DDR1 is a DDR/TKT type protein kinase. DDR1 is activated by various types of collagen, including types I through IV. Binding of collagen to DDR1 protein results in autophosphorylation and a delayed but sustained tyrosine kinase activation. DDR1 may function in cell-to-cell interaction or recognition. At least three mRNA variants, resulting in different protein isoforms of 875, 913 and 919 amino acids, have been reported. DDR1 protein has been shown to be over expressed in human breast, ovarian, esophageal and pediatric brain tumors.