Biomedical subjects

David D Roberts

Publications and source records attributed to David D Roberts.

At least 19 recordsLinked to original sources

PubMed2006

Trichostatin A and 5-aza-2'-deoxycytidine switch S1P from an inhibitor to a stimulator of motility through epigenetic regulation of S1P receptors.

The histone deacetylase inhibitor, trichostatin A (TSA), and the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (Aza-dC), induced epigenetic regulation of sphingosine-1-phosphate (S1P) receptors in human melanoma cells, switching S1P from motility inhibitor to stimulator. Quantitative PCR revealed increased expression of S1P(1) and S1P(3), associated with S1P-induced chemotaxis, and decreased expression of S1P(2), associated with motility inhibition. Expression of lysophosphatidic acid (LPA) receptors was less affected. The TSA effect was reversible suggesting no mutational change, and Aza-dC treatment resulted in demethylation of a putative S1P(1) promoter. S1P receptors, therefore, appear to be susceptible to epigenetic regulation, accompanied by altered cellular functionality.

Azacitidine↗

PubMed2006

Thrombospondin-1 limits ischemic tissue survival by inhibiting nitric oxide-mediated vascular smooth muscle relaxation.

The nitric oxide (NO)/cGMP pathway, by relaxing vascular smooth muscle cells, is a major physiologic regulator of tissue perfusion. We now identify thrombospondin-1 as a potent antagonist of NO for regulating F-actin assembly and myosin light chain phosphorylation in vascular smooth muscle cells. Thrombospondin-1 prevents NO-mediated relaxation of precontracted vascular smooth muscle cells in a collagen matrix. Functional magnetic resonance imaging demonstrated that an NO-mediated increase in skeletal muscle perfusion was enhanced in thrombospondin-1-null relative to wild-type mice, implicating endogenous thrombospondin-1 as a physiologic antagonist of NO-mediated vasodilation. Using a random myocutaneous flap model for ischemic injury, tissue survival was significantly enhanced in thrombospondin-1-null mice. Improved flap survival correlated with increased recovery of oxygen levels in the ischemic tissue of thrombospondin-1-null mice as measured by electron paramagnetic resonance oximetry. These findings demonstrate an important antagonistic relation between NO/cGMP signaling and thrombospondin-1 in vascular smooth muscle cells to regulate vascular tone and tissue perfusion.

Actins↗

PubMed2006

Conformational analysis of an alpha3beta1 integrin-binding peptide from thrombospondin-1: implications for antiangiogenic drug design.

The integrin alpha3beta1 plays important roles in development, angiogenesis, and the pathogenesis of cancer, suggesting potential therapeutic uses for antagonists of this receptor. Recently, an alpha3beta1 integrin-binding site was mapped to residues 190-201 (FQGVLQNVRFVF) of the N-terminal domain of the secreted protein thrombospondin-1 (TSP1). This sequence displays diverse biological activities in vitro and inhibits angiogenesis in vivo. Herein we describe the NMR solution conformation of this segment in both water and dodecylphosphocholine micelles. While essentially unstructured in water, a more well-defined conformation is populated in micelles, particularly in the C-terminal half of the peptide and correlated with increased biological activity of the micellar peptide. The data suggested that the residues that are critical for biological activity are contained in a structurally well-defined segment of the peptide. These data support the role of the NVR motif as a required element of full-length TSP1 for specific molecular recognition by the alpha3beta1 integrin.

Angiogenesis Inhibitors↗

PubMed2006

Versican-thrombospondin-1 binding in vitro and colocalization in microfibrils induced by inflammation on vascular smooth muscle cells.

