K252a Inhibits the Phosphorylation of pRb without Changing the Levels of G1 Cyclins and Cdk2 Protein in Human Hepatoma Cells

Abstract A protein kinase inhibitor K252a suppressed the growth of HuH7 hepatoma cells and the hyperphosphorylation of retinoblastoma protein (pRb) at late G 1 phase of cell cycle. However, K252a treatment did not alter the levels of cyclin D1, cyclin E, cyclin A and Cdk2 protein bound to cyclin E or cyclin A. Therefore, the K252a inhibition of pRb phosphorylation is considered to be brought about probably by inhibiting the action of Cdk-cyclin complex rather than by changing its cellular level. These results also suggest that K252a is a useful tool for investigating the mechanism of phosphorylation of pRb mediated by Cdk-cyclin.