Collagen I signals through DDR1-Pyk2 in BxPC3 cells. (A) RIPA extracts (60 μg of protein) from cells expressing shEGFP, shDDR1, or both shDDR1 and shIntegrin β1 and cultured on noncoated or collagen I–coated dishes for 4 h were resolved by SDS-PAGE and blotted for phospho-FAK (Y577; a), total FAK (b), phospho-Pyk2 (Y579/Y580; c), or total Pyk2 (d). (B) 1 mg of protein from BxPC3 cells extracted 4 h after plating on noncoated or collagen I–coated dishes was immunoprecipitated with rabbit IgG or anti-DDR1 rabbit pAb and blotted for total Pyk2, total FAK, or DDR1. (C) RIPA extracts (60 μg of protein) from cells expressing shEGFP, shDDR1, both shDDR1 and shIntegrin β1, FRNK, or FRNK together with shPyk2 and cultured on noncoated or collagen I–coated dishes for 4 h were resolved by SDS-PAGE and blotted for phospho-JNK (T183/Y185) or total JNK1. Immunoblots for p-JNK were quantified by densitometry using Photoshop and normalized to immunoblots for total JNK1. Shown is the ratio of phospho-JNK/total JNK for cells on collagen I–coated dishes divided by the ratio of phospho-JNK/total JNK for cells on noncoated dishes. The data represent the mean and standard deviation from three independent experiments.