Abstract
BackgroundThe VRK1 chromatin kinase regulates the organization of locally altered chromatin induced by DNA damage. The combination of ionizing radiation with inhibitors of DNA damage responses increases the accumulation of DNA damage in cancer cells, which facilitates their antitumor effect, a process regulated by VRK1.MethodsTumor cell lines with different genetic backgrounds were treated with olaparib to determine their effect on the activation of DNA repair pathways induced by ionizing radiation. The effect of combining olaparib with depletion of the chromatin kinase VRK1 was studied in the context of double-strand breaks repair pathway after treatment with ionizing radiation. The initiation and progression of DDR were studied by specific histone acetylation, as a marker of local chromatin relaxation, and formation of γH2AX and 53BP1 foci.ResultsIn this work, we have studied the effect that VRK1 by itself or in collaboration with olaparib, an inhibitor of PARP, has on the DNA oxidative damage induced by irradiation in order to identify its potential as a new drug target. The combination of olaparib and ionizing radiation increases DNA damage permitting a significant reduction of their respective doses to achieve a similar amount of DNA damage detected by γH2AX and 53BP1 foci. Different treatment combinations of olaparib and ionizing radiation permitted to reach the maximum level of DNA damage at lower doses of both treatments. Furthermore, we have studied the effect that depletion of the VRK1 chromatin kinase, a regulator of DDR, has on this response. VRK1 knockdown impaired all steps in the DDR induced by these treatments, which were detected by a reduction of sequential markers such as H4K16 ac, γH2AX, NBS1 and 53BP1. Moreover, this effect of VRK1 is independent of TP53 or ATM, two genes frequently mutated in cancer.ConclusionThe protective DNA damage response induced by ionizing radiation is impaired by the combination of olaparib with depletion of VRK1, and can be used to reduce doses of radiation and their associated toxicity. Proteins implicated in DNA damage responses are suitable targets for development of new therapeutic strategies and their combination can be an alternative form of synthetic lethality.
Highlights
The Vaccinia-related kinase 1 (VRK1) chromatin kinase regulates the organization of locally altered chromatin induced by DNA damage
In this work we have studied the effect that VRK1 depletion has on the cellular response to olaparib, a drug which is currently used to sensitize tumor cell to ionizing radiation, and facilitates tumor elimination in cells with altered DNA repair pathways, such as those with BRCA1 [17, 18] or Ataxia-telangiectasia mutated kinase (ATM) [15, 16] mutations
Olaparib sensitizes cells to DNA damage induced by ionizing radiation and is independent of p53 Initially, we studied the effect of several doses of IR, olaparib or their combinations using two markers of DNA
Summary
The VRK1 chromatin kinase regulates the organization of locally altered chromatin induced by DNA damage. DNA damage causes a local distortion of chromatin, which triggers several sequential reactions in order to start the appropriate DNA damage response (DDR) [3, 4] These sequential steps range from a local chromatin relaxation and remodeling, and protection of DNA at damaged sites, to the recognition of the type of damage and the activation of its specific DDR pathway. Among these early events is histone acetylation, which is associated with a local chromatin relaxation that facilitates accessibility to the proteins in the DDR sequential steps, which include phosphorylation of H2AX and recruitment of DNA repair proteins, such as NBS1, NBS1 and 53BP1, implicated in Non-homologous end-joining (NHEJ), a key DDR pathway in resting cells
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