We identified a specific interaction between two secreted proteins, thrombospondin-1 and versican, that is induced during a toll-like receptor-3-dependent inflammatory response in vascular smooth muscle cells. Thrombospondin-1 binding to versican is modulated by divalent cations. This interaction is mediated by interaction of the G1 domain of versican with the N-module of thrombospondin-1 but only weakly with the corresponding N-terminal region of thrombospondin-2. The G1 domain of versican contains two Link modules, which are known to mediate TNFalpha-stimulated gene-6 protein binding to thrombospondin-1, and the related G1 domain of aggrecan is also recognized by thrombospondin-1. Therefore, thrombospondin-1 interacts with three members of the Link-containing hyaladherin family. On the surface of poly-I:C-stimulated vascular smooth muscle cells, versican organizes into fibrillar structures that contain elastin but are largely distinct from those formed by hyaluronan. Endogenous and exogenously added thrombospondin-1 incorporates into these structures. Binding of exogenous thrombospondin-1 to these structures, to purified versican and to its G1 domain is potently inhibited by heparin. At higher concentrations, exogenous thrombospondin-1 delays the poly-I:C induced formation of structures containing versican and elastin, suggesting that thrombospondin-1 negatively modulates this component of a vascular smooth muscle inflammatory response.

Aggrecans↗

PubMed2006

CD47 is necessary for inhibition of nitric oxide-stimulated vascular cell responses by thrombospondin-1.

CD36 is necessary for inhibition of some angiogenic responses by the matricellular glycoprotein thrombospondin-1 and is therefore assumed to be the receptor that mediates its anti-angiogenic activities. Although ligation of CD36 by antibodies, recombinant type 1 repeats of thrombospondin-1, or CD36-binding peptides was sufficient to inhibit nitric oxide (NO)-stimulated responses in both endothelial and vascular smooth muscle cells, picomolar concentrations of native thrombospondin-1 similarly inhibited NO signaling in vascular cells from wild-type and CD36-null mice. Ligation of the thrombospondin-1 receptor CD47 by recombinant C-terminal regions of thrombospondin-1, thrombospondin-1 peptides, or CD47 antibodies was also sufficient to inhibit NO-stimulated phenotypic responses and cGMP signaling in vascular cells. Thrombospondin-1 did not inhibit NO signaling in CD47-null vascular cells or NO-stimulated vascular outgrowth from CD47-null muscle explants in three-dimensional cultures. Furthermore, the CD36-binding domain of thrombospondin-1 and anti-angiogenic peptides derived from this domain failed to inhibit NO signaling in CD47-null cells. Therefore, ligation of either CD36 or CD47 is sufficient to inhibit NO-stimulated vascular cell responses and cGMP signaling, but only CD47 is necessary for this activity of thrombospondin-1 at physiological concentrations.

Animals↗

PubMed2006

Superoxide fluxes limit nitric oxide-induced signaling.

Independently, superoxide (O2-) and nitric oxide (NO) are biologically important signaling molecules. When co-generated, these radicals react rapidly to form powerful oxidizing and nitrating intermediates. Although this reaction was once thought to be solely cytotoxic, herein we demonstrate using MCF7, macrophage, and endothelial cells that when nanomolar levels of NO and O2- were produced concomitantly, the effective NO concentration was established by the relative fluxes of these two radicals. Differential regulation of sGC, pERK, HIF-1alpha, and p53 were used as biological dosimeters for NO concentration. Introduction of intracellular- or extracellular-generated O2- during NO generation resulted in a concomitant increase in oxidative intermediates with a decrease in steady-state NO concentrations and a proportional reduction in the levels of sGC, ERK, HIF-1alpha, and p53 regulation. NO responses were restored by addition of SOD. The intermediates formed from the reactions of NO with O2- were non-toxic, did not form 3-nitrotyrosine, nor did they elicit any signal transduction responses. H2O2 in bolus or generated from the dismutation of O2- by SOD, was cytotoxic at high concentrations and activated p53 independent of NO. This effect was completely inhibited by catalase, suppressed by NO, and exacerbated by intracellular catalase inhibition. We conclude that the reaction of O2- with NO is an important regulatory mechanism, which modulates signaling pathways by limiting steady-state levels of NO and preventing H2O2 formation from O2-.

Animals↗

PubMed2006

Thrombospondin-1 antagonizes nitric oxide-stimulated vascular smooth muscle cell responses.

