Visualisation of [gamma]H2AX Foci Caused by Heavy Ion Particle Traversal; Distinction between Core Track versus Non-Track Damage

• Published in: PloS one 2013-08, Vol.8 (8), p.e70107
• Main Authors: Nakajima, Nakako Izumi, Brunton, Holly, Watanabe, Ritsuko, Shrikhande, Amruta, Hirayama, Ryoichi, Matsufuji, Naruhiro, Fujimori, Akira, Murakami, Takeshi, Okayasu, Ryuichi, Jeggo, Penny, Shibata, Atsushi
• Format: Article
• Language: English
• Subjects: Electrons; Radiation (Physics)
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0070107

Heavy particle irradiation produces complex DNA double strand breaks (DSBs) which can arise from primary ionisation events within the particle trajectory. Additionally, secondary electrons, termed delta-electrons, which have a range of distributions can create low linear energy transfer (LET) damage within but also distant from the track. DNA damage by delta-electrons distant from the track has not previously been carefully characterised. Using imaging with deconvolution, we show that at 8 hours after exposure to Fe (~200 keV/[micro]m) ions, [gamma]H2AX foci forming at DSBs within the particle track are large and encompass multiple smaller and closely localised foci, which we designate as clustered [gamma]H2AX foci. These foci are repaired with slow kinetics by DNA non-homologous end-joining (NHEJ) in G1 phase with the magnitude of complexity diminishing with time. These clustered foci (containing 10 or more individual foci) represent a signature of DSBs caused by high LET heavy particle radiation. We also identified simple [gamma]H2AX foci distant from the track, which resemble those arising after X-ray exposure, which we attribute to low LET delta-electron induced DSBs. They are rapidly repaired by NHEJ. Clustered [gamma]H2AX foci induced by heavy particle radiation cause prolonged checkpoint arrest compared to simple [gamma]H2AX foci following X-irradiation. However, mitotic entry was observed when ~10 clustered foci remain. Thus, cells can progress into mitosis with multiple clusters of DSBs following the traversal of a heavy particle.