Abstract
Background'Intrinsic' resistance to retroviral infection was first recognised with the Friend virus susceptibility gene (Fv1), which determines susceptibility to murine leukaemia virus (MLV) infection in different murine species. Similarly, the tripartite motif (TRIM) family of proteins determine lentiviral restriction in a primate host-species specific manner. For example rhesus TRIM5α (rhTRIM5α) can potently restrict HIV-1 infection while human TRIM5α (huTRIM5α) only has a mild effect on SIVmac and HIV-1 infectivity (Lv1). Human TRIM5α is able to restrict MLV-N virus replication, but is ineffective against MLV-B or MLV-NB virus infection. Lv2 restriction of some HIV-2 viruses is seen in human cells. Like Lv1, Lv2 is a post-entry restriction factor, whose viral determinants have been mapped to the viral capsid (CA). Unlike Lv1, however, Lv2 is determined by envelope (Env) in addition to CA. Here we present evidence of a novel Env determined post entry restriction to infection in human cells of pseudotyped MLV-B and MLV-NB cores.ResultsWe generated retroviral vectors pseudotyped with various gamma and lentiviral Envs on MLV-B and -NB CAs containing a green fluorescent protein (GFP) reporter. Flow cytometry was used to determine transduction efficiencies in NP2/CD4/CXCR4 (glioma cell line stably transduced with the HIV receptors) and HeLa/CD4 cell lines. The HeLa/CD4 cell line restricted both MLV CAs in an Env dependent manner, compared to NP2/CD4/CXCR4 cells. Quantitative polymerase chain reaction (QT-PCR) analysis of reverse transcription (RT) transcripts demonstrates that this restriction occurs at a post entry and RT level. siRNA knockdown of huTRIM5α ruled out a direct role for this cellular component in mediating this restriction. We describe a previously unobserved Env determined restriction of MLV-B and MLV-NB CAs in HeLa/CD4 cells when pseudotyped with HIV-2 and RD114 Envs, but not gibbon ape leukaemia virus (GALV), HIV-1 or Amphotrophic (Ampho) Envs.ConclusionsOur data further demonstrate the variability of Env and CA mediated susceptibility to post entry host cell restriction. We discuss the relevance of these findings in light of the growing evidence supporting the complexities involved in innate host immunity to retroviral infection.
Highlights
Retroviruses can cause a variety of diseases in their host species
This paper describes the restriction of murine leukaemia virus (MLV)-B and MLV-NB viral cores in human cells when pseudotyped with HIV-2 [20,21] and the feline endogenous virus RD114 Envs
HIV-2 Envs molecular clone non-restricted (MCN) and molecular clone restricted (MCR) mediate MLV-B and MLV-NB restriction in HeLa/CD4 cells which is rescued by different retroviral Envs Previously we had demonstrated that an Env and a CA derived from an HIV-2 isolate, MCR, were determinants of Lv2 restriction in HeLa/CD4 cells
Summary
Retroviruses can cause a variety of diseases in their host species. Over-expression, integration near oncogenic loci, or the hosts’ response to the proteins encoded by retroviral genes determine the type of disease manifested [1]. Friend virus susceptibility factor (Fv1) is a dominant allele expressed in mice or cell lines adapted from specific species of mice that confers resistance to different MLV strains [2]. Mice with the Fvn/b genotype are resistant to both strains of MLVs but are susceptible to viruses that are both N and B tropic, such as Moloney MLV (MLVNB) [3]. Fv1 blocks MLV virus prior to integration and does not block infection by other retroviruses [7]. More recent evidence suggests that residues up- or down- stream from this canonical site may influence virus susceptibility to host immunity [10,11,12]
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