Abstract 4609: Epigenetic regulation of BRM

Abstract BRM is part of the SWI/SNF complex and is key anticancer protein which is silenced in variety of tumor types. SWI/SNF is a prerequisite for the function of many different anticancer proteins such as Rb and p53 and it has essential roles in growth control, differentiation, development, cell adhesion, and DNA repair. Consequently, inactivation or impairment of this complex can stimulate tumor development and tumor progression through the abrogation of a number of anticancer mechanisms. Unlike many tumor suppressor proteins, BRM is not mutated, but rather epigenetically suppressed, which is validated by the fact that HDAC inhibitors were the first compounds found to restore BRM expression. Unfortunately, these compounds are too broadly active and in addition to restoring BRM expression, they inactivate it by acetylation. To try to better understand how BRM is epigenetically regulated, we knocked-out each of the known 11 HDACs, using shRNAs in BRM-deficient and BRM-positive cell lines to determine which ones regulate or inactivate BRM. We found that that shRNA knockdown of only HDAC3 or HDAC9 restores both BRM expression and function, while suppression of HDAC2 induces BRM acetylation. Similarly, we tested the impact of over-expression of 25 different Histone Acetyltransferases (HATs) on BRM expression and acetylation. We found ectopic expression of KAT6A, KAT6B, and KAT7 in BRM-deficient cell lines induces BRM whereas ectopic expression of KAT2B and KAT8 causes BRM acetylation in BRM-positive cell lines. We also uncovered that HDAC9 is greatly over-expressed only in BRM-deficient cell lines and its expression is driven by MEF2D and GATA3. Expression and knockdown experiments directed at MEF2D and GATA3 showed that these transcription factors regulate BRM and HDAC9. Similarly, we found that GATA3 expression is only expressed in BRM-deficient cell lines. This work outlines the complex array of proteins which are tied to the expression and regulation of BRM. It is important to note this epigenetic mechanism is not likely specific to BRM, but rather likely regulates a cadre of anticancer and cellular proteins as well. Hence, determining how BRM is aberrantly regulated is the first step in determining how to target BRM and this mechanism for therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4609. doi:1538-7445.AM2012-4609