Collagen induces the phosphorylation and activation of DDR1 in HRS cells. (A) Detection of DDR1 phosphorylation in L428 cells, and (B) L591 cells with anti-phosphotyrosine antibody (4G10). The addition of collagen induced the robust phosphorylation of DDR1 in cells peaking at 30 minutes. Cell lysates were immunoprecipitated with anti-DDR1, and then probed with 4G10 or reprobed with anti-DDR1 antibody.