number aberrations. Here, we report that SPOP mutant prostate cancers also harbor increased numbers of genomic rearrangements, and functional data suggest that SPOP mutation alters repair of DNA double strand breaks (DSB). Methods: We systematically investigated somatic alterations associated with genomic rearrangements, using a composite data set of 402 clinically localized prostate cancers. Functional analyses in vitro and in vivo were used to define pathways affected, and interrogate DNA repair phenotypes. Results: In human prostate cancers, SPOP mutation is an early event specifically associated with increased intrachromosomal genomic rearrangements. Using a zebrafish model, SPOP mutation results in a transcriptional response consistent with BRCA1 inactivation, implicating altered repair of DSB. In vitro data suggest that SPOP participates in repair of DSB, and SPOP mutation impairs homology-directed repair (HDR), instead promoting error-prone non-homologous end joining (NHEJ). Finally, SPOP mutation sensitizes prostate cancer cells to DNA damaging therapeutic agents such as PARP inhibitors. Conclusions: These results implicate SPOP as a novel participant in DSB repair, suggest that SPOP mutation drives prostate tumorigenesis in part through genomic instability, and indicate that SPOP mutant prostate cancer may be selectively responsive to DNA damaging therapeutics. Citation Format: Gunther Boysen, Christopher E. Barbieri, Davide Prandi, Sung-Suk Chae, Srilakshmi Nataraj, Mirjam Blattner, Clarisse Marotz, Limei Xu, Paola Lecca, Sagar Chhangawala, Pengbo Zou, Andrea Sboner, Francesca Demichelis, Yariv Houvras, Mark A. Rubin. SPOP mutation leads to genomic instability in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1108. doi:10.1158/1538-7445.AM2015-1108

Background: Genomic instability is a fundamental feature of human cancer, and DNA repair defects resulting in impaired genome maintenance promote pathogenesis of many types of cancers. In prostate cancer, structural genomic rearrangements, including translocations and copy number aberrations, are a key mechanism driving tumorigenesis. Recently, whole genome sequencing revealed a striking abundance, complexity, and heterogeneity of genomic rearrangements, potentially suggesting distinct mechanisms of instability in different molecular classes of prostate cancer. However, the somatic alterations underlying these phenomena remain largely undefined. Recurrent mutations in SPOP, the substrate-recognition component of an E3-ubiquitin ligase, represent the most common point mutations in primary prostate cancer, occurring in about 10% of tumors. SPOP mutations define a distinct molecular class of prostate cancer; they are mutually exclusive with TMPRSS2-ERG fusions, but harbor distinct patterns of copy number aberrations. Here, we report that SPOP mutant prostate cancers also harbor increased numbers of genomic rearrangements, and functional data suggest that SPOP mutation alters repair of DNA double strand breaks (DSB). Methods: We systematically investigated somatic alterations associated with genomic rearrangements, using a composite data set of 402 clinically localized prostate cancers. Functional analyses in vitro and in vivo were used to define pathways affected, and interrogate DNA repair phenotypes. Results: In human prostate cancers, SPOP mutation is an early event specifically associated with increased intrachromosomal genomic rearrangements. Using a zebrafish model, SPOP mutation results in a transcriptional response consistent with BRCA1 inactivation, implicating altered repair of DSB. In vitro data suggest that SPOP participates in repair of DSB, and SPOP mutation impairs homology-directed repair (HDR), instead promoting error-prone non-homologous end joining (NHEJ). Finally, SPOP mutation sensitizes prostate cancer cells to DNA damaging therapeutic agents such as PARP inhibitors. Conclusions: These results implicate SPOP as a novel participant in DSB repair, suggest that SPOP mutation drives prostate tumorigenesis in part through genomic instability, and indicate that SPOP mutant prostate cancer may be selectively responsive to DNA damaging therapeutics. Citation Format: Christopher E. Barbieri, Gunther Boysen, Davide Prandi, Sung-Suk Chae, Arun Dahiya, Srilakshmi Nataraj, Mirjam Blattner, Clarisse Marotz, Limei Xu, Julie Huang, Paola Lecca, Sagar Chhangawala, Pengbo Zhou, Andrea Sboner, Francesca Demichelis, Yariv Houvras, Mark A. Rubin. SPOP mutation is associated with genomic instability in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr NG01. doi:10.1158/1538-7445.AM2015-NG01

