HIV-1 Accessory Protein Vpr Interacts with REAF/RPRD2 To Mitigate Its Antiviral Activity.

The human immunodeficiency virus type 1 (HIV-1) accessory protein Vpr enhances viral replication in both macrophages and, to a lesser extent, cycling T cells. Virion-packaged Vpr is released in target cells shortly after entry, suggesting it is required in the early phase of infection. Previously, we described REAF (RNA-associated early-stage antiviral factor; RPRD2), a constitutively expressed protein that potently restricts HIV replication at or during reverse transcription. Here, we show that a virus without an intact vpr gene is more highly restricted by REAF and, using delivery by virus-like particles (VLPs), that Vpr alone is sufficient for REAF degradation in primary macrophages. REAF is more highly expressed in macrophages than in cycling T cells, and we detected, by coimmunoprecipitation assay, an interaction between Vpr protein and endogenous REAF. Vpr acts quickly during the early phase of replication and induces the degradation of REAF within 30 min of viral entry. Using Vpr F34I and Q65R viral mutants, we show that nuclear localization and interaction with cullin 4A-DBB1 (DCAF1) E3 ubiquitin ligase are required for REAF degradation by Vpr. In response to infection, cells upregulate REAF levels. This response is curtailed in the presence of Vpr. These findings support the hypothesis that Vpr induces the degradation of a factor, REAF, that impedes HIV infection in macrophages.IMPORTANCE For at least 30 years, it has been known that HIV-1 Vpr, a protein carried in the virion, is important for efficient infection of primary macrophages. Vpr is also a determinant of the pathogenic effects of HIV-1 in vivo A number of cellular proteins that interact with Vpr have been identified. So far, it has not been possible to associate these proteins with altered viral replication in macrophages or to explain why Vpr is carried in the virus particle. Here, we show that Vpr mitigates the antiviral effects of REAF, a protein highly expressed in primary macrophages and one that inhibits virus replication during reverse transcription. REAF is degraded by Vpr within 30 min of virus entry in a manner dependent on the nuclear localization of Vpr and its interaction with the cell's protein degradation machinery.

Cell Culture Models for Hepatitis E Virus.

Despite a growing awareness, hepatitis E virus (HEV) remains understudied and investigations have been historically hampered by the absence of efficient cell culture systems. As a result, the pathogenesis of HEV infection and basic steps of the HEV life cycle are poorly understood. Major efforts have recently been made through the development of HEV infectious clones and cellular systems that significantly advanced HEV research. Here, we summarize these systems, discussing their advantages and disadvantages for HEV studies. We further capitalize on the need for HEV-permissive polarized cell models to better recapitulate the entire HEV life cycle and transmission.

IFITM proteins inhibit HIV-1 protein synthesis.

Interferon induced transmembrane proteins (IFITMs) inhibit the cellular entry of a broad range of viruses, but it has been suspected that for HIV-1 IFITMs may also inhibit a post-integration replicative step. We show that IFITM expression reduces HIV-1 viral protein synthesis by preferentially excluding viral mRNA transcripts from translation and thereby restricts viral production. Codon-optimization of proviral DNA rescues viral translation, implying that IFITM-mediated restriction requires recognition of viral RNA elements. In addition, we find that expression of the viral accessory protein Nef can help overcome the IFITM-mediated inhibition of virus production. Our studies identify a novel role for IFITMs in inhibiting HIV replication at the level of translation, but show that the effects can be overcome by the lentiviral protein Nef.