Metastasis-associated protein S100A4 induces a network of inflammatory cytokines that activate stromal cells to acquire pro-tumorigenic properties

• Stroma bordering metastatic lesions is enriched with the S100A4 protein.
• S100A4 stimulates tumor cells to secrete a variety of pro-inflammatory factors.
• The secreted factors educate stromal cells to acquire tumor-supportive properties.
• We propose that S100A4 modulated tumor-stromal crosstalk promotes metastasis.

Tumor cells have the ability to exploit stromal cells to facilitate metastasis. By using malignant melanoma as a model, we show that the stroma adjacent to metastatic lesions is enriched in the known metastasis-promoting protein S100A4. S100A4 stimulates cancer cells to secrete paracrine factors, such as inflammatory cytokines IL8, CCL2 and SAA, which activate stromal cells (endothelial cells and monocytes) so that they acquire tumor-supportive properties. Our data establishes S100A4 as an inducer of a cytokine network enabling tumor cells to engage angiogenic and inflammatory stromal cells, which might contribute to pro-metastatic activity of S100A4.