Methylation Of Promoter And Expression Of XAF1 Gene In Papillary Thyroid Carcinoma

1 Background and objective:thyroid carcinoma(TC) is the most common thyroid malignant tumor, accounts for about 1% of the whole body malignant tumor, in recent years,and its incidence is rising.According to the type of tumor pathology,Thyroid carcinoma pathological types can be divided into:papillary thyroid carcinoma(PTC)/follicular thyroid carcinoma, undifferentiated thyroid carcinoma,and medullary thyroid carcinoma.including medullary cancer originated in the follicles cells, other type originated in the thyroid follicular epithelial cells. PTC is the most common malignant thyroid neoplasm.X-linked inhibitor of apoptosis protein (XIAP) is belong to IAPs family of caspase inhibitors, It can selectively binding and inhibitting caspase-3, caspase-7, caspase-9 so it a protein that anti-apoptotic activity can be negatively regulated.Fong was first identified XAF1 as an interacting Protein of X-linked inhibitor of apoptosis (XIAP). XAF1 can antagonist of XIAP and prevent the combination of Caspases, so as to promote cell apoptosis. A series of studies have shown that XAF1 can stimulation to improve the sensitively of TRAIL,TNF-a and MEK that inhibitor-induced apoptosis. So XAF1 is believed to play an imporyment role in the major apoptosis-related pathways.The pathogenesis of thyroid cancer is very complex and still unclear. It is able to provide answers to previously unanswered health-related questions and can explain differences in level of complexity between organisms. DNA methylation is one of the most intensely studied epigenetic modifications in mammals. DNA methylation is associated with histone modifications and the interaction of these epigenetic modifications is crucial to regulate the function of the gene by changing chromatin architecture. It involves the addition of a methyl group to the cytosine. This phenomenon which the cytosine in the CpG island methylation occurs widely, resulting in gene silencing. A numerous studies have demonstrated a broad range of genes silenced by the promoter region of DNA methylation in different cancer types.Until now, there have no related research to show that the relationship between status of methylation of XAF1 gene promoter and expression of its protein in papillary thyroid carcinoma(PTC).In this study, We use MSP,RT-PCR and Immunohistochemical to discuss the role of XAF1 as a tumor-suppressor gene in the papillary thyroid carcinoma. We hope to good understanding the role of XAF1 promoter methylation and phenotypic expression in PTC and feasible chemopreventive measures for the future.2 Material and method:1:70 cases of papillary thyroid carcinoma(PTC) and non-carcerous epithelium(NCE) tissue had been from April 2010 to September at Thyroid Surgery of the First Affiliated Hospital of ZhengZhou university, all specimens are confirmed by experienced pathological doctor,and have not been accepted radiation and chemotherapy and other immunology treatment.before operation, specimens are put into -80℃fridge to preserve.2:We use MSP to detect the methylation of promoter and expression of XAF1 gene in papillary thyroid carcinoma and use RT-PCR and Immunohistochemistry to detect XAF1 mRNA and the protein.3:Experimental data using statistical software SPSS13.0 statistical analysis. Two of the sample rate compares the 4 case for statistical significance by the X2-test, Significant differences between the two sample quantitative detection were compared with Students two-tailed t-test.All P-values were derived from two-sided tests and a probability less than 0.05 was considered statistically significant.3 Results:(1)The relative expression value of XAF1 mRNA in PTC was 0.12±0.03, while in NCE was 0.53±0.05 (t=2.13, P<0.05). In PTC, we found that the relative expression value of XAF1 mRNA was related to the tumor pathological grade and lymph node metastasis (P<0.05) (2)In NCE, no one case appeared XAF1 gene promoter methylation, while in PTC the rate was 35.7%(25/70) (P<0.01), and it was related to the tumor TNM stage, pathological grade and lymph node metastasis (P<0.05).In PTC,the positive rates of XAF1 protein expression in gradeⅠand gradeⅡwere 67.5%(27/40) and 40.0%(12/30), respectively, meanwhile in lymph node metastasis group and no metastasis group, it was 35.7%(10/28) and 69.0%(29/42), respectively, and there was significant difference between the two groups (P<0.05). Moreover, there was distinct correlation between methylation of XAF1 gene promoter and expression of its protein (X2=8.864 P<0.01).4 Conclusion:(1) mRNA expression of XAF1 gene in PTC were lower than in NCE. Lower expression of XAF1 gene might play an important role in carcinogenesis and progression of PTC.(2)The promoter methylation of XAF1 are related to the tumor pathological grade and lymph node metastasis. Methylation of promoter might be one of the important factors of inactivation of XAF1 gene, and might play an important role in carcinogenesis and progression of PTC.(3)In PTC,there is obvious correlation between the promoter methylation of XAF1 and its expression of protein,it is distinct correlation between XAF1 epigenetic gene structural alterations and XAF1protein expression.