Modifications in cell cycle kinetics and in expression of G1 phase-regulating proteins in human amniotic cells after exposure to electromagnetic fields and ionizing radiation

Low-frequency electromagnetic fields are suspected of being involved in carcinogenesis, particularly in processes that could be related to cancer promotion. Since development of cancer is associated with deregulated cell growth and we previously observed a MF-induced decrease in DNA synthesis (Lange et al. 2002), this study aims to document the influence of 50 Hz, 1 mT magnetic fields (MF), with or without initial gamma-ionizing radiation (IR), on the following cell proliferation-relevant parameters in AFC cells: cell cycle distribution, expression of the G₁ phase-regulating proteins Cdk4, cyclin D1, p21^CIP1, and p16^INK4a, and Cdk4 kinase activity. While IR induced a G₁ delay as well as a dose-dependent G₂ arrest, no discernible changes in cell cycle kinetics were observed due to MF exposure. Significant alterations in the protein expression of cyclin D1, p21^CIP1, and p16^INK4a could be detected after exposure to MF and/or IR, respectively, whereas only a slight diminution of Cdk4 kinase activity was noticed. Consequently, Cdk4 appears not to act as mediator of MF- or IR-induced changes in the cell cycle of AFC cells. Combined exposure to MF/IR affected neither cell cycle distribution nor protein expression or kinase activity additionally or synergisticly and, therefore, MF seems not to modify the mutagenic potency of IR.