FIGURE 4.

Induction of VLA-4 expression in adhesion-dependent acceleration of hemin-stimulated erythroid differentiation in response to TNIIIA2. Expression of cell surface integrins on K562 cells was analyzed by flow cytometry. Cells were stimulated as follows: isotype control of cells untreated (a); isotype control of cells stimulated with hemin (50 μm) plus TNIIIA2 (75 μg/ml) (b and c); hemin alone (e, h, and o); hemin plus Mn²⁺ (0.5 mm) (f and i); hemin plus TNIIIA2 (g, j, and p); hemin plus TNIIIA2 and the RGD peptide (200 μg/ml) (k and q); hemin plus TNIIIA2 and the CS-1 peptide (200 μg/ml) (l); TNIIIA2 alone (m). After culture for the indicated number of days, expression of integrin α4 and α5 was analyzed using normal IgG (a–c), anti-α4 mAb (d–m), and anti-α5 mAb (n–q), and the proportion of integrin-positive cells was determined, as described under “Experimental Procedures.” Data shown are representative of three individual experiments.