Expression And Regulation Of Thyroid Hormone Receptor B1 Gene In Breast Carcinoma

Breast carcinoma is a common malignant tumor; the morbidity is increased continually and obviously. It is well known that tumor is a disease because of gene altered, so studying the key genes related to malignant tumor can not only comprehend clearly the mechanic of tumor development and progression, but establish the theory foundation to overcome carcinoma finally.The thyroid hormone receptors(TRs) which are encoded by two genes, THRA and THRB, are ligand-dependent nuclear transcription factors. TRB have two major isforms TRB1 and TR B2. In recent years, many studies have analyzed the presence of quantitative ( abnormal levels) or qualitative (mutations) alterations in the expression of TRB1 genes in different types of human nevplasias. These data suggested that TRB1 gene may be involved in human cancer. However, the association between TRB1 and breast cancer remains an area where there is little knowledge. No studies were reported between TRB1 and the neoplastic illness in our country. Total RNA of fourty cases fresh frozen breast careinoma tissues and ten cases normal breast tissues were extracted and RT-PCR was used to detect the mRNA expression of TRB1 gene in the current. The results indicated the expression of TRB1gene mRNA as follow: 14cases were absent,20 cases were downregulation,and 6 cases were normal expression in 40 cases breast careinoma tissues. Accordingly,mRNA of 10 cases normal breast tissues were all expressed. mRNA expression of breast careinoma was more decreased than that of normal breast tissues,difference has statistically signifieanee. Our data might indicate TRB1 gene is altered obviously in primary breast careinoma and TRB1 gene takes important effect in the development of breast carcinoma. At present, many studies have analyzed the presence of quantitative or qualitative alterations in the expression of TRB1 genes in different types of human nevplasias. Its inactivation mechanism are not clear yet. The field of epigeneties has recently moved to the forefront of cancer studies. DNA methylation is the most common form of it. Therefore, Methylation specific polymerase chain reaction (MSP) combined with nest-PCR and sequencing was used to determine the methylation status of TR B1 gene promoter in 40 breast cancer tissue. The results showed 32 of the 40 breast tumor tissues were methylation. In 10 of 10 cases reduction mammoplasty normal tissue from women without breast cancer were unmethylated. Statistical analysis showed that difference were significant between tumor tissues and normal tissues. The result of sequencing was identical with the agarose gel electrophoresis results. Among 34 samples with down-regulated mRNA expression, 31 samples showed methylation in the promoter region of TRB1 gene. However, only 1 sample had methylated promoter in 6 samples with normal level of mRNA. Correlation between methylation and mRNA level was significant. Analyzing correlation between methylation of TR B1gene promoter and clinical pathologic parameters in breast cancer tissues, the result has showed TRB1gene methylation levels were not correlated with the age of patients. Similarly, no significant correlation was observed between lymph node metastasis and TR B1 methylation status.In addition, there was no significant association between TRB1 methylation status and clinical stage. Our data might indicate that promoter methylation level of TRB1 gene in breast cancer tissue is very high and an inverse relationship between TRB1 promoter methylation and mRNA expression. TRB1 gene promoter methylation could cause gene silencing and/or transcription interruption. In the second part of the experiment, promoter methylation was not observed in 2 of 34 TRB1 gene mRNA downexpression patients, It is reasonable that inactivation of TRB1 gene in breast cancer might be related with the other mechanism, for example, mutations. Therefore, PCR combined with sequencing was used to determine the mutation status of TRB1 gene in 10 breast cancer tissue. The results showed that exons 7-10 of TRB1 gene have mutations in 10 cases of breast cancer, especially exon8 had P247A while deletion A in 1028bp in 6 patients; 2 cases which promoter methylation but mRNA low expression deleted A in 1057bp causing frameshift mutations. We believe that TRB1 gene mutation may also be involved in the mechanism of TRB1gene inactivation.In conclusion, these results may provide valuable information for TRB1 genetic alteration is closely related to the occurrence of breast cancer. It was great significance for breast cancer risk assessment, early diagnosis and gene therapy to screen TRB1 gene.