Specific binding of heat shock protein 70 with HN-protein inhibits the HN-protein assembly in Sendai virus-infected Vero cells.

The production of hemagglutinating virus of Japan (HVJ; Sendai virus) was inhibited at 41 degrees C, whereas it was normal at 37 degrees C. In the infected Vero cells, viral specific proteins were synthesized even at 41 degrees C, but the synthesized HN protein was not integrated into the cell membrane, resulting in the inhibition of viral production. To investigate the relationship of HSP70 to the inhibition of HN-protein integration, the expression of HSP70 was induced by prostaglandin A1 (PGA1) at 37 degrees C, and the influence on viral infection was examined. The induction of HSP70 at 37 degrees C inhibited the viral production. Viral proteins were also synthesized, even in the presence of PGA1. However, HN protein was not as present on the cell membrane following PGA1-treatment as it was at 41 degrees C, whereas F protein was detected. An immunoprecipitation assay showed that HSP70 was coprecipitated with HN protein, but not with F protein. The results suggested that the specific interaction of HSP70 with HN protein prevented the protein from integrating into the cell membrane. In addition, the abnormal virus-like particles, of which HN protein and nucleocapsid were ablated, were released in the culture medium at 41 degrees C, although the size was smaller than the normal viral virions. The results suggest that HN protein is necessary for viral morphogenesis.