HIV-2/SIV viral protein X counteracts HUSH repressor complex.

Area of Science:

• Virology
• Immunology
• Epigenetics

Background:

• Human immunodeficiency viruses (HIV-1 and HIV-2) employ auxiliary proteins to overcome host immune defenses by targeting cellular restriction factors.
• Viral protein X (Vpx) from HIV-2 antagonizes SAMHD1, enhancing viral infection, but this interaction doesn't fully explain Vpx's functions.

Discussion:

• A proteomic screen identified the HUSH complex (TASOR, MPP8, periphilin) as a novel Vpx target involved in position-effect variegation.
• Vpx binds and degrades HUSH via DCAF1 recruitment, independent of SAMHD1 antagonism, leading to the reactivation of latent HIV proviruses.
• HUSH downregulation by Vpx occurs in primary cells and HIV-2 infected cells, suggesting HUSH acts as a restriction factor.

Key Insights:

• Vpx's antagonism of the HUSH complex is a key mechanism for reactivating latent HIV.
• The HUSH complex functions as a restriction factor in primary CD4+ T cells, influencing intrinsic immunity and epigenetic control.
• Vpx-mediated HUSH degradation is crucial for Vpx's ability to reactivate latent HIV, unlike Vpx mutants unable to degrade HUSH.

Outlook:

• HUSH antagonism is not conserved in HIV-1 but is present in Vpr from certain simian immunodeficiency viruses (SIVs), indicating an ancient lentiviral gene function.
• Further research can explore the broader role of HUSH in intrinsic immunity and its potential as an antiviral target.
• Understanding Vpx-HUSH interaction provides insights into lentiviral evasion strategies and epigenetic regulation in host defense.