Snail1-Expressing Fibroblasts in the Tumor Microenvironment Display Mechanical Properties That Support Metastasis

Abstract

Crosstalk between tumor and stromal cells in the tumor microenvironment alter its properties in ways that facilitate the invasive behavior of tumor cells. Here, we demonstrate that cancer-associated fibroblasts (CAF) increase the stiffness of the extracellular matrix (ECM) and promote anisotropic fiber orientation, two mechanical signals generated through a Snail1/RhoA/aSMAdependent mechanism that sustains oriented tumor cell migration and invasiveness. Snail1-depleted CAF failed to acquire myofibroblastic traits in response to TGFb, including RhoA activation, aSMA-positive stress fibers, increased fibronectin fibrillogenesis, and production of a stiff ECM with oriented fibers. Snail1 expression in human tumor-derived CAF was associated with an ability to organize the ECM. In coculture, a relatively smaller number of Snail1-expressing CAF were capable of imposing an anisotropic ECM architecture, compared with nonactivated fibroblasts. Pathologically, human breast cancers with Snail1 þ CAF tended to exhibit desmoplastic areas with anisotropic fibers, lymph node involvement, and poorer outcomes. Snail1 involvement in driving an ordered ECM was further confirmed in woundhealing experiments in mice, with Snail1 depletion preventing the anisotropic organization of granulation tissue and delaying wound healing. Overall, our results showed that inhibiting Snail1 function in CAF could prevent tumor-driven ECM reorganization and cancer invasion. Cancer Res; 75(2); 284-95. Ó2014 AACR.

Mechanical signals regulate and activate SNAIL1 protein to control the fibrogenic response of cancer-associated fibroblasts

“…Next, we determined and contrasted the nature of the ECM produced by CAFs and CAFs lacking SNAIL1. As reported by Stanisavljevic et al (2015) , we also observed that matrix produced by WT CAFs, as assessed by fibronectin fiber organization (Fig. 7C) and second harmonic generation (SHG) analysis of collagen fibers (Fig.…”

“…In response to ECM stiffness, CAFs increase matrix production and remodeling in a SNAIL1-dependent manner Recently, the action of SNAIL1 in CAFs has been shown to control the production of ECM and orientation of fibronectin fibers (Stanisavljevic et al, 2015). In contrast to breast tumor CAFs, normal breast fibroblasts did not express SNAIL1 protein, although they did express other EMT factors (SNAIL2, TWIST1 and ZEB1; Fig.…”

“…Breast tumors that result in a poor prognosis are often associated with increased collagen deposition within the tumor stroma and a resulting increase in tissue stiffness (Paszek et al, 2005). Given that tumor CAFs produce the matrix associated with tumors, and SNAIL1 has recently been shown to be important for CAF function (Stanisavljevic et al, 2015), we asked whether exposure of breast tumor CAFs to a stiff matrix influenced SNAIL1 protein level and activity.…”

“…Cancer-associated fibroblasts (CAFs) are the stromal cells primarily responsible for generating the interstitial matrix associated with tumors (Bhowmick et al, 2004). But CAFs can also remodel the tumor ECM (Gaggioli et al, 2007) and promote matrix stiffness (Calvo et al, 2013;Stanisavljevic et al, 2015). Together, these CAF-mediated changes in the physical properties of the ECM facilitate or enhance tumor cell invasion.…”

“…Recently, the epithelial-to-mesenchymal transition (EMT) factor SNAIL1 (also known as SNAI1) has been found to be crucial for production of ECM by CAFs and also to affect their capacity to increase matrix stiffness. Although SNAIL1 was initially described as a TGFβ target gene that promotes EMT during developmental programs and epithelial tumor progression, accumulating data has shown that SNAIL1 also has important functions in mesenchymal cells, independent of its EMT function (Rowe et al, 2009;Batlle et al, 2013;Stanisavljevic et al, 2015).…”