The Scaffolding Protein Dlg1 Is a Negative Regulator of Cell-Free Virus Infectivity but Not of Cell-to-Cell HIV-1 Transmission in T Cells

Patrycja Nzounza,Maxime Chazal,Jean-Marc Massé,Alain Schmitt,Bertha Cecilia Ramirez,Claudine Pique,Chloé Guedj,Clotilde Randriamampita

doi:10.1371/journal.pone.0030130

Abstract

BackgroundCell-to-cell virus transmission of Human immunodeficiency virus type-1 (HIV-1) is predominantly mediated by cellular structures such as the virological synapse (VS). The VS formed between an HIV-1-infected T cell and a target T cell shares features with the immunological synapse (IS). We have previously identified the human homologue of the Drosophila Discs Large (Dlg1) protein as a new cellular partner for the HIV-1 Gag protein and a negative regulator of HIV-1 infectivity. Dlg1, a scaffolding protein plays a key role in clustering protein complexes in the plasma membrane at cellular contacts. It is implicated in IS formation and T cell signaling, but its role in HIV-1 cell-to-cell transmission was not studied before.Methodology/Principal FindingsKinetics of HIV-1 infection in Dlg1-depleted Jurkat T cells show that Dlg1 modulates the replication of HIV-1. Single-cycle infectivity tests show that this modulation does not take place during early steps of the HIV-1 life cycle. Immunofluorescence studies of Dlg1-depleted Jurkat T cells show that while Dlg1 depletion affects IS formation, it does not affect HIV-1-induced VS formation. Co-culture assays and quantitative cell-to-cell HIV-1 transfer analyses show that Dlg1 depletion does not modify transfer of HIV-1 material from infected to target T cells, or HIV-1 transmission leading to productive infection via cell contact. Dlg1 depletion results in increased virus yield and infectivity of the viral particles produced. Particles with increased infectivity present an increase in their cholesterol content and during the first hours of T cell infection these particles induce higher accumulation of total HIV-1 DNA.ConclusionDespite its role in the IS formation, Dlg1 does not affect the VS and cell-to-cell spread of HIV-1, but plays a role in HIV-1 cell-free virus transmission. We propose that the effect of Dlg1 on HIV-1 infectivity is at the stage of virus entry.

Highlights

Retrovirus spread depends on the correct assembly, budding and transmission of viral particles both by cell-free viral particles and by virus cell-to-cell transfer
We propose that the effect of Dlg1 on Human immunodeficiency virus type-1 (HIV-1) infectivity is at the stage of virus entry
The virological synapse (VS) forms a tight cleft between an infected cell and a target cell [7,8,9,10,11] and appears to be the dominant structure involved in cell-to-cell spread of HIV-1 in T cells [12,13]

Summary

Introduction

Retrovirus spread depends on the correct assembly, budding and transmission of viral particles both by cell-free viral particles and by virus cell-to-cell transfer. VS formation is initiated by the interaction between the viral envelope glycoprotein Env on the surface of the infected cell and the cellular receptor CD4 and the co-receptors CXCR4 or CCR5 on the target cell. This cellular conjugate is stabilized by the adhesion molecule lymphocyte function-associated antigen 1 (LFA-1) together with talin and actin on the target cell [7,8] and the intracellular adhesion molecule 1 (ICAM-1), which interacts with LFA-1, on the infected cell [13]. A scaffolding protein plays a key role in clustering protein complexes in the plasma membrane at cellular contacts It is implicated in IS formation and T cell signaling, but its role in HIV-1 cell-to-cell transmission was not studied before

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