Effect of increased Rac1 activity on the rearrangement of F-actin and the distribution of cortactin.

<p> Cells were treated with TNF-α (B) for 2 hours or with O-Me-cAMP (C) for 1 hour or co-treated with O-Me-cAMP and TNF-α (D). In untreated cells, few stress fibers were seen, cortactin was detected both in the cytoplasm and along with some parts of the cell membrane (A). Exposure to TNF-α (B) induced stress fiber formation and the disappearance of cortactin from the cell periphery (shown by arrows); O-Me-cAMP (C) led to a loss of stress fibers and strengthened the peripheral actin band, moreover, caused an increase in the formation of lamellipodia and a change in cortactin localization to cell periphery forming a continuous linear staining pattern (C) (shown by arrows). Co-treatment with O-Me-cAMP prevented the TNF-α response (D) remarkably. Moreover, O-Me-cAMP induced lamellipodia increasing, dramatically attenuated the disappearance of cortactin from the cell periphery, and resulted in partial disappearance of central stress fibers (shown by arrows). All the images shown are representative of four independent experiments.