FIGURE 6.

Implication of p38 MAP kinase activation in acceleration of hemin-stimulated erythroid differentiation in response to TNIIIA2. A, K562 cells were seeded on a culture plate coated with FN and stimulated with TNIIIA2 (75 μg/ml) alone (+TN), hemin (50 μm) alone (+H), or their combination (+H+TN) for the indicated times at 37 °C. B, cell suspension without (−) or with the CS-1 (+CS1) or RGD (+RGD) peptide (200 μg/ml) was seeded on a culture plate coated with FN and then stimulated for 24 h with hemin (50 μm) in the absence (+H) or presence (+H+TN) of TNIIIA2 (75 μg/ml). C, cells transfected with control siRNA or integrin α4 siRNA (see the legend to Fig. 5) were stimulated for 24 h without (−) or with hemin (50 μm) (H) or hemin plus TNIIIA2 (75 μg/ml) (H+TN). Cell lysates were subjected to Western blot analysis using anti-phospho-p38, anti-phospho-ERK1/2, or anti-p38 mAb, as described under “Experimental Procedures.” Data are representative of three individual experiments.