Human fibroblasts transfected with an ATM antisense vector respond abnormally to ionizing radiation

ATM, the gene mutated in ataxia-telangiectasia (A-T), mediates multiple cel lular responses to DNA damage. A-T homozygotes have a high risk of cancer a nd exhibit spontaneous chromosomal instability, and cultured A-T cells reac t abnormally to ionizing radiation. We have developed an ATM antisense vect or that confers an A-T phenotype on normal cells. An episomal antisense Vec tor was created that contained a 1.3 kb segment of the ATM cDNA, and was tr ansfected into normal human fibroblasts. Intracellular levels of ATM protei n were typically reduced 10-fold in antisense-expressing (GM639-46 alpha) c lones. GM639-46 alpha clones exhibited the low threshold for radiation-indu ced apoptosis, low clonogenic survival, and cell cycle defects normally see n in A-T cells. Transfection with the corresponding ATM sense strand vector had no effect on the behavior of normal cells, and neither vector affected the behavior of A-T cells. Our results demonstrate that interference with ATM gene expression recreates the A-T phenotype in normal cells, and provid e functional evidence linking the ATM gene to cellular DNA damage responses . The ATM antisense Vector should prove a useful tool for studying ATM func tion in a variety of normal, mutant, and malignant cell lines.