Radiation-induced Hierarchical Topologically Associated Domain Change and Its Role in Cellular Responses to Radiation / 中国生物化学与分子生物学报

The three-dimensional (3D) genome organization plays an important role in gene regulation. As a basic functional unit of the genome, topologically associated domain (TAD) regulates multiplebiological processes such as gene expression and DNA replication and plays a role in radiation-inducedDNA damage repair. Recent studies showed that TAD is not a completely independent domain butcontains hierarchical internal domains, which could be a new mechanism of gene regulation. To explorethe role of hierarchical TAD in cellular responses to radiation, we apply the OnTAD algorithm, anoptimized nested TAD caller from Hi-C data, to identify hierarchical TAD in 26 Hi-C data from Geneexpression omnibus (GEO) database. These data were from irradiated fibroblasts, lymphoblasts andfibroblasts deficient in the ataxia telangiectasia mutated (ATM) gene with 5 Gy X-ray. We observe thatX-ray can regularly affect the hierarchy of TAD in which high-level TAD is prone to change and low-levelTAD is more conservative. We propose that radiation-induced TAD hierarchy change can regulate cellularresponses to radiation by regulating gene expression, and ATM is a necessary factor for radiation-inducedTAD hierarchy change and recovery. This study provides new insights into the role of the 3D genome inradiation-induced cellular responses from the perspective of hierarchical TAD structures.

Study on radioprotection of indole-3-carbinol acid condensation products / 国际生物医学工程杂志

Objective To study the radioprotective effect of indole-3-carbinol (I3C) acid condensation products.Methods Cell colony formation assay was used to determine cell survival rate,and Western Blot assay was employed to measure protein expression.Results Seven kinds of the I3C acid condensation products showed different radioprotective effect on normal fibrous epithelial cells 184A1,among which 24 h pre-treatment of CTET (1 μmol/L),LTET (1 μmol/L),HI-IM (1 μmol/L) and 3,3'-diindoly methane (DIM) (0.3 μmol/L) showed significant increase of cell survival rate following irradiation with γ-ray,and the difficence was statistically significant (P＜0.05,P＜0.01).However,CT (1 μmol/L),LTr-1 (1 μmol/L) and ICZ (1 μmol/L) showed no effect on cell survival rate caused by radiation (P＞0.05).Furthermore,CTET,LTET,HI-IM and DIM activated the phosphorylation of ATM,BRCA1 and NBS1 proteins.HI-IM significantly decreased radiation-caused cell death and apoptosis.Conclusions CTET,LTET,HI-IM,and DIM can significantly reduce the radiosensitivity in 184A1 cells,and the mechanism may be related to the regulation of DNA damage and the repair of protein phosphorylation.

Response of the G2-prophase checkpoint to genotoxic drugs in lymphocytes from healthy individuals

We analyzed the in vitro effects of the anti-tumoral drugs doxorubicin, cytosine arabinoside and hydroxyurea on the G2-prophase checkpoint in lymphocytes from healthy individuals. At biologically equivalent concentrations, the induced DNA damage activated the corresponding checkpoint. Thus: i) there was a concentration-dependent delay of G2 time and an increase of both the total DNA lesions produced and repaired before metaphase and; ii) G2-checkpoint adaptation took place as chromosome aberrations (CAs) started to appear in the metaphase, indicating the presence of unrepaired double-strand breaks (DSBs) in the previous G2. The checkpoint ATM/ATR kinases are involved in DSB repair, since the recorded frequency of CAs increased when both kinases were caffeine-abrogated. In genotoxic-treated cells about three-fold higher repair activity was observed in relation to the endogenous background level of DNA lesions. The maximum rate of DNA repaired was 3.4 CAs/100 metaphases/hour, this rise being accompanied by a modest 1.3 fold lengthening of late G2 prophase timing. Because of mitotic chromosome condensation, no DSBs repair can take place until the G1 phase of the next cell cycle, when it occurs by DNA non-homologous end joining (NHEJ). Chromosomal rearrangements formed as a consequence of these error-prone DSB repairs ensure the development of genome instability through the DNA-fusion-bridge cycle. Hence, adaptation of the G2 checkpoint supports the appearance of secondary neoplasia in patients pretreated with genotoxic drugs.

