title: The TMPRSS2-ERG Gene Fusion Blocks XRCC4-Mediated Nonhomologous End-Joining Repair and Radiosensitizes Prostate Cancer Cells to PARP Inhibition.
abstract: Exposure to genotoxic agents, such as ionizing radiation (IR), produces DNA damage, leading to DNA double-strand breaks (DSB); IR toxicity is augmented when the DNA repair is impaired. We reported that radiosensitization by a PARP inhibitor (PARPi) was highly prominent in prostate cancer cells expressing the TMPRSS2-ERG gene fusion protein. Here, we show that TMPRSS2-ERG blocks nonhomologous end-joining (NHEJ) DNA repair by inhibiting DNA-PKcs. VCaP cells, which harbor TMPRSS2-ERG and PC3 cells that stably express it, displayed γH2AX and 53BP1 foci constitutively, indicating persistent DNA damage that was absent if TMPRSS2-ERG was depleted by siRNA in VCaP cells. The extent of DNA damage was enhanced and associated with TMPRSS2-ERG's ability to inhibit DNA-PKcs function, as indicated by its own phosphorylation (Thr2609, Ser2056) and that of its substrate, Ser1778-53BP1. DNA-PKcs deficiency caused by TMPRSS2-ERG destabilized critical NHEJ components on chromatin. Thus, XRCC4 was not recruited to chromatin, with retention of other NHEJ core factors being reduced. DNA-PKcs autophosphorylation was restored to the level of parental cells when TMPRSS2-ERG was depleted by siRNA. Following IR, TMPRSS2-ERG-expressing PC3 cells had elevated Rad51 foci and homologous recombination (HR) activity, indicating that HR compensated for defective NHEJ in these cells, hence addressing why TMPRSS2-ERG alone did not lead to radiosensitization. However, the presence of TMPRSS2-ERG, by inhibiting NHEJ DNA repair, enhanced PARPi-mediated radiosensitization. IR in combination with PARPi resulted in enhanced DNA damage in TMPRSS2-ERG-expressing cells. Therefore, by inhibiting NHEJ, TMPRSS2-ERG provides a synthetic lethal interaction with PARPi in prostate cancer patients expressing TMPRSS2-ERG.
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio. School of Biomedical Sciences, Kent State University, Kent, Ohio.
authors.forename: Payel
authors.initials: P
authors.lastname: Chatterjee
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio. Department of Pathology, Case Western Reserve University School of Medicine, Ohio.
authors.forename: Gaurav S
authors.initials: GS
authors.lastname: Choudhary
authors.affiliation: Department of Chemistry, Cleveland State University, Cleveland, Ohio.
authors.forename: Turkeyah
authors.initials: T
authors.lastname: Alswillah
authors.affiliation: Department of Radiation Oncology, Case Western Reserve University School of Medicine, Cleveland, Ohio.
authors.forename: Xiahui
authors.initials: X
authors.lastname: Xiong
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Warren D
authors.initials: WD
authors.lastname: Heston
authors.affiliation: Glickman Urological and Kidney Institute, Cleveland Clinic, Cleveland, Ohio. Robert J. Tomisch Pathology and Laboratory Medicine Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Cristina
authors.initials: C
authors.lastname: Magi-Galluzzi
authors.affiliation: Department of Radiation Oncology, Case Western Reserve University School of Medicine, Cleveland, Ohio.
authors.forename: Junran
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Glickman Urological and Kidney Institute, Cleveland Clinic, Cleveland, Ohio.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Klein
authors.affiliation: Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio. Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, Ohio. almasaa@ccf.org.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Almasan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D059447:Cell Cycle Checkpoints / Q000235:genetics / Q000528:radiation effects; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D004249:DNA Damage; D059766:DNA End-Joining Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008297:Male; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D015514:Oncogene Proteins, Fusion / Q000235:genetics* / Q000378:metabolism; D000067856:Poly(ADP-ribose) Polymerase Inhibitors / Q000494:pharmacology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000378:metabolism*; D011836:Radiation Tolerance / Q000187:drug effects* / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; C413163:MDC1 protein, human; D009687:Nuclear Proteins; D015514:Oncogene Proteins, Fusion; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C515553:TMPRSS2-ERG fusion protein, human; D015534:Trans-Activators; C101467:XRCC4 protein, human; D011065:Poly(ADP-ribose) Polymerases