Speaker
Dr
Aroumougame Asaithamby
(Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Texas, USA)
Description
Clustered DNA damages induced by ionizing radiation are refractory to repair and may trigger carcinogenic events for reasons that are not understood. Here, we employ an in situ method to directly monitor induction and repair of clustered DNA lesions at the single-cell level. We showed, consistent with biophysical modeling, that the kinetics of loss of clustered DNA lesions was substantially compromised in human fibroblasts. The unique spatial distribution of different types of DNA lesions within the clustered damages, but not the physical location of these damages within the sub-nuclear domains, determined the cellular ability to repair these damages. Importantly, examination of metaphase cells derived from HZE particles irradiated cells revealed that the extent of chromosome aberrations directly correlated with the levels of unrepaired clustered DNA lesions. In addition, we used a novel organotypic human lung three-dimensional (3D) model to investigate the biological significance of unrepaired DNA lesions in differentiated lung epithelial cells. We found that, unlike simple DSBs, complex DNA lesions induced by iron particles were irreparable in organotypic 3D culture. Levels of expression of multiple DNA damage repair pathway genes were significantly reduced in the organotypic 3D culture compared with those in 2D culture providing molecular evidence for the defective DNA damage repair in organotypic culture. Further, when differentiated cells with unrepaired DNA lesions re-entered the cell cycle, they manifested a spectrum of gross-chromosomal aberrations in mitosis. Our data suggest that down-regulation of multiple DNA repair pathway genes in differentiated cells renders them vulnerable to DSBs, promoting genome instability that may lead to carcinogenesis. As the organotypic 3D model mimics human lung, it opens up new experimental approaches to explore the effect of radiation in vivo and will have important implications for evaluating radiation risk on human lung carcinogenesis and cancer therapy.
Primary author
Dr
Aroumougame Asaithamby
(Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Texas, USA)
Co-author
Prof.
David J. Chen
(Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Texas, USA)
