Abstract 468: Delayed tumor growth in breast cancer is associated with reduced activity of the a2 isoform of vacuolar ATPase

Abstract

Abstract In cancer cells, vacuolar ATPase (V-ATPase), a multi-subunit enzyme, is expressed on the plasma as well as vesicular membranes and critically influences metastatic behavior. The soluble, cleaved N-terminal domain of a2 isoform of V-ATPase (a2NTD) is associated with in vitro induction of both tumor associated macrophages (TAMs) phenotype and activity in macrophages. This activity caused us to further investigate the role of a2NTD in cancer progression. We evaluated the effects of the knock down of a2 isoform (a2V) in tumor cells and the concomitant tumor microenvironment in the 4T-1 mouse breast cancer model. In vitro experiments showed that macrophages co-cultivated with a2V knocked down (sh-a2) tumor cells produced lower amounts of tumorigenic factors and have a reduced ability to suppress T cell activation and proliferation compared to control tumor cells. Furthermore, sh-a2 4T1 or control 4T-1 cells were inoculated into female Balb/c mice to generate mammary tumors. Data analysis showed that tumor growth in mice inoculated with sh-a2 4T-1 cells was delayed up to ten fold compared to control (mean±SD: 1.3 ± 1.15 vs 13.96 ± 4.06, P>0.01) at day 8 after inoculation. The expression of TAM associated molecules like mannose receptor-1 or CD206, IL-10, Arginase-1, matrix metalloproteinase and vascular endothelial growth factor were significantly down regulated in tumors from sh-a2 inoculated mice compared to control (P<0.01). Additionally, a significant reduction in the number of TAMs (F4/80+CD206+: mean = 6) and increase in macrophage with anti-tumor activity (F4/80+CD11c+: mean = 10.4) was also observed in these tumors which contributed towards delay in tumor growth. Further, we successfully deleted a2V gene in mice and its effect on tumor generation and microenvironment is evaluated. These findings demonstrated that in the absence of a2V in tumor cells, the resident TAM population in the tumor microenvironment is altered, which affected in vivo tumor growth. The data show that by involving the host innate immune system, tumor growth can be control through targeting of a2V and other related factors in tumor cells. Citation Format: Gajendra K. Katara, Arpita Kulshrestha, Alice Gilman-Sachs, Kenneth D. Beaman. Delayed tumor growth in breast cancer is associated with reduced activity of the a2 isoform of vacuolar ATPase. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 468. doi:10.1158/1538-7445.AM2015-468