Study On The Methylation Status Of RASSFIA Promoter In Thyroid Tumors

Objective :Aberrant methylation of CpG islands in the promoter region of tumor suppressor genes (TSGs) has been established as the major mechanism for gene silencing.Inactivation of TSGs by DNA methylation is regarded as one of the important processes for the development of thyroid tumors.The present study was to observe the methylation status of RASSF1A in thyroid tumors and to explore the relationship between the hypermethylation of RASSF1A promoter and the clinical pathological character. Meanwhile,maybe a wonderfur objective evidence can be found to serve as molecular diagnosis and clinical prognosis as well as gene treatment.Method: We collected 94 cases of paraffin embed tissues of benign and malignant thyroid tumor (including 61 cases of PTC,15 cases of FTC,2 cases of medullary thyroid carcinoma,1 case of anaplastic thyroid carcinoma,15 cases of thyroid adenoma).and 10 cases of normal tissue. All of the samples were taken from 1986 to 2007.The DNA was modified by bisulfite reaction using the CpGenomeTM Universal DNA Modification Kit. Modified DNA was amplified by methylation-specific PCR(MSP) procedure to analyze the status of methylation..Results: 1 Hypermethylation of the promoter of RASSF1A was detected in 67%(63/94) of benign and malignant thyroid tissues,In 61 PTC cases, the methylation rate of the promoter of RASSF1A gene was 68.9%(42/61).In 15 FTC cases,the methylation rate of RASSFIA was 73. 3% (11/15). In 15 cases of thyroid adenoma,the methylation rate of the promoter of RASSF1A gene was 46.7%(7/15).In 10 normal thyroid tissues we did not detect the promoter methylation of RASSF1A gene. 2. The methylation rate of the tumor tissues was remarkably higher than that of normal thyroid tissues, the difference was significant, P<0. 05. The difference in methylation rate between PTC and FTC was not significant and it also was not between cancer tissues and thyroid benign adenoma,P>0. 05. 3. The difference of methylation rate of RASSF1A genes was not significant among gender,metastasis of lymph node and recurrence of thyroid carcinoma in 76 thyroid cancer tissues(61 PTC cases and 15 FTC cases).However,Hypermethylation of RASSFIA promoter was found to be significantly associated with the age, P < 0. 05 compared with < 40 year.Conclusion: 1. Hypermethylation of the promoter of RASSF1A was detected in thyroid tumors and the methylation rate of the tumor tissues was remarkably higher than that of normal thyroid tissues,therefore,suggest that methylation of RASSF1A promoter in thyroid tumors may be an important molecular change. and plays an important role in the development and progression of thyroid tumorigenesis.2.we found that the high prevalence of RASSF1A hypermethylation among benign adenoma examined,The difference in methylation rate between cancer thyroid and benign adenoma tissues was not significant.therefore,suggest that the promoter of RASSF1A through aberrant methylation is an early step in thyroid tumorigenesis3. Hypermethylation of RASSF1A promoter was found to be significantly associated with the age, suggesting that there may be different molecular basis invollved in thyroid cancer from the young and old patients and suggesting that hypermethylation of RASSF1A may be one of the prognostic indicators for thyroid cancer .4. The status of methylation of RASSF1A genes in thyroid tumors provide objective evidence for demethy- -latlon tumor therapy5.MSP was proved to be a specific, sensitive and reliable method to detect the methylation status of tumor in paraffin-embedded biopsy samples. therefore, MSP of the status of methylation of RASSF1A genes may be used as a useful method for earlier period clinical diagnosis in thyroid cancer.