OBJECTIVE: Endothelial-derived nitric oxide (NO), by increasing cGMP, is a major physiological regulator of vascular tone and of vascular smooth muscle cell (VSMC) adhesion, chemotaxis, and proliferation. Thrombospondin-1 is a potent antagonist of NO/cGMP signaling in endothelial cells. Because endothelial and VSMC typically exhibit opposing responses to thrombospondin-1, we examined thrombospondin-1 effects on NO signaling in VSMC. METHODS: Effects of exogenous thrombospondin-1 on human VSMC adhesion, chemotaxis, proliferation, and cGMP signaling were examined. Endogenous thrombospondin-1 function was characterized by comparing NO signaling in VSMC from wild type and thrombospondin-1 null mice. RESULTS: Picomolar concentrations of exogenous thrombospondin-1 prevented adhesive, chemotactic, and proliferative responses of human aortic VSMC stimulated by low dose NO. A recombinant CD36-binding domain of thrombospondin-1 or antibody ligation of CD36 similarly inhibited NO-stimulated VSMC responses. Thrombospondin-1 and CD36 ligation inhibited NO responses in VSMC by preventing cGMP accumulation. Thrombospondin-1 null VSMC responses to NO and cGMP signaling were enhanced relative to wild type murine VSMC. CONCLUSIONS: In the presence of NO, thrombospondin-1 is converted from a weak stimulator to a potent inhibitor of VSMC responses. Both exogenous and endogenous thrombospondin-1 inhibit NO signaling in VSMC. This activity is mediated by the type 1 repeats and utilizes the same CD36-dependent cGMP signaling pathway in endothelial and VSMC.

Animals↗

PubMed2005

Guanylyl cyclase-dependent chemotaxis of endothelial cells in response to nitric oxide gradients.

Nitric oxide (NO) is an important regulator of angiogenesis and neovascularization. The nature of endothelial cell motility responses to NO was examined using a Boyden chamber method. NO generated via decomposition of either DEA/NO or DETA/NO produced increases in human umbilical vein endothelial cell (HUVEC) chemotaxis, which were completely abrogated by ODQ, a soluble guanylyl cyclase inhibitor. Measurements of NO either directly by chemiluminescence or its chemistry with diaminofluorescein revealed that chemotaxis was driven by subtle NO gradients between the lower and the upper wells in this system. In addition to diffusion and volatilization from the upper chambers, the data showed that HUVEC consumption of NO contributed to these sustained gradients. Comparison of DEA/NO- and DETA/NO-mediated responses suggested that the persistence of spatial NO gradients is as significant as the absolute magnitude of NO exposure per unit time. The findings suggest that subnanomolar NO gradients are sufficient to mobilize endothelial cell migration into hypoxic tissue during neovascularization events, such as in wound healing and cancer.

Cell Movement↗

PubMed2005

Thrombospondin-1 inhibits endothelial cell responses to nitric oxide in a cGMP-dependent manner.

Redox signaling plays an important role in the positive regulation of angiogenesis by vascular endothelial growth factor, but its role in signal transduction by angiogenesis inhibitors is less clear. Using muscle explants in 3D culture, we found that explants from mice lacking the angiogenesis inhibitor thrombospondin-1 (TSP1) exhibit exaggerated angiogenic responses to an exogenous NO donor, which could be reversed by providing exogenous TSP1. To define the basis for inhibition by TSP1, we examined the effects of TSP1 on several proangiogenic responses of endothelial cells to NO. NO has a biphasic effect on endothelial cell proliferation. The positive effect at low doses of NO is sensitive to inhibition of cGMP signaling and picomolar concentrations of TSP1. NO stimulates both directed (chemotactic) and random (chemokinetic) motility of endothelial cells in a cGMP-dependent manner. TSP1 potently inhibits chemotaxis stimulated by NO. Low doses of NO also stimulate adhesion of endothelial cells on type I collagen in a cGMP-dependent manner. TSP1 potently inhibits this response both upstream and downstream of cGMP. NO-stimulated endothelial cell responses are inhibited by recombinant type 1 repeats of TSP1 and a CD36 agonist antibody but not by the N-terminal portion of TSP1, suggesting that CD36 or a related receptor mediates these effects. These results demonstrate a potent antagonism between TSP1 and proangiogenic signaling downstream of NO. Further elucidation of this inhibitory signaling pathway may identify new molecular targets to regulate pathological angiogenesis.

