DNA‑PKcs PARylation regulates DNA‑PK kinase activity in the DNA damage response.

DNA‑dependent protein kinase catalytic subunit (‑PKcs) is the core protein involved in the non‑homologous end‑joining repair of double‑strand breaks. In addition, it can form a complex with poly(ADP‑ribose) polymerase 1 (PARP1), which catalyzes protein PARylation. However, it is unclear how DNA‑PKcs interacts with PARP1 in the DNA damage response and how PARylation affects DNA‑PK kinase activity. Using immunoprecipitation, immunofluorescence and flow cytometry the present study found that DNA‑PKcs was PARylated after DNA damage, and the PARP1/2 inhibitor olaparib completely abolished DNA‑PKcs PARylation. Olaparib treatment prevented DNA‑PKcs protein detachment from chromatin after DNA damage and maintained DNA‑PK activation, as evidenced by DNA‑PKcs Ser2056 phosphorylation. Furthermore, olaparib treatment synergized with DNA‑PK inhibition to suppress cell survival. All of the above results are suggestive of the important role of DNA‑PKcs PARylation in regulating DNA‑PK activity.