Abstract
In vivo modulation of gene expression profiles after low dose and low dose-rate irradiation has been observed in a variety of experimental systems. However, few studies actually investigated the underlying mechanisms for these genetic responses. In this study, we used pre-existing microarray data and identified gene modulations in response to long term, low dose-rate irradiation. Nucleotide sequences in the neighboring region of the up-regulated, down-regulated, and unaffected genes were retrieved from the Entrez Gene database, and recognition sequences for transcription factors (TFs) were searched using the TFSEARCH database. As a result, we identified 21 potential TF-binding sites with significantly different incidence between the three gene groups (up-regulated, down-regulated and unaffected genes). The binding sites for sterol regulatory element-binding protein 1 (SREBP-1), aryl hydrocarbon receptor (AhR/Ar) and olfactory 1 (Olf-1) were suggested to be involved in up-regulation, while the binding sites for glucocorticoid receptor (GR) (GGTACAANNTGTYCTK) and hepatocyte nuclear factor 1 (HNF-1) were suggested to be involved in down-regulation of the genes. In addition, the binding sites for activating enhancer-binding protein 4 (AP-4), nuclear factor-kappaB (NFkB), GR (NNNNNNCNNTNTGTNCTNN) and early growth response 3 (Egr-3) were correlated with modulation of gene expression regardless of the direction of modulation. Our results suggest that these TF-binding sites are involved in gene modulations after long-term continuous irradiation with low dose-rate gamma-rays. Among them, GR and/or SREBP-1 might be associated with the altered metabolic process observed in liver after exposure to low dose-rate irradiation.
