The efficiency of R5 HIV-1 infection is determined by CD4 T-cell surface CCR5 density through G alpha i-protein signalling.

OBJECTIVE AND DESIGN

The intensity of replication of CCR5-using HIV-1 strains is highly dependent on the number of CCR5 molecules on the surface of CD4-positive T cells. The molecular mechanisms responsible for this phenomenon remained so far unclear. As CCR5 co-receptors are coupled to G alpha i and G alpha q proteins, we tested the hypothesis that the activation triggered through these proteins secondary to the interaction between the viral envelope and CCR5 could account for the effect of the level of CCR5 expression on HIV-1 production.

METHODS

We transduced the wild-type or a G-protein signalling-defective CCR5 gene into CD4/CCR5 HOS cells and peripheral blood mononuclear cells. The effect on cell activation in presence of a CCR5-binding chemokine and on HIV infection was monitored by measuring calcium mobilization and p24 antigen production, respectively. The role of G alpha i protein signalling was tested by adding pertussis toxin to the cell cultures or by transfecting small interfering (si) RNAs into the HOS cells.

RESULTS

The over-expression of the wild-type form, but not of a G-protein signalling-defective form of CCR5, on the surface of CCR5 expressing peripheral blood mononuclear cells markedly increased their infectability. In addition, both pertussis toxin and G alpha i 1-specific siRNA drastically inhibited R5 infection.

CONCLUSIONS

The signalling through G alpha i-protein induced upon R5 virion binding to CCR5 is responsible for the difference in HIV-1 infectability between CD4-positive T cells expressing low or high levels of cell surface CCR5 density. This observation sheds new light on the physiopathology of HIV infection, and opens new therapeutic opportunities targeting G alpha i signalling.