Nonsynonymous sequence variations do not alter sensitivity to cognate ligands. Collagen stimulation of DDR1 mutants for evaluation of ligand hypersensitivity. Ba/F3 cells stably transfected with wild-type and mutant DDR1 as in Figure 2. Cells were serum starved overnight at which time they were collagen stimulated with (A) a time course or (B) a dose response for the indicated times and doses. Cell lysates were subjected to immunoblot analysis for phosphotyrosine (4G10) and total DDR1.