載脂蛋白E(apoE)在膽固醇以及磷脂質的代謝中扮演重要角色，它能攜帶各種脂蛋白將其運送至肝臟以進行代謝。三種常見的對偶基因(e2、e3、e4)分別轉錄轉譯出三種不同的同質體-apoE2、apoE3以及apoE4。文獻指出apoE與家族性高膽固醇症、心血管疾病、阿茲海默症、癡呆、動脈硬化症、多發性硬化症、糖尿病以及中風等許多疾病有關。最近甚至有報告指出apoE與癌症相關，然而其在癌症當中所扮演的角色仍尚未明確。在先前的研究當中，我們發現肺腺癌患者的惡性肋膜積水具有大量apoE的表現。進ㄧ步的研究更顯示許多肺癌細胞株有apoE的表現，尤其是從惡性肋膜積水所衍生出來的肺腺癌細胞株，而在來自鱗狀上皮癌的細胞株當中卻未見到apoE的表現。肺癌病人組織切片的免疫染色結果發現55%具有惡性肋膜積水的肺腺癌病人具有apoE的表現，其他無惡性肋膜積水的肺腺癌以及鱗狀上皮癌的病人檢體分別有30%以及10%偵測到apoE的表現，這些結果似乎暗示著apoE的表現與癌細胞的組織分型有些許相關性。臨床顯示，apoE基因型的不同會影響某些疾病的表現，因此我們利用限制酶切割的方式分析，針對肺癌細胞株做apoE基因型的檢定，結果發現實驗室現有的細胞株皆隸屬於最常見的apoE3/E3型，我們因此推測apoE的基因型可能不是肺癌癌化的重要因子。由於人類肺腺癌細胞株-PC14PE6/AS2 (AS2)有過量的apoE表現，為了研究apoE在肺癌細胞中所扮演的角色，我們利用轉染技術將特定的apoE-siRNA送入AS2細胞內，建立了apoE表現量被降低的細胞株-AS2-siRNA2 (AS2-S2)以及AS2-siRNA3 (AS2-S3)。在細胞型態上，表現少量apoE的細胞比對照組的細胞要來的圓小、較不易攤開生長且生長地較不密集。相較於對照組的細胞，表現少量apoE的細胞於細胞培養皿中生長速率略顯緩慢，且於軟洋菜膠內形成的群落也較少。但是無論apoE表現量高或低，這些細胞在細胞週期的表現上並無顯著差異。細胞對於抗癌藥物(Paclitaxel以及Cisplatin)或是降血脂藥物(Lovastatin)的感受性也不受apoE表現量高低的影響。此外我們藉由傷口癒合實驗以及細胞穿透試驗發現，相較於對照組的細胞，apoE表現量較低的細胞移行能力較差。從F-actin螢光染色實驗中我們發現，apoE表現量較低的細胞呈現較少量的纖維絲，卻有較大量的(Tyr 397)-FAK磷酸化以及RhoA蛋白的表現。我們推測細胞骨架失去動態平衡也許是造成apoE表現量低的細胞株移行能力受限的原因。此外，於動物體內，apoE表現量少的細胞也影響了腫瘤生成的能力。結語：apoE表現傾向於肺腺癌細胞，尤其是從惡性肋膜積水所衍生出來的肺腺癌細胞。表現於肺腺癌細胞的apoE影響了細胞的生長以及移行能力，然而其中詳細的機制則需要未來更進一步的研究及探討。

　　Apolipoprotein E (apoE) is one of the key regulatory proteins in cholesterol and phospholipids metabolism. It acts as a transporter by binding to various types of lipoproteins, and transports them to liver for lipids metabolism. There are three common alleles (e2, e3, e4) of the apoE gene code for the isoforms E2, E3, and E4. ApoE has been proposed to be involved in familial hypercholesterolemia, cardiovascular disease, Alzheimer’s disease, dementia, atherosclerosis, multiple sclerosis, diabetes, stroke, and most recently, cancers. However, its role in human cancers is still not well known. In the previous studies, we found apoE overexpression in the malignant pleural effusions (MPE) of patients with lung adenocarcinoma. Further studies showed that apoE expressed in several lung cancer cell lines, especially in cells derived from MPE of lung adenocarcinoma, but not in cells from squamous cell carcinoma. In tissue samples of lung cancer patients, apoE expressions were found in 55%, 30%, and 10% of patients with MPE-associated lung adenocarcinoma, non-MPE-associated lung adenocarcinoma, and lung squamous cell carcinoma, respectively, suggesting apoE expression is associated with histological subtype of tumor cells. ApoE genotype-specific differences have been implicated in several clinical diseases; we therefore analyzed the genotypes in our lung cancer cell lines. Because the genotypes of these lung cancer cell lines are all belonged to the most common type – the apoE3/E3 form, we assumed that the genotype variation might not be important for lung carcinogenesis. The human lung adenocarcinoma cell lines - PC14PE6/AS2 (AS2) - has overexpression of apoE. In order to study the role of apoE in lung cancer cells, we established the AS2-siRNA2 (AS2-S2) and AS2-siRNA3 (AS2-S3) cell lines in which apoE protein was knockdown by transfecting apoE siRNA. ApoE-knockdown cells are smaller and rounded-up in morphology. ApoE-knockdown cells grew slower in culture plates and formed fewer colonies in agar than control cells did. Between apoE high and low cells, no significant difference in cell cycle progression was found. The differences between responses of apoE high and low cells to anti-cancer drugs (Paclitaxel and Cisplatin) or cholesterol-lowering agent (Lovastatin) were not significant either. In wound healing assay and transwell inserts assay, the apoE-knockdown cells migrated slower than control cells did. The apoE-knockdown cells had less fiber filaments by immunofluorescent staining of F-actin, but more abundant phosphorylated (Tyr 397) FAK and RhoA protein. The loss of balance in actin cytoskeleton dynamics may contribute to the impaired migration in apoE-knockdown cells. Furthermore, the in vivo tumor formation ability is also impaired in apoE-knockdown lung cancer cells. In summary, apoE tends to be expressed in lung adenocarcinoma cells, especially those associated with MPE generation. ApoE expression in lung adenocarcinoma cells is implicated in cellular proliferation and migration. The mechanisms underlying the phenomenon require further investigations.

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