Establishment of a lung cancer cell line A549 highly expressing DNA oxidative damage related repair gene hOGG1 / 第二军医大学学报

Objective: To establish a human lung cancer cell line A549 highly expressing human 8-oxoguanine-DNA glycosylase (hOGG1) by co-transfecting pcDNA 3.1 (+)/Myc-HisA-hOGG1 and PGL3 promoter, and to observe the biological behavior of the transfected cells. Methods: PcDNA3.1 (+)/Myc-His A-hOGG1 and PGL3 promoter were steadily co-transfected into A549 cells via mediation of Fu GENE 6 (transfected group); untransfected cells served as blank control and cells transfected with PGL3 + pcDNA3.1 (+)/Myc-HisA served as negative control. The hOGG1 mRNA expression in A549 cells was detected by Bio-luciferase activity and the hOGG1 protein expression by Western blotting analysis. Cells in the three groups were exposed to hyperoxia condition, and the morphological changes were observed by phase-contrast microscope. Comet cell rate and olive tail moment of cells were tested after different exposure periods. After exposure, the cells were incubated for 0, 60, 120, and 180 min, and the same indices were determined by modified comet assay; changes of DNA oxidative damage markers 8-hydroxy-desoxoguanosine (8-OHdG) was tested at the same time. Results: The bio-luciferase activity was stable in the co-transfected cells. Western blotting analysis showed that the expression of hOGG1 protein in co-transfected A549-T cells was significantly higher than those in the other two groups, indicating the successful establishment of hOGG1 highly expressing cells. Under the same hyperoxia condition, the morphological changes of transfected cells were greatly alleviated, and the Comet cell rate and olive tail moment of cells were obviously lower than those of the other two groups(P< 0.05). Transfected A549-T cells had significantly increased ability of DNA repair and shorter repair time compared with cells in the other two groups (P<0.05). Furthermore, the level of 8-OHdG in transfected A549-T cells was significantly lower than those of the other two groups under the same hyperoxia condition, indicating a significantly higher ability of DNA damage resisting and repair (P<0.05). Conclusion: High hOGG1 expression can decrease the cell sensitivity to DNA damage and improve the repair ability of cells.

EFFECTS OF ZINC ON LEARNING AND MEMORY IN D-GALACTOSE-INDUCED AGING MICE / 营养学报

Objective: To study the effects of zinc-deficiency(ZD)and zinc-supplement(ZS)on learning and memory in aging mice. Methods: Seventy 3-month-old male mice were divided randomly into 5 groups:normal young , aging model , aging+ZD, aging+pair-fed , aging+ZS . The aging model was established with D-galactose (100 mg/kg bw) by nape subcutaneous injection, while the young control group was injected with normal saline in the same way, which lasted 30 days. Aging+ZD and aging+ZS group were fed with ZD feed(zinc 1.61 mg/kg), others with normal feed(zinc 50 mg/kg). ZS feed(zinc 100 mg/kg)was given to aging+ZS for last 2 weeks. During the last week, the behavior tests were carried on. Finally the mice were all killed and samples were collected immediately for detection of indices . Results:Compared with the aging model group, ZD made serum zinc decrease significantly, the locomotor activity reduced and the ability of learning and memory weakened. Comet assay also showed that ZD induced DNA damage of cerebrum cells more serious in aging mice than the control. The ratio of tail length/comet cell length in Group ZD also increased significantly. However, moderate ZS could turn those indices better significantly. Conclusion: Zinc can ameliorate the learning and memory function of aging significantly. By reducing the function of DNA repair, ZD can act on learning and memory, while moderate ZS seems to be beneficial.