Abstract 2129: Breast tumor microenvironment & metastasis is controlled by activity of a2 isoform of V-ATPase in mammary epithelium

Abstract

Abstract Extracellular matrix (ECM) critically impacts tumor progression and is influenced by both cancer and host tissue cells. While our understanding of cancer cell ECM remodeling is widespread, the importance of host tissue ECM, which provides an initial congenial environment for primary tumor formation, is only partly understood. Previously, we have shown that epithelial cell associated vacuolar (V)-ATPase ‘a2' isoform (a2V) regulates stiffness of mammary gland ECM. Here, we investigated how a2V mediated alterations in ECM of breast tissues affects the tumor microenvironment and metastasis of breast cancer. We also established the correlation of a2V expression in the normal breast tissue with metastatic occurrence in cancer patients. In this study, using the MMTV-Cre-Lox system, we deleted the a2V gene in epithelial cells of mouse mammary glands. Tumors were transplanted in mammary fat pads of a2V conditional knockout mice (a2VcKO) using E0771/Py230 mouse mammary cancer cells. These tumors were evaluated for the histopathology, ECM stiffness, immune cell populations, cytokines, angiogenic factors and metastasis. We show that in a2VcKO, breast tumors exhibit less tumor rigidity, increased inflammation and a more necrotic tumor microenvironment. These mice showed an increased metastasis of tumors compared to control evident by cytokeratin (Ck)14 staining of cancer cells in lung tissues (3.3 fold increase, P=0.004). Immuno-phenotyping of breast tumor microenvironment revealed increased infiltration of CD45 cells with higher number of anti-tumor M1 macrophages (2.1 fold increase, P=0.007) and elevated expression of inflammatory cytokines TNF-α and iNOS in a2VcKO mice compared to control (P=0.01). The tumors in a2VcKO mice were much more highly vascularized and angiogenic compared to control (P=0.01) evident by increased number of Meca32+SMA+ cells. Clinically, in cancer patients, low a2V expression levels in normal breast tissue correlated directly with lymph-node metastasis. Thus, this study has identified a2V expression in epithelial cells as a key modulator of tumor microenvironment and its expression levels can significantly modulate breast tumor dissemination. Citation Format: Gajendra K. Katara, Arpita Kulshrestha, Manoranjan Sahoo, Kenneth Beaman. Breast tumor microenvironment & metastasis is controlled by activity of a2 isoform of V-ATPase in mammary epithelium [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2129.