Abstract
BackgroundHigh mammographic density has been correlated with a 4-fold to 6-fold increased risk of developing breast cancer, and is associated with increased stromal deposition of extracellular matrix proteins, including collagen I. The molecular and cellular mechanisms responsible for high breast tissue density are not completely understood.MethodsWe previously described accelerated tumor formation and metastases in a transgenic mouse model of collagen-dense mammary tumors (type I collagen-α1 (Col1α1)tm1Jae and mouse mammary tumor virus - polyoma virus middle T antigen (MMTV-PyVT)) compared to wild-type mice. Using ELISA cytokine arrays and multi-color flow cytometry analysis, we studied cytokine signals and the non-malignant, immune cells in the collagen-dense tumor microenvironment that may promote accelerated tumor progression and metastasis.ResultsCollagen-dense tumors did not show any alteration in immune cell populations at late stages. The cytokine signals in the mammary tumor microenvironment were clearly different between wild-type and collagen-dense tumors. Cytokines associated with neutrophil signaling, such as granulocyte monocyte-colony stimulated factor (GM-CSF), were increased in collagen-dense tumors. Depleting neutrophils with anti-Ly6G (1A8) significantly reduced the number of tumors, and blocked metastasis in over 80 % of mice with collagen-dense tumors, but did not impact tumor growth or metastasis in wild-type mice.ConclusionOur study suggests that tumor progression in a collagen-dense microenvironment is mechanistically different, with pro-tumor neutrophils, compared to a non-dense microenvironment.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0703-7) contains supplementary material, which is available to authorized users.
Highlights
High mammographic density has been correlated with a 4-fold to 6-fold increased risk of developing breast cancer, and is associated with increased stromal deposition of extracellular matrix proteins, including collagen I
To characterize whether there is a change in the tumor-promoting COL immune microenvironment, we conducted chemiluminescent enzyme-linked immunosorbent assay (ELISA) to analyze the expression levels of 23 cytokines found in lysed whole mammary tumors from 15week-old mice (Fig. 1a, b)
Expression of interleukin-4 (IL-4), regulation on activation, normal T cell expressed and secreted (RANTES, chemokine ligand 5 (CCL5)), macrophage inflammatory protein 1α (MIP-1α, chemokine ligand 3 (CCL3)), and Interferon-γ (IFNγ) was at least two-fold higher in WT tumors compared to COL tumors
Summary
High mammographic density has been correlated with a 4-fold to 6-fold increased risk of developing breast cancer, and is associated with increased stromal deposition of extracellular matrix proteins, including collagen I. To better understand the role of increased collagen density, we utilize a mouse model in which the Collagen 1α1 gene is mutated to make the molecule resistant to collagenase, resulting in decreased collagen turnover and a net increase in stromal collagen (Col1α1tm1Jae) [12] These animals are crossed to the mouse mammary tumor virus-polyoma middle T antigen (MMTVPyVT) model, which is commonly used because it is comparable with human breast disease, it progresses from premalignant to malignant tumor and to lung metastasis. We previously noted an increase in the stromal cell populations surrounding tumors within collagen-dense environments, suggesting activation of the stromal compartment [12]
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