Intercellular Adhesion Molecule 1 Promotes HIV-1 Attachment but Not Fusion to Target Cells

Abstract

Incorporation of intercellular adhesion molecule 1 (ICAM-1) into HIV-1 particles is known to markedly enhance the virus binding and infection of cells expressing lymphocyte function-associated antigen-1 (LFA-1). At the same time, ICAM-1 has been reported to exert a less pronounced effect on HIV-1 fusion with lymphoid cells. Here we examined the role of ICAM-1/LFA-1 interactions in productive HIV-1 entry into lymphoid cells using a direct virus-cell fusion assay. ICAM-1 promoted HIV-1 attachment to cells in a temperature-dependent manner. It exerted a marginal effect on virus binding in the cold, but enhanced binding up to 4-fold at physiological temperature. ICAM-1-independent attachment in the cold was readily reversible upon subsequent incubation at elevated temperature, whereas ICAM-1-bearing particles were largely retained by cells. The better virus retention resulted in a proportional increase in HIV-1 internalization and fusion, suggesting that ICAM-1 did not specifically accelerate endocytosis or fusion steps. We also measured the rates of CD4 engagement, productive endocytosis and HIV-endosome fusion using specific fusion inhibitors. These rates were virtually independent of the presence of ICAM-1 in viral particles. Importantly, irrespective of the presence of ICAM-1, HIV-1 escaped from the low temperature block, which stopped virus endocytosis and fusion, much later than from a membrane-impermeant fusion inhibitor targeting surface-accessible particles. This result, along with the complete inhibition of HIV-1 fusion by a small molecule dynamin inhibitor, implies this virus enters lymphoid cells used in this study via endocytosis and that this pathway is not altered by the viral ICAM-1. Our data highlight the role of ICAM-1 in stabilizing the HIV-1 attachment to LFA-1 expressing cells, which leads to a proportional enhancement of the receptor-mediated uptake and fusion with endosomes.

HIV-1 Vpu Downmodulates ICAM-1 Expression, Resulting in Decreased Killing of Infected CD4 + T Cells by NK Cells

“…7B), quantitative analysis over several experiments revealed no significant change in gp120 levels in released WT and Vpu mutant virions (Fig. 7C), in line with previous reports demonstrating that ICAM-1 levels do not affect Env packaging or processing (45,46).…”

Distinct Requirements for HIV-Cell Fusion and HIV-mediated Cell-Cell Fusion

“…ELISA and Western Blotting-The amount of HIV-1 p24 in virus preparations was determined by ELISA, as described previously (41,42). For Western blotting, concentrated viral samples containing equal amounts of p24 were boiled for 10 min at 95°C in a sample buffer (Bio-Rad) supplemented with 5% ␤-mercaptoethanol and loaded onto a 10% polyacrylamide gel (Bio-Rad).…”

SERINC5 protein inhibits HIV-1 fusion pore formation by promoting functional inactivation of envelope glycoproteins

“…The p24 content of viral stocks was determined by ELISA, as described previously (62). For immunoprecipitation experiments, the extracts of HEK293T/17 producer cells were prepared using RIPA without SDS (50 mM Tris-HCl (pH 7.4), 1% Nonidet P-40, 0.1% sodium deoxycholate, and 150 mM NaCl) buffer with complete protease inhibitors (Roche Applied Science), followed by centrifugation at 1500 ϫ g for 5 min to sediment nuclei.…”