The discoidin domain receptors (DDRs) are receptor tyrosine kinases with a discoidin homology repeat in their extracellular domains, activated by binding to extracellular matrix collagens. So far, two mammalian DDRs have been identified: DDR1 and DDR2. They are widely expressed in human tissues and may have roles in smooth muscle cell-mediated collagen remodeling . Research studies have implicated aberrant expression and signaling of DDRs in human diseases related to increased matrix degradation and remodeling, such as cardiovascular disease, liver fibrosis, and tumor invasion . Injection of colon tumor cells into DDR2 knock out mice predisposes the hepatic stellate cells to colon tumor metastasis.
