The influenza replication blocking inhibitor LASAG does not sensitize human epithelial cells for bacterial infections.

Severe influenza virus (IV) infections still represent a major challenge to public health. To combat IV infections, vaccines and antiviral compounds are available. However, vaccine efficacies vary with very limited to no protection against newly emerging zoonotic IV introductions. In addition, the development of resistant virus variants against currently available antivirals can be rapidly detected, in consequence demanding the design of novel antiviral strategies. Virus supportive cellular signaling cascades, such as the NF-κB pathway, have been identified to be promising antiviral targets against IV in in vitro and in vivo studies and clinical trials. While administration of NF-κB pathway inhibiting agents, such as LASAG results in decreased IV replication, it remained unclear whether blocking of NF-κB might sensitize cells to secondary bacterial infections, which often come along with viral infections. Thus, we examined IV and Staphylococcus aureus growth during LASAG treatment. Interestingly, our data reveal that the presence of LASAG during superinfection still leads to reduced IV titers. Furthermore, the inhibition of the NF-κB pathway resulted in decreased intracellular Staphylococcus aureus loads within epithelial cells, indicating a dependency on the pathway for bacterial uptake. Unfortunately, so far it is not entirely clear if this phenomenon might be a drawback in bacterial clearance during infection.

Late activation of the Raf/MEK/ERK pathway is required for translocation of the respiratory syncytial virus F protein to the plasma membrane and efficient viral replication.

Activation of the Raf/MEK/ERK cascade is required for efficient propagation of several RNA and DNA viruses, including human respiratory syncytial virus (RSV). In RSV infection, activation of the Raf/MEK/ERK cascade is biphasic. An early induction within minutes after infection is associated with viral attachment. Subsequently, a second activation occurs with, so far, unknown function in the viral life cycle. In this study, we aimed to characterise the role of Raf/MEK/ERK-mediated signalling during ongoing RSV infection. Our data show that inhibition of the kinase MEK after the virus has been internalised results in a reduction of viral titers. Further functional investigations revealed that the late-stage activation of ERK is required for a specific step in RSV replication, namely, the secretory transport of the RSV fusion protein F. Thus, MEK inhibition resulted in impaired surface accumulation of the F protein. F protein surface expression is essential for efficient replication as it is involved in viral filament formation, cell fusion, and viral transmission. In summary, we provide detailed insights of how host cell signalling interferes with RSV replication and identified the Raf/MEK/ERK kinase cascade as potential target for novel anti-RSV strategies.

Host and viral determinants of Mx2 antiretroviral activity.

Myxovirus resistance 2 (Mx2/MxB) has recently been uncovered as an effector of the anti-HIV-1 activity of type I interferons (IFNs) that inhibits HIV-1 at an early stage postinfection, after reverse transcription but prior to proviral integration into host DNA. The mechanistic details of Mx2 antiviral activity are not yet understood, but a few substitutions in the HIV-1 capsid have been shown to confer resistance to Mx2. Through a combination of in vitro evolution and unbiased mutagenesis, we further map the determinants of sensitivity to Mx2 and reveal that multiple capsid (CA) surfaces define sensitivity to Mx2. Intriguingly, we reveal an unanticipated sensitivity determinant within the C-terminal domain of capsid. We also report that Mx2s derived from multiple primate species share the capacity to potently inhibit HIV-1, whereas selected nonprimate orthologs have no such activity. Like TRIM5α, another CA targeting antiretroviral protein, primate Mx2s exhibit species-dependent variation in antiviral specificity against at least one extant virus and multiple HIV-1 capsid mutants. Using a combination of chimeric Mx2 proteins and evolution-guided approaches, we reveal that a single residue close to the N terminus that has evolved under positive selection can determine antiviral specificity. Thus, the variable N-terminal region can define the spectrum of viruses inhibited by Mx2. Importance: Type I interferons (IFNs) inhibit the replication of most mammalian viruses. IFN stimulation upregulates hundreds of different IFN-stimulated genes (ISGs), but it is often unclear which ISGs are responsible for inhibition of a given virus. Recently, Mx2 was identified as an ISG that contributes to the inhibition of HIV-1 replication by type I IFN. Thus, Mx2 might inhibit HIV-1 replication in patients, and this inhibitory action might have therapeutic potential. The mechanistic details of how Mx2 inhibits HIV-1 are currently unclear, but the HIV-1 capsid protein is the likely viral target. Here, we determine the regions of capsid that specify sensitivity to Mx2. We demonstrate that Mx2 from multiple primates can inhibit HIV-1, whereas Mx2 from other mammals (dogs and sheep) cannot. We also show that primate variants of Mx2 differ in the spectrum of lentiviruses they inhibit and that a single residue in Mx2 can determine this antiviral specificity.