The significance of aberrant gene expression of PDGFR-α in the carcinogenesis of follicular thyroid carcinoma

• Main Authors: Kuei-Tien Chen, 陳桂添
• Other Authors: C. Allen Chang
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/04358099747205355058

博士 === 國立交通大學 === 生物科技系所 === 93 === Thyroid cancer accounts for about 1% of all cancers. Thyroid cancer occurs at all ages and increases frequently in each decade. The female:male ratio is about 3:1. Definite diagnosis is possible only by histological examination. Fine needle aspiration cytology (FNAC) reports are sometime unreliable, especially for follicular thyroid tumors. Frequently, the pathologist cannot diagnose follicular carcinoma on FNAC or (to a lesser extent) papillary carcinoma. To develop an early detection method by using biological markers, we have first searched the potent tumor markers by outline the differentially gene expressions in various thyroid tissues or thyroid cell lines. The cDNA expression array technology is utilized herein to profile differentially expressed genes from human follicular thyroid carcinoma and reveals new tumor markers. An expression profile of genes that are associated with malignant process of follicular thyroid cancer was further discussed. Further investigation is required to understand the precise relationship between the altered expression of these genes and the malignant process of follicular thyroid cancer. After analysis of differentially gene expression by a cDNA microarray technique, we found that mRNA of PDGF-A and PDGFR-α were highly expressed in thyroid carcinomas but not in nodular hyperplasia cells. These results cause the motive to understand whether PDGF autocrine activation exists in thyroid cells and play a crucial role in carcinogenesis. Platelet-derived growth factor receptor (PDGFR) possesses a kinase activity and can be activated through binding with PDGF. The activation of PDGFR is associated with the carcinogenesis of some cell types, including astrocytomas, oligodendrogliomas, and glioblastoma. In a cDNA microarray analysis, we discovered the over-expressed mRNA of both PDGF-A and PDGF α-receptor in thyroid carcinoma cells. And the elevated protein expressions of PDGF-A and PDGF α-receptor in thyroid carcinoma cells were confirmed by a western blot analysis. Furthermore, the phosphorylation of PDGF α-receptor measured by an antibody against Tyr 720-phosphate was found in thyroid carcinoma cells. The tyrosine kinase activity of PDGF α-receptor was inhibited by tyrphostin AG1295 and showed a dose-dependent inhibition for cell proliferation. In an immunohistochemistry study, data showed that the expression of PDGF α-receptor was primarily localized around the follicle and significantly correlated with malignant tumor stage. These findings imply that autocrine activation of PDGF-α receptor plays a crucial role in the carcinogenesis of thyroid cells. To identify whether inhibition of the aberrant signal transduction could have the potential to dismiss the possibility of carcinogenesis, we examined the efficacy of PDGFR-α siRNA and tyrphostin AG1295 on repressing cell proliferation of follicular thyroid carcinoma cell line (CGTH W-1). Some tyrosine kinase inhibitors have shown to block the tyrosine-like receptors and achieve the inhibition of some aberrant signal transduction. Here we designed short interfering RNAs (siRNA) specific for PDGFR-α to repress cell proliferation in CGTH W-1. Real-time quantitative PCR, flow cytometry, immunofluorescence cell staining, and MTT assay results demonstrated that the transfected CGTH W-1 cells reduce the cellular PDGFR-α mRNA level, reduce the PDGF α-receptor in cell membrane, and repress cell proliferation. While control studies of non-silencing siRNA showed no significant effects in PDGFR-α expression and cell proliferation. Finally, we compared the effects of repressing cell proliferation of CGTH W-1 cells by PDGFR-α siRNA and a tyrosine kinase inhibitor, tyrphostin AG1295. PDGFR-α siRNA required 24 hours more than tyrphostin AG1295 to show significant inhibition of cell proliferation, but the effects last up to 240 hours. The findings indicate that the PDGFR-α siRNA could be a potential tool to suppress aberrant PDGFR-α gene expression and furthermore show that PDGF-α receptor plays a crucial role in the carcinogenesis of thyroid cells.