DDR2

null Encoded by the DDR2 gene, this discoidin domain receptor is the second collagen-binding receptor tyrosine kinase and the close paralog of DDR1. DDR2 shares the discoidin collagen-recognition module and kinase domain but is expressed chiefly in mesenchymal tissues such as cartilage, bone, heart, and fibroblasts rather than in epithelium. Binding of fibrillar collagen type I triggers delayed, sustained kinase activation that modulates matrix metalloproteinase expression, cell spreading, and proliferation. DDR2 signaling supports chondrocyte and osteoblast function, and missense mutations in its kinase domain cause spondylo-meta-epiphyseal dysplasia with joint laxity. Elevated DDR2 activity has also been linked to tissue fibrosis and to the invasive behavior of certain carcinomas.