Abstract A35: Characterizing the role of the nuclear coactivator AIB1 in triple-negative breast cancer

Abstract

Individuals diagnosed with triple-negative breast cancer (TNBC), a highly invasive and frequently metastatic breast cancer subtype, do not benefit from targeted therapies. TNBC is a heterogenous disease and can be further subdivided by intrinsic molecular subtyping into basal-like 1 or 2 (BL-1, BL-2), immunomodulatory (IM), mesenchymal (M), mesenchymal stem-like (MSL), and luminal androgen receptor (LAR). Amplified in Breast Cancer 1 (AIB1) is an oncogene that is frequently overexpressed in higher-grade and invasive breast cancers. AIB1 regulates the transcription of several genes through hormone or growth factor signaling. Many of these signaling pathways are involved in cellular growth, differentiation, migration, and metabolism—all of which become deregulated during oncogenesis. In this study, we silence AIB1 by shRNA and study the phenotypic effects in a panel of TNBC cell lines from different TNBC subtypes in vitro. We have established TNBC HCC1806 cell lines expressing low levels of AIB1 and have characterized their phenotype compared to scramble control cells. We observe significant reduction in AIB1 message and protein as detected by RT-qPCR and Western blot. shAIB1 TNBC cells have a significant reduced survival following the initial knockdown. However, serial passaging of surviving cells show differences in proliferation, especially in low serum conditions. These AIB1LOW cells have a significant increase in motility shown in chemotaxis experiments. However, we observe delayed adhesion of AIB1LOW cells when seeded onto plastic culture vessels. Furthermore, when grown onto Matrigel, AIB1LOW cells have a significant reduced tube formation capacity related to their delayed adhesion or reduced motility on substratum. Additionally, AIB1LOW cells have a differential expression of cell surface markers associated with cancer stem cells (i.e., CD24, CD44, CD133). Consistent with these findings, AIB1LOW cells generate tumorspheres more efficiently under serum free in suspension and when embedded in Matrigel. Moreover, AIB1LOW cells develop aggressive phenotypically different tumors in the cleared mammary fat pad of nude mice compared to controls. The AIB1LOW cells are significantly less sensitive to chemotherapy agents and may represent a resistant population that emerges from cancer stem cells following therapy. Interestingly, AIB1LOW cells have a different regulation of genes associated with hypoxia, glycolysis, and apoptosis and these changes may give guidance as to therapy following emergence of resistance in TNBC patients. Citation Format: Francisco R. Saenz, Anton Wellstein, Anna T. Riegel. Characterizing the role of the nuclear coactivator AIB1 in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A35.