Photorepair prevents ultraviolet-induced apoptosis in human cells expressing the marsupial photolyase gene

Photolyase absorbs blue light and employs the energy to remove UV-induced D NA damage, cyclobutane pyrimidine dimers, or pyrimidine pyrimidone (6-4) Le sions. These enzymes have been found in many living organisms ranging from bacteria to aplacental mammals, but their photoreactivation effect, such as survival increase of W-irradiated cells by light-illumination, has not bee n identified in placental mammals, including humans. Therefore, we introduc ed a photolyase gene derived from the marsupial rat kangaroo, Potorous trid actylus, into HeLa cells and established the first human cell line capable of photorepairing UV-induced pyrimidine dimers, Several clones were found t o increase cell survival after UV irradiation when illuminated by fluoresce nt light. The induction of apoptosis by UV irradiation was investigated in these photoreactivation-proficient cells. Several typical features of the p rogrammed cell death, such as internucleosomal DNA degradation, presence of subdiploid cells, loss of membrane integrity, and chromosomal condensation , were found to be induced by UV in the HeLa cells, but they can be reduced by photorepair, This implicates that cyclobutane pyrimidine dimers cause W -induced apoptosis in human cells.