鑑定並分析和A型流行性感冒病毒核蛋白交互作用之細胞蛋白質

Abstract

A型流行性感冒病毒 (Influenza A virus) 的核蛋白 (nucleoprotein, NP) 會結合病毒之vRNA及病毒聚合酶 (RNA-dependent RNA polymerase) 形成病毒核糖核蛋白複合體 (viral ribonucleoprotein complex, vRNP)。透過和病毒vRNA及病毒聚合酶的結合，NP在病毒基因體的複製上扮演著一個重要的角色。為了進一步了解A型流感病毒的複製，我們希望透過酵母菌雙雜體篩選 (yeast two-hybrid screening) 鑑定出可以和NP進行交互作用的細胞蛋白質。利用酵母菌雙雜體篩選得到11個細胞蛋白質可能和NP進行交互作用。由前人的研究得知，Hsp27和MEK2都有可能會影響A型流感病毒的複製，因此挑選此二個蛋白質進行進一步的研究。 利用病毒複製之螢光酶報導系統觀察，我們觀察到MEK2在受到RNAi抑制後會造成病毒RNA的複製及轉錄顯著性地下降，然而Hsp27的抑制卻不會影響病毒RNA的複製及轉錄。這個結果暗示我們在A型流感病毒的複製和轉錄過程中，扮演著關鍵角色的為MEK2而非Hsp27。在MEK2受到抑制後，亦觀察到流感病毒M基因片段的轉錄 (M的mRNA合成) 及複製 (M的vRNA合成) 受到了抑制，這個結果支持了在病毒複製之螢光酶報導系統中觀察到的現象。接下來，為了研究NP實際上是否會和MEK2進行交互作用，於是進行GST pull-down assay。我們的結果指出GST-NP (Glutathione S-transferase-fused NP) 可以抓下HA-MEK2 (hemagglutinin-fused MEK2)，單單GST蛋白幾乎不會抓下HA-MEK2。為了探討NP和MEK2的交互作用在生理功能上的影響，我們測試NP是否會活化MEK2的下游蛋白，ERK1/2。我們觀察到NP可以刺激ERK1/2的磷酸化，這個結果暗示我們，NP或許在和MEK2交互作用後，可以活化MEK-ERK signaling。然而NP實際上是否可以和MEK2交互作用及刺激MEK2的活性，仍需進一步的研究探討。在本篇中，NP和MEK2的交互作用在A型流感病毒複製上可能造成的影響也將被討論。

Influenza A virus nucleoprotein (NP) binds viral genomic RNA and interacts with viral RNA-dependent RNA polymerase to form viral ribonucleoprotein complex (vRNP) . Through interacting with viral RNA and viral RNA polymerase complex, NP plays an important role in viral genome replication. To further understand influenza A viral replication, we aimed to identify cellular proteins that interact with NP by using yeast two-hybrid screening. Eleven genes whose products may interact with NP were identified. Among them, heat shock protein 27 (Hsp27) and MEK2, both of which have potential to affect influenza A viral replication, were selected for further study. By using influenza A viral replication/transcription reporter system, we found that viral replication/transcription was significantly inhibited upon MEK2 knockdown but not upon Hsp27 knockdown. This data indicates that MEK2, but not Hsp27, plays a critical role in influenza A replication/transcription. This conclusion was also supported by the observation that viral transcription of M segment (production of M mRNA) and replication of M segment (production of M vRNA) was inhibited upon MEK2 knockdown. To study whether NP can indeed interact with MEK2, a GST pull-down assay was performed. Our data indicated that HA-MEK2 (hemagglutinin-fused MEK2) could be pull down by GST-NP (Glutathione S-transferase-fused NP) but barely by GST alone, indicating that NP may interact with MEK2. To study the physiological effect of NP interaction with MEK2, we tested whether NP could activate ERK1/2, a downstream target of MEK2. We found that NP could stimulate the phosphorylation of ERK1/2, indicating that NP can activate the MEK-ERK signaling pathway possibly by interacting with MEK2. Whether NP could indeed interact with MEK2 and stimulate the kinase activity of the latter requires further investigation. The possible effect of NP interaction with MEK2 on influenza A viral replication is discussed.