Reduced contractility of discoidin domain receptor 2 (DDR2)-/- fibroblasts. (a) Representative histogram of collagen contraction assay. Collagen gels were seeded with 1 × 105 cells/mL fibroblast derived from DDR2+/+ or DDR2-/- mice or with DDR2-/- skin fibroblasts retrovirally infected with wild-type DDR2 (-/-/WTR2). Cells were maintained for 2 days culture under basal conditions (control) or under keratinocyte supernatants with or without (untreated) 3 μM β-aminoproprionitrile (BAPN; a lysyl oxidase inhibitor) or 1 μM N-[(2R)-2-(hydroxamido carbonylmethyl)-4-methylpentanoyl]-l-tryptophan methylamide (GM6001; a matrix metalloproteinase (MMP) inhibitor). Then, collagen was removed from the well sides and soluble type I collagen (30 μg/ml) was added. Cells were allowed to contract the lattices for 72 h. Digital images were taken and the gel area was calculated. *P < 0.01, significantly different compared with untreated DDR2+/+; **P < 0.01, significantly different compared with untreated DDR2-/- cells. &P < 0.05, significantly different compared with GM-treated DDR2+/+ cells. Control DDR2+/+ and DDR2-/- cells retained 85% and 95%, respectively, of initial gel area. (b) Representative western blot analysis for SrcY418 and total Src expression by skin fibroblasts after gel contraction. Tubulin expression is utilized as loading control. Bands were quantified by scanning densitometry analysis.