Analysis of Factors That Regulate HIV-1 Fusion in Reverse.

Area of Science:

• Virology
• Cell Biology
• Molecular Biology

Background:

• HIV-1 envelope (Env) proteins mediate cell entry by fusing with host cells expressing CD4 receptors and CXCR4 co-receptors.
• Understanding Env-mediated fusion is critical for developing antiviral strategies and gene therapy vectors.

Purpose of the Study:

• To investigate a novel mechanism, termed "fusion in reverse," where lentiviral vectors infect Env-expressing cells.
• To identify factors influencing this reverse fusion process and its potential for targeting HIV-1 infected cells.

Main Methods:

• Utilized lentiviral vectors pseudotyped with CD4 and CXCR4 variants to infect cells expressing HIV-1 Env proteins.
• Assessed the impact of cell surface Env levels, fusion inhibitors, and specific lentiviral protein modifications (GPI-anchored CD4, truncated CXCR4) on infection efficiency.
• Investigated the role of cellular lipid membrane composition (cholesterol, sphingolipids, lipid scramblase) in Env protein activity and viral infectivity.

Main Results:

• Infection via "fusion in reverse" is dependent on cell surface Env levels and can be inhibited by an HIV-1 fusion inhibitor.
• Optimal infection requires lentiviral vectors with a GPI-anchored CD4 variant and a cytoplasmic tail-truncated CXCR4.
• This mechanism successfully infected latently HIV-1-infected cells, with activation enhancing efficiency.
• Viral infectivity was increased in viruses assembled in cells deficient for long-chain sphingolipids but abolished when incorporating a lipid scramblase; cholesterol levels had no effect.

Conclusions:

• "Fusion in reverse" offers a targeted approach for infecting latent HIV-1 reservoirs.
• Cellular lipid membrane composition significantly influences HIV-1 Env protein function and viral infectivity.
• These findings provide new insights into the biophysical mechanisms governing HIV-1 Env-mediated membrane fusion.