Effect of ultraviolet (UV) A, UVB or ionizing radiation on the cell cycle of human melanoma cells

Summary Background One important component of the cellular response to irradiation is the activation of cell cycle checkpoints. It is known that both ultraviolet (UV) radiation and ionizing radiation (IR) can activate checkpoints at transitions from G1 to S phase, from G2 phase to mitosis and during DNA replication. Objectives To evaluate the effects of irradiation with different wavelengths on cell cycle alterations. Methods p53‐deficient IPC‐298 melanoma cells were irradiated with 10 J cm−2 UVA, 40 mJ cm−2 UVB, or with 7·5 Gy IR. Cell cycle effects were then determined by DNA/5‐bromodeoxyuridine dual‐parameter flow cytometry. Results IPC‐298 cells irradiated in G1 with UVA were not arrested at the G1/S transition, but at the G2/M transition. Despite p53 deficiency, the cells showed a G1 arrest after UVB exposure. Furthermore, IR did not affect G1 or S phase, but induced G2 phase arrest. Hence, the effects of UVA, but not of UVB, on the cell cycle in p53‐deficient melanoma cells are comparable with those of IR. Conclusions UVA and IR induce radical‐mediated strand breaks and DNA lesions, and UVB essentially induces thymine dimers that lead to excision repair‐related strand breaks. Different cell cycle effects may be a consequence of different types of DNA damage. The results showed that UVB‐irradiated p53‐deficient cells are arrested in G1. Irradiation with the solar radiation component UVB can therefore result in a beneficial retardation of tumour promotion in human skin carrying p53‐mutated cell clones.