Effect of wortmannin and 3-AB on G2 phase arrest and transient failure to activate MPF induced by ionizing irradiation

Active mitosis promoting factor (MPF) composed of p34^odc2 with cyclin B1 is required for the cell cycle transition from G₂ to M phase. Recent studies have demonstrated that ionizing radiation (IR) exposures associated with inhibition of p34^odc2 activity was the mechanism of G₂ arrest. At low dose, IR causes transient failure to dephosphorylate p34^odc2 instead of suppression of cyclin B or MPF formation of cyclin B with p34^odc2 complex. But the signaling events that regulate p34^odc2 in irradiated cells remain unclear. This note demonstrates that PI3 kinase family inhibitor wortmannin (wort) and PARP specific inhibitor 3-AB can reduce the G₂ arrest induced by 2Gy γ-ray. Immunoprecipitation studies demonstrate that wort and 3-AB can facilitate dephosphorylation of p34^odc2 in G₂ phase arrest induced by radiation. These findings suggest that wort sensitive pathway and PARP may be involved in initiating the signal transduction of G₂ phase arrest caused by IR.