Fig. 2.

UVC-induced DNA damage generates bystander responses. (A) Schematic: cells were exposed to UVC with half shielded with foil. After incubation, DNA DSBs were assessed in control, irradiated and bystander (BS) cell populations as above. Images are representative of NHF cell cultures 3 h after sham treatment (left column, control), direct exposure to 100 J/m² UVC (middle column) or shielding (right column). Cultures were stained for γ-H2AX (red, top row) and 53BP1 (green, second row). Merged images (third row) exhibit yellow foci where the two proteins colocalize. The bottom row images show cells stained for thymine dimers (green) and DNA (red, propidium iodide). UVC-induced photo products are present only in exposed cells. (B) Quantification of γ-H2AX induced in NHF bystander cell populations 3 h after various doses of UVC. Colocalized γ-H2AX and 53BP1 fpc (left) and γ-H2AX intensity (right) are shown. Differences in γ-H2AX foci numbers were statistically significant at all doses tested, whereas differences in intensity were significant at the 20 and 50 J/m² doses. (C) Quantification of γ-H2AX induced in bystander HeLa cell populations various times after 6000 J/m² UVC exposure. Colocalized γ-H2AX and 53BP1 fpc (left) and γ-H2AX intensity (right) are shown. All time points tested were significantly different from control levels in both systems. The inset shows immunoblot analysis of control and bystander populations 3 h after irradiation.