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Updated: Jun 8, 2026
Retroviral Scanning: Mapping MLV Integration Sites to Define Cell-specific Regulatory Regions
Published on: May 28, 2017
A novel envelope mediated post entry restriction of murine leukaemia virus in human cells is Ref1/TRIM5α independent
Nidia M M Oliveira1, Roochi Trikha, Áine McKnight
1HIV/AIDS Group, Centre for Immunology and Infectious Disease, Blizard Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, 4 Newark Street, Whitechapel, London E1 2AT, UK.
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.
Results:
We 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.
Conclusions:
Our 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.
Insights
Human cells exhibit novel restrictions against MLV-B and MLV-NB retroviral cores, dependent on viral envelope proteins. This finding highlights the complex innate immunity controlling retroviral infections.
Area of Science:
- Virology
- Immunology
- Genetics
Background:
- Innate resistance to retroviral infection, like Friend virus susceptibility gene (Fv1) for murine leukemia virus (MLV), is host-species specific.
- Tripartite motif (TRIM) proteins, such as TRIM5α, mediate lentiviral restriction in primates, with variations in potency (e.g., rhesus TRIM5α vs. human TRIM5α).
- Human TRIM5α restricts MLV-N but not MLV-B or MLV-NB, and Lv2 restriction of HIV-2 involves viral capsid (CA) and envelope (Env) proteins.
Purpose of the Study:
- To investigate a novel post-entry restriction of MLV-B and MLV-NB cores in human cells.
- To identify the viral determinants, specifically envelope (Env) proteins, involved in this restriction.
- To elucidate the role of Env in mediating host cell restriction of retroviral infection.
Main Methods:
- Generation of retroviral vectors with MLV-B and -NB capsids (CA) pseudotyped with various gamma and lentiviral Envs.
- Flow cytometry to assess transduction efficiencies in NP2/CD4/CXCR4 and HeLa/CD4 cell lines.
- Quantitative polymerase chain reaction (QT-PCR) to analyze reverse transcription (RT) transcripts and determine the restriction step.
Main Results:
- HeLa/CD4 cells demonstrated Env-dependent restriction of MLV CAs compared to NP2/CD4/CXCR4 cells.
- Restriction occurred post-entry and at the reverse transcription (RT) level, as shown by QT-PCR.
- A novel Env-determined restriction was observed for MLV-B and MLV-NB CAs in HeLa/CD4 cells when pseudotyped with HIV-2 and RD114 Envs, but not GALV, HIV-1, or Amphotrophic Envs.
- siRNA knockdown of human TRIM5α excluded its direct role in this specific restriction.
Conclusions:
- Host cell restriction of retroviral infection is highly variable, influenced by both viral envelope (Env) and capsid (CA) proteins.
- These findings underscore the intricate nature of innate host immunity against retroviral pathogens.
- The study contributes to understanding the complex interplay between host factors and viral components in determining retroviral infectivity.
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