The hemagglutinin-neuraminidase (HN) and fusion (F) glycoproteins of two paramyxoviruses, human parainfluenza virus type 2 (PIV2) and simian virus 41 (SV41), were expressed in HeLa cells by transfecting with recombinant plasmid harboring each glycoprotein gene. Expressed F proteins could not induce cell fusion by themselves, but evoked prominent cell fusion when coexpressed with homologous HN proteins. It was also proved that PIV2 HN protein could weakly promote SV41 F-mediated cell fusion. By analyzing the fusion-promoting function of chimeric HN proteins of PIV2 and SV41, it was revealed that the N-terminal region (about 16% of total amino acids) of either PIV2 HN or SV41 HN protein could define the type-specific fusion-promoting function for homologous F protein. Analyses of additional chimeras indicated that the N-terminal region in PIV2 HN protein (designated region I, consisting of 94 amino acids) could be reduced to a 58-amino-acid region (region I') which was located at the membrane-proximal end of the ectodomain. Furthermore, PIV2 HN protein proved to promote cell fusion mediated by PIV4A F protein. Unexpectedly, analyses of another set of chimeras revealed that the promoting function of PIV2 HN protein for PIV4A F-mediated cell fusion was not merely carried by its region I but also by another region ranging from residue 148 to 209 (region II). Finally, it was indicated that regions I' (in the presumed stalk domain) and II (in the globular head) in PIV2 HN protein might play important roles in promoting cell fusion mediated by the F proteins.

No abstract

No abstract

Anti-FRP mAbs induced polykaryocyte formation of U2ME-7 cells (CD4+U937 cells transfected with the HIV gpl60 gene). Anti-FRP-1 mAb immunoprecipitated gp8O-85, gpl20 and homodimers of these peptides, and anti-FRP-2 mAb reacted with gp135 identically to the A3 subunit of integrin. Both anti-FRP-1 and anti-FRP-2 mAb-induced cell fusion was blocked by anti-(l 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).