Activity of Cdk2 and abundance of G1/S cell cycle regulatory proteins in MF-treated cancer cells. Whole-protein extracts from cells treated with either vehicle (-), the IC50 (A) or the IC75 (B) concentrations of MF (+) for 24 h. The whole cell extracts were either immunoprecipitated with anti-Cdk2 antibody and assayed for their capacity to phosphorylate histone H1 in vitro in the presence of [32P]ATP (upper panels in A and B), or separated by electrophoresis and the immunoblots probed with antibodies against the cell cycle regulatory proteins p21cip1, p27kip1, cyclin E, and Cdk2. β-actin was included as a protein loading control (lower panels in A and B). Cyclin E and Cdk2 were immunoblotted in one membrane whereas p21cip1 and p27kip1 were blotted in a separate membrane. Consequently, each membrane was blotted separately with anti-β-actin. This experiment was repeated twice with a similar outcome. MDA-231 means MDA-MB-231.