UV-induced chromatin changes require PARP1 activity. (A) Distribution of GFP-H4 at sites of local damage (100 J/m2 through 5-µm pores) in SWI/SNF-deficient C33A cells marked by the accumulation of DDB2-mCherry. (B and C) Distribution of GFP-H1 (B) or GFP-H4 (C) at sites of local damage (100 J/m2 through 5-µm pores) in U2OS that were either treated with DMSO (top rows) or 10 µM PARP inhibitor (PARPi) KU-0058948 for 3 h (bottom rows). (D) Western blot analysis of PARP1 expression levels after a single transfection or two consecutive transfections with siRNAs targeting luciferase (siLuc) or PARP1 (siPARP1) in U2OS cells. (E) Distribution of GFP-H4 at sites of local damage (100 J/m2 through 5-µm pores) in U2OS that were transfected twice with siLuc (top row) or siPARP1 (bottom row). (F) Quantification of the intensity of GFP-tagged histones at sites of UV-induced DNA damage shown in a box plot (between 50 and 100 cells for each condition in two independent experiments). The dotted line represents a ratio of 1, which means that the intensity in the local damage is the same as the intensity elsewhere in the nucleus. Asterisks indicate significant differences based on a t test (P < 0.05). Open circles are data points that are considered outliers, as their value is greater than the upper quartile, +1.5 the interquartile distance, or less than the lower quartile, −1.5 the interquartile distance.
