Discoidin domain receptors (DDRs) are members of the transmembrane receptor tyrosine kinase (RTK) superfamily which are distinguished from others by the presence of a discoidin motif in the extracellular domain and their utilization of collagens as internal ligands. Two types of DDRs, DDR1 and DDR2, have been identified with distinct expression profiles and ligand specificities.
Upon collagen binding, DDRs transduce cellular signaling involved in various cell functions, including cell adhesion, proliferation, differentiation, migration, and matrix homeostasis. Altered DDR function resulting from either mutations or overexpression has been implicated in several types of disease, including atherosclerosis, inflammation, cancer, and tissue fibrosis. DDRs have been considered as novel potential molecular targets for drug discovery and increasing efforts are being devoted to the identification of new small molecule inhibitors targeting the receptors.