ANALYSIS OF FACTORS THAT REGULATE HIV-1 FUSION IN REVERSE

Area of Science:

• Virology
• Cell Biology
• Immunology

Background:

• HIV-1 envelope (Env) proteins mediate viral entry by fusing with host cells expressing CD4 receptors and CXCR4 co-receptors.
• Cellular Env proteins can also mediate fusion with enveloped viruses or cells expressing CD4 and CXCR4.

Purpose of the Study:

• To investigate the mechanism of "fusion in reverse," where cellular Env proteins mediate fusion with lentiviral vectors.
• To identify factors influencing this novel infection pathway and its potential for targeting latent HIV-1.

Main Methods:

• Utilized lentiviral vectors pseudotyped with CD4 and CXCR4 variants.
• Tested infection of Env-expressing cells using the "fusion in reverse" mechanism.
• Assessed the impact of cell surface Env levels, fusion inhibitors, and lipid membrane composition on infectivity.

Main Results:

• Infection via "fusion in reverse" depends on cell surface Env levels and is inhibited by a specific fusion inhibitor.
• Optimal infection required lentiviral vectors with a GPI-anchored CD4 variant and a truncated CXCR4.
• Latently HIV-1-infected cells were specifically infected, with higher efficiency upon activation.
• Viruses produced in sphingolipid-deficient cells showed increased infectivity, while those with a lipid scramblase were non-infectious.

Conclusions:

• "Fusion in reverse" is a viable mechanism for infecting Env-expressing cells, including latently HIV-1-infected cells.
• Cellular Env protein activity is modulated by the lipid composition of the viral and cellular membranes.
• This study provides new insights into HIV-1 envelope protein function and potential therapeutic strategies.