The recent landmark Phase III clinical trial with a VEGF-specific antibody suggests that antiangiogenic therapy must be combined with cytotoxic therapy for the treatment of solid tumors. However, there are no guidelines for optimal scheduling of these therapies. Here we show that VEGFR2 blockade creates a "normalization window"--a period during which combined radiation therapy gives the best outcome. This window is characterized by an increase in tumor oxygenation, which is known to enhance radiation response. During the normalization window, but not before or after it, VEGFR2 blockade increases pericyte coverage of brain tumor vessels via upregulation of Ang1 and degrades their pathologically thick basement membrane via MMP activation.

Angiogenesis, or new blood vessel formation, is critical for the growth and spread of tumors. Multiple phases of this process, namely, migration, proliferation, morphogenesis, and vascular stabilization, are needed for optimal tumor growth beyond a diffusion-limited size. The sphingosine 1-phosphate (S1P) receptor-1 (S1P(1)) is required for stabilization of nascent blood vessels during embryonic development. Here we show that S1P(1) expression is strongly induced in tumor vessels. We developed a multiplex RNA interference technique to downregulate S1P(1) in mice. The small interfering RNA (siRNA) for S1P(1) specifically silenced the cognate transcript in endothelial cells and inhibited endothelial cell migration in vitro and the growth of neovessels into subcutaneous implants of Matrigel in vivo. Local injection of S1P(1) siRNA, but not a negative control siRNA, into established tumors inhibited the expression of S1P(1) polypeptide on neovessels while concomitantly suppressing vascular stabilization and angiogenesis, which resulted in dramatic suppression of tumor growth in vivo. These data suggest that S1P(1) is a critical component of the tumor angiogenic response and argue for the utility of siRNA technology in antiangiogenic therapeutics.

S1P1 (also known as EDG-1) is a G-protein coupled receptor for the bioactive lipid, sphingosine-1-phosphate (S1P). Activation of S1P1 receptor in endothelial cells induces diverse cellular effects, including cell proliferation, survival, migration and morphogenesis. Recent in vivo studies showed that the S1P1 receptor is required in vascular maturation during development. While a number of studies reported a functional role of S1P1 in vascular system and the presence of S1P1 transcripts in various mouse organs, tissue distribution of S1P1 has not been fully defined. In this study, we determined the expression pattern of S1P1 by beta-galactosidase reporter gene expression, which is knocked into the S1P1 locus. We show that S1P1 is widely expressed in various cell types of adult mouse tissues, suggesting a regulatory role of this receptor in numerous physiological processes in both vascular and non-vascular tissues.

Important discoveries within the past decade,which demonstrated the ability of small duplex RNAs to profoundly regulate gene expression, have opened the door to a new era of gene regulation research while providing a powerful tool to specifically down-regulate genes. Originally discovered in the nematode C. elegans, RNA interference, or RNAi, is defined as the sequence specific silencing of gene expression brought about by the introduction of exogenous double stranded RNA (Fire et al. 1998). In the initial experiments, researchers found that the injection of long (>500bp) dsRNA into nematodes interfered with the expression of specific genes that were homologous in sequence to the injected dsRNAs. Since this initial discovery, it has been shown that long dsRNA is not the direct effector of RNAi. It is cleaved into 21–23 nt duplex RNAs, termed small interfering RNAs, or siRNAs, which are the bona fide effectors of RNAi (Elbashir et al. 2001a). Prior to this discovery, it was not possible to induce RNAi in mammalian cells since the introduction of long dsRNAs induces the interferon response, leading to cell cycle alterations and apoptosis (Elbashir et al. 2001a). However, duplex RNA less than 30 nucleotides in length does not trigger the interferon response (Elbashir et al. 2001a, Elbashir et al. 2001b), and it has become possible to silence specific genes in mammalian cells with the use of siRNA.

