ABSTRACT
DNA methylation regulates gene expression. Aberrant methylation plays an important role in human tumorigenesis. We have previously detected reduced NIS mRNA expression in thyroid tumors as compared to non-tumor tissues. Thus, in this study we investigated whether the methylation of the CpG-island located in the NIS gene promoter was associated with reduced mRNA expression in thyroid tumors. Methylation levels of 30 pairs of samples from 10 benign and 20 malignant thyroid tumors (T) along with matched non-tumor (NT) areas were determined by semiquantitative methylation specific-PCR. NIS methylation was detected in all samples. Methylation levels and frequencies did not differ between the groups and were not associated with BRAF mutational status. Highest methylation levels and frequencies were detected in the 5' region of the CpG-island decreasing toward the 3' end. Intraindividual analysis (T versus NT) showed high tumor methylation levels in 40 % of the samples in the benign group and 30 % in the malignant group, associated with low NIS mRNA expression. No quantitative correlation was detected between methylation levels and mRNA expression in any the groups. The results of this study showed that methylation of NIS promoter is a very frequent event in both benign and malignant tumors as well as in their surrounding tissues, and characterized a non-homogeneous methylation pattern along the CpG island. Therefore, further investigations involving other sites that may be implicated in methylation regulation of NIS expression are warranted.
Subject(s)
DNA Methylation , Neoplasm Proteins/metabolism , Promoter Regions, Genetic , Symporters/metabolism , Thyroid Gland/metabolism , Thyroid Neoplasms/metabolism , Thyroid Nodule/metabolism , 3' Flanking Region , 5' Flanking Region , Adult , CpG Islands , Epigenesis, Genetic , Female , Gene Expression Regulation, Neoplastic , Humans , Male , Middle Aged , Neoplasm Proteins/genetics , RNA, Messenger/metabolism , Real-Time Polymerase Chain Reaction , Reproducibility of Results , Symporters/geneticsABSTRACT
BACKGROUND: Thyroid follicular neoplasms (adenoma and carcinoma) may pose considerable difficulties to the differential diagnosis. Because such a distinction is not possible at fine-needle aspiration, surgery is often necessary. Clinical information such as age, sex, and node size is important in case of suspected carcinoma. Follicular carcinoma is characterized by capsular invasion, vascular invasion, and metastatic dissemination mainly by the hematogenic pathway. This invasion depends on collagen degradation in capsule and in subendothelial basement membrane. Collagen degradation has been widely researched in the angiogenesis process and in the hematogenic dissemination mechanism. In this study, we performed clinical and histopathologic assessment of 74 follicular neoplasms, as well as immunohistochemical reactions for CD-34 protein to estimate angiogenesis and for metalloproteinase-9, an enzyme that degrades type IV collagen. METHODS: The research was carried out retrospectively in 74 patients who had surgery and were followed up at HC-FMUSP and IBCC. Clinical, histologic, and immunohistochemical variables were compared among the groups of follicular neoplasms and a control group of 36 patients with colloid goiter. RESULTS: No significant statistical difference was found between patients with follicular adenoma and thyroid follicular carcinoma concerning sex (p =.092), age (p =.098), thyroid node size (p =.426), vascularization (p =.388), and immunostaining intensity for metalloproteinase-9 (p =.055). The proportion of immunoreactive cells for metalloproteinase-9 in follicular carcinoma cases was higher than that observed in follicular adenoma cases (p <.001). Patients in more advanced stages of carcinoma were more than 45 years old (p =.006), presented extensive invasion (p <.001), had less vascularization (p =.046), and a had higher proportion of immunoreactive cells for metalloproteinase-9 (p <.001). CONCLUSIONS: The proportion of immunoreactive cells for metalloproteinase-9 in follicular carcinoma was higher than that observed in follicular adenoma, with a significant statistical difference (p <.001). This method must be developed to apply in material obtained by fine-needle aspiration to differentiate follicular adenoma from carcinoma.
