Abstract C47: Obesity enhances tumor colonization and promotes expression of the spliced variant MBD2_v2 and splicing factor SRSF2 in triple-negative breast cancer
Authors: Girsch Emily A. , Dyson Gregory , Mitrea Cristina , Bao Bin , Polin Lisa , Bollig-Fischer Aliccia 
Published: February 2019

Introduction: Triple-negative breast cancer (TNBC) is a molecular subtype that accounts for approximately 15-20% of invasive breast cancer diagnoses in the United States. TNBC occurs more prevalently in premenopausal African American women (AAW), and obesity coupled with chronic inflammation is a risk factor for both incidence and recurrence. TNBC is lacking therapeutic options and persons diagnosed with TNBC have the lowest 5-year survival rates among all breast cancer patients, with AAW disproportionally bearing this burden. In order to improve TNBC patient outcomes, etiologic factors driving disparities in disease progression need to be better understood. We previously showed in TNBC cell cultures that intrinsic oncogenic redox signaling promotes self-renewal capacity of cancer stem-like cells (CSC) by maintaining expression of an epigenetic reader protein and mRNA spliced variant, methyl binding domain protein 2 variant 2 (MBD2_v2). We hypothesized that obesity-induced chronic inflammation in vivo could promote a similar cancer phenotype.

Methods: To study this potential phenomenon, we developed and characterized a diet-induced obesity mouse tumor xenograft (MTX) model of TNBC in C57BL/6J Rag1 (-/-) mice, a strain that maintains a functional innate immune system, to recapitulate the proinflammatory environment induced by increased adiposity. TNBC cell lines MDA-MB-468 and MDA-MB-231 were used to generate ectopic tumor xenografts in this model. Tumor colonization and growth were measured over 150 days. RT-PCR and microarray based assays were used to detect transcriptional changes in TNBC MTXs.

Results: At 5 weeks post-diet consumption, mice fed a high-fat diet displayed a 5-10% increase in body weight and increased blood glucose concentration. By the end of the study high-fat fed mice displayed a 33-43% increase in body weight and appeared to have greater central adiposity post-mortem. In overweight mice relative to healthy weight controls, TNBC cell line tumor colonization rate and MBD2_v2 expression were significantly higher. Furthermore, staining for CSC marker EpCam was greater in overweight versus control MTXs, indicating that CSC self-renewal capacity could have been enhanced. Upon global gene expression analysis of overweight MTXs, we observed a significant upregulation of stem-related factors based on fold-change expression, as well as functional enrichment for RNA splicing, including SRSF2, a splicing factor that has been shown to drive MBD2_v2 expression in pluripotent stem cells. Knockdown of SRSF2 led to decreased expression of MBD2_v2 in MDA-MB-468 cells, and decreased CSC self-renewal capacity in vitro.

Conclusions: Altogether these data support MBD2_v2 regulation by redox signaling, which may be driven by a proinflammatory environment in the presence of increased adiposity. Future studies will be conducted to confirm MBD2_v2's importance in obesity-related tumor colonization in in vivo overexpression and knockdown studies, and to determine its transcriptional regulatory functions in TNBC.

Citation Format: Emily A. Girsch, Gregory Dyson, Cristina Mitrea, Bin Bao, Lisa Polin, Aliccia Bollig-Fischer. Obesity enhances tumor colonization and promotes expression of the spliced variant MBD2_v2 and splicing factor SRSF2 in triple-negative breast cancer [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr C47.