The Nonstructural Proteins 3 And 5 From Flavivirus Modulate Nuclear-Cytoplasmic Transport And Innate Immune Response Targeting Nuclear Proteins

Abstract

Viruses hijack cellular proteins and components to be replicated in the host cell and to evade the immune response. Although flaviviruses have a cytoplasmic replicative cycle, some viral proteins such as the capsid (C) and the RNA dependent RNA polymerase, NS5, can reach the nucleus of the infected cells. Considering the important roles of NS5 in viral replication and in the control of the immune response, and its striking presence in the nucleus, the possible functions of this protein in some mechanisms orchestrated by the nucleus was analyzed. We isolated and identified nuclear proteins that interact with NS5; one of them, the DEAD-box RNA helicase DDX5 is relocated to the cytoplasm and degraded during infection with DENV, which correlates with its function in IFN dependent response. Since DDX5 and many other proteins are relocated from the nucleus to the cytoplasm during flavivirus infection, the integrity and function of the main regulator of the nuclear-cytoplasmic transport, the nuclear pore complex (NPC) was evaluated. We found that during DENV and ZIKV infection nucleoporins (NUPs) such as TPR, Nup153, Nup98, and Nup62 were cleavaged/degraded. The protease NS2B-NS3 induces NUPs degradation and it causes a dramatic inhibition of mature mRNAs export to the cytoplasm but not the export of DDX5 protein, which is dependent on NS5. Here we describe for the first time that the NS3 and NS5 proteins from flavivirus play novel functions hijacking the NPC and some nuclear proteins relevant in triggering immune response pathways, inducing a favorable environment for viral replication.\n\nIMPORTANCEViruses, as intracellular obligate parasites, hijack cellular components to enter and replicate in infected cells. Remarkably, in many cases, viruses hijack molecules with crucial functions for the cells. Here it is described how RNA viruses such as DENV and ZIKV, with a cytoplasmic replicative cycle, use NS3 and NS5, two of their unique non-structural proteins with enzymatic activity, to modulate nuclear-cytoplasmic transport. We found that NS3 disrupts the nuclear pore complex, the main regulator in nuclear-cytoplasmic transport, causing a strong reduction in the amount of mature mRNAs in the cytoplasm and an inhibition in innate immune response. Additionally, NS5 induces the relocation of nuclear proteins to the cytoplasm such as DDX5, involved in immune response, which is later degraded by NS3. These findings allow the understanding of crucial mechanisms that viruses use to deal with the control of the immune response to grant the production of new viral particles.