肺癌為全世界死因之首，由於肺癌缺乏早期診斷之利器來有效控制癌症轉移。在過去由本實驗室中藉由比較不同轉移程度之細胞分泌蛋白質體研究顯示Alpha-actinin-4 (ACTN4)為在轉移能力之細胞株中有較高之分泌量。ACTN4屬於ACTN家族的其中一員，結合細絲以保持細胞骨架的結構與細胞型態，由於在轉錄調控中扮演了重要的角色，被認為與癌症的轉移有很大的關係。在本研究中，將探討ACTN4對於肺腺癌細胞之功能影響。當在肺腺癌細胞中使用小片段干擾核糖核酸轉殖試驗，使ACTN4表現量降低時，顯示出ACTN4為調控癌細胞遷移與侵襲的調節者。免疫螢光染色法搭配共軛焦顯微鏡的研究，發現ACTN4可能與間接地影響細胞中Actin的分布，在細胞偽足或是片狀偽足結構的形成中扮演重要的角色。除此之外，使用免疫組織化學染色的方法來量測ACTN4在肺腺癌組織中的表現量，結果顯示ACTN4的表現量在組織中在臨床期程上有顯著相關特別是在腫瘤大小、淋巴結的侵犯或轉移等與轉移相關之期程上。而在腫瘤組織與周圍一般組織中，其ACTN4的表現量也有顯著的不同。此外，更進一步使用酵素免疫分析法，來量測一般健康受試者與肺腺癌病人的ACTN4含量，發現在肺腺癌病人的ACTN4含量遠大於一般健康受試者的含量。因此，由這些結果顯示出，ACTN4可能與肺腺癌轉移有很大的關係，以及ACTN4在臨床上可作為具有潛力的早期偵測肺腺癌轉移的指標。

Lung cancer is the leading cause of cancer related death worldwide. There is a lack of diagnostic tests that specifically address metastasis. In our previous research of comparison of cell secretomes with low and high metastatic abilities, Alpha-actinin-4 (ACTN4) exhibited high expression levels in the cell secretome with high metastatic ability. ACTN4 is one of the members in the ACTN family of binding filaments that preserve cytoskeletal structure and cell morphology. It is also known to have a critical role in transcriptional regulation; this suggests that ACTN4 may have an association with cancer metastasis. In this study, ACTN4 was investigated for its role in lung adenocarcinoma metastasis. Knockdown of ACTN4 expression in lung adenocarcinoma cell lines showed that ACTN4 was a critical mediator in the regulation of carcinoma invasion and cell migration. In the immunofluorescence and confocal microscopy studies, ACTN4 had an indirect effect on the distribution of Actin to plays an important role in the formation of a pseudopod or lamellipodium structure in the cell. Immunohistochemistry was also performed to study the expression levels of ACTN4 in tissues. We found that the ACTN4 expression significantly correlated with the staging of lung cancer; especially in T-staging and N-staging (which are the factors of metastasis progression). The expressed levels of ACTN4 were significantly higher in the tumor tissues than in the normal tissues. Furthermore, the plasma expression levels of ACTN4 in lung adenocarcinoma patients were significantly higher than in the normal controls by enzyme-linked immunosorbent assay. Our results suggest that ACTN4 protein has a significant association with lung cancer metastasis and thus may be a potential biomarker for early detection of lung adenocarcinoma metastasis.

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