Formation of UV-induced apoptosis relates to the cell cycle

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Abstract
The relationship of the rate of epidermal proliferation to UV-induced cell death, namely sunburn cell (SC) formation, was investigated in vivo using the guinea pig model. The number of SC was correlated with cellophane tape stripping which stimulates the proliferation rate and treatment with antimitotic and antimetabolic agents which suppress the proliferation rate. The tape stripping performed 14 h before UV irradiation significantly increased the number of SC counted 24 h after UV irradiation from a mean of 17.4 to 62.6/section, and the tritiated thymidine (TdR-3H)-labeling index (LI) increased from a mean of 8.1 to 27.4%. SC counts and LI were markedly decreased by the intradermal injection of colchicine, methotrexate, hydroxyurea or 5-fluorouracil given once immediately after the tape stripping. The autoradiographic study showed that 23.2% of SC were labeled when TdR-3H was given intradermally 1 h before UV exposure, while no SC were labeled when TdR-3H was given immediately after UV exposure. The labeled SC count (23.2%) which presumably represents S phase cells at the time of UV exposure, was higher than the LI (mean 8.1%). Proliferating cells, possibly S phase cells, may be responsible for SC formation.
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