ASSOCIATION OF THE PARAINFLUENZA VIRUS FUSION AND HEMAGGLUTININ-NEURAMINIDASE GLYCOPROTEINS ON CELL-SURFACES

We previously observed that cell fusion caused by human parainfluenza virus type 2 or type 3 requires the expression of both the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins from the same virus type, indicating that a type-specific interaction between F and HN is needed for the induction of cell fusion, In the present study we have further investigated the fusion properties of F and HN proteins of pa rainfluenza virus type 1 (PI1), type 2 (PI2), and type 3 (PI3), Sendai virus (SN), and simian virus 5 (SV5) by expression of their glycoprot ein genes in HeLa T4 cells using the vaccinia virus-T7 transient expre ssion system. Consistent with previous results, cell fusion was observ ed in cells transfected with homotypic F/HN proteins; with one excepti on, coexpression of any combination of F and HN proteins from differen t viruses did not result in cell fusion, The only exception was found with the closely related PII HN and SN HN glycoproteins, either of whi ch could interact with SN F to induce cell fusion upon coexpression as previously reported. By specific labeling and coprecipitation of prot eins expressed on the cell surface, we observed that anti-PI2 HN antis erum coprecipitated PI2 F when the homotypic PI2 F and PI2 HN were coe xpressed, but not the F proteins of other paramyxoviruses when heterot ypic F genes were coexpressed with PI2 HN, suggesting that the homotyp ic F and HN proteins are physically associated with each other on cell surfaces. Furthermore, we observed that PI3 F was found to cocap with PI3 HN but not with PI2 HN, also indicating a specific association be tween the homotypic proteins. These results indicate that the homotypi c F and HN glycoproteins are physically associated with each other on the cell surface and suggest that such association is crucial to cell fusion induced by paramyxoviruses.