DDR1 is necessary for collagen I–induced changes in BxPC3 cells. (A) BxPC3 cells were extracted in TNE buffer 12 h after plating on noncoated or collagen I–coated dishes. 600 μg of protein was immunoprecipitated with nonspecific rabbit IgG or anti-DDR1 rabbit pAb and blotted with anti-phosphotyrosine mAb (PY20) or anti-DDR1 pAb. TNE extracts from cells stimulated with soluble collagen type I (sol col; 50 μg/ml) for 120 min served as a positive control (lane 4). (B) RIPA extracts (30 μg of protein) from cells expressing shEGFP or shDDR1 and cultured on noncoated or collagen I–coated dishes for 2 d were resolved by SDS-PAGE and blotted for DDR1, N-cadherin, or tubulin. (C) BxPC3 cells expressing shEGFP (a and b), shDDR1 (c and d), or both shDDR1 and shIntegrin β1 (e and f) were cultured on noncoated (a, c, and e) or collagen I–coated (b, d, and f) dishes for 2 d. Bar, 100 μm. (D) RIPA extracts (30 μg of protein) from cells expressing shEGFP or both shDDR1 and shIntegrin β1 and cultured on noncoated or collagen I–coated dishes for 2 d were blotted for DDR1 (a), integrin β1 (b), N-cadherin (c), or tubulin (d).