Involvement of HSC70-4 and other inducible HSPs in Bombyx mori nucleopolyhedrovirus infection.

Heat shock proteins (HSPs) and heat shock cognate proteins (HSCs) function as molecular chaperones under normal cellular conditions. In this report, we describe the role of Bombyx mori heat shock cognate protein 70-4 (BmHSC70-4), which is a constitutively expressed member of the heat shock protein 70 (HSP70) family, in B. mori nucleopolyhedrovirus (BmNPV) infection. We first generated the BmHSC70-4 antibody, which can react specifically with an endogenous BmHSC70 from BmN cells. Immunohistochemistry has demonstrated that BmHSC70-4 was expressed at steady-state levels throughout the BmNPV infection and was accumulated in the nucleus of BmNPV-infected cells at a very late phase of infection. Western blot experiments have also shown that BmHSC70-4 is a novel component protein of budded virus (BV) and occlusion-derived virus (ODV). Next, we investigated the effect of KNK437, a known inhibitor of inducible HSPs, in BmNPV-infected BmN cells and found that both reduced BV production and delayed viral DNA replication were observed in virus-infected cells treated with KNK437. Furthermore, the formation of occlusion bodies (OBs) was not observed in KNK437-treated cells because this compound reduced the promoter activity of the polyhedrin gene severely. Collectively, the present results suggest that BmHSC70-4 is a novel structural protein of BmNPV and may have important roles in BmNPV propagation.