Abstract 5151: A687V EZH2 is a driver of histone H3 lysine 27 (H3K27) hyper-trimethylation

Abstract The EZH2 methyltransferase silences gene expression through methylation of histone H3 on lysine 27 (H3K27). Recently, EZH2 mutations have been reported at Y641, A677, and A687 in non-Hodgkin's lymphoma. While the Y641F/N/S/H/C and A677G mutations exhibit clearly increased activity with substrates di-methylated at lysine 27 (H3K27me2), the A687V mutant has been shown to prefer a mono-methylated lysine 27 (H3K27me1) with little gain of activity toward H3K27me2. Herein, we demonstrate that despite this unique substrate preference, A687V EZH2 still drives increased H3K27me3 when transiently expressed in cells. However, unlike the previously described mutants which dramatically deplete global H3K27me2 levels, A687V EZH2 retains normal levels of H3K27me2. Sequencing of B-cell derived cancer cell lines identified a cell line harboring this mutation. Similar to exogenous expression of A687V EZH2, this cell line exhibited elevated H3K27me3 while possessing H3K27me2 levels higher than Y641 or A677 mutant lines. Treatment of A687V EZH2 mutant cells with GSK126, a selective EZH2 inhibitor, induced global H3K27me3 demethylation, robust gene activation, caspase activation, and decreased proliferation. These findings suggest that A687V EZH2 likely increases global H3K27me3 indirectly through increased catalytic activity with H3K27me1 and cells harboring this mutation are highly dependent on EZH2 activity for their survival. Citation Format: Heidi Ott, Alan Graves, Melissa Pappalardi, Ryan Kruger, Peter Tummino, Caretha Creasy, Michael T. McCabe. A687V EZH2 is a driver of histone H3 lysine 27 (H3K27) hyper-trimethylation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5151. doi:10.1158/1538-7445.AM2014-5151