Fig. 5.

USP3 regulates the phosphorylation of chromatin-bound CHK1 after UV treatment. (A) CHK1 S345 phosphorylation was increased in the chromatin fraction by USP3 knockdown in 293T cells. Cells were collected at the indicated time after UV irradiation (15 J/m²). Cell fractionation was done as described in Fig. 4A. (B) CHK1 pS317 foci were more prominent and sustained by depletion of USP3 in HCT116 cells, as assessed by confocal microscopy. Staining of pS317 is shown in SI Appendix, Fig. S5. The mean ± SD from three experiments is shown. UT, untreated. (C) USP3 depletion promoted CHK1 nuclear retention after UV treatment, as assessed by confocal microscopy. (D) The intensity of CHK1 was quantified, and the cell population with increased CHK1 nuclear presence was determined. Data are shown as the mean ± SD from three independent experiments.