Radiation with 1 Gy prevents the activation of the mitotic inducers mitosis-promoting factor (MPF) and cdc25-C in HeLa cells.
The mechanism of the transient G2 arrest induced by small doses of ionizing radiation involves the failure to activate the correctly formed pre-mitosis-promoting factor (MPF) complex of cyclin B and p34cdc2 by dephosphorylation at Tyr15 of the latter, as recent studies of other laboratories have indicated. Similar data were obtained with the G2 arrest-inducing agents epidermal growth factor and the phorbol ester 12-0- tetradecanoylphorbol-13-acetate (H. Barth and V. Kinzel, Exp. Cell Res., 212: 383-388, 1994, and H. Barth and V. Kinzel, J. Cell. Physiol., 162: 44-51, 1995). To differentiate the radiation consequences in synchronized HeLa cells from those of 12-0-tetradecanoylphorbol-13-acetate and epidermal growth factor, experiments with a very small dose (1 Gy) have been carried out in cells close to the G2-M border and, for comparison, in mitotic cells. We show that in addition to the failure of p34cdc2 dephosphorylation at Tyr15, radiation with 1 Gy also prevents the activation of the phosphatase cdc25-C, the enzyme catalyzing the MPF activation. In contrast, irradiation of mitotic cells with 1 Gy did not influence that fraction of either MPF or cdc25-C already activated. Moreover, the gain in MPM-2 antigenicity of cdc25-C, usually indicative of an activating phosphorylation, is shown to be prevented by 1 Gy. The data indicate that the initiation of the proposed autocatalytic loop between MPF and cdc25-C becomes interrupted by radiation, but they give no hint at which point.
Barth
H
H
Department of Pathochemistry, German Cancer Research Center, Heidelberg.
Hoffmann
I
I
Kinzel
V
V
D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D016195:G2 Phase / Q000235:genetics / Q000528:radiation effects*; D006367:HeLa Cells / Q000378:metabolism / Q000528:radiation effects*; D006801:Humans; D016200:Maturation-Promoting Factor / Q000378:metabolism*; D008938:Mitosis / Q000235:genetics / Q000528:radiation effects*; D009363:Neoplasm Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D006656:Protamine Kinase / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D020687:cdc25 Phosphatases
D018797:Cell Cycle Proteins; D009363:Neoplasm Proteins; D004815:Epidermal Growth Factor; D006656:Protamine Kinase; D016203:CDC2 Protein Kinase; D016200:Maturation-Promoting Factor; D010749:Phosphoprotein Phosphatases; D020687:cdc25 Phosphatases; D013755:Tetradecanoylphorbol Acetate