Abstract 1396: Role of epigenetic reader and alternative mRNA splicing variant MBD2 variant 2 in triple-negative breast cancer
Authors: Girsch Emily A. , Bao Bin , Mitrea Cristina , Dyson Gregory , Boerner Julie , Polin Lisa , Terlecky Stan R. , Bollig-Fischer Aliccia 
Published: July 2017

Abstract
Background: Among all breast cancer patients, those diagnosed with the triple-negative breast cancer (TNBC) subtype have the worst prognosis, in part attributable to the fact that TNBC lacks targets for effective molecularly-targeted therapies. The concept that EGFR inhibitor drugs could be used as a targeted treatment against TNBC has been put forth because roughly 50% of TNBC express high levels of EGFR. However clinical trials targeting EGFR did not significantly improve patient outcomes. Our recent work offers a potential explanation as to why EGFR inhibitors failed and supports an innovative therapeutic approach combining an EGFR tyrosine kinase inhibitor with the novel antioxidant biologic, CAT-SKL. Our data indicate that inhibition of cancer stem cell-like cells depends on antioxidant-induced downregulation of an alternative mRNA splice variant of the methyl-CpG binding domain 2 gene, MBD2_v2.
Objective and Methods: The purpose of the present study was to evaluate the importance of MBD2_v2 in TNBC and better understand how CAT-SKL regulates its expression. Using TNBC cell lines we investigated the effects of MBD2_v2 expression on tumor initiation capacity. Furthermore we studied MBD2_v2 mRNA levels in an in vivo tumor xenograph mouse model of TNBC and in human TNBC samples using an existing database. Then by RNA-seq analysis we assessed how CAT-SKL regulates MBD2_v2 expression in TNBC cells through differential gene expression.
Results: The results support that MBD2_v2 expression is regulated by redox signaling in TNBC cells, which is tightly linked to TNBC cell tumor initiation capacity. Furthermore, MBD2_v2 was upregulated in tumors harvested from overweight mice, which also displayed increased tumor take rate, suggesting that a pro-inflammatory tumor microenvironment could play a role in promoting MBD2_v2 expression. In addition, RNA-seq analysis identified an overrepresentation of mRNA splicing factors with expression downregulated by CAT-SKL treatment of TNBC cells. From this gene set two splicing co-factors are highlighted: SRRM1 and CPSF3. These co-factors are critical for splicing factor function, 3’ end formation and polyadenylation; and both have been linked via protein-protein interaction to a relevant exonic splicing enhancer site in exon 3 of the MBD2 _v2 transcript. Finally, according to the Kaplan Meier Plotter database high MBD2_v2 levels in BC were associated with shorter relapse free survival.
Conclusion: Our investigation sheds light on the relevance of MBD2_v2 expression in TNBC, and how a select antioxidant regulates its expression. The application of which holds promise of a novel, targeted therapeutic modality for TNBC, the subtype with the worst prognosis and highest need for treatment options.
Citation Format: Emily A. Girsch, Bin Bao, Cristina Mitrea, Gregory Dyson, Julie Boerner, Lisa Polin, Stan R. Terlecky, Aliccia Bollig-Fischer. Role of epigenetic reader and alternative mRNA splicing variant MBD2 variant 2 in triple-negative breast cancer [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 1396. doi:10.1158/1538-7445.AM2017-1396