Study Of The Gene Expression Of Tbx3 And Its Alternative Splicing Variants In Human Breast Carcinoma Tissues And The Related Significance

Tbx3 gene is a member of the big T-box gene family. The transcription factors coded by this family play important roles in the morphogenesis and organogenesis of vertebrates and invertebrates. Previous studies have found that over twenty transcription factors coded by the gene family are all expressed in human tissues and organs. All T-box transcription factors, also named as T protein, have a particular structure, i.e. all of them have the DNA binding domain comprising about 180 amino acid residues named as the T-box domain at N-terminal, in which the DNA sequence is highly conservative but the regions preceding and following the T-box domain vary in length and primary sequence. Tbx3 gene codes a peptide chain constituted by 743 amino acid residues, and DNA binding domain is located at No. 105 - 285 amino acids. The latest researches show that the overexprssion of Tbx3 gene in mammary epithelial cells probably allows cells to have another cell divisions during its prohibiting growth or proliferative environment to continue growing. So, the consecutive overexpression of this gene will repeat the process mentioned above, leading to the uncontrolled growth of mammary epithelial cells and conversion of mammary epithelial cells into malignancy, which may promote the occurrence of breast cancer. The mechanisms of Tbx3 gene and its coded transcription factor Tbx3 protein in the pathogenesis of ulnar-mammary syndrome, an autosomal dominant inherited disorder, have been well studied, but little has been reported on the expression of Tbx3 gene and its relationship with the breast carcinoma.In this study, we conducted a preliminary investigation of the changes of Tbx3 gene and its alternative splicing variants in breast carcinoma tissues and peritumor tissues by detection of the gene expression of Tbx3 and its alternative splicing variants using RT-PCR technology, by observation of the pathological lesions using light microscopy, and by the detection of the expressions of estrogen/progestin (ER/PR) and proliferating cell nuclear antigen (PCNA) in breast carcinoma using immunohistochemistry. In addition, the clinicopathological significance was also investigated.The main results and conclusions of this study are as follows.1. Our results showed that the expressions of the alternative splicing variants of Tbx3 gene, Tbx3-l and Tbx3-2, were up-regulated in breast carcinoma tissues, resulting in the significantly higher expression of Tbx3 mRNA at the transcriptional level in breast carcinoma tissues than those in peritumor tissues, suggesting that Tbx3 gene may have the promotive effect on the genesis and progression of breast carcinoma.2. RT-PCR products of Tbx3 gene showed that there was alternative splicing at the level of pre-mRNA in this gene, resulting in splicing variants Tbx3-l and Tbx3-2. Sequencing of the RT-PCR products showed that the splicing style was to skip outside of exon3 and directly spliced with exon2 and exon4, resulting in the production of the splicing variant Tbx3-l.3. The rate of Tbx3-l expression in breast carcinoma tissues was significantly higher than that in the peritumor tissues, but the rate of Tbx3-2 expression declined in breast carcinoma tissues, implying that changes occurred in the alternative splicing method of Tbx3 gene at the level of pre-mRNA in breast carcinoma tissues. As a result of that, more variants of Tbx3-l were formed, resulting in abnormal expression of the variants. This may be one of the mechanisms that this kind of gene expression was up-regulated and participated in the genesis and progression of breast carcinoma.4. Tbx3 gene expression level and the ratios of Tbx3-l mRNA and Tbx3-2 mRNA to the total Tbx3 mRNA in breast carcinoma tissues were not associated with the tumor size and ages of patients. However, the histological grading of breast carcinoma, tumor infiltrating degree, TNM stagings, axillary lymph node metastasis, and quantity of metastases were positively correlated with the expression level of Tbx3 gene and the expression rate of Tbx3-l mRNA...