Fig. 4. Rapid mobilization of TG2 by FXIIIA is essential for stimulation of p38 phosphorylation. (A) Plasma-membrane-bound TG2. Aliquots of 5x10³ human articular chondrocytes were starved in serum-free high-glucose DMEM for 2 hours and then stimulated with WT or mutant sFXIIIA. TG2-specific antibodies were used to detect membrane-bound TG2, quantified through successive incubations with biotin anti-rabbit and streptavidin-AP antibodies as described in Materials and Methods (n=9). (B) p38 MAP kinase phosphorylation. Aliquots of 3x10⁵ human articular chondrocytes were starved in serum-free high-glucose DMEM for 2 hours and then stimulated with WT or mutant sFXIIIA for the time indicated. Cell lysates were analyzed by western blotting for phosphorylated p38 (p-p38) and total p38. Representative of three donors in three separate experiments (n=9).