Tumor-Secreted LOXL2 Activates Fibroblasts through FAK Signaling

Abstract

Cancer-associated fibroblasts enhance cancer progression when activated by tumor cells through mechanisms not yet fully understood. Blocking mammary tumor cell-derived lysyl oxidase-like 2 (LOXL2) significantly inhibited mammary tumor cell invasion and metastasis in transgenic and orthotopic mouse models. Here, we discovered that tumor-derived LOXL2 directly activated stromal fibroblasts in the tumor microenvironment. Genetic manipulation or antibody inhibition of LOXL2 in orthotopically grown mammary tumors reduced the expression of a-smooth muscle actin (a-SMA). Using a marker for reticular fibroblasts, it was determined that expression of a-SMA was localized to fibroblasts recruited from the host tissue. This marker also revealed that the matrix present in tumors with reduced levels of LOXL2 was more scattered compared with control tumors which exhibited matrices with dense, parallel alignments. Importantly, in vitro assays revealed that tumor-derived LOXL2 and a recombinant LOXL2 protein induced fibroblast branching on collagen matrices, as well as increased fibroblast-mediated collagen contraction and invasion of fibroblasts through extracellular matrix. Moreover, LOXL2 induced the expression of a-SMA in fibroblasts grown on collagen matrices. Mechanistically, it was determined that LOXL2 activated fibroblasts through integrinmediated focal adhesion kinase activation. These results indicate that inhibition of LOXL2 in tumors not only reduces tumor cell invasion but also attenuates the activation of host cells in the tumor microenvironment.Implications: These findings reveal new insight into the mechanisms of fibroblast activation, a novel function of LOXL2, and further highlight the importance of generating LOXL2-targeted therapies for the prevention of tumor progression and metastasis.

Tumor-Derived Osteopontin Reprograms Normal Mammary Fibroblasts to Promote Inflammation and Tumor Growth in Breast Cancer

“…Our results, demonstrating that inhibition of osteopontin in tumor cells did not alter their growth rates in vitro, but significantly hindered their ability to form tumors in vivo support a key role for osteopontin in tumor-stroma communication. Functional activation of collagen deposition by CAFs contributes to tumor growth and progression (21,46). Our study implicates osteopontin in functional activation of fibroblasts, leading to the formation of a growth-permissive desmoplastic stroma.…”

“…To test whether reprogrammed NMFs gained additional CAF-like features, we further tested their activation status. Activated myofibroblasts are known to have enhanced matrix adhesions, leading to increased contraction of collagen gel matrices in an integrin-dependent manner (21,22). We therefore investigated the effect of tumor-secreted factors on fibroblast-mediated collagen contraction.…”

Tumor Cell Invasion Can Be Blocked by Modulators of Collagen Fibril Alignment That Control Assembly of the Extracellular Matrix

“…Overexpression of LOXL2 in normal epithelial cells induced aberrant acinar morphogenesis (16). In the tumor stroma, LOXL2 mediates fibroblast activation through integrin engagement and FAK signaling (17). Genetic depletion of both LOX and LOXL2 in various animal models for cancer resulted in impeded disease progression and reduction in metastasis (18,19).…”

Stroma as an Active Player in the Development of the Tumor Microenvironment

“…An example of LOX family deregulated activity has been documented for LOXL2. Remodeling of ECM promoted by LOXL2 was found to be associated with regulation of epithelial-to-mesenchymal transition, epithelial cell polarity and differentiation mediated by transcriptional repression mechanisms [51], sprouting angiogenesis by modulation of type IV collagen assembly in endothelial basement membrane [52] and fibroblast activation [53]. LOX and LOXL2 resulted in being regulated by hypoxia, with a relevant role in hypoxia-induced metastases [54].…”