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 °C, whereas it was normal at 37 °C. In the infected Vero cells, viral specific proteins were synthesized even at 41 °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 °C, and the influence on viral infection was examined. The induction of HSP70 at 37 °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 °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 °C, although the size was smaller than the normal viral virions. The results suggest that HN protein is necessary for viral morphogenesis.