Neuroinvasive herpesviruses display a remarkable propensity to enter the nervous system of healthy individuals in the absence of obvious trauma at the site of inoculation. We document a repurposing of cellular ubiquitin during infection to switch the virus between two invasive states. The states act sequentially to defeat consecutive host barriers of the peripheral nervous system and together promote the potent neuroinvasive phenotype. The first state directs virus access to nerve endings in peripheral tissue, whereas the second delivers virus particles within nerve fibers to the neural ganglia. Mutant viruses locked in either state remain competent to overcome the corresponding barrier but fail to invade the nervous system. The herpesvirus “ubiquitin switch” may explain the unusual ability of these viruses to routinely enter the nervous system and, as a consequence, their prevalence in human and veterinary hosts.

Retinoic acid inducible gene-I (RIG-I) receptor recognizes 5′-triphosphorylated RNA and triggers a signaling cascade that results in the induction of type-I IFN-dependent responses. Its precise regulation represents a pivotal balance between antiviral defenses and autoimmunity. To elucidate cellular cofactors that regulate RIG-I signaling, we performed two global RNAi analyses to identify both positive and negative regulatory nodes operating on the signaling pathway during virus infection. These factors were integrated with experimentally and computationally derived interactome data to build a RIG-I protein interaction network. Our analysis revealed diverse cellular processes, including the unfolded protein response, WNT signaling, and RNA metabolism, as critical cellular components governing innate responses to non-self RNA species. Importantly, we identified K-Homology Splicing Regulatory Protein (KHSRP) as a negative regulator of this pathway. We find that KHSRP associates with the regulatory domain of RIG-I to maintain the receptor in an inactive state and attenuate it’s sensing of viral RNA (vRNA). Consistent with increased RIG-I antiviral signaling in the absence of KHSRP, viral replication is reduced when KHSRP expression is knocked down both in vitro and in vivo. Taken together, these data indicate that KHSRP functions as a checkpoint regulator of the innate immune response to pathogen challenge.

NFAT activating protein with ITAM motif 1 (NFAM1) is an ITAM bearing-transmembrane receptor that has been reported to play a role in B cell signaling and development. We performed expression analysis of NFAM1 using publicly available gene expression data sets and found that NFAM1 expression is significantly induced in intestinal biopsies from Crohn’s disease (CD) and ulcerative colitis (UC) patients. At the cellular level, we further observed high expression of NFAM1 in monocytes and neutrophils, and low expression in B and T cells. To explore the role of NFAM1 in multiple immune cells and its potential role in IBD, we generated NFAM1-/- mice. In contrast with previous reports using NFAM1-transgenic mice, NFAM1-/- mice have no obvious defects in immune cell development, or B cell responses. Interestingly, NFAM1-/- monocytes produce reduced levels of TNF-α in response to activation by multiple IBD-relevant stimuli, including CD40L, TLR ligands and MDP. Additional cytokines and chemokines such as IL-6, IL-12, CCL3 and CCL4 are also reduced in CD40L stimulated NFAM1-/- monocytes. Collectively, these findings indicate that NFAM1 promotes monocyte activation, thereby amplifying the response to diverse stimuli. Similarly, we observed that deletion of NFAM1 in human monocytes reduces expression of CD40L-induced CCL4. Lastly, to assess the role of NFAM1 in IBD, we compared development of anti-CD40 induced colitis in NFAM1+/+ and NFAM1-/- mice. We found that although NFAM1 deletion had no impact on development of gut pathology, we did observe a decrease in serum TNF-α, confirming that NFAM1 promotes pro-inflammatory cytokine production in vivo. Taken together, we conclude that NFAM1 functions to amplify cytokine production and should be further evaluated as a therapeutic target for treatment of autoimmune disease.