The Genomic Instability Induced By ～(60)Co-γ Ray Radiation In Normal Human Liver Cells

The direct biological consequences of exposure to ionizing radiationinclude gene mutation, chromosome aberration, malignant transformationand cell death. These effects are attributed to the production of irreversibledamage at the time of the irradiation. However, there is now considerableevidence that radiation may induce a process of genomic instability that istransmissible over many generation of cell replication, and has theconsequence of enhancing the progeny of the irradiated cell after manygenerations of cell replication.In this experiment, the human normal liver cell (7702) line was used inorder to study the genomic instability induced by ⁶⁰Coγ-ray. Firstly, wedetected the immediate damage. 7702 cells were irradiated by ⁶⁰Coγ-ray, andthen the cloning survival rate and micronucleus efficiency of the irradiatedcells were determined, and the method of single cell gel electrophoresis(SCGE) was carried out. Secondly, we got the irradiated cells' progeny thatmay have genomic instability, and then the genomic instability at cell,chromosome and gene level had been studied. Also, using the expandingeffect of the second event to detect indirectly the delayed effect irradiated by⁶⁰Coγ-ray. After 40 populations doubling of the survival cells irradiated by⁶⁰Coγ-ray, the progenies were secondly irradiated with 2 Gy of ⁶⁰Coγ-ray,and then the irradiated damage effects were detected. Finally, cDNA genechip was used to detect the transcriptional profile of 7702 cells irradiatedwith 4 Gy or 8 Gy of ⁶⁰Coγ-ray for exploring the screening ofradiation-induced genes in irradiated cell. The microarray contains 14112cDNA probing corresponding to 14412 human genes. Then PR-PCR wereused to confirm the results of gene chips.The results showed that the immediate damage induced by radiationhave dose-response character. The delayed damage after second irradiationwas correlated to the original irradiation dose. The genomic instability hadbeen induced by radiation and persisted in the 7702 cell. Furthermore, the transcription level of 58 genes changed in the progeny of survival cellsirradiated by 4 Gyγ-ray, among which 50 genes were down-regulated, 8genes were up-regulated. In the progeny of survival cells irradiated by 8 Gyγ-ray, the transcription level of 882 genes changed, among which 560 geneswere down-regulated, 322 genes were up-regulated. Most of them wereassociated with signal transduction, cell cycle regulation, cellular immunity,cytoskeleton and movement, cell replication and repair mechanism, etc. Theresults of RT-PCR were consistent with the results of gene chips.All of the results suggest that the genomic instability, different from thetraditional damage and malignant transformation, is a de novo damagemechanism. It maybe plays a critical role in the multi-carcinogenesis andfacilitates the research in the apoptosis and cancer. Induced genomicinstability is different from the direct damage of ionizing radiation exposure.It is transmissible over many generations of cell replication, that can lead toan enhancement in the frequency with which can lead to an enhancement inthe frequency with which mutations arise among the progeny of the originalirradiated cell. While the multiple phenotypes associated with radiationinduced genomic instability are relatively well characterized, the initiate andperpetuate mechanism of genomic instability is unknown as yet. It maybe isinvolved in co-operation of multi gene expression regulation. The expandingeffect of the second event plays an important role in research on genomicinstability; it could enlarge the genomic instability, and make it to be detectedeasily. Therefore, the second damage helps to study the genomic instability.