| Summary: | 碩士 === 國立成功大學 === 分子醫學研究所 === 94 === 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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