手足口病是威胁我国儿童健康的高发疾病，A6型柯萨奇病毒（CV-A6）为该病的新型主要病原，但有关该病毒的研究甚少，阻碍了手足口病药物的开发。研究报道指出，高渗应激转录因子NFAT5与固有免疫、细胞存活及病毒感染密切相关，但其在CV-A6感染中的作用尚不清楚。我们的前期工作发现，外源表达的CV-A6蛋白酶2A切割NFAT5，并造成多个下游基因转录下调。据此，我们提出如下假设：CV-A6蛋白酶切割NFAT5，阻断下游与固有免疫和细胞存活相关的信号通路，从而促进病毒复制和细胞病变。为此，我们将：1）鉴定CV-A6蛋白酶在NFAT5上的酶切位点；2）明确NFAT5及其切割对病毒复制和细胞死亡的影响；3）研究NFAT5下游细胞存活相关基因表达和NFκB固有免疫通路变化，阐明其影响病毒感染的分子机制。本项目的研究旨在揭示CV-A6通过NFAT5与宿主细胞互作的新机制，为手足口病的治疗提供新的药物靶点。

Hand, foot and mouth disease (HFMD) is a high-risk disease that threatens the health of children in China. Coxsakievirus A6 (CV-A6) has become the new major pathogen of HFMD in recent years, surpassing the traditional HFMD viruses, such as enterovirus 71 and coxsakievirus A16. However, the research on CV-A6 is limited, hindering the drug development for HFMD. It has been reported that nuclear factor of activated T cells 5 (NFAT5), the master transcription factor induced in hypertonic stresses, is closely related to innate immunity, cell survival and viral infection, but its role in CV-A6 infection remains unclear. Our previous study showed that ectopically expressed CV-A6 protease 2A cleaves NFAT5 and impairs the transcription of multiple downstream genes. Based on these findings, we propose our hypothesis that NFAT5 is proteolytically cleaved by viral protease(s) in CV-A6 infection, which blocks downstream signaling pathways driving innate immunity and cell survival, thereby promoting viral replication and host cell death. We will test this hypothesis by pursuing the following specific aims: 1) to identify the cleavage site(s) of CV-A6 protease(s) on NFAT5; 2) to clarify the effects of NFAT5 and its truncates on CV-A6 replication and virus-induced cell death; 3) to elucidate the molecular mechanism underlying NFAT5’s role in CV-A6 infection by assessing the alteration of cell survival genes downstream of NFAT5 and the NFAT5/NFκB-mediated innate immune pathway. This proposed project aims to reveal a novel mechanism for the interplay between CV-A6 and host cells mediated by NFAT5, providing potential drug targets for the treatment of HFMD.