Variability in HIV-1 transmitted/founder virus susceptibility to combined APOBEC3F and APOBEC3G host restriction

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• APOBEC3 (A3) enzymes are crucial for innate immunity against retroviruses like HIV-1 by inducing lethal G-to-A mutations in viral DNA.
• HIV-1 Vif protein antagonizes A3 enzymes through proteasomal degradation, a key step in viral replication.
• The specific contributions of individual A3 enzymes and their interactions in restricting diverse HIV-1 subtypes remain incompletely understood.

Purpose of the Study:

• To investigate the synergistic antiviral activity of co-expressed APOBEC3F and APOBEC3G against HIV-1 Subtype B and C transmitted/founder viruses.
• To elucidate the mechanism by which APOBEC3F and APOBEC3G interact and influence Vif-mediated degradation.
• To identify variations in HIV-1 Vif that contribute to differential susceptibility to APOBEC3 restriction.

Main Methods:

• Co-expression of APOBEC3F and APOBEC3G in human cells to assess their activity against HIV-1 Subtype B and C.
• Interaction studies to determine the binding domain between APOBEC3F and APOBEC3G.
• Analysis of Vif-mediated degradation of APOBEC3 enzymes using Western blotting.
• Sequencing of Vif proteins from different HIV-1 subtypes to identify variations.
• Measurement of viral infectivity following single-cycle replication.

Main Results:

• APOBEC3F interacts with APOBEC3G via its N-terminal domain, conferring partial resistance to Vif-mediated degradation.
• HIV-1 Subtype C Vifs exhibited reduced activity against co-expressed APOBEC3F and APOBEC3G compared to Subtype B Vifs.
• Co-expression of APOBEC3F and APOBEC3G led to a significant decrease in the infectivity of Subtype C HIV-1, but not Subtype B.
• Variations in amino acid sequences adjacent to conserved regions in Vif influenced its ability to degrade APOBEC3 enzymes.

Conclusions:

• The interaction between APOBEC3F and APOBEC3G provides a mechanism for enhanced HIV-1 restriction, even in the presence of Vif.
• HIV-1 Subtype C appears more susceptible to combined APOBEC3F/APOBEC3G restriction due to less effective Vif antagonism.
• Variability in Vif sequences outside previously known regions contributes to subtype-specific differences in APOBEC3 degradation and antiviral activity.