M.A. Coleman1, E. Yin1, L.E. Peterson2,
K. Sorensen, J. Tucker and A.J. Wyrobek1
1. Biology and Biotechnology Research Program. Lawrence Livermore National
Laboratory, Livermore, CA. 94551. 2. Department of Medicine, Baylor College
of Medicine, Houston, TX 77030.
Previous studies have shown that a low dose of ionizing radiation can induce beneficial protection to a subsequent high dose of irradiation. This radioadaptive response has been attributed to increased DNA repair and increased expression of stress response genes, but the responsible pathways and genes are not well understood. The purpose of this research was to elucidate the molecular mechanisms underlying the radioadaptive response using human lymphoblastoid (HLB) cells from the Corriel cell depository. Radioadaptation was experimentally examined in each cell line by comparing the frequencies of micronuclei in cells that received a combination of priming (5 cGy) and challenge (200 cGy) doses with those that received only a challenge dose without a priming dose. A total of 20 experiments were conducted in 10 cell lines, and significant radioadaptation was detected 60% of the time, synergism 15% of the time, and no change 25% of the time. These findings were similar to the degree of variation generally associated with this phenomenon. Gene expression profiles were then compared for two cell line using Affymetrix U95A microarray chips that were hybridized with RNA sampled 4 hours after the challenge doses for both the adapting and nonadapting conditions within each experiment. All findings were replicated. Applying a variety of statistical approaches, ~ 2700 genes showed differences in transcription levels between adapting and nonadapting conditions in at least one cell line. Of these, 211 genes showed consistent and significant responses across 2 independent HLB cell lines, including 101 genes that were up-regulated and 110 that were down-regulated under adaptive conditions. We also utilized CLUSFAVOR to identify clusters of genes across dose groups (0 cGy, 200 cGy and 5/200 cGy) and cell lines. Examples of genes associated with adaptive response across cell lines include PKC and MAP kinase as well as genes involved in the heat shock response, which is reported to be associated with adaptive response. There also appears to be an association between adaptive response and genes involved in cell cycle control and DNA repair (e.g., ATM, RAD51C, PCNA, E2F1, p130 and G-cyclins), suggesting that radioadaptation may be linked to induced changes in these cellular functions. In addition, numerous novel non-annotated genes were identified warranting future investigations. [This work was conducted under the auspices of DOE and LLNL under contract W-7405-ENG-48 with support from NIH (ES09117-02) and DOE (KP110202).]