Effects of CRM1-dependent nuclear export inhibition on viral structural protein nuclear accumulation during Autographa californica multiple nucleopolyhedrovirus infection

Abstract Autographa californica multiple nucleopolyhedrovirus (AcMNPV) assembles its nucleocapsids and occlusion-derived virions (ODVs) in the nucleus, which requires AcMNPV regulation for viral structural proteins to accumulate in the nucleus during its replication in cells. It is generally accepted that the nuclear import receptor plays a predominant role in this process. CRM1 is a nuclear export receptor that forms an export complex with its cargo protein to exit the nucleus. We previously discovered that AcMNPV inhibited CRM1-dependent nuclear export by the viral protein Ac34. This finding suggested that Ac34 could sequester CRM1-dependent proteins in the nucleus and play a novel role in the nuclear accumulation of viral structural proteins. Using the CRM1 inhibitor leptomycin B (LMB), we demonstrated that CRM1 inhibition promoted AcMNPV replication, as LMB treatment readily increased the virus titer, and even functionally surrogate Ac34 to rescue the infectivity of an ac34-knockout virus. To elucidate whether CRM1 inhibition contributes to the nuclear accumulation of viral structural proteins, we systematically analyzed the impact of CRM1 inhibition on viral protein spatial distribution patterns. We found that the nucleocapsid protein Ac102 and ODV envelope protein E26 were retained in the nucleus in response to CRM1 inhibition by Ac34. This finding indicates that AcMNPV is evolving to simultaneously exploit bidirectional nucleocytoplasmic trafficking to assist in viral replication.