Abstract:

To study the changes of mRNA and protein expressions of Kras gene in thymic lymphomas induced by ionizing radiation,and to detect the methylation of CpG islands in promoter region of Kras gene,then to investigate the mechanisms for the occurrence of radiation carcinogenesis.Methods The thymic lymphoma models of BALB/c mice were made by X-ray irradiation,then the total RNA was extracted,cDNA was synthesized and the total protein was extracted from both thymic lymphoma tissue and normal thymus tissue;the mRNA and protein expressions of Kras gene in thymic lymphoma tissue and normal thymus tissue were detected by RT-PCR and Western blotting method,and the methylation of CpG islands in promoter region of Kras gene was detected by bisulfite sequencing PCR.Results The mRNA expression level of Kras gene in thymic lymphoma tissue was significantly higher than that in normal thymus tissue（P<0.01）.The protein expression level in thymic lymphoma tissue was about 1.41 times higher than that in normal thymus tissue;4 CpG sites were methylated detected by bisulfite sequencing PCR in normal thymus tissue,however,1 CpG site was methylated in thymic lymphoma tissue,the CpG islands in promoter region of Kras gene were demethylation state in thymic lymphoma.Conclusion Ionizing radiation can cause the changes of mRNA and protein expression levels  of Kras gene in thymic lymphoma tissue   by demethylation state of Kras gene,eventually lead to the occurrence of tumor;it might be one of the mechanisms for the occurrence of radiation carcinogenesis.

Key words: thymic lymphomas, methylation, bisulfite sequencing PCR, CpG islands