Involvement of a tick-borne orthomyxovirus matrix protein in vRNP nuclear export

Thogotoviruses, a group of arthropod-borne orthomyxoviruses, replicate in the nucleus and, similar to influenza A virus (IAV), require export of progeny viral ribonucleoproteins (vRNPs) to the cytoplasm prior to virion assembly and budding. This study elucidates the mechanism of vRNP nuclear export in Dhori virus (DHOV), a tick-borne member of the Thogotovirus genus. Although thogotoviruses share nuclear replication strategy with IAV, the viral factor responsible for vRNP export has not been defined yet. The authors showed that DHOV replication is markedly suppressed by the CRM1-specific nuclear export inhibitor leptomycin B, demonstrating reliance on a CRM1-dependent pathway. Immunofluorescence analyses confirm that CRM1 inhibition results in nuclear sequestration of both NP-containing vRNPs and the viral matrix (M) protein. In contrast to IAV, which employs a dedicated nuclear export protein (NEP), DHOV utilizes its M protein to mediate export. The DHOV M protein contains a functional nuclear export sequence (NES) spanning amino acids 111–128 that directly interacts with CRM1. Substitution of six key hydrophobic residues within this NES disrupts CRM1 binding, eliminates nuclear export activity in reporter assays, and prevents efficient recovery of recombinant DHOV. The authors also postulated that the hydrophobic residues I121 and L122 may be key contributors to CRM1 engagement. Collectively, these findings identify the M protein as the viral nuclear export factor in DHOV, establish the first mechanistic model for vRNP export in thogotoviruses, and highlight a potential antiviral target.
(TMR)