Chondrocytes respond to IL-7 stimulation with increased PYK2 phosphorylation and production of MMP-13. (a) Chondrocytes isolated from normal adult cartilage were stimulated with 10 ng/mL recombinant IL-7 and lysates were made at indicated time points for immunoblotting with an antibody to phosphorylated proline-rich tyrosine kinase (PYK)2 (Tyr402). The blot was then stripped and probed with total PYK2 antibody to confirm equal loading. (b) Densitometric scanning of the blot shown in panel a. (c) Medium was collected from serum-free chondrocyte cultures after overnight stimulation with 10 ng/ml recombinant IL-7 and examined for the presence of multiple matrix metalloproteinase (MMP) family members using an MMP antibody array. MMP-13 spots are shown in circles. (d,e) Media was collected from serum-free chondrocyte cultures after overnight stimulation with 10 ng/ml recombinant IL-7 or IL-1β, or the two together, and examined for the presence of MMP-13 using a commercially available ELISA. Results are the mean of seven experiments.