Angiogenesis, also known as new blood vessel formation, is regulated coordinately with other tissue differentiation events during limb development. Although vascular endothelial cell growth factor (VEGF) is important in the regulation of angiogenesis, chondrogenesis and osteogenesis during limb development, the role of other angiogenic factors is not well understood. Sphingosine 1-phosphate, a platelet-derived lipid mediator, regulates angiogenesis and vascular maturation via its action on the G-protein-coupled receptor S1P(1) (also known as EDG-1). In addition to vascular defects, abnormal limb development was also observed in S1p(1)(-/-) mice. Here we show that strong induction of S1P(1) expression is observed in the blood vessels and the interdigital mesenchymal cells during limb development. Deletion of S1P(1) results in aberrant chondrocyte condensation and defective digit morphogenesis. Interestingly, the vasculature in the S1p(1)(-/-) limbs was hyperplastic and morphologically altered. In addition, the hypoxia inducible factor (HIF)-1 alpha and its response gene VEGF were induced in S1p(1)(-/-) limbs. However, aberrant regulation of HIF-1 alpha and VEGF were not observed in embryonic fibroblasts derived from S1p(1)(-/-) mice, suggesting a non-cell autonomous effect of S1P(1) on VEGF expression. Indeed, similar limb defects were observed in endothelium-specific S1P(1) null mice in vivo. These data suggest that the function of S1P(1) in the developing vasculature is essential for proper limb development.

The enzyme sphingosine kinase (SK) catalyzes the formation of sphingosine 1-phosphate (S1P), a bioactive lipid that acts extracellularly on G protein-coupled receptors of the S1P(1)/EDG-1 subfamily. Although S1P is formed in the cytosol of various cells, S1P release is not understood and is controversial because this lipid mediator is also regarded as a second messenger. In this report, we describe the existence of an extracellular S1P-generating system in vascular endothelial cells. Endothelial cells release SK constitutively and form S1P in the range of receptor stimulation. Levels of sphingosine but not ATP in the extracellular environment are rate-limiting. Treatment of endothelial cells with small interfering RNA for SK-1 transcript specifically inhibited SK export, and SK-1-transfected human embryonic kidney 293 cells exhibited enhanced release of SK-1. The export of SK-1 is constitutive and is inhibited by cytochalasin D and treatment at 4 degrees C but not by brefeldin A or nocodazole, suggesting that a nonclassical secretory pathway that requires the actin cytoskeleton dynamics is involved. Because S1P regulates angiogenesis and vascular maturation, we overexpressed SK-1 using an adenoviral vector in vivo in the Matrigel system of angiogenesis. Overexpression of SK-1 resulted in enhanced release of SK activity and induced angiogenesis and vascular maturation. These findings suggest that S1P is made in the extracellular milieu and that extracellular export of SK contributes to the action of S1P in the vascular system.

Stable-isotope dilution coupled to targeted mass spectrometry, applying selected reaction monitoring (SRM), provides good selectivity, reproducibility, and sensitivity rendering it highly suitable for robust and high-throughput protein quantification. Historically, SRM sensitivity for measuring protein concentration in biofluids such as blood plasma has been limited to the low μg/mL level. Application of front-end sample preparation methods such as immunoaffinity depletion and strong cation exchange (SCX) chromatographic fractionation has improved the SRM detection limit to low ng/mL level. The ability to detect and quantify low abundance proteins present in blood plasma/serum at sub-ng/mL levels, however, relies on the availability of specific affinity reagents (e.g., antibodies that have the associated disadvantage of an expensive, lengthy, and high failure rate de novo process). To address this limitation, we have recently developed an antibody-free, targeted quantification capability that enables protein quantification of prostate-specific antigen and other exogenous proteins at 50-100 pg/mL levels in plasma/serum. Unlike the traditional SCX fractionation approach where all resulting fractions are analyzed by the second dimension LC-SRM, this new capability, PRISM (high-pressure high-resolution separations with intelligent selection and multiplexing), uses high resolution. Citation Format: Jintang He, Xuefei Sun, Tujin Shi, Athena Schepmoes, Thomas Fillmore, Vladislav Petyuk, Fang Xie, Marina Gritsenko, Feng Yang, Naoki Kitabayashi, Sung Suk Chae, Mark Rubin, Javed Siddiqui, John Wei, Arul Chinnaiyan, Wei-Jun Qian, Richard Smith, Jacob Kagan, Sudhir Srivastava, Tao Liu, Karin Rodland, David Camp. Application of an antibody-free, highly sensitive PRISM-SRM proteomics approach for monitoring low abundance proteins and protein isoforms in cell lines and tumor tissue. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3207. doi:10.1158/1538-7445.AM2013-3207