Stromally Derived Lysyl Oxidase Promotes Metastasis of Transforming Growth Factor-β–Deficient Mouse Mammary Carcinomas

Abstract

The tumor stromal environment can dictate many aspects of tumor progression. A complete understanding of factors driving stromal activation and their role in tumor metastasis is critical to furthering research with the goal of therapeutic intervention. Polyoma middle T-induced mammary carcinomas lacking the type II TGF-ß receptor (PyMTmgko) are highly metastatic compared to control PyMT-induced carcinomas (PyMTfl/fl). We hypothesized that the PyMTmgko activated stroma interacts with carcinoma cells to promote invasion and metastasis. We show that the extracellular matrix associated with PyMTmgko tumors is stiffer, has more fibrillar collagen, and increased expression of the collagen crosslinking enzyme lysyl oxidase (LOX) compared to PyMTfl/fl mammary carcinomas. Inhibition of LOX activity in PyMTmgko mice had no effect on tumor latency and size, but significantly decreased tumor metastasis through inhibition of tumor cell intravasation. This phenotype was associated with a decrease in keratin 14 positive myoepithelial cells in PyMTmgko tumors following LOX inhibition as well as a decrease in focal adhesion formation. Interestingly, the primary source of LOX was found to be activated fibroblasts. LOX expression in these fibroblasts can be driven by myeloid cell-derived TGF-ß, which is significantly linked to human breast cancer. Overall, stromal expansion in PyMTmgko tumors is likely caused through the modulation of immune cell infiltrates to promote fibroblast activation. This feeds back to the epithelium to promote metastasis by modulating phenotypic characteristics of basal cells. Our data indicate that epithelial induction of microenvironmental changes can play a significant role in tumorigenesis and attenuating these changes can inhibit metastasis.

Molecular Pathways: Connecting Fibrosis and Solid Tumor Metastasis

“…The deposition and linearization of collagens at this interface, driven by the activation of resident fibroblasts and subsequent secretion of LOX, are required for malignant progression in the MMTV-Neu mammary cancer model. Building on these findings, Pickup and colleagues (24) confirmed in the PyMT model of mammary carcinoma that the source of LOX and collagen secretion is activated fibroblasts in the tumor stroma, is TGFb dependent, increases ECM stiffness, and acts to enhance metastasis (by $4-fold) in this model through increasing primary tumor escape. Thus, it is without doubt that the same cells are responsible for driving tissue fibrosis and creating fibrotic milieus at both primary tumor and secondary metastatic sites that enhance tumor progression and metastasis.…”

Physical and Chemical Gradients in the Tumor Microenvironment Regulate Tumor Cell Invasion, Migration, and Metastasis

“…The relevance of ECM stiffness to breast tumor metastasis was further demonstrated by transgenic mouse studies in which collagen cross-linking and ECM stiffness were manipulated. These studies identified TGF-b and microRNAs that target tumor suppressors like the PI3K repressor phosphatase and tensin homolog (PTEN) as critical molecular modulators of the durotactic phenotype (Pickup et al 2013;Mouw et al 2014). Recently, a role for ECM rigidity in promoting pancreatic tumor progression and glioblastoma aggression that expand upon in vitro studies was demonstrated (Ulrich et al 2009;Laklai et al 2016;Miroshnikova et al 2016).…”

Lysyl oxidase is associated with the epithelial–mesenchymal transition of gastric cancer cells in hypoxia

“…LOX families are involved in a variety of pathological processes related to connective tissue [12,13], including cancer progression and metastasis [11,14]. Involvement of the LOX family is widely accepted as a poor prognostic factor for patients with cancer [15][16][17][18][19][20]. By contrast, Kaneda et al [21] reported that LOX is a tumor suppressor gene inactivated by heavy methylation of the 5 0 untranslated region and loss of heterozygosity in gastric cancers, and several studies have reported that LOX-PP has tumor suppressor activity [22][23][24].…”