Abstract 2405: The 8p11 amplicon oncogenes ASH2L and NSD3 alter the epigenomic landscape and provide the foundation for novel application of epigenetic therapy in luminal B breast cancers
Authors: Mills Jamie N. , Ethier Stephen P. 
Published: July 2017

The 8p11-p12 genomic region is amplified in 15% of breast cancers and is associated with poorer prognosis, especially in the luminal B (ER+) subtype. This region harbors several oncogenes, three of which are epigenetic modifiers of chromatin: NSD3 (WHSC1L1) and ASH2L, which are histone methyltransferases, and KAT6A, a histone acetyltransferase. NSD3 preferentially di-methylates histone 3 lysine 36 (H3K36me2) in gene bodies to facilitate elongation, and ASH2L primarily tri-methylates histone 3 lysine 4 (H3K4me3) in promoter regions, which is also associated with active transcription. Previous work in the amplicon-bearing cell line SUM-44 implicated NSD3 in growth, survival, and overexpression and estrogen-independent activation of the estrogen receptor. Current work is focused on elucidating the mechanism behind these transforming features and exploring the epigenomic interactions of 8p11 oncogenes. Chromatin immunoprecipitation and high throughput sequencing (ChIP-seq) using an NSD3 antibody confirmed the presence of this factor in the gene body of ESR1, as well as several other important genes. As NSD3 lacks the ability to bind chromatin directly, it relies on adaptor proteins such as BRD4, a member of the BET bromodomain family that binds acetylated histones such as those generated by KAT6A. Indeed, we have shown that BRD4 binds NSD3 in SUM-44 cells. Similar to our previous findings with NSD3, knockdown of BRD4 and ASH2L reduced cell proliferation and clonogenic potential. To examine the influence of ASH2L on histone methylation in gene promotors, we performed ChIP-seq using an H3K4me3 antibody. The data showed a dramatic decrease in the number of peaks called following knockdown of ASH2L and peaks in the NSD3 promotor disappeared. This finding solidifies the connection between these oncogenes and their cooperative regulation of the epigenome, and therefore the transcriptome, in this cell line, explaining the effects of NSD3 on cell growth and behavior. Amplification and overexpression of oncogenes in the 8p11 region is most prevalent in ER+ breast cancer, treated clinically with endocrine therapies. Patients with poor response to these therapies have few alternatives and often succumb to their disease. This study and continued investigation of 8p11 amplicon oncogenes opens an important new treatment opportunity for these patients: epigenetic therapy. Previous work identifying these patients as candidates for novel anti-estrogen SERD compounds suggests that combination therapy with a BET bromodomain inhibitor could have major therapeutic benefit in a patient group currently without treatment options, thereby improving patient outcomes by a novel mechanism in luminal B breast cancer.

Citation Format: Jamie N. Mills, Stephen P. Ethier. The 8p11 amplicon oncogenes ASH2L and NSD3 alter the epigenomic landscape and provide the foundation for novel application of epigenetic therapy in luminal B breast cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2405. doi:10.1158/1538-7445.AM2017-2405