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      CD47-Independent Effects Mediated by the TSP-Derived 4N1K Peptide

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      1 , 2 , 3 , 1 , 3 , *
      PLoS ONE
      Public Library of Science

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          Abstract

          4N1K is a peptide fragment derived from the C-terminal, globular domain of thrombospondin which has been shown to mediate integrin-dependent cell adhesion and promote integrin activation acting via the cell-surface receptor, CD47. However, some studies found that 4N1K could act independently of CD47, putting in question the specificity of 4N1K for CD47. This led us to characterize the cellular and non-cellular effects of 4N1K. We found that 4N1K stimulated a potent increase in binding of a variety of non-specific IgG antibodies to cells in suspension. We also found that these same antibodies, as well as CD47-deficient cells, could bind substrate-immobilized 4N1K significantly better than a control peptide, 4NGG. Furthermore, we found that cells treated with 4N1K at higher concentrations inhibited, while lower concentrations promoted cell adhesion to immobilized fibronectin as an integrin substrate. Importantly, both the stimulatory and the inhibitory activity of 4N1K occurred as efficiently in the CD47-deficient JinB8 cells, as it did in the CD47-expressing parental or in JinB8 cells reconstituted with CD47 expression. Given these results, we suggest that 4N1K interacts non-specifically with epitopes commonly found on the cell surface, and conclude that it is not a suitable peptide for use to study the consequences of CD47 receptor ligation.

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          Most cited references39

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          The bone marrow microenvironment as a tumor sanctuary and contributor to drug resistance.

          The bone marrow microenvironment facilitates the survival, differentiation, and proliferation of hematopoietic cells. These cells are supported by fibroblast-like bone marrow stromal cells, osteoblasts, and osteoclasts which secrete soluble factors and extracellular matrix proteins that mediate these functions. This rich environment serves as a safe haven not only for normal and malignant hematopoietic cells, but also for epithelial tumor cells that metastasize to bone, offering protection from chemotherapeutic agents by common mechanisms. Soluble factors produced in the bone marrow, such as stromal cell-derived factor-1 and interleukin-6, mediate homing, survival, and proliferation of tumor cells, and integrin-mediated adhesion sequesters tumor cells to this protective niche. Environment-mediated drug resistance includes a combination of soluble factors and adhesion, and can be subdivided into soluble factor-mediated drug resistance and cell adhesion-mediated drug resistance. Because it is induced immediately by the microenvironment and is independent of epigenetic or genetic changes caused by the selective pressure of drug exposure, environment-mediated drug resistance is a form of de novo drug resistance. In this form of drug resistance, tumor cells are transiently and reversibly protected from apoptosis induced by both chemotherapy and physiologic mediators of cell death. This protection allows tumor cells to survive the insult of chemotherapy, leading to minimal residual disease, and thereby increases the probability for the development of acquired drug resistance.
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            The ins and outs of leukocyte integrin signaling.

            Integrins are the principal cell adhesion receptors that mediate leukocyte migration and activation in the immune system. These receptors signal bidirectionally through the plasma membrane in pathways referred to as inside-out and outside-in signaling. Each of these pathways is mediated by conformational changes in the integrin structure. Such changes allow high-affinity binding of the receptor with counter-adhesion molecules on the vascular endothelium or extracellular matrix and lead to association of the cytoplasmic tails of the integrins with intracellular signaling molecules. Leukocyte functional responses resulting from outside-in signaling include migration, proliferation, cytokine secretion, and degranulation. Here, we review the key signaling events that occur in the inside-out versus outside-in pathways, highlighting recent advances in our understanding of how integrins are activated by a variety of stimuli and how they mediate a diverse array of cellular responses.
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              Role for CD47-SIRPalpha signaling in xenograft rejection by macrophages.

              We have previously proven that human macrophages can phagocytose porcine cells even in the absence of Ab or complement opsonization, indicating that macrophages present a pivotal immunological obstacle to xenotransplantation. A recent report indicates that the signal regulatory protein (SIRP)alpha is a critical immune inhibitory receptor on macrophages, and its interaction with CD47, a ligand for SIRPalpha, prevents autologous phagocytosis. Considering the limited compatibility (73%) in amino acid sequences between pig and human CD47, we hypothesized that the interspecies incompatibility of CD47 may contribute to the rejection of xenogeneic cells by macrophages. In the present study, we have demonstrated that porcine CD47 does not induce SIRPalpha tyrosine phosphorylation in human macrophage-like cell line, and soluble human CD47-Fc fusion protein inhibits the phagocytic activity of human macrophages toward porcine cells. In addition, we have verified that manipulation of porcine cells for expression of human CD47 radically reduces the susceptibility of the cells to phagocytosis by human macrophages. These results indicate that the interspecies incompatibility of CD47 significantly contributes to the rejection of xenogeneic cells by macrophages. Genetic induction of human CD47 on porcine cells could provide inhibitory signaling to SIRPalpha on human macrophages, providing a novel approach to preventing macrophage-mediated xenograft rejection.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2014
                21 May 2014
                : 9
                : 5
                : e98358
                Affiliations
                [1 ]Department of Pediatrics, University of British Columbia, Vancouver, British Columbia, Canada
                [2 ]Department of Cell and Developmental Biology, University of British Columbia, Vancouver, British Columbia, Canada
                [3 ]Child and Family Research Institute, BC Children's Hospital, Vancouver, British Columbia, Canada
                University of Toledo, United States of America
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: PL CJL. Performed the experiments: PL. Analyzed the data: PL CJL. Wrote the paper: PL CJL.

                Article
                PONE-D-14-04160
                10.1371/journal.pone.0098358
                4029904
                24848268
                bb5b76fb-0338-4540-a36a-7da124ec77c1
                Copyright @ 2014

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 29 January 2014
                : 1 May 2014
                Page count
                Pages: 8
                Funding
                This study was supported by grants from the Canadian Institutes of Health Research, National Science and Engineering Research Council, and the Canadian Foundation for Innovation awarded to C.J.L. P.L. received a Child and Family Research Institute-Michael Cuccione Graduate award. C.J.L. was supported by the Michael Cuccione Foundation and holds an investigatorship from the Child and Family Research Institute. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology and Life Sciences
                Biochemistry
                Proteins
                Extracellular Matrix Proteins
                Protein Interactions
                Cell Biology
                Cell Adhesion
                Integrins
                Cellular Types
                Animal Cells
                Blood Cells
                White Blood Cells
                T Cells
                Immune Cells
                Molecular Cell Biology
                Immunology

                Uncategorized
                Uncategorized

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