Defects in double-strand break response are restored by the expression of Usp28 in RTS and RecQL4-depleted cells.A and B, percentages of Mre11-, phospho-ATM-, or Rad51 foci-positive cells after neocarzinostatin treatment in RecQL4-depleted U2OS cells (A) and RTS (AG17524) cells (B) transfected with empty (−), wildtype Usp28 (wt), or C171A mutant Usp28 plasmids. C, HR repair assay using DR-GPF-integrated U2OS cells. Mock (GL) or RecQL4 (R4)-depleted cells were transfected with I-SceI and WT or C171A mutant Usp28 plasmids. Right panel is the Western blots showing the expression levels of RecQL4, Usp28, and I-SceI. Data in graphs are means ± SD; n = 4 (for A) or 3 (for B and C). ∗∗p < 0.01, ∗p < 0.05.