Integrin αvβ6 plays a bi-directional regulation role between colon cancer cells and cancer-associated fibroblasts

Tumor microenvironment (TME) is the cellular environment in which tumor exists, and it contributes to tumor formation and progression. The TME is composed of tumor cells, stromal cells, cytokines, and chemotactic factors of which fibroblasts are the main cellular components. In our present study, we found that colorectal cancer (CRC) cells expressing integrin αvβ6 clearly could induce morphological changes in inactive fibroblasts and increased the expression of activated fibroblast markers such as alpha smooth muscle actin (α-SMA) and fibroblast-activating protein (FAP). Those activated fibroblasts in the TME are called cancer-associated fibroblasts (CAFs). In order to investigate the mechanism by which CRC cells expressing integrin αvβ6 activated CAFs, a series of assays have been carried out in the follow up. We found that CRC cells could secrete inactive transforming growth factor beta (TGF-β); however, integrin αvβ6 activated TGF-β, which subsequently activated fibroblasts. This process was disrupted by knockdown of integrin αvβ6. In contrast, activated fibroblasts could promote CRC cell invasion. In particular, the strengthening effect on expression of integrin αvβ6 in colon cancer cells was obvious. Additionally, we found that CAFs could secrete stromal cell derived factor-1 (SDF-1) and promote CRC cell metastasis in distant organs via the SDF-1/C-X-C chemokine receptor type 4 (CXCR4) axis. Taken together, we assumed that CRC cells and CAFs activated one another and worked together to promote cancer progression, with integrin αvβ6 playing a role in the bi-directional regulation of these cells. Hence, integrin αvβ6 may serve as a therapeutic target for the future CRC treatment.