HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENVELOPE GLYCOPROTEIN GP120 INDUCES EXPRESSION OF FUSION REGULATORY PROTEIN (FRP)-1 CD98 ON CD4(+) T-CELLS - A POSSIBLE REGULATORY MECHANISM OF HIV-INDUCED SYNCYTIUM FORMATION/

Syncytium formation is one of major cytopathic effects of human immuno deficiency virus (HIV) infection, and requires the interaction of CD4 molecules on uninfected cells with HIV envelope glyoprotein gp120 expr essed on HIV-infected cells. Recent evidence suggests chemokine recept ors function as fusion cofactors. We have recently found that fusion r egulatory protein (FRP)-1/ CD98 is involved in syncytium formation of HIV gp160-expressing U2ME-7 cells and TALL-1 cells persistently infect ed with HIV. However, resting lymphocytes were found to express no FRP -1 molecule. In this study, we demonstrated that recombinant gp120 (rp g120) has the ability to induce expression of FRP-1 on peripheral bloo d mononuclear cells (PBMC). Three-color flow cytometric analysis showe d that rgp 120-induced FRP-1 was expressed selectively on CD4(+) T cel ls in a dose-dependent manner, FRP-1 expression level was maximum 3 da ys after addition of rgp120, Anti-CD4 and anti-gp120 antibodies blocke d rgp 120-induced FRP-1 expression. Go-cultivation of PBMC with HIV-1 gp160-expressing HeLa cells also resulted in the increased expression of FRP-1 on T cells. These results suggest that FRP-1 molecules are in duced on CD4(+) T cells via CD4-gp120 interaction and may play an impo rtant role in regulation of HIV-induced syncytium formation.