探討鷹架蛋白IQGAP2在EB病毒感染中所扮演之角色

The roles of scaffold protein IQGAP2 in Epstein-Barr virus infection

林楷敏(Kai-Min Lin)

指導教授 ： 蔡錦華

國立臺灣大學/醫學院/微生物學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.10685

摘要

EB病毒是第一個被發現與腫瘤高度相關的DNA病毒，可以作為研究病毒致癌分子機制的範本，對病毒如何調控細胞因子來幫助其感染、潛伏於宿主，甚至使宿主細胞癌化的研究，有很大的助益。近年的研究逐漸發現，EB病毒的致病機制，除了與其潛伏期有關，病毒的裂解複製期，亦能對EB病毒相關疾病的產生造成影響，惟EB病毒在宿主細胞內複製、進入裂解期的分子機制尚未完全明瞭。我們利用人類白血球濃厚液分離出的B細胞，感染EB病毒，發現細胞內一個鷹架蛋白IQGAP2的表現量增加。IQGAP2目前被認定為腫瘤抑制因子，所以在致癌EB病毒感染中會增加讓人好奇。除了病毒感染，當病毒進入裂解期時，IQGAP的表現量也會增加。我們接著發現EB病毒的裂解轉活化因子Rta會讓細胞內的IQGAP2增加。實驗結果顯示，Rta可能透過IQGAP2驅動子上的Rta反應元素來調控其轉錄。有趣的是，我們發現Rta會將IQGAP2蛋白帶入細胞核內，而Rta與IQGAP2在細胞核的複合體，會影響EB病毒裂解期蛋白的表現。Rta會和IQGAP2共同作用，並且調控EB病毒進入裂解期。最後，我們發現在EB病毒感染而不朽化的類淋巴母细胞中，IQGAP2能透過鈣黏蛋白E影響細胞之間的團聚。綜上所述，我們發現當EB病毒進入裂解期時，其裂解轉活化因子Rta會透過IQGAP2驅動子上的作用而使細胞核內的IQGAP2蛋白增加。這樣的一個Rta-IQGAP2複合體會在細胞核內調控Rp的活化。我們的發現找出一個新的參與EB病毒進入裂解期，使其進入複製期的調控因子，這些結果對我們了解EB病毒的生活史，有助於控制EB病毒的複製知相關研究。

關鍵字

EB病毒 ； Rta (BRLF1) ； 鷹架蛋白 ； IQGAP2 ； 裂解期

並列摘要

As the first defined human oncogenic virus, Epstein-Barr virus (EBV) provides a good model to investigate how pathogens “hijack” cellular factors to promote their infection, persistence and even tumorigenesis. Although prolonged latency is the key feature of EBV, growing evidence suggests that lytic replication is crucial to EBV pathogenesis, yet how the virus promotes lytic cycle is not fully elucidated. In our B cell EBV infection model, we found that IQGAP2, a scaffold protein recognized as a tumor suppressor, was up-regulated after EBV infection. EBV lytic activation also increases IQGAP2 expression. We then identified that EBV immediate-early transactivator Rta was responsible to this up-regulation, most likely through a putative Rta responsive element (RRE) on IQGAP2 promoter. Surprisingly, we demonstrated that Rta was able to recruit IQGAP2 to the nucleus. This nuclear complex may play a role in lytic activation since lytic protein expression decreased when IQGAP2 transcription was suppressed due to impaired Rta auto-activation. Furthermore, in LCLs, IQGAP2 mediate cell-to-cell adhesion through regulation of adhesion molecule E-cadherin. To sum up, we found that, upon lytic stimuli, Rta increased IQGAP2 expression and translocalized it to the nucleus. The Rta-IQGAP2 complex activated Rta promoter (Rp) and promote lytic progression. This novel finding shed lights on a new path to understanding the intricate mechanism of EBV lytic cycle.

並列關鍵字

Epstein-Barr virus (EBV) ； Rta (BRLF1) ； IQ-motif containing GTPase activating-like protein 2 (IQGAP2) ； lytic replication

參考文獻

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