title: 53BP1 and MDC1 foci formation in HT-1080 cells for low- and high-LET microbeam irradiations.
abstract: An improved assessment of the biological effects and related risks of low doses of ionizing radiation is currently an important issue in radiation biology. Irradiations using microbeams are particularly well suited for precise and localized dose depositions, whereas recombinant cell lines with fluorescent proteins allow the live observation of radiation-induced foci. Living cells of the fibrosarcoma cell line HT-1080 stably expressing 53BP1 or full-length reconstituted MDC1 fused to Green Fluorescent Protein (GFP) were irradiated with protons and α-particles of linear energy transfers (LETs) of 15 and 75 keV/μm, respectively. Using a microbeam, the irradiations were carried out in line patterns, which facilitated the discrimination between undefined background and radiation-induced foci. As expected, foci formation and respective kinetics from α-particle irradiations with a high LET of 75 keV/μm could be detected in a reliable manner by both fusion proteins, as reported previously. Colocalization of γ-H2AX foci confirmed the DSB nature of the detected foci. As a novel result, the application of protons with low LET of 15 keV/μm generated 53BP1- and MDC1-mediated foci of almost equal size and slightly different kinetics. This new data expands the capability of 53BP1 and wild-type MDC1 on visible foci formation in living cells after irradiation with low-LET particles. Furthermore, the kinetics in HT-1080 cells for α-particle irradiation show a delay of about 20 s for 53BP1 foci detection compared to wild-type MDC1, confirming the hierarchical assembly of both proteins. Preliminary data for proton irradiations are shown and also these indicate a delay for 53BP1 versus MDC1.
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116, Braunschweig, Germany. marita.mosconi@ptb.de
authors.forename: Marita
authors.initials: M
authors.lastname: Mosconi
authors.forename: Ulrich
authors.initials: U
authors.lastname: Giesen
authors.forename: Frank
authors.initials: F
authors.lastname: Langner
authors.forename: Christian
authors.initials: C
authors.lastname: Mielke
authors.forename: Ilaria
authors.initials: I
authors.lastname: Dalla Rosa
authors.forename: Wilhelm G
authors.initials: WG
authors.lastname: Dirks
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000512:Alpha Particles; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002470:Cell Survival; D002999:Clone Cells; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D018499:Linear Energy Transfer; D008164:Luminescent Proteins / Q000235:genetics; D057054:Molecular Imaging; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D011522:Protons; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D000071857:Tumor Suppressor p53-Binding Protein 1; D000097573:Red Fluorescent Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D049452:Green Fluorescent Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D009687:Nuclear Proteins; D011522:Protons; D015534:Trans-Activators; D000071857:Tumor Suppressor p53-Binding Protein 1; D000097573:Red Fluorescent Protein; C413163:MDC1 protein, human; C498301:TP53BP1 protein, human