臺灣博碩士論文加值系統

中文摘要
甲狀腺激素 (T3) 具有調控細胞的生長、分化、發育之功能，其主要透過與細胞核內甲狀腺素受體 (thyroid hormone receptor；TR) 的結合，調控標的基因之轉錄活性。在先前的研究中利用cDNA microarray研究受T3調控的基因，結果發現 Dickkopf 4 (DKK4) 基因受到 T3 正向調控 (up-regulation)。DKK4 屬於分泌型蛋白參與 Wnt 訊息傳遞中並扮演負向調控的角色，DKK4 主要是透過結合至細胞表現 Wnt/Fz 的co-receptor LRP5/6 進而造成 LRP5/6 吞噬作用，因此影響Wnt訊息傳遞，並且抑制Wnt下游基因表現。例如: c-Myc、CD44、Fibronectin、uPAR---等。然而這些基因與細胞增生和轉移有很大的關聯。
在本研究中已證實 HepG2-TR1 和 -TR1 細胞經由 T3 處理下，能夠誘導 DKK4 mRNA 和 protein 的表現。這實驗結果與去除甲狀腺老鼠之動物模式結果ㄧ致，並發現人類肝癌組織癌化周圍的正常組織 (N) 其 DKK4 蛋白的表現量大於癌化組織 (T)。為了更進一步探討 DKK4 在肝癌細胞內所扮演之角色，我們建立高度表現 DKK4肝癌細胞株 (J7和SK-Hep-1)。經由 in vivo 和 in vitro 實驗結果發現高度表現 DKK4 的肝癌細胞株能夠降低癌細胞的移動能力和生長速率，也證實了 DKK4，能抑制肝癌細胞中 Wnt 訊息傳遞並抑制 Wnt下游基因的表現，例如: c-Myc、CD44 和 Fibronectin。
綜合以上結果我們證實了 T3/TRs 正向調控 DKK4 之表現，因而抑制 Wnt/-catenin 訊息路徑並影響肝癌細胞的增生、移行和侵犯能力，因此間接證實了甲狀腺素受體可能具有腫瘤抑制能力。

The thyroid hormone, 3, 3', 5-triiodo-L-thyronine (T3) mediate cellular growth, development and differentiation by binding to nuclear thyroid hormone receptor to regulate target genes transcriptional activities. In previous study, we have carried out cDNA microarray to identify genes regulated by T3, the results indicate that Dickkopf 4 (DKK4) is up-regulated by T3. DKK4, a secreted protein, participates in Wnt signal pathway and plays an inhibition role via binding to Wnt/FZ co-receptor LRP5/6 to suppress Wnt signal. The expression metastasis related proteins such as c-Myc, CD44, fibronectin and uPAR….ect was also down-regulated. All those genes play critical roles in aberrant cellular proliferation and carcinogenesis. In this study, we demonstrate that the induction of DKK4 protein expression according to T3 in TR1 over-expressing cell at the mRNA and protein levels. Similar observation was made on the regulation of DKK4 by using on rats which received surgical thyroidectomies (TX) as an in vivo model. Also, DKK4 is abundantly expressed in noncancerous liver tissues and downregulated in cancerous tissues. Function assays with stable DKK4 transfecting in J7 and SK-Hep-1 revealed that DKK4 expression decreased cell growth, migration and invasion. DKK4 reduced cytoplasmic accumulation of -catenin. Further, downregulation of c-Myc, fibronectin and CD44 was found in the DKK4 expressing clones supporting an inhibitory role of DKK4 in tumor progression. Therefore, we conclude that TRs/DKK4/Wnt-catenin cascade influences the proliferation and migration of hepatoma cells during the metastasis process. Finally, we establish that thyroid hormone receptor may play a tumor suppressor role.

指導教授推薦書----------------------------------------------i
口試委員會審定書--------------------------------------------ii
博士論文著作授權書-----------------------------------------iii
致謝------------------------------------------------------iv
中文摘要----------------------------------------------------v
英文摘要---------------------------------------------------vi
Table of contents----------------------------------------vii
Introduction-----------------------------------------------1
Materials and Methods--------------------------------------6
Results--------------------------------------------------12 Discussion-----------------------------------------------18
Figures and legends---------------------------------------21
References------------------------------------------------40

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