c High-risk human papillomavirus type 16 (HPV16) is the primary causative agent of cervical cancer and therefore is responsible for significant morbidity and mortality worldwide. Cellular transformation is mediated directly by the expression of viral oncogenes, the least characterized of which, E5, subverts cellular proliferation and immune recognition processes. Despite a growing catalogue of E5-specific host interactions, little is understood regarding the molecular basis of its function. Here we describe a novel function for HPV16 E5 as an oligomeric channel-forming protein, placing it within the virus-encoded "viroporin" family. The development of a novel recombinant E5 expression system showed that E5 formed oligomeric assemblies of a defined luminal diameter and stoichiometry in membranous environments and that such channels mediated fluorescent dye release from liposomes. Hexameric E5 channel stoichiometry was suggested by native PAGE studies. In lieu of high-resolution structural information, established de novo molecular modeling and design methods permitted the development of the first specific smallmolecule E5 inhibitor, capable of both abrogating channel activity in vitro and reducing E5-mediated effects on cell signaling pathways. The identification of channel activity should enhance the future understanding of the physiological function of E5 and could represent an important target for antiviral intervention.H uman papillomaviruses (HPVs) are small, double-stranded DNA viruses that infect squamous epithelial cells and produce a range of clinical lesions, including common warts, genital warts, and cancers of the anogenital tract and oropharynx. A subset of HPVs are carcinogenic, and among these high-risk types, HPV16 is detected in approximately 60% of all cervical cancer cases worldwide (4). The virus encodes three oncoproteins: E5, E6, and E7. The roles of E6 and E7 in cervical carcinogenesis have been extensively studied, and the contributions of both proteins to HPV pathogenesis are well accepted. The least characterized of the three oncoproteins is the highly hydrophobic, 83-amino-acid E5 protein, which associates with internal membranes, most notably those of the endoplasmic reticulum, Golgi apparatus, and perinuclear region (24). HPV16 E5 is classified as an oncoprotein due to its ability to induce anchorage-independent growth in murine fibroblasts and human keratinocytes (34). Transgenic mouse model systems demonstrate that high levels of E5 expression in the skin induce epithelial hyperproliferation, resulting in spontaneous tumor formation (15, 30). These mice also display increased dysplastic disease in the cervical epithelium (29). E5 mRNA is highly abundant in HPV lesions (37), and the protein is expressed in the early stages of malignant transformation, where the episomal viral genome is present (2). Therefore, E5 represents a target for early-stage intervention, prior to the progression of premalignant lesions to cervical cancer.E5 hyperactivates ligand-dependent epidermal growth fact...
The innate immune response provides a critical defense against microbial infections, including viruses. These are recognised by pattern recognition receptors including Toll-like receptors (TLRs) and RIG-I like helicases (RLHs). Detection of virus triggers signalling cascades that induce transcription of type I interferons including IFNβ, which are pivotal for the initiation of an anti-viral state. Despite the essential role of IFNβ in the anti-viral response, there is an incomplete understanding of the negative regulation of IFNβ induction. Here we provide evidence that expression of the Nemo-related protein, optineurin (NRP/FIP2), has a role in the inhibition of virus-triggered IFNβ induction. Over-expression of optineurin inhibited Sendai-virus (SeV) and dsRNA triggered induction of IFNβ, whereas depletion of optineurin with siRNA promoted virus-induced IFNβ production and decreased RNA virus replication. Immunoprecipitation and immunofluorescence studies identified optineurin in a protein complex containing the antiviral protein kinase TBK1 and the ubiquitin ligase TRAF3. Furthermore, mutagenesis studies determined that binding of ubiquitin was essential for both the correct sub-cellular localisation and the inhibitory function of optineurin. This work identifies optineurin as a critical regulator of antiviral signalling and potential target for future antiviral therapy.
Current interferon-based therapy for hepatitis C virus (HCV) infection is inadequate, prompting a shift toward combinations of direct-acting antivirals (DAA) with the first protease-targeted drugs licensed in 2012. Many compounds are in the pipeline yet primarily target only three viral proteins, namely, NS3/4A protease, NS5B polymerase, and NS5A. With concerns growing over resistance, broadening the repertoire for DAA targets is a major priority. Here we describe the complete structure of the HCV p7 protein as a monomeric hairpin, solved using a novel combination of chemical shift and nuclear Overhauser effect (NOE)-based methods. This represents atomic resolution information for a full-length virus-coded ion channel, or “viroporin,” whose essential functions represent a clinically proven class of antiviral target exploited previously for influenza A virus therapy. Specific drug-protein interactions validate an allosteric site on the channel periphery and its relevance is demonstrated by the selection of novel, structurally diverse inhibitory small molecules with nanomolar potency in culture. Hit compounds represent a 10,000-fold improvement over prototypes, suppress rimantadine resistance polymorphisms at submicromolar concentrations, and show activity against other HCV genotypes. Conclusion: This proof-of-principle that structure-guided design can lead to drug-like molecules affirms p7 as a much-needed new target in the burgeoning era of HCV DAA. (Hepatology 2014;59:408–422)
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