Epigenetische onderdrukking van het pro-apoptotisch gen Bim in multipel myeloom

Student thesis: Master's Thesis

Abstract

Multiple myeloma (MM) is a malignant blood cancer characterized by an uncontrolled growth of monoclonal plasma cells in the bone marrow (BM). Bim is a pro-apoptotic protein that induces apoptosis. In MM, silencing of the Bim expression by the BM microenvironment was shown and increased expression of anti-apoptotic genes has been demonstrated. Furthermore, there are indications that Bim expression is also regulated epigenetically. Here, we try to examine if the Bim expression is indeed epigenetically regulated and tried to identify the relative contribution of the two major epigenetic modifications, namely DNA methylation and histon modifications. Western Blot analyses showed strong expression of the BimEL, BimL and BimS isoforms in the human multiple myeloma cell lines RPMI8226 and U266. In contrast, in the human MM LP-1 cell line there was no expression of the three isoforms. Next, we attempted to induce (LP-1) or increase (RPMI8226 and U266) Bim expression by treatment with a methylation inhibitor (decitabine, DAC) and/or a histon deacetylase inhibitor (HDACi, LBH589). First, we ascertained the optimal concentration of both inhibitors. For decitabine a concentration inducing 50 % growth inhibition after 72 hours of treatment was chosen, for LBH589 a concentration resulting in 40 % apoptosis after 48 hours of treatment was chosen. For the LP-1, RPMI8226 and U266 cells respectively 250, 750 and 750 nM DAC and 15, 50 and 50 nM LBH589 was used. There was no effect on the Bim expression after treatment of the LP-1 and U266 cell line with LBH589 and/or DAC. For the RPMI8226 cell line, there was an increased Bim expression after treatment with LBH589, but not with DAC. A combination of both inhibitors strengthens the effect of LBH589. The data suggest that methylation and histone deacetylation play an important role in the epigenetic silencing of Bim in the RPMI8226 cells, with histon deacetylation being the principal mechanism.
Date of Award1 Jun 2008
Original languageDutch
SupervisorKarin Vanderkerken (Promotor) & Elke De Bruyne (Co-promotor)

Keywords

  • multiple myeloma

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