ABSTRACT
Objective To study the whole genome DNA methylation changes induced by low dose radiation (LDR) in mouse,and mRNA expression profiles of DNMT1 and MBD2 in peripheral blood mononuclear cell (PBMC) and tissues.Methods Thirty male BALB/c mice were randomly divided into 3 groups:control,single exposure (0.5 Gy),and fractionated exposure of 6 MV X-rays for 10 d (0.05 Gy/d × 10 d).Control mice were sham-treated.To determine the immediate (early) effect of irradiation,15 mice (5/group) were sacrificed 2 h after the last irradiation.The other 15 mice were sacrificed 1 month after the last irradiation (delayed effect).Before sacrifice,blood was sampled immediately.Kidney,liver,spleen,brain and lung tissues were collected.A global DNA methylation quantification Kit and highperformance liquid chromatography (HPLC) were used to investigate the methylation level in blood DNA.The expressions of DNMT1 and MBD2 were determined by RT-PCR.Results For the early effects of irradiation,as compared with controls,fractionated exposure to X-ray irradiation led to the significant depression of global DNA methylation level in blood (t =10.19 and 8.93,P ＜ 0.05).DNMT1 and MBD2 mRNA were down-regulated in PBMC,kidney and liver (t =5.06,3.01,3.97,12.25,3.50 and 3.73,P ＜0.05),and MBD2 was also down-regulated in spleen (t =3.03,P ＜ 0.05).However,no changes were observed in single exposed group.As for the delayed effects,the methylation levels of blood were not changed in the single or fractionated exposed groups,and only MBD2 mRNA was down-regulated in PBMC and brain of fractionated exposed group (t =3.52 and 2.85,P ＜ 0.05).Conclusions Fractionated LDR exposure can induce genome DNA hypomethylation,which is tissue-specific,and may be related with down-regulation of DNMT1 and MBD2.
ABSTRACT
PURPOSE: DNA methylation is a major epigenetic mechanism for modification of genetic expression without a change in the DNA sequence. MBD2 (methyl-CpG-binding domain 2 protein) belongs to a family of enzymes concerning of DNA demethylation and suppresses the hypermethylation of the CpG island and DNA transcription. In this study, we investigated the change of MBD2 expression in the blood and tissue of colorectal cancer patients and compared the two expression levels. METHODS: The 68 patients included in this study were patients with colorectal cancer who had undergone surgery at our hospital, and 50 other patients with no malignant disease were recruited from normal populations. Total RNA samples were isolated from whole blood samples and cancer tissues of specimens using a TRI REAGENT BD kit. MBD 2 expression was measured by real-time quantitative reverse transcription-polymerase chain reaction assays. RESULTS: The mean age was older in the case group than in the control group. The mean expression level of MBD2 in blood was not different between the two groups. In the case group, the tissue MBD2 expression was lower than the blood MBD2 expression under all conditions, and that difference was statistically significant (P<0.01). The expression of MBD2 in cancer tissue showed a negative correlation with that in the blood of cancer patients, correlation coefficient of R=0.073, but that result was not statistically significant (P=0.611). CONCLUSIONS: The blood MBD2 expression was statistically the same in the cancer and the control groups. In the cancer group, blood MBD2 expression was significantly higher than tissue MBD2 expression. The reverse correlation between blood MBD2 expression and tissue MBD2 expression in cancer patients suggests that MBD2 may affect the mechanism of carcinogenesis.