Project description:Colorectal cancer is one of the most frequently occurring malignancies and a major cause of cancer death. Distant metastases in this disease most commonly develop in the liver and are often untreatable. Here, we show that citrullination of the extracellular matrix (ECM) by cancer cell derived peptidylarginine deiminase 4 (PAD4) is essential for the growth of liver metastases. Citrullination of proteins, a post-translational conversion of arginine residues to citrulline, is well recognized in rheumatoid arthritis, but largely undocumented in cancer. PAD4, a key enzyme responsible for catalyzing citrullination, is produced by metastatic colorectal cancer cells and found at higher levels in human liver metastases than in normal liver. Functional significance for citrullination in metastatic growth was evident in murine models where inhibition of citrullination, either globally by pharmacologic inhibition of PADs or specifically in colorectal cancer cells by PAD4 knockdown substantially reduced liver metastatic burden. Additionally, citrullination of a key ECM component collagen type I led to greater adhesion and decreased migration of colorectal cancer cells along with increased expression of characteristic epithelial markers, suggesting a role for citrullination in promoting mesenchymal-to-epithelial transition (MET) and liver metastasis. Overall, our study revealed the potential for PAD4-dependant citrullination to drive the progression of liver metastasis. These data indicate that inhibition of citrullination could be exploited to prevent the development of liver metastases in colorectal cancer.
