Inhibition of PI3 kinase decreases cdk4 kinase activity.

Indicated cells were grown to subconfluence, harvested by centrifugation, and replated for 24 hours with either media alone, DMSO (0.1%), LY294002 (25 μM), or STI571 (1 μM). After incubation, cells were harvested and lysed. Lysates were immunoprecipitated with cdk4 antibody and cdk4-associated Rb kinase activity was assayed. Kinase reaction products were separated by SDS-PAGE. Gel was dried and visualized by autoradiography with the use of a Molecular Dynamics PhosphoImager. Visual display of results is shown in top of figure and quantitation of results is shown below.