DOE Low Dose Radiation Research Program Workshop I Abstracts November 10-12, 1999, Washington, D.C.

David A. Boothman and Bruce Aronow
Departments of Radiation Oncology and Pharmacology, Case Western Reserve University, BRB-326 East, 10900 Euclid Avenue, Cleveland, OH 44106-4942
dab30@po.cwru.edu

Summary: A low dose inducible protein has been found which induces cell death of genetically unstable cells. The protein is a sensitive indicator of low level radiation and its loss may indicate a prelude to the formation of cancer cells.

Abstract: We isolated apolipoprotein J [apoJ, also known as TRPM-2, SGP-2, and X-ray- inducible protein-8 (XIP8)], a protein implicated in apoptosis, tissue injury and aging, by Ku70 yeast two-hybrid cloning. Its interaction with Ku70 in vivo was confirmed by coimmuno-precipitation where Ku70 and Ku80 were associated with an ionizing radiation-inducible form of apoJ, nuclear apoJ/XIP8. Nuclear apoJ/XIP8 accumulated and colocalized with Ku70/Ku80 in the nuclei of irradiated MCF-7 cells by confocal microscopy. Cells over-expressing nuclear apoJ/XIP8 or its minimum Ku70 binding domain show reduced cell growth and significant lethality compared to GFP-alone constructs or apoJ/XIP8-GFP full-length protein expression wherein GFP fusion partially disrupted its interaction with Ku70.

We recently demonstrated that induction of this protein can occur by as little as 2 cGy (rads). Furthermore, evidence will be presented that this protein is p53-regulated, since agents which induce p53 stimulate expression of this protein, E6 expression blocks its induction, and overexpression of wild-type, but not p73, p51, or mutant p53 forms, cause dramatic elevations in apoJ/XIP8 expression. Taken together, our results suggest that a p53-dependent formation of apoJ/XIP8-Ku70/Ku80 trimeric protein complexes represent a signal for cell death after low level IR stress.