FIGURE 5.

PP2Ac_α knockdown enhances p38 and ERK1/2 activation in 293 cells and blockade of ERK1/2 signaling abolishes the increased adhesiveness of PP2Ac_α-depleted cells. Lysates obtained from 293 α_IIbβ₃ cells treated with either control or PP2Ac_α, and siRNA was separated by 10% SDS-PAGE. Mitogen-activated protein kinase activation was assessed by immunoblotting using antibodies specific for the active (dual tyrosine and threonine-phosphorylated) forms of activated p38 (pP38) (A) and p44/42 ERK (pERK1/2) (C). Cells treated with 0.5 m sorbitol (Lys) in A serves as positive control for p38 activation. The blots were stripped and reprobed for total p38 (p38) or ERK1/2 to assess the equivalency of loading. Densitometric quantification of the enhanced activation of p38 (B) and ERK1/2 (D) in PP2Ac_α siRNA-treated cells compared with the control treated cells. Data are mean ± S.E. of three experiments for p38 and five experiments for ERK1/2 and was significant at *, p = 0.04 for p38 and #, p = 0.005 for ERK1/2. E, effect of ERK1/2 inhibitor (U0126) or p38 inhibitor (SB203580) on the increased adhesion of PP2Ac_α-depleted cells to fibrinogen. Results are mean ± S.E. of three experiments performed in triplicate with the following p values: *, p = 0.0001; †, p = 0.373; #, p = 0.012.