Cytochalasin D or phalloidin treatment inhibits CD98-induced adhesion of MCF-7 cells to fibronectin, but not surface expression and clustering of β1 integrins in MCF-7 cells. (A) MCF-7 cells were incubated with anti-CD98 mAb in the presence or absence of cytochalasin D (4 µM) or phalloidin (10 µM) for 1 h. The effects of DMSO vehicle control are also shown. The effect of cytochalasin D treatment on cell adhesion was determined as described in Materials and Methods. In addition, whether addition of 0.5 µM Mn2+ interferes with the effect of cytochalasin D or phalloidin on cell adhesion was determined by the same way. Results are expressed as Figure 3B. *P < 0.05, **P < 0.01, ***P < 0.001 (B) MCF-7 cells treated with anti-CD98 mAb in the presence or absence of cytochalasin D or phalloidin were analyzed for expression of β1 integrin using flow cytometry. Results are expressed as in Figure 3 (C). **P < 0.01 (C) Confocal microscopy was performed as described above to investigate the effect cytochalasin D or phalloidin of on clustering of β1 integrins. Scale bar, 50 µm. Original magnification, × 400.