SUMMARY
High level of collagen deposition in human and mouse breast tumors are associated with poor outcome due to increased local invasion and distant metastases. Using a genetic approach we show, in mice, that the action of the fibrillar collagen receptor, discoidin domain receptor 2 (DDR2) in both tumor and tumor stromal cells is critical for breast cancer metastasis, yet does not affect primary tumor growth. In tumor cells, DDR2 in basal epithelial cells regulates collective invasion of tumor organoids. In stromal cancer-associated fibroblasts (CAFs) DDR2 is critical for extracellular matrix production and organization of collagen fibers. The action of DDR2 in CAFs also enhances tumor cell collective invasion through a pathway distinct from the tumor cell-intrinsic function of DDR2. This work identifies DDR2 as a potential therapeutic target that controls breast cancer metastases through its action in both tumor cells and tumor stromal cells at the primary tumor site.
Increased deposition of collagen in extracellular matrix (ECM) leads to increased tissue stiffness and occurs in breast tumors. When present, this increases tumor invasion and metastasis. Precisely how this deposition is regulated and maintained in tumors is unclear. Much has been learnt about mechanical signal transduction in cells, but transcriptional responses and the pathophysiological consequences are just becoming appreciated. Here, we show that the SNAIL1 (also known as SNAI1) protein level increases and accumulates in nuclei of breast tumor cells and cancer-associated fibroblasts (CAFs) following exposure to stiff ECM in culture and in vivo. SNAIL1 is required for the fibrogenic response of CAFs when exposed to a stiff matrix. ECM stiffness induces ROCK activity, which stabilizes SNAIL1 protein indirectly by increasing intracellular tension, integrin clustering and integrin signaling to ERK2 (also known as MAPK1). Increased ERK2 activity leads to nuclear accumulation of SNAIL1, and, thus, avoidance of cytosolic proteasome degradation. SNAIL1 also influences the level and activity of YAP1 in CAFs exposed to a stiff matrix. This work describes a mechanism whereby increased tumor fibrosis can perpetuate activation of CAFs to sustain tumor fibrosis and promote tumor metastasis through regulation of SNAIL1 protein level and activity.
The -YAP panels on stiff substrate in Fig. 8C were incorrectly duplicated in Fig. 6A. The journal has seen the original data for Fig. 6A and the corrected and original panels are shown below. This error does not affect the results or conclusions. The online full-text and PDF versions of the paper have been updated.The authors apologise to readers for this error.1
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