Fig. 4. A, effect of p16Ink4a expression on the levels of p21Cip1 and p27Kip1 associated with cdk2, cdk4, and cdk6 in NCI-H460 cells. cdk2, cdk4, and cdk6 immunoprecipitates from control-infected (Ad-GFP) and Ad-p16Ink4a-infected cells were boiled in SDS-PAGE sample buffer, resolved by gel electrophoresis, and Western blotted with antibodies to the immunoprecipitated protein, p21Cip1 and p27Kip1. For cdk2, coimmunoprecipitation of cyclin E was also assayed. B, identical coimmunoprecipitation experiments performed with lysates prepared from control-infected and Ad-p16Ink4a-infected NCI-H661 cells. C, identical coimmunoprecipitation experiments performed with lysates prepared from control-infected and Ad-p16Ink4a-infected primary lung epithelial (NHBE) cells.