PARENT SESSION
1:30 PM to 3:30 PM
Tuesday, April 23, 2002
Poster Session 17 Induced Gene Expression
Room: Nevada Exhibition Center

(P22-233) Low dose -rays-induced changes in gene expression: possible involvement of post-transcriptional gene silencing.

Abul-Hassan, Khaled^*,1, Lehnert, Bruce¹, ¹ Los Alamos National Laboratory, Los Alamos, NM

ABSTRACT-
We previously reported significant down-regulation of Cockayne syndrome protein B (CSB) mRNA from cultured human lung fibroblasts (HLF) exposed to 1 cGy dose of -rays. Treating irradiated cells with Trichostatin A (a specific histone deacetylase inhibitor) was shown to increase CSB silencing, while treatment with Aza-cytidine (a DNA methylase inhibitor) relives it. These results indicate the possible involvement of DNA methylation in down-regulating CSB mRNA. In this study, we used bisulfite-DNA sequencing, Chromatin Immunoprecipitaion (CHIP) using antibodies against acetylated and methylated Histone3/Lysine9 (H3/Lys9) residues, or against methyl-DNA binding proteins; MBD1 and MeCP2, and chromatin accessibility to CSB promoter region to investigate the mechanism(s) by which CSB mRNA is/are down-regulated in irradiated cells. Analysis of CSB promoter region showed no CpG island. The only two CpGs pairs (in 400 nucleotides) upstream of its transcription start site were not methylated. CHIP analysis showed that only acetylated H3/Lys9 were significantly higher (p<0.01) in irradiated compared with sham-irradiated cells. Chromatin accessibility assay showed a higher accessibility to CSB promoter region in irradiated cells compared with sham-irradiated cells. Results from this study indicate that the down-regulation of CSB mRNA is not transcriptional (i.e. from promoter region) and further suggest post-transcriptional gene silencing mechanism such as the involvement of aberrant/double stranded RNA, which could induce DNA methylation.

KEYWORDS: CSB, Transcriptional, Post-transcriptional, Gene silencing