Absence of vacuolar ATPase in hematopoietic stem cells promotes breast tumor progression and pathogenesis

Abstract

Abstract Vacuolar ATPase (V-ATPase) is expressed on surface of most cancer cells where it acidifies the extracellular milieu and promotes metastasis. We have previously demonstrated that the a2 isoform of V-ATPase (a2V) of mammary epithelial cells, plays a key role during breast tumor progression and metastasis. However, the role of a2V in hematopoietic stem cells (HSC) during breast tumor progression is not known. Therefore, to understand the role of a2V in HSC during breast tumor progression, we conditionally knocked out a2V (cKO) from the HSC of mice. We observed that deletion of a2V leads to a significant reduction of CD4+ and CD8+ T cells in the spleen of the a2V cKO mice compared to control mice. We hypothesized that the reduction of helper CD4+ cells, or cytotoxic CD8+ T cells would result in larger and faster growing tumors in the a2V-cKO mice. After implantation of a syngeneic tumor cell line (E0771) in the breast tissue of mice, we observed that lack of a2V leads to larger and faster growing breast tumors compared to controls. Further investigation of the tumor microenvironment revealed that there was a significant reduction in percentage of CD4+ and CD8+ T cells in the a2V-cKO mice compared to control mice. Targeted RNAseq of the tumor microenvironment demonstrated that out of 499 genes those were analyzed, only 3 genes were significantly upregulated while 144 genes were significantly downregulated in the a2V cKO mice. The 144 downregulated genes included genes for pro-inflammatory cytokines, T cell specific genes, death receptors and pro-apoptotic genes. Collectively, these results demonstrate that deletion of a2V from the HSC leads to a decrease in CD4+ and CD8+ T cells in the periphery, which results in a faster growing and larger breast tumor.