Animals↗

PubMed2005

Nitric oxide regulates angiogenesis through a functional switch involving thrombospondin-1.

Nitric oxide (NO) donors have been shown to stimulate and inhibit the proliferation, migration, and differentiation of endothelial cells in vitro and angiogenesis in vivo. Recently, we have shown distinct thresholds for NO to regulate p53-Ser-15P, phosphorylated extracellular signal-regulated kinase (pERK), and hypoxia inducible factor 1alpha in tumor cells. Because these signaling pathways also promote the growth and survival of endothelial cells, we examined their roles in angiogenic responses of venous endothelial cells and vascular outgrowth of muscle explants elicited by NO. An additional protein involved in the regulation of angiogenesis is thrombospondin-1 (TSP1), a matricellular glycoprotein known to influence adhesion, migration, and proliferation of endothelial cells. Here we demonstrate a triphasic regulation of TSP1 mediated by a slow and prolonged release of NO that depends on ERK phosphorylation. Under conditions of 5% serum, a 24-h exposure of NO donor (0.1-1,000 microM) mediated a triphasic response in the expression of TSP1 protein: decreasing at 0.1 microM, rebounding at 100 microM, and decreasing again at 1,000 microM. Under the same conditions, we observed a dose-dependent increase in P53 phosphorylation and inverse biphasic responses of pERK and mitogen-activated protein kinase phosphatase-1. Both the growth-stimulating activity of low-dose NO for endothelial cells and suppression of TSP1 expression were ERK-dependent. Conversely, exogenous TSP1 suppressed NO-mediated pERK. These results suggest that dose-dependent positive- and negative-feedback loops exist between NO and TSP1. Limiting TSP1 expression by positive feedback through the ERK mitogen-activated protein kinase pathway may facilitate switching to a proangiogenic state at low doses of NO.

Animals↗

PubMed2005

The N-terminal module of thrombospondin-1 interacts with the link domain of TSG-6 and enhances its covalent association with the heavy chains of inter-alpha-trypsin inhibitor.

We recently found that leukocytes from thrombospondin-1 (TSP1)-deficient mice exhibit significant reductions in cell surface CD44 relative to those from wild type mice. Because TSG-6 modulates CD44-mediated cellular interactions with hyaluronan, we examined the possibility that TSP1 interacts with TSG-6. We showed that recombinant full-length human TSG-6 (TSG-6Q) and the Link module of TSG-6 (Link_TSG6) bind 125I-TSP1 with comparable affinities. Trimeric recombinant constructs containing the N-modules of TSP1 or TSP2 inhibit binding of TSP1 to TSG-6Q and Link_TSG6, but other recombinant regions of TSP1 do not. Therefore, the N-modules of both TSP1 and TSP2 specifically recognize the Link module of TSG-6. Heparin, which binds to these domains of both proteins, strongly inhibits binding of TSP1 to Link_TSG6 and TSG-6Q, but hyaluronan does not. Inhibition by heparin results from its binding to TSP1, because heparin also inhibits TSP1 binding to Link_TSG6 mutants deficient in heparin binding. Removal of bound Ca2+ from TSP1 reduces its binding to full-length TSG-6. Binding of TSP1 to Link_TSG6, however, is enhanced by chelating divalent cations. In contrast, divalent cations do not influence binding of the N-terminal region of TSP1 to TSG-6Q. This implies that divalent cation dependence is due to conformational effects of calcium-binding to the C-terminal domains of TSP1. TSP1 enhances covalent modification of the inter-alpha-trypsin inhibitor by TSG-6 and transfer of its heavy chains to hyaluronan, suggesting a physiological function of TSP1 binding to TSG-6 in regulation of hyaluronan metabolism at sites of inflammation.

