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      The Effect of Phenotype on Mechanical Stretch-Induced Vascular Smooth Muscle Cell Apoptosis

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          Abstract

          The present study evaluated mechanical stretch-induced apoptosis in swine vascular smooth muscle cells (VSMC) of different phenotypes. We demonstrated that differentiated VSMC express a greater level of Bcl-2-associated death factor (BAD) and have a significant cell loss when exposed to mechanical stretch (10% elongation, 1 Hz) for 24 h. We further demonstrated that apoptosis was significantly increased only in differentiated VSMC exposed to mechanical stretch. To test the hypothesis that the intracellular level of BAD in VSMC determines its response to mechanical stretch-induced apoptosis, we examined whether BAD expression was upregulated by mechanical stretch-induced apoptosis and was associated with the increase in the apoptosis level of differentiated VSMC. When exposed to mechanical stretch, the expression of BAD in differentiated VSMC was elevated at 1 h and remained at higher levels during the application of stretch (24 h). In contrast, Bcl-2 expression was suppressed during the application of stretch. Moreover, the proapoptotic function of BAD was inhibited by overexpression of Bcl-2 through transient transfection of VSMC with pCEP4-Bcl-2 or incubation of VSMC with vascular epithelial growth factor. These results suggest that mechanical stretch-induced VSMC apoptosis is phenotype dependent. The higher levels of apoptosis of differentiated VSMC upon mechanical stretch were, at least in part, dependent on their intrinsic level of BAD.

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          Most cited references 16

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          Serine phosphorylation of death agonist BAD in response to survival factor results in binding to 14-3-3 not BCL-X(L)

          Extracellular survival factors alter a cell's susceptibility to apoptosis, often through posttranslational mechanisms. However, no consistent relationship has been established between such survival signals and the BCL-2 family, where the balance of death agonists versus antagonists determines susceptibility. One distant member, BAD, heterodimerizes with BCL-X(L) or BCL-2, neutralizing their protective effect and promoting cell death. In the presence of survival factor IL-3, cells phosphorylated BAD on two serine residues embedded in 14-3-3 consensus binding sites. Only the nonphosphorylated BAD heterodimerized with BCL-X(L) at membrane sites to promote cell death. Phosphorylated BAD was sequestered in the cytosol bound to 14-3-3. Substitution of serine phosphorylation sites further enhanced BAD's death-promoting activity. The rapid phosphorylation of BAD following IL-3 connects a proximal survival signal with the BCL-2 family, modulating this checkpoint for apoptosis.
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            BCL-2 family: regulators of cell death.

            An expanding family of BCL-2 related proteins share homology, clustered within four conserved regions, namely BCL-2 homology (BH1-4) domains, which control the ability of these proteins to dimerize and function as regulators of apoptosis. Moreover, BCL-XL, BCL-2, and BAX can form ion-conductive pores in artificial membranes. The BCL-2 family, comprised of both pro-apoptotic and anti-apoptotic members, acts as a checkpoint upstream of CASPASES and mitochondrial dysfunction. BID and BAD possess the minimal death domain BH3, and the phosphorylation of BAD connects proximal survival signals to the BCL-2 family. BCL-2 and BCL-XL display a reciprocal pattern of expression during lymphocyte development. Gain- and loss-of-function models revealed stage-specific roles for BCL-2 and BCL-XL. BCL-2 can rescue maturation at several points of lymphocyte development. The BCL-2 family also reveals evidence for a cell-autonomous coordination between the opposing pathways of proliferation and cell death.
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              VEGF(165) promotes survival of leukemic cells by Hsp90-mediated induction of Bcl-2 expression and apoptosis inhibition.

              Similar to endothelial cells (ECs), vascular endothelial growth factor (VEGF) induces Bcl-2 expression on VEGF receptor-positive (VEGFR(+)) primary leukemias and cell lines, promoting survival. We investigated the molecular pathways activated by VEGF on such leukemias, by performing a gene expression analysis of VEGF-treated and untreated HL-60 leukemic cells. One gene to increase after VEGF stimulation was heat shock protein 90 (Hsp90). This was subsequently confirmed at the protein level, on primary leukemias and leukemic cell lines. VEGF increased the expression of Hsp90 by interacting with KDR and activating the mitogen-activated protein kinase cascade. In turn, Hsp90 modulated Bcl-2 expression, as shown by a complete blockage of VEGF-induced Bcl-2 expression and binding to Hsp90 by the Hsp90-specific inhibitor geldanamycin (GA). GA also blocked the VEGF-induced Hsp90 binding to APAF-1 on leukemic cells, a mechanism shown to inhibit apoptosis. Notably, VEGF blocked the proapoptotic effects of GA, correlating with its effects at the molecular level. Earlier, we showed that in some leukemias, a VEGF/KDR autocrine loop is essential for cell survival, whereas here we identified the molecular correlates for such an effect. We also demonstrate that the generation of a VEGF/VEGFR autocrine loop on VEGFR(+) cells such as ECs, also protected them from apoptosis. Infection of ECs with adenovirus-expressing VEGF resulted in elevated Hsp90 levels, increased Bcl-2 expression, and resistance to serum-free or GA-induced apoptosis. In summary, we demonstrate that Hsp90 mediates antiapoptotic and survival-promoting effects of VEGF, which may contribute to the survival advantage of VEGFR(+) cells such as subsets of leukemias.
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                Author and article information

                Journal
                JVR
                J Vasc Res
                10.1159/issn.1018-1172
                Journal of Vascular Research
                S. Karger AG
                1018-1172
                1423-0135
                2006
                May 2006
                17 May 2006
                : 43
                : 3
                : 229-237
                Affiliations
                aColumbus Children’s Research Institute, Children’s Hospital, bDepartment of Pediatrics, and cDavis Heart and Lung Research Institute, Ohio State University, Columbus, Ohio, USA
                Article
                91102 J Vasc Res 2006;43:229–237
                10.1159/000091102
                16432304
                © 2006 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

                Page count
                Figures: 7, References: 25, Pages: 9
                Categories
                Research Paper

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