Transcription of five p53- and Stat-3-Inducible genes after ionizing radiation

Ionizing radiation (IR) produces temporal- and dose-dependent changes in multiple gene mRNA targets that are potential biomarkers of radiation dose. We confirmed IR-induced changes in expression of gadd45a, ddb-2, and cdkn1a downstream transcripts of p53 by quantitative reverse transcription-polymerase chain reaction (QRT-PCR) assay in total RNA samples from the whole blood of radiotherapy patients undergoing total-body irradiation [Amundson, S.A., Grace, M.B., McLeland, C.B., Epperly, M.W., Yeager, A., Zhan, Q., Greenberger, J.S., Fornace Jr., A.J., 2004. Human in vivo radiation-induced biomarkers: gene expression changes in radiotherapy patients. Cancer Res. 64, 6368-6371.]. We now confirm dose-dependent up-regulation of bax in addition to these p53-dependent transcripts, and bcl-2, a downstream transcript of Stat-3, in ex vivo irradiated blood samples from healthy unrelated volunteers. Together these biomarkers represent pathways involved in growth arrest, DNA damage, and apoptosis. The objectives of this study were to (1) investigate the relationship between baseline mRNA expression levels, and (2) define expression patterns in response to IR in a large cohort (n=20). Whole-blood samples were irradiated ex vivo to measure gene expression in samples from (i) three healthy donors over a broad dose range (0, 0.25, 0.50, 0.75, 1, 2, and 3 Gy), and (ii) 20 healthy donors at two doses, 0.25 and 2.5 Gy. Expression level variance (σ2) of baseline values (0 Gy) showed negligible inter-individual variation with all values ⩽1.0. σ2 values=0.50bax, 0.25 bcl-2, 0.73 gadd45a, 0.66 cdkn1a, and 1.0 ddb-2. Meaningful IR dose-responses were observed for bax, gadd45a, and ddb-2 profiles and the ratio of bax:bcl-2 mRNA expression over a broad dose range. QRT-PCR studies were extended in the lower dose range (0, 0.1, 0.5, 0.75, and 1 Gy). Results showed that bax:bcl-2 ratio initially favors bax expression at doses of <1Gy, with IR-induced dose responses observed between 1 and 3 Gy. These data suggest that profiles of these sentinel gene targets and utilization of bax:bcl-2 ratios will be useful for assessment of radiation injuries.