Figure 2

Knockdown of c-MYC reduces MB cell growth, induces G1 cell cycle arrest and CDK inhibitor p21 ^(waf1/Cip1) expression. c-MYC siRNA-transfected cells show reduced cell viability over time and inhibition of clonogenic survival compared with the control siRNA-transfected cells as determined by the MTS assay (A) and by a clonogenic survival assay (B). Cell cycle analysis of control and c-MYC siRNA-transfected cells harvested after 48 h by trypsinization, fixed in ethanol and stained with propidium iodide as described in Methods. A total number of 30'000 events per sample were counted. Results are presented as the mean percentages of cells in G1, S, and G2/M of two independent experiments (± standard deviation) (C). c-MYC siRNA-mediated up-regulation of CDK inhibitor p21 ^(waf1/Cip1) expression compared with control siRNA-transfected cells as determined by Western blotting and photometrical quantification at 72 h post transfection. Values represent the percentage of p21 ^(waf1/Cip1)relative to control siRNA-transfected cells (D). * Indicates a significant difference compared to control values, as determined by the Student's t-test (***: P < 0.001, **: P < 0.01,*: P < 0.05).