Abstract 3294: Notch signaling is regulated by vacuolar ATPase in triple negative breast cancer

Abstract

Abstract Triple Negative Breast Cancer (TNBC) constitutes 15 % of all diagnosed breast cancers. It is more common among African American and younger women. TNBC cells do not express Estrogen, Progesterone and Her2 receptors. As a result, patients have limited treatment options. To effectively treat TNBC, it is important to identify and target specific signaling pathways that contribute to TNBC tumorigenesis. Notch signaling is an evolutionarily conserved juxtacrine pathway that is important in normal mammary development and has been shown to play a role in TNBC progression. Although there has been considerable research on role of Notch in TNBC, little is known about its regulation. Identifying novel molecules that can regulate Notch can lead to the development of effective combinatorial treatments. The Vacuolar ATPase (V-ATPase) has been shown to regulate Notch Signaling in Drosophila. V-ATPase is an ATP driven proton pump, which is responsible for maintaining pH. Tumor cells increase expression of V-ATPase, which aids in cancer proliferation and metastasis. Here, we report that the a2 isoform of V-ATPase regulates Notch Signaling in breast cancer. Among isoforms a1, a2, a3 and a4, breast cancer cell lines robustly expressed a2 V-ATPase on their surface. a2 V-ATPase is present towards the leading edge of cells and is higher in TNBC cell lines (MDA-MB-231, MDA-MB-468) as compared to normal chemically transformed cell line (184A1) and hormonal positive cell line (MCF7). Expression of Notch ligands, receptors and target genes was also higher in TNBC cell lines as compared to Non-TNBC cell lines. siRNA mediated knockdown of a2 V-ATPase resulted in an increase of Notch Signaling in the Triple Negative MDA-MB-231 cell line. To understand the molecular mechanism behind this regulation, we used Bafilomycin to inhibit V-ATPase activity. Following V-ATPase inhibition, the expression of Jagged1, a Notch ligand was increased. Our results suggest that Vacuolar ATPase can regulate Notch Signaling by affecting ligand internalization through endocytosis. We further assessed the effect of V-ATPase and Notch signaling inhibitors on cell proliferation of the breast cancer cell lines (184A1, MCF7, MDA-MB-231, MDA-MB-468). Combined inhibition of V-ATPase and Notch signaling caused significant cell death in all cell lines tested. Together our results identify a2 V-ATPase as a novel regulator of Notch signaling in Breast Cancer and that targeting both V-ATPase and Notch Signaling can be beneficial for Triple Negative Breast Cancer. Citation Format: Sahithi Pamarthy, Kenneth D. Beaman. Notch signaling is regulated by vacuolar ATPase in triple negative breast 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 3294. doi:10.1158/1538-7445.AM2014-3294