Abstract 2217: Genomic alteration of bromodomain protein ATAD2 in cancer
Authors: Takeda Tomoyo , Matsumura Yuta , Nagasaki Hirotoshi , Eguchi Ken , Takatsuka Miki , Shinkai Yoichi , Nakagawa Hiroyuki , Kawashima Hitoshi , Ueno Hiroyuki , Li Chiang J. 
Published: May 2015

ATPase family, AAA domain containing 2 (ATAD2), is a member of the bromodomain-containing protein family. ATAD2 associates with co-factors such as hormone receptors, E2Fs and c-Myc to control a specific subset of genes. Overexpression and copy number alteration of ATAD2 are observed in many types of cancer, and these alterations are correlated with poor clinical outcome in breast, lung, and endometrial cancers. Here, we present an integrated genomic analysis of ATAD2 using the Oncomine™ database that shows cancer-associated features of ATAD2. In The Cancer Genome Atlas, amplifications of ATAD2 are observed in 63% of ovarian, 52% of breast, 39% of colorectal, and 18% of lung cancer patients. By contrast, no amplification of ATAD2 is observed in corresponding normal tissues. In most cases, amplifications are modest ranging up to a copy number of six. Moreover, a high correlation between ATAD2 mRNA expression levels and its copy number is observed in cultured cell lines. In order to investigate the role of the bromodomain in ATAD2, we conducted a cell-free physicochemical binding analysis and in vitro physiological studies using human colon cancer cells (HCT-116). To identify binding partners for the ATAD2 bromodomain, we constructed ATAD2 AlphaScreen systems and examined the binding activity of the ATAD2 bromodomain protein to various acetylated or non-acetylated histone peptides. The ATAD2 bromodomain interacted with histone H4 acetylated at lysine 5, 8 or 12, but not with other acetylated and non-acetylated histone peptides. Subcellular localization analysis by immunofluorescence, demonstrated that ATAD2 is mainly localizes to nucleus and that treatment with trichostatin A, an inhibitor of histone deacetylases increased nuclear ATAD2 protein levels, suggesting that the acetylation level of histone tails may affect ATAD2 expression or localization. In in silico expression analysis using the Cancer Cell Line Encyclopedia, showed most genes that correlated with ATAD2 expression have a role in proliferation or survival. To determine if the ATAD2 protein directly controls transcription of these genes, we performed ChIP-PCR assays and found that ATAD2 protein occupies the DNA promoter regions of downstream targets, eg. TOP2A, but does not occupy the promoters of non-target negative controls, such as β-actin. In conclusion, we show ATAD2 copy number alteration in a large number of cancer patients, suggesting that ATAD2 expression, or genomic alteration, may be useful prognostic markers of cancer. We also show that physicochemical binding of the ATAD2 bromodomain to specific acetylated histone peptides suggesting a physiological function of ATAD2 in nucleus as a transcriptional regulator of tumor-related genes. These results suggest that a blockade of ATAD2 bromodomain binding to specific acetylated histone tails may provide a novel approach to anti-tumor drug development.

Citation Format: Tomoyo Takeda, Yuta Matsumura, Hirotoshi Nagasaki, Ken Eguchi, Miki Takatsuka, Yoichi Shinkai, Hiroyuki Nakagawa, Hitoshi Kawashima, Hiroyuki Ueno, Chiang J. Li. Genomic alteration of bromodomain protein ATAD2 in cancer. [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 2217. doi:10.1158/1538-7445.AM2014-2217