HIV-1 GLYCOPROTEIN GP120 DISRUPTS CD4-P56(LCK)/CD3-T CELL-RECEPTOR INTERACTIONS AND INHIBITS CD3 SIGNALING

Using the CD4(+) human T cell clone P28, we demonstrated that the HIV-1 glycoprotein gp120 inhibited CD3-induced inositol trisphosphate production, calcium influx and T cell proliferation. Additionally, gp120 was shown to dissociate the tyrosine kinase p56(lck) from CD4 in CEM cells, with a concommittant inhibition of CD4-linked kinase activity. We have addressed the question whether disruption of CD4/p56(lck) or CD4/CD3-T cell receptor interactions, or both, could account for the inhibitory effect of gp120 in P28 cells. By comparing the effects of various anti-CD4 monoclonal antibodies (mAb) with those of gp120, we show that gp120 and IOT4a modulate CD4 expression, and decrease CD4-associated p56(lck) and CD4-linked kinase activity at the plasma membrane. In contrast, OKT4A and OKT4 anti-CD4 mAb have no inhibitory effect. Interestingly, gp120 also inhibits CD3-induced Lck activation and cellular tyrosine phosphorylation, particularly of phosphoinositide-specific phospholipase C-gamma-1. Kinetic experiments reveal that the inhibitory effect of gp120 on CD3-induced tyrosine phosphorylation appears as early as 30 min, but culminate when CD4-p56(lck) complexes disappear from the cell surface after 4 h. These results suggest that a negative signal is triggered by gp120 that results, after a few hours, in down-modulation of CD4-p56(lck) complexes and the impairment of CD3 signaling. Supporting this hypothesis, gp120 inhibits CD3-linked kinase activity as shown by the inhibition of the phosphorylation of CD3 chains, leading to the inhibition of subsequent signal transduction.