Our findings indicate that DNA-PK recognizes DSBs regardless of chemical complexity but cannot recognize the protein-linked DSBs produced by etoposide and topoisomerase II. In contrast, the protein-linked DSBs produced by etoposide and topoisomerase II failed to bind and activate DNA-PK. The data indicate that DSBs produced by bleomycin, calicheamicin and two types of ionizing radiation ( 137 Cs γ rays and $$ ions: high and low linear energy transfer, respectively) activate DNA-PK to levels matching the kinase activation obtained with simple restriction endonuclease-induced DSBs. The DNA breaks were tested for the ability to activate purified DNA-PK. Here we show that CRISPR/Cas9-induced double-stranded DNA breaks enrich for cells deficient in p53 and in genes of a core CRISPRp53 tumor suppressor. To determine whether DNA-PK could recognize DNA strand breaks generated by agents used in the treatment of cancer, we damaged plasmid DNA with anticancer drugs and ionizing radiation. These nucleotides are often damaged when DSBs are introduced by anticancer agents and could therefore prevent recognition by DNA-PK. We have previously shown that PRKDC is activated when the enzyme interacts with the terminal nucleotides of a DSB. DNA-PK is composed of a DNA-binding subunit, Ku, and a catalytic subunit, DNA-PKcs (PRKDC). The DNA-dependent protein kinase (DNA-PK) is a DNA-end activated protein kinase that is required for efficient repair of DNA double-strand breaks (DSBs) and for normal resistance to ionizing radiation.
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