Effect of CDK4/CDK6 inhibitor on Rb phosphorylation in MCL cells. (A) SP53 and Mino MCL cell lines were exposed to the depicted concentrations of PD 0332991 for 2 hours and analyzed in Western blot for the Rb phosphorylation at serines 795, 780, and 807/811. (B) Kinetics of Rb dephosphorylation in the presence of PD 0332991 at 50 nM. (C) Visualization of the Rb phosphorylation at serine 807/811 in the MCL cells by immunofluorescence before (left panel) and after (right panel) 16-hour exposure of Mino cells to 100 nM PD 0332991. (D) Rb phosphorylation at the depicted serine moieties in patient-derived primary MCL cells after 1-hour exposure to 200 nM PD 0332991. N/D indicates not done. Results are representative of at least 3 independent experiments.