Abstract: Snail1 is the master regulator of the Epithelial-to-Mesenchymal Transition (EMT) and is also crucial for fibroblast activation upon TGFβ signaling. In cancer, Snail1 expression in primary tumors correlates with the appearance of metastasis. We have previously shown that Snail1-expressing cancer-associated fibroblasts (CAF) enhance metastasis. Here we demonstrate that Snail1-expressing CAF attenuate the anti-tumor effector immune response. We observed that Snail1-expressing CAF determine macrophages to present a pro-tumor phenotype in vitro and in the in vivo model of breast cancer MMTV-PyMT what enhanced tumor progression. Moreover, in the context of metastasis, we show that Snail1-dependent TGFβ-induced activation of liver fibroblasts is determinant for colorectal cancer colonization of the organ. Snail1-expressing CAF determine cancer cell evasion of the adaptive anti-tumor effector immunity. In consequence, the absence of Snail1 prevents CAF activation in newly formed metastases and allows immune rejection. These new roles for Snail1-expressing CAF during primary tumor progression and secondary niche colonization increase the relevance of Snail1 protein in oncology.
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