組蛋白甲基轉移酶G9a藉由Ep-CAM調控肺癌轉移之探討

Histone Methyltransferase G9a Regulated Metastasis in Lung Cancer through Epigenetic Inactivation of Ep-CAM

高訢榕(Hsin-Jung Kao)

指導教授 ： 郭明良

國立臺灣大學/醫學院/毒理學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.03127

摘要

表觀遺傳修飾(epigenetic modification)參與在染色質重組和基因轉錄的過程中，而發生在特定組蛋白 (histone) 殘基上的甲基化可調控基因轉錄。胚胎發育和癌症發生的過程中，組蛋白H3上離胺酸 (K9) 的甲基化對基因轉錄的抑制扮演關鍵性的角色。G9a為一組蛋白甲基轉移酶，負責催化組蛋白H3K9的甲基化。已知在缺氧的情形下，會誘發G9a表現及增加其甲基轉移酶活性進而調控基因表現。在乳癌細胞中，G9a也被發現可降低腫瘤抑制基因的表現，除此之外目前對於G9a在癌症上扮演的角色仍不甚清楚。因此，我們企圖探討G9a在癌症發展過程中的重要性及其調控機轉。
在本篇研究中，我們發現G9a高度表現在不同類型癌症病人的腫瘤組織中，且與腫瘤分化的情形呈現高度相關性，顯示G9a可能參與、調控癌症轉移的過程。此外G9a的表現與肺癌細胞株的轉移浸襲能力呈正相關。短暫轉殖DN-G9a質體阻斷G9a的組蛋白甲基轉移活性，可以抑制肺癌細胞之轉移浸襲能力，顯示G9a的酵素活性參與在G9a調控肺癌轉移的機轉中。接下來我們在惡性度高的肺癌細胞株中剔除G9a的表現，發現可以顯著抑制肺癌細胞之轉移浸襲能力，同時增加Ep-CAM的表現量。我們進一步研究Ep-CAM是否參與在G9a所調控之肺癌細胞浸襲能力中，實驗結果顯示，當剔除Ep-CAM表現，可以回復剔除G9a所抑制之肺癌細胞浸襲能力。此外動物實驗結果顯示，剔除G9a可以抑制癌細胞轉移及腫瘤生長，顯示G9a在癌症發生過中扮演重要的調控角色。綜合以上實驗結果，G9a極可能為肺癌之生物指標分子，未來有機會運用在腫瘤轉移之臨床檢測與治療上。

關鍵字

組蛋白甲基轉移酶肺癌 ； 轉移

並列摘要

Epigenetic modifications are important for chromatin organization and gene transcription. Methylation of specific histone residues has important regulatory functions in gene transcription. Notably, methylated histone H3 lysine 9 (H3K9me) is a critical epigenetic marker for gene repression and plays critical role in embryogenesis and carcinogenesis. G9a, a mammalian histone methyltransferase, is a candidate for histone 3 lysine 9 dimethylation (H3K9me2). Here, we attempt to study the role of G9a in lung cancer progression.
Results of our present study indicated that G9a was expressed in tumors of different cancer types and correlated with tumor differentiation status. In addition, G9a expression was also inversely correlated with in vitro migration and invasion abilities in lung cancer cells. Blockage of G9a methyltransferase activity by transfecting with a dominant negative (DN)-G9a inhibited cell migration/invasion abilities, suggesting that the histone methyltransferase activity of G9a was essential for the regulation of lung cancer metastasis. In CL1-5 and H1299 cells, G9a knockdown inhibited migration/invasion abilities through up-regulation of Ep-CAM. Treatment with Ep-CAM shRNA restored the invasion ability of stable G9a knockdown cells. Moreover, in vivo animal model showed that G9a knockdown suppressed metastatic colonization in lung and primary tumorigenesis. In conclusion, our data suggested that G9a promoted aggressive phenotypes in lung cancer may be a potential target for cancer treatment.

並列關鍵字

histone mehtyltransferase G9a ； Lung cancer ； Metastasis

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