Earthworms repair H2O2-induced oxidative DNA adducts without removing UV-induced pyrimidine dimers.
Ultraviolet (UV) radiation is a natural insult to various organisms. Earthworms, although possessing similar biomolecules to those in mammalian skin, do not suffer from skin cancer nor any other types of cancer as humans do. However, little is known about the molecular mechanism of the earthworm's tolerance to UV. In this study, we evaluated the genotoxicity of UV and the capacity of earthworm cell to repair UV-induced damage. The T4 UV endonuclease UV-incorporated comet assay was used to examine the excision and rejoining steps of UV-induced pyrimidine dimer. Earthworm testis cells were treated with a combination of 5 mM hydroxyurea plus 50 μM cytosine-β-D-arabinofuranoside for 6 h to block DNA rejoining capacity and to investigate excision dynamics. Compared with H(2)O(2)-induced oxidative repair capacity, the excision step of repair of UV-induced lesions in earthworm testis cells was significantly lower. After 6-h treatment of 5 mM hydroxyurea plus 50 μM cytosine-β-D-arabinofuranoside, the medium was totally replaced with fresh medium and cells were allowed to rejoin the accumulated DNA strand breaks. We found that the capacity for rejoining UV-induced breaks was also significantly lower than that for the H(2)O(2)-induced breaks. Our results strongly suggest that earthworms seem to be efficient at repairing H(2)O(2)-induced oxidative DNA adducts, but not so capable of removing UV-induced pyrimidine dimers from their genome.
Terry Fox Cancer Research Laboratory, China Medical University Hospital, 2 Yuh-Der Road, Taichung, 404 Taiwan, ROC.
Wen-Shin
WS
Chang
Chia-Wen
CW
Tsai
Cheng-Chieh
CC
Lin
Chih-Hsueh
CH
Lin
Wu-Chung
WC
Shen
Song-Shei
SS
Lin
Da-Tian
DT
Bau
D000818:Animals; D020552:Comet Assay; D018736:DNA Adducts / Q000737:chemistry*; D004260:DNA Repair; D006861:Hydrogen Peroxide / Q000633:toxicity*; D009835:Oligochaeta / Q000502:physiology*; D018384:Oxidative Stress; D011740:Pyrimidine Dimers / Q000302:isolation & purification*; D014466:Ultraviolet Rays
D018736:DNA Adducts; D011740:Pyrimidine Dimers; D006861:Hydrogen Peroxide