ZFP36L1蛋白質抗病毒的作用機制

Abstract

ZFP36L1可利用兩個鋅手指狀的蛋白質構型（zinc finger domain）與mRNA結合，並藉由徵募細胞中的RNA五端到三端或是三端到五端的降解機制，來促進結合的mRNA降解。目前為止，報導過可被ZFP36L1調控的mRNA侷限於細胞中的mRNA，像是TNFα、GM-CSF和IL-3等等。此篇研究中，我們利用同屬黃質病毒的日本腦炎病毒（JEV）以及登革病毒（DENV），其基因體為具五端cap但缺三端poly(A)-tail的正向RNA，首次證實了ZFP36L1具有抗病毒的能力。在細胞中過度表現ZFP36L1能夠抑制JEV以及DENV的複製，利用移除（deletion）和點突變（point mutation）實驗，證實ZFP36L1上兩個鋅手指狀構型對於病毒RNA的結合是必須的，也會影響到ZFP36L1抑制JEV和DENV的能力。ZFP36L1憑藉細胞中降解mRNA的酵素exosome complex和XRN1，來降解病毒的RNA以達成制止病毒的複製。有趣的是，細胞中降解mRNA的初始步驟deadenylation參與在ZFP36L1抗DENV，但不參與抗JEV的機制當中。降低細胞內ZFP36L1表現顯示，細胞中的ZFP36L1也有抑制病毒複製的能力，而且JEV感染可增加ZFP36L1蛋白質降解，來逃避其抗病毒作用。總結上述，我們將ZFP36L1蛋白質的功能延伸至宿主細胞抵抗JEV和DENV的感染，並且找出抑制病毒複製的機制，使我們對這個細胞內帶有鋅手指狀構型的蛋白質有更深入的了解。

ZFP36L1, containing tandem CCCH-type zinc finger domains, is an RNA binding protein, which promotes targeted mRNA decay by recruiting the cellular 5'→3' and 3'→5' RNA degradation machinery. To date, the reported mRNA abundance regulated by ZFP36L1 is restricted to cellular mRNA such as TNFα, GM-CSF, and IL-3 etc. In this study, we demonstrated for the first time that ZFP36L1 exhibited antiviral activity. Overexpression of ZFP36L1 inhibited the infection of Japanese encephalitis virus (JEV) and dengue virus (DENV), which are flaviviruses containing positive-sensed RNA genome with 5'cap but not 3' poly(A)-tail. Deletion and mutation studies showed that both of the zinc finger domains of ZFP36L1 were important for viral RNA binding and antiviral activity against JEV and DENV. The cellular mRNA decay machinery, exosome complex and XRN1, were involved in the targeting of viral RNA mediated by ZFP36L1. Interestingly, deadenylation, the initial step of cellular mRNA decay, was involved in the anti-DENV but not anti-JEV action of ZFP36L1. Endogenous ZFP36L1 took part in the antiviral effect against flavivirus infection as demonstrated by knockdown experiments and JEV could target ZFP36L1 by protein degradation. Altogether, we extend the function of ZFP36L1 to host antiviral defense and reveal the antiviral mechanism to gain more insight on the antiviral effect of this cellular zinc finger containing protein.