Increased repair and cell survival in cells treated with DIR1 antisense oligonucleotides: implications for induced radioresistance

Purpose: To determine whether repression of a recently isolated, X-ray-resp onsive gene, DIR1, using antisense oligonucleotides could affect clonogenic cell survival and repair of DNA strand breaks and have a possible role in the mechanism underlying the phenomenon of 'induced radioresistance' (IRR). Materials and methods: Three cell lines, V79, RT112 and UM-UC-3, which are known to exhibit low-dose hypersensitivity (HRS) and induced radioresistanc e (IRR), and the radiosensitive cell line ATBIVA, were transfected with ant isense oligonucleotides directed towards the DIR1 gene. Scrambled oligonucl eotides were used as controls. DNA single-strand break (ssb) repair, using the alkaline comet assay, and cell survival using a standard clonogenic ass ay was measured after exposure to S-rays. Results: Following treatment with 4 Gy X-rays, the V79, RT112 and UM-UC-3 c ell lines all exhibited significantly increased rates of ssb repair after t ransfection with DIR1 antisense oligonucleotides compared with cells transf ected with scrambled oligonucleotides. They also demonstrated significantly enhanced survival after exposure to 2 Gy X-rays; the radiosensitive ATBIVA cells did not show these effects. Conclusions: Repression of the DIR1 gene product leads to an increase in th e rate of repair and cell survival in three radioresistant cells lines but not in the radiosensitive ATBIVA cell line. Because DIR1 is repressed by S- rays in the dose range where IRR is observed, it may represent a candidate gene involved in the IRR phenomenon.