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(PP079) Dissecting the role of PrkdcBALB polymorphisms in radiation-induced mammary cancer.
Ramaiah, Lila*,1, Weil, Michael2, Desaintes, Christian3, Ullrich, Robert2, 1 Department of Microbiology, Immunology, & Pathology, Fort Collins, CO, USA2 Department of Environmental and Radiological Health Sciences, Fort Collins, CO, USA3 Radiobiology Unit, Boeretang, Mol, Belgium
ABSTRACT- Investigations in our laboratory have described a heritable, naturally occurring susceptibility to radiogenic breast cancer that is unique to BALB/c mice. We demonstrated significant phenotypic differences between the BALB (susceptible) and C57BL/6 (resistant) strains, and provided evidence for a genetically determined link between susceptibility to radiation-induced chromosomal instability, and mammary neoplasia. Sequencing revealed two unique single nucleotide polymorphisms in the BALB Prkdc gene (PrkdcBALB) that code for two amino acid substitutions in the DNA-PKcs protein product. DNA-PKcs is the catalytic subunit of DNA-dependent protein kinase (DNA-PK), which plays an integral role in bringing DNA double stranded ends together in V(D)J recombination as well as in the non-homologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair. The variant Prkdc appears to encode an aberrant protein resulting in decreased tissue expression and kinase activity as well as in slow post-irradiation DSB repair kinetics. In studies using both F1 hybrids of BALB and C57BL/6 strains and F1 x BALB backcross progeny, homozygosity for PrkdcBALB was strongly correlated with susceptibility to radiation-induced chromosomal instability and ductal dysplasia. We have employed a direct genetic approach using newly developed congenic mouse strains to demonstrate a mechanistic linkage between the Prkdc locus and the BALB phenotype. We have developed and characterized two new inbred mouse strains that are congenic for Prkdc (B6.C-Prkdc: PrkdcBALB allele on C57BL/6 background, and C.B6-Prkdc: PrkdcB6 allele on BALB background), and are using these strains to determine the functional consequences of PrkdcBALB expression on DNA-PKcs protein metabolism and function in the context of radiation-induced DNA damage. Using this approach, we have demonstrated that PrkdcBALB is both sufficient and required to decrease DNA-PKcs protein expression. Study endpoints include DNA-PKcs half-life, DNA binding affinity, autophosphoryalation, inherent kinase activity, DSB repair capacity, and radiation-induced chromosomal instability. Future congenic mouse studies will examine the role of >i>PrkdcBALB in susceptibility to radiation-induced ductal dysplasia and radiation-induced mammary neoplasia.
Key words: breast cancer, genomic instability, radiation carcinogenesis, DNA repair
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