探討EB 病毒轉活化子Rta 在人類上皮細胞中，促使微核形成、DNA 股斷裂及加速細胞週期M phase進行之研究

Abstract

Epstein-Barr virus（EBV）是第一個被認為與人類腫瘤疾病有關的人類DNA 病毒。過去研究已發現EB 病毒感染與許多人類惡性腫瘤疾病相關，其中之一就是鼻咽癌（Nasopharyngeal carcinoma, NPC）。鼻咽癌為發生於鼻咽部上皮細胞的惡性腫瘤，患者主要分佈在台灣及中國東南部。在鼻咽癌患者組織中，利用細胞遺傳學（cytogenetic）的研究方法分析，發現有廣泛的染色體異常 之情形。這樣的結果顯示基因體不穩定（genomic instability）可能促使鼻咽癌的形成。因此本研究希望探討EB 病毒特早期活化子Rta 是否會造成宿主細胞基因體不穩定？並深入瞭解Rta 藉由哪些機制造成宿主細胞基因體不穩定。 首先， 我們證明在293 衍生細胞株中， Rta 的確可以誘使微核 （micronucleus，MN）的形成。其次，在HEp2 與HEp2 衍生細胞株中，則發現Rta 會加速G2/M phase 到G1 phase 細胞週期的進行，並且伴隨著微核形成的增加。此外，我們也發現Rta 可能造成DNA 雙股斷裂（DNA double strandbreak）。然而，在宿主細胞質體再活化試驗（host cell reactivation assay）中，卻發現Rta 可促進細胞修復DNA 的能力。綜合以上的實驗結果，我們證明了EB 病毒轉活化子Rta 在人類上皮細胞中，可以促使微核的形成、DNA 股斷裂以及加速細胞週期M phase 之進行。

Epstein-Barr virus（EBV）was the first human DNA virus to be proposed as a tumor virus and EBV infection is associated with the development of many types of malignancies, including nasopharyngeal carcinoma（NPC）. NPC is one of the most common cancer in Taiwan and Southeast China. The cytogenetic studies have demonstrated broad chromosomal abnormalities in NPC tissues. It is suggested that chromosomal instability may play an essential role in the development of NPC, just as in many solid tumors. We investigated whether EBV immediate early gene BRLF1, Rta, contribute to the induction of genomic instability in the human epithelial cells. At first, we demonstrated that EBV Rta could induce micronucleus（MN)formation in 293 inducible stable clone. Secondly, we found EBV Rta accelerates G2/M-to-G1 cell cycle progression in transfected HEp2 cells and HEp2 inducible stable clone. This accelerated cell cycle M phase progression was accompanied with the increase micronuclei formation. Furthermore, we demonstrated that Rta induces DNA strand breaks. However, Rta still enhances the ability of DNA repair in host cell reactivation（HCR）assay. Taken together, these studies suggest that EBV Rta enhances micronucleus formation, DNA strand break and accelerates M phase progression in human epithelial cells.