Molecular and biological characterization of fusion regulatory proteins (FRPs): anti-FRP mAbs induced HIV-mediated cell fusion via an integrin system.

Anti-FRP mAbs induced polykaryocyte formation of U2ME-7 cells (CD4+U937 cells transfected with the HIV gp160 gene). Anti-FRP-1 mAb immunoprecipitated gp80-85, gp120 and homodimers of these peptides, and anti-FRP-2 mAb reacted with gp135 identically to the alpha 3 subunit of integrin. Both anti-FRP-1 and anti-FRP-2 mAb-induced cell fusion was blocked by anti-beta 1 integrin antibody, fibronectin or inhibiting anti-FRP-1 antibody. Therefore, anti-FRP mAbs were thought to induce the fusion via an integrin system(s). FRP-mediated fusion was temperature, cytoskeleton, energy and Ca2+ dependent. These experiments showed a possible regulatory function of cell fusion by an integrin system(s).