DNA double-strand breaks form in bystander cells after microbeam irradiation of three-dimensional human tissue models.
The "radiation-induced bystander effect," in which irradiated cells can induce genomic instability in unirradiated neighboring cells, has important implications for cancer radiotherapy and diagnostic radiology as well as for human health in general. Although the mechanisms of this effect remain to be elucidated, we reported previously that DNA double-strand breaks (DSBs), directly measured by gamma-H2AX focus formation assay, are induced in bystander cultured cells. To overcome the deficiencies of cultured cell studies, we examined alpha-particle microbeam irradiation-induced bystander effects in human tissue models, which preserve the three-dimensional geometric arrangement and communication of cells present in tissues in vivo. In marked contrast to DNA DSB dynamics in irradiated cells, in which maximal DSB formation is seen 30 min after irradiation, the incidence of DSBs in bystander cells reached a maximum by 12 to 48 h after irradiation, gradually decreasing over the 7-day time course. At the maxima, 40% to 60% of bystander cells were affected, a 4- to 6-fold increase over controls. These increases in bystander DSB formation were followed by increased levels of apoptosis and micronucleus formation, by loss of nuclear DNA methylation, and by an increased fraction of senescent cells. These findings show the involvement of DNA DSBs in tissue bystander responses and support the notion that bystander DNA DSBs are precursors to widespread downstream effects in human tissues. Bystander cells exhibiting postirradiation signs of genomic instability may be more prone than unaffected cells to become cancerous. Thus, this study points to the importance of considering the indirect biological effects of radiation in cancer risk assessment.
Sedelnikova
Olga A
OA
Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA. sedelnio@mail.nih.gov
Nakamura
Asako
A
Kovalchuk
Olga
O
Koturbash
Igor
I
Mitchell
Stephen A
SA
Marino
Stephen A
SA
Brenner
David J
DJ
Bonner
William M
WM
D000512:Alpha Particles; D017209:Apoptosis / Q000528:radiation effects; D001980:Bronchi / Q000166:cytology; D004247:DNA / Q000235:genetics / Q000528:radiation effects*; D004249:DNA Damage; D019175:DNA Methylation / Q000528:radiation effects; D004847:Epithelial Cells / Q000166:cytology / Q000528:radiation effects; D006657:Histones / Q000235:genetics; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000528:radiation effects; D046509:Tissue Culture Techniques; D014132:Trachea / Q000166:cytology
C468783:H2AX protein, human; D006657:Histones; D004247:DNA