A Teleost - Specific Sema4E - like Protein Promotes Grass Carp Reovirus Infection by Upregulating HSP70 Expression

Hemorrhagic disease caused by grass carp reovirus (GCRV) poses a severe threat to the grass carp aquaculture industry. Semaphorin 4E-like (Sema4E-like), a teleost-specific signaling molecule, remains poorly understood in immune regulation. In this study, the grass carp Sema4E-like gene was cloned and characterized, revealing a protein with the canonical "Sema-PSI-Ig" domain architecture. Expression analysis revealed that Sema4E-like was highly expressed in the hepatopancreas and intestine and underwent notable subcellular relocalization following GCRV infection. In vitro experiments demonstrated that overexpression of Sema4E-like significantly upregulated the transcription of GCRV viral genes and exacerbated cytopathic effects, whereas siRNA-mediated knockdown markedly suppressed GCRV infection, thereby bidirectionally corroborating its pro-viral function. Transcriptomic analysis further revealed profound alterations in host gene expression associated with Sema4E-like overexpression, including sustained suppression of most MAPK signaling pathway genes and differential regulation of heat shock protein family members, among with HSP70 exhibited the most prominent response. Consistently, pharmacological inhibition of HSP70 markedly attenuated the pro-viral effects mediated by Sema4E-like. Collectively, these findings indicate that Sema4E-like functions as a critical host factor exploited by GCRV, with HSP70 playing a central role in its pro-viral activity. This study offers a theoretical foundation for elucidating the regulation of fish semaphorins in antiviral innate immunity.