TP53BP1 and cancer: With FACS, we observed a five-fold increase in the number of phospho-histone γH2AX (Ser139)-positive A549 cancer cells in response to the U12 ASO (Figs. 6B,C and EV7B) and a marked increase in phospho-53BP1 (Ser1778) (Fig. 6D), which like γH2AX, is phosphorylated upon DNA damage, triggering their recruitment to double-strand breaks.