Alpha-Globulins↗

PubMed2005

Endothelial monocyte activating polypeptide-II induced gene expression changes in endothelial cells.

In the current study we used microarray (MA) analysis to examine gene expression changes in human umbilical vein endothelial cells (HUVEC) exposed to the tumor-derived cytokine, endothelial monocyte-activating polypeptide-II (EMAP-II). HUVEC treated with EMAP-II for 0.5, 1, 2, 4 and 8 h, were analyzed using 10K cDNA arrays. Our results demonstrated that changes in gene expression of <0.5 and >2 fold were seen for 69 genes and the majority of gene changes occurred early. Validation of MA analysis for 10 genes by real time RT-PCR, demonstrated the gene changes to be consistent and specific to HUVEC when compared to human fibroblasts treated with EMAP-II. Among these genes, downregulated in ovarian cancer 1 (DOC1) gene was studied further because of its possible role in EMAP-II induced cytoskeletal remodeling. DOC1 expression was silenced using small interfering RNA. SiRNA to DOC1 completely abolished EMAP-II stimulated gene expression of DOC1. Silencing of DOC1 gene expression reversed the modulatory effect of EMAP-II on 4 other genes, suggesting that DOC1 might play a role in mediating some of the effects of EMAP-II on endothelial cells.

Cell Proliferation↗

PubMed2005

Endogenous thrombospondin-1 is not necessary for proliferation but is permissive for vascular smooth muscle cell responses to platelet-derived growth factor.

We have reexamined the role of endogenous thrombospondin-1 (TSP1) in growth and motility of vascular smooth muscle cells (SMCs). Based on the ability of aortic-derived SMCs isolated from TSP1 null mice and grown in the absence of exogenous TSP1 to grow at comparable rates and to a slightly higher density than equivalent cells from wild-type mice, TSP1 is not necessary for their growth. Low concentrations of exogenous TSP1 stimulate growth of TSP1 null SMCs, but higher doses of TSP1 or its C-terminal domain are inhibitory. However, SMCs from TSP1 null mice are selectively deficient in chemotactic and proliferative responses to platelet-derived growth factor and in outgrowth in three-dimensional cultures. Recombinant portions of the N- and C-terminal domains of TSP1 stimulate SMC chemotaxis through different integrin receptors. Based on these data, the relative deficiency in SMC outgrowth during an ex vivo angiogenic response of muscle tissue from TSP1 null mice is probably due to restriction of platelet-derived growth factor dependent SMC migration and/or proliferation.

Animals↗

PubMed2005

Nitric oxide in wound-healing.

Modulation of the complex process of wound-healing remains a surgical challenge. Little improvement beyond controlling infection, gentle tissue handling, and debridement of necrotic tissue has been had in the modern era. However, increasing appreciation of the process from a biomolecular perspective offers the potential for making significant strides in wound modulation. The bioactive molecule nitric oxide was found to have wide-ranging impact on cellular activities, including the cellular responses engendered by wound healing. Current research suggests that nitric oxide and several nitric oxide donors can exert biologic effects, although the particular net responses of cells contributing to wound repair are context-dependent.

Humans↗

PubMed2005

Novel integrin antagonists derived from thrombospondins.

Specific antagonists have been successfully developed for several different integrins. Clinical trials have been initiated to study therapeutic uses of these inhibitors in cancer, thrombosis, and inflammatory diseases. Most efforts to date have focused on the platelet integrin alphaIIbbeta3, endothelial alphavbeta3, and the leukocyte integrin alpha4beta1. However, the integrin family contains additional members with interesting tissue specificities and functional properties that could also be useful molecular targets for disease intervention. In many cases, specific recognition motifs for these integrins have not been identified, which has precluded development of specific antagonists. Our recent studies of thrombospondin-1 and thrombospondin-2 recognition by integrins have revealed novel motifs for alpha3beta1 and alpha6beta1 integrins as well as new motifs recognized by the well studied alpha4beta1 integrin. These three integrins play distinct roles in angiogenesis and its modulation by thrombospondins. This review will discuss recent insights into the specificities of alpha3beta1 and alpha6beta1 integrins, their functions in angiogenesis, and potential applications for antagonists of these integrins and of alpha4beta1 to control pathological angiogenesis and other diseases.

