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Research Articles: Therapeutics, Targets, and Development

Silencing Bcl-2 in models of mantle cell lymphoma is associated with decreases in cyclin D1, nuclear factor-B, p53, bax, and p27 levels

Departments of ¹ Advanced Therapeutics, ² Cancer Endocrinology, ³ Medical Biophysics, and ⁴ Cancer Genetics and Developmental Biology, BC Cancer Research Center; ⁵ Department of Pathology and Laboratory Medicine, University of British Columbia; Divisions of ⁶ Pathology and ⁷ Medical Oncology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada

Requests for reprints: Catherine A. Tucker, Department of Advanced Therapeutics, BC Cancer Research Center, Vancouver, British Columbia, Canada V5Z 1L3. Phone: 604-675-7024; Fax: 604-675-8183. E-mail: ctucker{at}bccrc.ca

Abstract

Molecular mechanisms responsible for lymphoma resistance to apoptosis often involve the bcl-2 pathway. In this study, we investigated the cell signaling pathways activated in bcl-2-overexpressing human mantle cell lymphoma cell lines (JVM-2 and Z-138) that have been treated with oblimersen, a molecular gene silencing strategy that effectively suppresses bcl-2 in vitro and in vivo. Z-138 cells expressed higher levels of bcl-2 and were more sensitive to the effects of bcl-2 silencing, mediated by oblimersen or bcl-2 small interfering RNA, in vitro. Tumors derived following injection of Z-138 cells were sensitive to oblimersen as judged by decreases in tumor growth rate and decreases in cell proliferation (as measured by Ki-67). Immunohistochemistry and Western blot analysis of oblimersen-treated Z-138 tumors revealed a dose-dependent decrease in bcl-2 levels and an associated increase in the proapoptotic proteins caspase-3 and caspase-9. Silencing bcl-2 in Z-138 xenografts revealed an associated dose-dependent suppression of bax, a decrease in nuclear factor-B and phospho-nuclear factor-B, and transient loss of p53 levels. Coimmunoprecipitation studies suggest that the latter observation is mediated by an association between bcl-2 and phospho-mdm2. Bcl-2 silencing also led to p27 down-regulation and coimmunoprecipitation studies point to a role for bcl-2 in regulation of p27 localization/degradation. Bcl-2 silencing was also correlated with loss of cyclin D1a protein levels but not cyclin D1b levels. Coimmunoprecipitation studies indicate that bcl-2 may mediate its effects on cyclin D1a via interaction with p38 mitogen-activated protein kinase as well as a previously unreported interaction between bcl-2 and cyclin D1a. [Mol Cancer Ther 2008;7(4):749–58]

Grant support: Lymphoma Research Foundation (R.D. Gascoyne and R.J. Klasa), Canadian Institutes of Health Research (M. Bally), and Academy of Finland and Cultural Foundation of Finland salary award (A.I. Kapanen).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

⁸ C.A. Tucker, A.H. Kyle, B.G. Hoffman, et al. Abnormal expression of soluble and membrane bound Fas ligand in mantle cell lymphoma: potential for resistance to Fas-mediated cell death and immune evasion. In preparation.

Received 4/28/07; revised 12/20/07; accepted 2/21/08.