['Discoidin domain receptor 1 (DDR1) is a collagen-binding receptor tyrosine kinase which mediates the migration and proliferation of several cell types. DDR1 is expressed in vascular smooth muscle cells (SMCs) during atherosclerosis and following vascular injury, mediating cell migration and contributing to disease pathogenesis. However, very little is known about the signaling pathways activated by the DDR1 in SMCs. Therefore we have studied the involvement of Src and mitogen-activated protein kinase (MAPK) signaling pathways downstream of DDR1 in vascular SMCs.', 'Cells harvested from DDR1(-/-), DDR1(+/+) mice, and DDR1(+/+) cells overexpressing human DDR1b (O/hDDR1b) were used for these studies.', 'Stimulation of O/hDDR1b cells with type I collagen resulted in increased tyrosine phosphorylation of DDR1. The non-receptor kinase Src co-immunoprecipitated with DDR1, and the Src inhibitor PP2 inhibited type I collagen-induced tyrosine phosphorylation of DDR1. Stimulation of DDR1-expressing cells with collagen resulted in the activation of extracellular signal-regulated kinase 1/2 (ERK1/2); however, ERK1/2 was not activated in DDR1-deficient cells. By contrast, p38 MAPK (p38) was activated by collagen stimulation in both DDR1-expressing and DDR1-deficient cells. Treatment with PP2 attenuated DDR1-dependent ERK1/2 activation, but not p38 activation. Finally, treatment of SMCs with PP2, or the MEK inhibitor PD98059, inhibited migration toward type I collagen in a chemotaxis chamber. However, PP2 but not PD98059 had a greater effect in reducing the migration of DDR1(+/+) cells compared to DDR1(-/-) cells, suggesting that Src but not ERK1/2 was important in regulating DDR1-dependent SMC migration.'] Does collagen stimulate discoidin domain receptor 1-mediated migration of smooth muscle cells through Src?