UVA causes specific mutagenic DNA damage through ROS production, rather than CPD formation, in Drosophila larvae

Evidence is accumulating that ultraviolet A (UVA) plays an important role in photo-carcinogenesis. However, the types of DNA damage involved in the resulting mutations remain unclear. Previously, using Drosophila, we found that UVA from light-emitting diode (LED-UVA) induces double-strand breaks in DNA through oxidative damage in an oxidative damage-sensitive (urate-null) strain. Recently, it was proposed that cyclobutane pyrimidine dimers (CPDs), which also are induced by UVA irradiation, might play a significant role in the induction of mutations. In the present study, we investigated whether reactive oxygen species (ROS) and CPDs are produced in larval bodies following LED-UVA irradiation. In addition, we assessed the somatic cell mutation rate in urate-null Drosophila induced by monochromatic UVA irradiation. The production of ROS through LED-UVA irradiation was markedly higher in the urate-null strain than in the wild-type Drosophila. CPDs were detected in the DNA of both of UVA- and UVB-irradiated larvae. The level of CPDs was unexpectedly higher in the wild-type strain than in urate-null flies following UVA irradiation, whereas this parameter was expectedly similar between the urate-null and wild-type Drosophila following UVB irradiation. The somatic cell mutation rate induced by UVA irradiation was higher in the urate-null strain than in the wild-type strain. These results suggest that mutations induced by UVA-specific pathways occur through ROS production, rather than via CPD formation.