Effect of the kinase inhibitor 2-aminopurine on the cell cycle stage-dependent phosphorylation state of the retinoblastoma protein.

We investigated the effect of 2-aminopurine (2-AP) on the cell cycle stage-dependent phosphorylation state of the retinoblastoma growth suppressor protein (pRB). Our results suggest that 2-AP does not affect dephosphorylation of pRB scheduled during metaphase/anaphase of mitosis, even though 2-AP-treated cells never enter metaphase or anaphase. Phosphorylation of pRB, which is important for G1 exit, appeared to be impeded by 2-AP late during G1, coincident with a slowing of G1 cell progression into S phase. The significance of these data with regard to cell cycle regulation is discussed.