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  • 學位論文

EB病毒之潛伏膜蛋白1透過PI3K/Akt/FOXO3a路徑抑制人類表皮細胞的DNA修復能力

Epstein-Barr Virus Latent Membrane Protein 1 Represses DNA Repair through the PI3K/Akt/FOXO3a Pathway in Human Epithelial Cells

指導教授 : 陳振陽

摘要


EB病毒(Epstein-Barr virus, EBV)的潛伏膜蛋白1(latent membrane protein 1, LMP1)被視為是致癌蛋白,因其可模擬持續活化的腫瘤壞死因子受體(tumor necrosis factor receptor)且觸發包括phosphatidylinositol 3-kinase (PI3K)/Akt在內的數條訊號傳遞路徑。此外LMP1亦可致使數種細胞株轉形並且對EBV所造成之B細胞轉形為必需。細胞轉形與基因體不穩定有高度關聯性,其中細胞之DNA修復系統對於基因體之穩定性扮演重要的角色。在過去之研究中,我們已經發現到LMP1可透過其CTAR1區域抑制表皮細胞之DNA修復。在本篇研究中,我們進一步證明LMP1透過CTAR1區域觸發PI3K/Akt這條訊號傳遞路徑,進而造成細胞DNA修復之抑制。此外,藉由此路徑之活化,過去曾被證明可促進細胞DNA修復之FOXO3a轉錄因子,亦會受到磷酸化之影響而改變其在細胞內之位置。而另一參與核苷酸切除修復(nucleotide excision repair)且受到FOXO3a轉錄因子所調控之DDB1蛋白,也會因此降低表現量。反之,當回補FOXO3a或DDB1時, 此LMP1抑制DNA修復之現象可獲緩解。這些結果顯示,LMP1乃透過其CTAR1區域觸發PI3K/Akt訊號傳遞路徑,進而使FOXO3a轉錄因子不活化,接著使DNA修復蛋白質DDB1之表現降低,最終致使細胞DNA修復能力之抑制。而此現象有可能會造成基因體之不穩定,進而引導細胞走向癌化。

並列摘要


Latent membrane protein 1 (LMP1), an Epstein-Barr virus (EBV) oncoprotein, mimics a constitutively activated tumor necrosis factor receptor and activates various signaling pathways including phosphatidylinositol 3-kinase (PI3K)/Akt. LMP1 is essential for EBV-mediated B-cell transformation and is sufficient to transform several cell lines. Cellular transformation has been associated strongly with genomic instability, while DNA repair plays an important role in maintaining genomic stability. Previously, we have shown that LMP1 represses DNA repair by the C-terminal activating region 1 (CTAR1) in human epithelial cells. In the present study, we demonstrate that the PI3K/Akt pathway is required for LMP1-mediated repression of DNA repair. Through the LMP1/PI3K/Akt pathway, FOXO3a, which can induce DNA repair, is inactivated because of phosphorylation and relocalization. Expression of a constitutively active FOXO3a mutant can rescue LMP1-mediated repression of DNA repair. Furthermore, LMP1 can decrease the expression of DNA damage-binding protein 1 (DDB1), which functions in nucleotide excision repair, through the PI3K/Akt/FOXO3a pathway. LMP1-mediated repression of DNA repair is restored by DDB1, although only partially. These results suggest that LMP1 triggers the PI3K/Akt pathway to inactivate FOXO3a and decrease DDB1, which can lead to repression of DNA repair and may contribute to genomic instability in human epithelial cells.

並列關鍵字

EBV LMP1 PI3K/Akt signaling pathway FOXO3a DDB1 DNA repair Genomic instability

參考文獻


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