Fig. 6

Expression of mutant T210A Plk1 inhibits the PDGF-induced phosphorylation of MEK1/2 and ERK1/2, and cell proliferation. a Smooth muscle cells were transfected with plasmids encoding Flag-wild type (WT) or T210A Plk1. Blots of cell extracts were detected with antibodies against Flag and GAPDH. Duplicated samples of each treatment are shown. Ratios of Plk1/GAPDH protein in cells transfected with plasmids were normalized to untransfected cells. Values are mean ± SE (n = 4, *P < 0.01 vs. untransfected cells). b and c Cells expressing WT or T210A Plk1 were treated with 20 ng/ml PDGF for 10 min, or they were not treated. Protein phosphorylation was then evaluated by immunoblotting. MEK1/2 phosphorylation (n = 5) and ERK1/2 phosphorylation (n = 4) induced by PDGF was significantly reduced in cells expressing T210A Plk1 compared to cells expressing WT Plk1 (*P < 0.05). Protein phosphorylation under various treatments was normalized to the levels in unstimulated cells expressing WT Plk1. Values are mean ± SE. NS, basal MEK1/2 or ERK1/2 phosphorylation in Plk1 KD was not significantly different from cells expressing control shRNA (P > 0.05). d Smooth muscle cells expressing WT or T210A Plk1 were treated with 20 ng/ml PDGF for 24–72 h. The numbers of viable cells were then determined. Data are mean ± SE (n = 4, *P < 0.05, **P < 0.01)