Fig. 5. Recombinant FXIIIA engages the 1-integrin subunit in human chondrocytes. (A) Western blot. Aliquots of 10⁵ human articular chondrocytes were starved for 2 hours in serum-free DMEM and then incubated for the indicated times with 100 ng/ml sTG2 or sFXIIIA. The cells were washed prior to lysis and then examined for the presence of the Xpress epitope on the recombinant proteins by SDS-PAGE and western blotting. (B) Integrin immunoprecipitation. Aliquots of 10⁶ human articular chondrocytes were incubated for 3 days in medium A containing 100 ng/ml of sTG2 or sFXIIIA where indicated. Cell lysates (200 µg protein) were immunoprecipitated using 1 µg/ml of 1- (clone TS2/7), 2-, 5- or 6-integrin-subunit-specific antibody, and precipitated proteins were analyzed for the Xpress tag or each respective -integrin subunit by western blotting. Representative of three separate experiments using three different donors.