Discoidin domain receptors (DDRs) are a subfamily of receptor tyrosine kinases, the only members known to respond to an ECM component. DDR1 binds several of the major fibrillar collagens (types I, II, III, and V) and the non-fibrillar collagen IV (Shrivastava et al. 1997, Vogel et al. 1997, Hou et al. 2001). DDR proteins bind collagen as dimers (Leitinger 2003, 2011). DDR1 is mostly found in epithelial cells and leukocytes. It control developmental processes and regulates cell adhesion, migration, proliferation, and remodelling of the extracellular matrix by controlling the expression and activity of matrix metalloproteinases (Leitinger & Hohenester 2007).