The antiviral innate immune response is the first line of defense against a viral infection. Antiviral innate immunity is initiated when cellular proteins, such as RIG-I, sense the presence of a virus inside an infected cell. This sensing starts a signaling cascade that ultimately triggers the production of hundreds of antiviral genes, including interferon (IFN). Dysregulation of this innate immune response can lead to excessive inflammation or viral infection. As such, the innate immune response is tightly regulated in order to promote viral clearance and to avoid excessive or prolonged inflammation. Regulation is mediated by both protein modifications and protein-protein interactions. Our preliminary studies have identified that a cellular protein, an E3 ufmylation ligase called UFL1, regulates signaling to induce IFN in order to limit flavivirus replication. Additionally, we have identified that a number of cellular trafficking proteins that relocalize to signaling membranes to positively regulate antiviral innate immunity, such as RAB1B, gain the post-translation modification known as ufmylation during IFN induction in a RIG-I dependent manner. Therefore, the goal of this proposal is to define the novel targets of ufmylation and how ufmylation of these targets positively regulates IFN induction. Based on our preliminary data, the central hypothesis of this proposal is that ufmylation of positive regulators of innate immunity, such as RAB1B, repurposes their functions to coordinate the signaling transduction that leads to IFN-induction and the antiviral response. Guided by our preliminary data, this hypothesis will be tested by pursuing the following two specific aims: 1) Define how ufmylation of RAB1B regulates IFN induction and the antiviral response; 2) Identify the protein targets of ufmylation during RIG-I pathway signaling.
In Aim 1, the molecular mechanisms by which ufmylation regulates the function role of RAB1B in IFN induction and the antiviral response to flavivirus infection will be defined.
In Aim 2, the specific ufmylated targets of UFL1 during RIG-I pathway signaling will be identified and functionally validated. Taken together, the work proposed in this application will be significant and innovative because it will define a new role for the post-translational modification ufmylation in coordinating the function of trafficking proteins that positively regulate antiviral innate immune responses. This work will have implications for the treatment and prevention of RNA virus infection and IFN-mediated autoimmune disease. Further, an increased understanding of the regulation of innate immune pathways will improve our knowledge of the mechanistic causes of dysregulated IFN production that can lead to autoimmune disease, and it will define the mechanisms of immune protection for RNA virus infection that will have implications for therapeutic and vaccine strategies to limit RNA virus infection.
RNA viruses, which encompass both established and emerging pathogens, cause significant morbidity and mortality worldwide and remain a constant threat to global public health, with antiviral therapies lacking for many of these viruses. The proposed study will define the molecular mechanisms of how the host senses RNA virus infection and activates the antiviral defense program, as well as defining a novel regulator of this sensing program. This study will reveal new targets that may be harnessed for the development of novel antiviral and immune therapeutics designed to limit viral infection, viral-mediated disease, and autoimmune disease.