Abstract
In an attempt to understand the biological effect of physiological and chronic low-dose rate UV-B irradiation, cultured human cells were irradiated with low-dose rate UV-B in situ using a CO2 incubator equipped with a UV-B tube. The dose-dependent formation of cyclobutane pyrimidine dimers and (6-4) photoproducts in normal human fibroblastic cells, XP 2OS cells, and human keratinocytes (HaCaT) were observed during the chronic irradiation. Synthesis of DNA and RNA in the cells were substantially reduced during the chronic exposure associated with the accumulation of G1/S phase cells, indicating that DNA replication and transcription were immediately blocked. The intracellular oxidative level elevated continuously with increasing irradiation time. Furthermore, all of the signaling molecules examined, ERK, JNK, p38, and p53, were kept phosphorylated during the irradiation. These observations suggest that DNA damage-dependent S-phase block and p53 phosphorylation, as well as continuous generation of reactive oxygen species followed by MAPK phosphorylation, were coincidentally taking place during the chronic exposure. [J Radiat Res 44:415 (2003)]
