Tumor-associated vacuolar ATPase subunit promotes tumorigenic characteristics in macrophages

Abstract

Macrophage polarization contributes to distinct human pathologies. In tumors, a polarized M2 phenotype called tumor-associated macrophages (TAMs) are associated with promotion of invasion and angiogenesis. In cancer cells, vacuolar ATPase (V-ATPase), a multi-subunit enzyme, is expressed on the plasma/vesicular membranes and critically influences the metastatic behavior. In addition, the soluble, cleaved N-terminal domain of a2 isoform of V-ATPase (a2NTD) is associated with in vitro induction of pro-tumorigenic properties in monocytes. This activity of a2 isoform of V-ATPase (a2V) caused us to investigate its role in cancer progression through the evaluation of the immunomodulatory properties of a2NTD. Here, we present direct evidence that surface expression of V-ATPase is associated with macrophage polarization in tumor tissue. Macrophages from BALB/c mice (peritoneal/bone marrow derived) were stimulated with recombinant a2NTD in both ex vivo and in vivo systems and evaluated for TAM characteristics. a2V was highly expressed in tumor tissues (breast and skin) as well as on the surface of tumor cell lines. The a2NTD-stimulated macrophages (a2MΦ) acquired TAM phenotype, which was characterized by elevated expression of mannose receptor-1, Arginase-1, interleukin-10 and transforming growth factor-β. a2MΦ also exhibited increased production of other tumorigenic factors including matrix metalloproteinase-9 and vascular endothelial growth factor. Further, a2MΦ were cocultured with mouse B-16F0 melanoma cells for their functional characterization. The coculture of these a2MΦ subsequently increased the invasion and angiogenesis of less invasive B-16F0 cells. When cocultured with naive T cells, a2MΦ significantly inhibited T-cell activation. The present data establish the role of V-ATPase in modulating a macrophage phenotype towards TAMs through the action of a2NTD, suggesting it to be a potential therapeutic target in cancer.

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer

“…Other studies have described expression of V‐ATPase/specific subunits in pancreatic cancer,32, 33 nonsmall cell lung cancer,34 oral squamous cell carcinoma,35, 36 ovarian cancer,37 cervical cancer,38 breast cancer,39, 40 gliomas,41 and hepatocellular carcinoma 42. A summary of studies investigating clinical significance of V‐ATPase in cancer is provided in Table 1.…”

“…For example, a soluble cleavage fragment of V o a2 (a2NTD) has been shown to polarize macrophages toward a “tumor‐associated” or M2 macrophage phenotype 40, 69…”

Selective upregulation of TNFα expression in classically-activated human monocyte-derived macrophages (M1) through pharmacological interference with V-ATPase

“…Thus, the lysosomal adaptor protein Lamtor1, which forms an amino-acid sensing complex with V-ATPase, was recently shown to be required for M2 polarization [55]. Moreover, V-ATPase was reported to modulate macrophage polarization in tumor-bearing mice [56], and inhibition of the V-ATPase a2 isoform in murine tumor cells delayed tumor growth by decreasing M2-like TAMs in the tumor microenvironment [57].…”

Phagocytes as Corrupted Policemen in Cancer-Related Inflammation

“…The relevance of the a2V role has been tested in in vitro studies, exposing macrophages to the cleaved N-terminal domain of a2V. In these conditions, macrophages express and secrete TAM-associated molecules such as mannose receptor-1, arginase-1, interleukin-10, TGF-β, MMP-9, and VEGF (Katara et al, 2014). A member of the TGF-β family has recently been reported to promote M2-like polarization of TAMs and to inhibit IL-12 (Wang et al, 2014).…”