Amino Acid Sequence↗

PubMed2004

Identification of novel beta1 integrin binding sites in the type 1 and type 2 repeats of thrombospondin-1.

In addition to the three known beta(1) integrin recognition sites in the N-module of thrombospondin-1 (TSP1), we found that beta(1) integrins mediate cell adhesion to the type 1 and type 2 repeats. The type 1 repeats of TSP1 differ from typical integrin ligands in that recognition is pan-beta(1)-specific. Adhesion of cells that express one dominant beta(1) integrin on immobilized type 1 repeats is specifically inhibited by antagonists of that integrin, whereas adhesion of cells that express several beta(1) integrins is partially inhibited by each alpha-subunit-specific antagonist and completely inhibited by combining the antagonists. beta(1) integrins recognize both the second and third type 1 repeats, and each type 1 repeat shows pan-beta(1) specificity and divalent cation dependence for promoting cell adhesion. Adhesion to the type 2 repeats is less sensitive to alpha-subunit antagonists, but a beta(1) blocking antibody and two disintegrins inhibit adhesion to immobilized type 2 repeats. beta(1) integrin expression is necessary for cell adhesion to the type 1 or type 2 repeats, and beta(1) integrins bind in a divalent cation-dependent manner to a type 1 repeat affinity column. The widely used TSP1 function blocking antibody A4.1 binds to a site in the third type 2 repeat. A4.1 proximally inhibits beta(1) integrin-dependent adhesion to the type 2 repeats and indirectly inhibits integrin-dependent adhesion mediated by the TSP1 type 1 repeats. Although antibody A4.1 is also an antagonist of CD36 binding to TSP1, these data suggest that some biological activities of A4.1 result from antagonism of these novel beta(1) integrin binding sites.

Antibodies, Monoclonal↗

PubMed2004

Sensing the host environment: recognition of hemoglobin by the pathogenic yeast Candida albicans.

Adhesion to host cells and tissues is important for several steps in the pathogenesis of disseminated Candida albicans infections. Although such adhesion is evident in vivo and for C. albicans grown in vitro in complex medium, some adhesive activities are absent when cultures are grown in defined media. However, addition of hemoglobin to defined media restores binding and adhesion to several host proteins. This activity of hemoglobin is independent of iron acquisition and is mediated by a cell surface hemoglobin receptor. In addition to regulating expression of adhesion receptors, hemoglobin rapidly induces expression of several genes. One of these, a heme oxygenase, allows the pathogen to utilize exogenous heme or hemoglobin to acquire iron and to produce the cytoprotective molecules alpha-biliverdin and carbon monoxide. The specific recognition of and responses to hemoglobin demonstrate a unique adaptation of C. albicans to be both a commensal and an opportunistic pathogen in humans.

Binding Sites↗

PubMed2004

Functional regulation of T lymphocytes by modulatory extracellular matrix proteins.

In addition to the major structural molecules, which are constitutively present in extracellular matrices, several proteins appear in the extracellular matrix only at specific stages in development or in association with specific pathological conditions. These proteins include thrombospondin-1 and -2, tenascin C, osteopontin, members of the cysteine-rich 61/connective tissue growth factor/nephroblastoma overexpressed family, and secreted protein acidic and rich in cysteine (osteonectin). These proteins play important roles in regulating cell fate during development and in the pathogenesis of several diseases in adult animals. We will review the interactions of T cells with this class of molecules and their resulting effects on T cell behavior. Receptors and signal transduction pathways that mediate the actions of matricellular proteins on T cells are beginning to be defined. Transgenic mice are providing new insights into the functions of these proteins in vivo and are yielding insights into the significance of their reported dysregulation in several human diseases.

Animals↗