Protein tyrosine kinase activation provides an early and obligatory signal in anti-FRP-1/CD98/4F2 monoclonal antibody induced cell fusion mediated by HIV gp160

Abstract

The mechanism by which anti-fusion regulatory protein-1 (FRP-1) monoclonal antibody (mAb) induced cell fusion was investigated using U2ME-7 cells that are CD4⁺U937 cells transfected with the HIV gp160 gene. Protein kinase inhibitors (H-7, H-89, herbimycin A and genistein) suppressed cell fusion of Cd⁺U2ME-7 cells induced by anti-FRP-1 mAb. H-7 and H-89 also inhibited the cell aggregation, but herbimycin A and genistein did not. Intriguingly, only when herbimycin A was added either before or simultaneously with addition of anti-FRP-1 mAb, was cell fusion suppressed, suggesting that tyrosine kinase is related with the initial step of polykaryocyte formation. Anti-FRP-1 mAb induced the rapid tyrosine phosphorylation of multiple cellular proteins. These effects occurred within 1 min and returned to near baseline by 60 min. The rapid tyrosine phosphorylation was suppressed by herbimycin A and genistein. Although it remains to be determined which protein tyrosine kinase(s) is involved in this response, pp130 tyrosine phosphorylation appears to be a specific and early signal transmitted after the interaction of FRP-1 with a specific antibody. pp130 was present in the cytosol fraction and was distinct from pp125^FAK, p130^CAS, vinculin, and β1-integrin. Thus, our study may present evidence for a novel pathway of protein tyrosine kinases that phosphorylate specific, still unknown protein substrates during polykaryocyte formation.