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

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

^* To whom correspondence should be addressed. 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]

Key Words: MCL, oblimersen, siRNA, bcl-2, cyclin D1a