Non-homologous end-joining protein expression screen from radiosensitive cancer patients yields a novel DNA double strand break repair phenotype

Abstract

Background: Clinical radiosensitivity is a significant impediment to tumour control and cure, in that it restricts the total doses which can safely be delivered to the whole radiotherapy population, within the tissue tolerance of potentially radiosensitive (RS) individuals. Understanding its causes could lead to personalization of radiotherapy. Methods:We screened tissues from a unique bank of RS cancer patients for expression defects in major DNA double-strand break repair proteins, using Western blot analysis and subsequently reverse-transcriptase polymerase chain reaction and pulsed-field gel electrophoresis.Results: We hypothesized that abnormalities in expression of these proteins may explain the radiosensitivity of some of our cancer patients. The cells from one patient showed a reproducibly consistent expression reduction in two complex-forming DNA double-strand break repair protein components (DNA Ligase IV and XRCC4). We also showed a corresponding reduction in both gene products at the mRNA level. Additionally, the mRNA inducibility by ionizing radiation was increased for one of the proteins in the patient's cells. We confirmed the likely functional significance of the non-homologous end-joining (NHEJ) expression abnormalities with a DNA double strand break (DNA DSB) repair assay. Conclusions:We have identified a novel biological phenotype linked to clinical radiosensitivity. This is important in that very few molecular defects are known in human radiotherapy subjects. Such knowledge may contribute to the understanding of radiation response mechanisms in cancer patients and to personalization of radiotherapy.

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

“…Furthermore, healthy participants with the rs1805388 polymorphism of LIG4 were more sensitive to radiation based on γH2AX foci analysis than healthy participants without this polymorphism 308 . Nevertheless, a Lig4 −/− p53 −/− cell line had a higher sensitivity to high-LET radiation than a Lig4 +/+ p53 −/− cell line, suggesting that LET-induced DNA damage is partially repaired through LIG4 309 McKay et al 310 screened tissues from a unique bank of samples from radiosensitive cancer patients for expression defects in major DSB proteins such as LIG4. LIG4 and RCC4 proteins showed reduced expression in addition to a corresponding reduction in both gene products at the mRNA level.…”