# Conserved use of tetraspanin CD9 as an entry receptor by rhabdoviruses spanning multiple genera

## TL;DR

Researchers found that CD9 is a common entry receptor for multiple rhabdoviruses and identified a drug that could block infection.

## Contribution

CD9 is identified as a conserved entry receptor across multiple rhabdovirus genera, with implications for broad-spectrum antiviral strategies.

## Key findings

- CD9 interacts with viral glycoproteins to mediate rhabdovirus entry.
- Nitazoxanide inhibits infection by disrupting the CD9-virus interaction.
- CD9 functions as a receptor for VHSV, SCRV, and VSV across species.

## Abstract

Rhabdoviruses infect a wide range of hosts, but the cellular receptors enabling this cross-species infection were unclear. We identified the tetraspanin protein cluster and differentiation 9 (CD9) as a conserved functional entry receptor for diverse rhabdoviruses, including viral hemorrhagic septicemia virus (VHSV), Siniperca chuatsi rhabdovirus (SCRV), and vesicular stomatitis virus (VSV). Our work shows that CD9 directly interacts with viral glycoproteins to mediate virus entry through specific endocytic pathways. Importantly, we found that nitazoxanide (NTZ), an Food and Drug Administration (FDA)-approved antiparasitic agent, is currently being repurposed and evaluated as an antiviral candidate against multiple rhabdoviruses. These findings reveal a shared mechanism of rhabdovirus infection across species and suggest a potential broad-spectrum antiviral strategy.

Rhabdoviruses exhibit a broad host range, yet the cellular receptors underlying their cross-species tropism remain poorly defined. Here, we identified tetraspanin CD9 as a conserved functional entry receptor for diverse rhabdoviruses across genera, including viral hemorrhagic septicemia virus (VHSV) (Novirhabdovirus), Siniperca chuatsi rhabdovirus (SCRV) (Siniperhavirus), and vesicular stomatitis virus (VSV) (Vesiculovirus). We demonstrated that the domain IV of VHSV glycoprotein G directly interacted with the large extracellular loop domain of Lateolabrax japonicus CD9 (LjCD9). CD9 knockout, CD9 protein, or CD9 antibody significantly reduced VHSV infection in vitro and CD9 knockout zebrafish, while HEK293T cells, which are nonsusceptible but permissive to VHSV, become susceptible when expressing LjCD9, suggesting that LjCD9 is an entry receptor for VHSV. We further confirmed that LjCD9 functions as a functional receptor of SCRV. Importantly, the human CD9 orthologue can serve as a receptor of VSV. Our findings also revealed that LjCD9 mediated VHSV entry via clathrin- and caveolae-mediated endocytosis. Notably, nitazoxanide (NTZ) was identified as a broad-spectrum inhibitor of VHSV, SCRV, and VSV likely by interfering with the G protein–CD9 interaction. This study establishes CD9 as a cross-species receptor for rhabdoviruses and highlights NTZ as a promising broad-spectrum antiviral agent.