Mechanisms of Low Dose Radio-Suppression of Genomic Instability

Bevin Engelward
Division of Biological Engineering, MIT, Cambridge, MA
Email: bevin@MIT.EDU
Web site: http://web.mit.edu/be/people/engelward.htm

Why this Project?

This project is designed to study homologous recombination events which are an important class of mutations that contribute to cancer.

Project Goals

The major goal of these studies is to identify the molecular basis for radio-suppression of homologous recombination in vivo.

Experimental Approach

Mice have recently been engineered that carry a recombination substrate, Fluorescent Yellow Direct Repeat (FYDR), that yields a fluorescent phenotype following homologous recombination events. These mice have shown that chronic exposure to ionizing radiation can suppress homologous recombination in vivo.

1.  Animals will be exposed to chronic ionizing radiation at successively lower doses and in vivo recombination rate and relative levels of several DNA repair proteins will be quantified This will investigate the dose range required for radio-suppression and determine if occupationally relevant levels of ionizing radiation induce, suppress or have no effect on recombination in vivo.
   
   
2. Chronically irradiated cells will be assayed for increased sensitivity to interstrand crosslink-induced toxicity and diminished sensitivity to crosslink induced recombination. An extrachromosomal plasmid assay will be used to measure the capacity of cells to repair DNA damage via homology directed repair. This approach makes it possible to determine if chronic irradiation suppresses the homology directed repair pathway.
   
   
3. The project will determine if base excision repair and non-homologous end-joining contribute to radio-sensitivity by comparing cell lines that carry defects in specific components of base excision repair and non-homologous end-joining. This should reveal if radio-suppression is mediated in part by increased clearance of recombinogenic lesions. The levels of recombination and the frequency of H2AX foci will be assessed in control and chronically irradiated cells that carry various repair defects.

Expected Outcomes

The results of these studies will contribute to our understanding of the cause and effect of radiation-induced adaptation, and will reveal the levels of radiation required to suppress and to induce genomic instability in mammals.