UV light induces ROS generation and apoptosis in HMEC-1 cells. (A) Exposure to different doses of UV light enhances generation of ROS as determined by DHE staining. (B) UV light induces a dose-dependent activation of caspase-3 and caspase-7 and a decrease in internal ATP content. Both parameters were measured 3 hours after irradiation. Data are given as mean ± SD of 3 independent experiments. (C) Increasing amount of UV light triggers fragmentation of nuclear DNA as demonstrated by TUNEL staining 24 hours after irradiation. Necrosis occurs at high doses of UV light as seen by annexin V/propidium iodide-staining in the lower right micrograph. Bars represent 50 μm.