Effects of ERK5-siRNA on ERK5 mRNA and protein assessed by quantitative RT-PCR, western blot and immunocytochemical assays. siRNA was transciently transfected into the HL-60 cells for 24-72 h. ERK5 protein (A, B) and mRNA (C) and of siERK5 cells were significantly inhibited in a time-dependant way than those of nontransfection or siControl cells respectively (*P < 0.05, **P < 0.01). In the siERK5 stably transfected HL-60 cells, ERK5 protein (D, E) and Mrna (F) of siERK5 cells were also significantly inhibited (**P < 0.01).