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

Abstract

Abstract.  Low‐frequency electromagnetic fields are suspected of being involved in carcinogenesis, particularly in processes that could be related to cancer promotion. Because development of cancer is associated with deregulated cell growth and we previously observed a magnetic field‐induced decrease in DNA synthesis [Lange et al. (2002) Alterations in the cell cycle and in the protein level of cyclin D1p, 21^CIP1, and p16^INK4a after exposure to 50 HZ. MF in human cells. Radiat. Environ. Biophys.41, 131], this study aims to document the influence of 50 Hz, 1 mT magnetic fields (MF), with or without initial γ‐ionizing radiation (IR), on the following cell proliferation‐relevant parameters in human amniotic fluid cells (AFC): cell cycle distribution, expression of the G₁ phase‐regulating proteins Cdk4, cyclin D1, p21^CIP1 and p16^INK4a, and Cdk4 activity. While IR induced a G₁ delay and a dose‐dependent G₂ arrest, no discernible changes in cell cycle kinetics were observed due to MF exposure. However, a significant decrease in the protein expression of cyclin D1 and an increase in p21^CIP1‐ and p16^INK4a‐expression could be detected after exposure to MF alone. IR‐exposure caused an augmentation of p21^CIP1‐ and p16^INK4a‐ levels as well, but did not alter cyclin D1 expression. A slight diminution of Cdk4 activity was noticed after MF exposure only, indicating that Cdk4 appears not to act as a mediator of MF‐ or IR‐induced changes in the cell cycle of AFC cells. Co‐exposure to MF/IR affected neither cell cycle distribution nor protein expression or kinase activity additionally or synergistically, and therefore MF seems not to modify the mutagenic potency of IR.