- 學位論文
EB 病毒潛伏膜蛋白LMP1調控人類表皮細胞基因的研究
Analysis of Epstein-Barr Virus LMP1-regulated Genes in Human Epithelial Cells
摘要
EB病毒(Epstein-Barr Virus)，是一種廣泛分佈於全世界的人類皰疹病毒，主要感染人類淋巴球及上皮細胞(epithelial cells)，感染B淋巴球造成細胞轉型與不死化，並表現病毒基因產物包括六種不同的EBV核抗原EBNA1、EBNA2、EBNA3A、EBNA3B、EBNA3C、EBNALP以及三種潛伏膜蛋白（LMP1、LMP2A、LMP2B）。它被認為與許多疾病有很高的關連性，包括感染性單核球增多症、鼻咽癌、巴氏淋巴瘤、霍浦金氏腫瘤、T細胞淋巴癌等。其中鼻咽癌為東南亞國家好發的疾病，尤其集中於中國東南沿海以及台灣等地區，也是我國癌症十大死因的第十名，是屬於頭頸部的上皮細胞腫瘤。 Latent membrane protein 1 (LMP1) 是EB病毒所產生的潛伏膜蛋白，為已知致癌蛋白質且與鼻咽癌形成有密切的關係。為了全面瞭解細胞內受LMP1調控的基因，我們在人類上皮細胞RHEK-1建立可受doxycycline誘導而表現LMP1的細胞株RHEK-LMP1-(IND15)，並以cDNA microarray的方法尋找細胞內受LMP1調控的基因。經過兩次cDNA微矩陣分析的結果合併比對，發現在7684個人類基因中，mRNA被LMP1活化超過2倍的基因共計有389個，被LMP1抑制的基因共計有366個。我們以定量反轉錄聚合酶連鎖反應(real-time RT-PCR)的方法，驗證26個基因的表現，其中BMP-6、MMP-19 這兩個基因有顯著的增加。我們進一步以不同劑量的doxycycline及不同的誘導時間處理證實當LMP1誘導表現增加的情形下，這兩個基因確實都受到LMP1向上調節(up-regulation)影響。 為瞭解LMP1調控BMP-6、MMP-19基因表現的機制，我們以質體共轉染方式及螢光酶試驗分析了LMP1對BMP-6、MMP-19啟動子的影響，結果發現LMP1對BMP-6、MMP-19啟動子僅有輕微向上調節的作用。由於BMP-6 mRNA上具有AU-rich 的序列，該序列曾被報導會造成mRNA不穩定容易被分解，又先前的文獻資料也顯示BMP-6 mRNA的半衰短且經我們查證BMP-6 mRNA在3’UTR有6個AU-rich 序列，因此我們測試LMP1是否會促進BMP-6 mRNA的穩定度，經Actinomycin D抑制新的mRNA合成，並以定量反轉錄聚合酶連鎖反應分析BMP-6 mRNA的分解情形，實驗結果顯示LMP1對BMP-6 mRNA並沒有穩定的作用，有關LMP1調控BMP-6及MMP-19表現的詳細機制尚待進一步的研究。
並列摘要
Epstein-Barr Virus (EBV) is a wide-spread human herpesvirus, which mainly infects human B-lymphocytes, T-lymphocytes and epithelial cells. EBV infection of B-lymphocytes resulting in B-lymphocyte transformation and immortalization and also induces the expression of eight latent proteins including six EBV nuclear antigens EBNA1, EBNA2, EBNA3A, EBNA3B, EBNA3C, EBNALP and three latent membrane proteins: LMP1, LMP2A and LMP2B. Latent membrane protein 1(LMP1) is the most important oncoprotein expressed by EBV, which has been shown to be closely associated with Burkitt’s lymphoma, nasopharyngeal carcinoma, infectious mononucleosis, oral hairy leukoplakia, Hodgkin’s disease, T cell lymphoma and gastric carcinoma. In order to understand the role of LMP1 in EBV-induced tumorigenesis, we started to investigate which genes are regulated by LMP1 in human epithelial cells. Previously we had established an LMP1-inducible RHEK cell line named RHEK-LMP1-(IND15) which can express LMP1 after doxycycline addition. We then compared the gene expression profile of cells with and without LMP1 expression by cDNA microarray analysis. Our data showed that after doxycycline treatment 389 genes were up-regulation and 366 genes were down-regulation in a total of 7,684 cDNA clones. We then used real-time RT-PCR to analyse the expression level of 26 genes that are known to be involved in regulation of cell proliferation and migration. Among these genes, BMP-6 and MMP-19 were shown to be significantly upregulation after LMP1 induction. How these genes are upregulated were by LMP1 also investigated by the promoter-reporter assay. Our data indicated that LMP1 can only marginally activate BMP-6 and MMP-19 promoters. Since BMP-6 mRNA contains six AU-rich sequences in it’s 3’UTR, we also investigated whether LMP1 could induce the stabilization of BMP-6 mRNA. Our data indicated that LMP1 had no such ability.The mechanism by which LMP1 stimulate BMP-6 and MMP-19 expression needs further investigation.