Mutagenesis of HIV-1 GP120 V3 Loop to Determine Effects on GP120-Mediated CCR5 and CXCR4 Signal Transduction in Resting CD4 T Cells

Abstract

The M-tropic HIV-1 viruses use CCR5 as the co-receptor for entry. The V3 loop in the M-tropic envelope protein, gp120, is largely responsible for the selection of the CCR5 co-receptor. Mutations in the V3 loop frequently lead to viral tropism switch to use CXCR4, which is associated with rapid disease progression. Recent studies from our laboratory have suggested that during viral entry, HIV-1 also triggers signal transduction through gp120 binding to CXCR4 on resting CD4 T cells. This signal transduction leads to actin dynamics, facilitating viral post entry steps. In this study, I examined the role of individual mutations in the V3 loop for viral tropism switch. We selected and mutated six amino acids in the V3 loop of the M-tropic YU2 gp120. Effects of these mutations on viral entry and viral tropism switch (R5- to X4-tropism) were analyzed. In addition, I also investigated whether these mutations alter gp120 signaling through CCR5 or CXCR4 in resting CD4 T cells. My results demonstrated that these mutations alter the ability of HIV-1 to trigger signal through CCR5, diminishing HIV infectivity. However, these mutations were not sufficient to confer viral tropism switch and the ability to trigger signal transduction through CXCR4.