Donna M. Gadbois

Staurosporine is a potent inhibitor of p34cdc2 and p34cdc2-like kinases

We previously demonstrated that nontransformed cells arrest in the G1 phase of the cell cycle when treated with low concentrations (21 nM) of staurosporine (1). Both normal and transformed cells are blocked in the G2 phase of the cell cycle when treated with higher concentrations (160 nM) of staurosporine (1,2). In the present study, we show that staurosporine inhibits the activity of fractionated p34cdc2 and p34cdc2-like kinases with IC50 values of 4-5 nM. We propose that the G2 phase arrest in the cell cycle caused by staurosporine is due, at least in part, to the inhibition of the p34cdc2 kinases.

Alterations in the progression of cells through the cell cycle after exposure to alpha particles or gamma rays.

A G1-phase delay after exposure to alpha particles has not been report ed previously, perhaps because immortalized cell lines or cell lines from tumor cells were used in past studies. Therefore, we compared the effects of alpha particles (0.19 or 0.57 Gy) and approximately equitoxic doses of gamma rays (2 or 4 Gy) on progression of cells through the cell cycle in normal human skin fibroblasts. Cell cycle analyses were performed using flow cytometry by measuring incorporation of bromodeoxyuridine (BrdUrd) in each phase of the cell cycle up to 44 h after irradiation. We observed an alpha-particle-induced G1-phase delay in human skin fibroblasts even at the lowest dose, 0.19 Gy. At equitoxic doses, more pronounced and persistent G1-phase delays and arrests were observed in gamma-irradiated cultures in that increased fractions of the G1-phase cells remained BrdUrd- over the course of the study after gamma-ray exposure compared to cells exposed to alpha particles. In addition, G1-phase cells that became BrdUrd+ after gamma irradiation re-arrested in G1 phase, whereas BrdUrd+ G1-phase cells in alpha-particle-irradiated cultures continued cycling. In contrast, comparable percentages of cells were delayed in G2 phase after either alpha-particle or gamma irradiation. Both gamma and alpha-particle irradiation caused increases in cellular p53 and p2lCip1 shortly after the exposures, which suggests that the G1-phase delay that occurs in response to alpha-particle irradiation is dependent on p53 like the initial G1-phase delay induced by gamma rays.