Abstract
The Chikungunya virus (CHIKV) is an emerging mosquito-borne virus, transmitted by Aedes mosquitoes, with a significant impact on human health. In humans, it can cause debilitating and persistent arthralgia. Currently, there is no vaccine or specific antiviral treatment targeting CHIKV.The CHIKV genome encodes four non-structural proteins. Among them, the viral methyl-guanylyl transferase nsP1 is responsible for anchoring the viral replication complex to the lipid bilayer. Assembled in a dodecameric form, nsP1 creates a pore located at the neck of CHIKV replication organelles, ensuring the organization and maintenance of these membranous compartments essential for viral genome replication. When expressed alone, nsP1 induces dramatic membrane deformations of the host plasma membrane resembling filopodia. This phenotype requires the presence of the nsP1 palmitoylation domain. However, the mechanisms involved in the membrane deformation function of nsP1 remained unknown. Therefore, the objective of this thesis was to investigate the cellular mechanisms contributing to nsP1-mediated membrane deformation.We characterized the filopodia formed by nsP1 as actin-rich, highly dynamic membrane protrusions. Using siRNA knockdown and chemical inhibitors, we identified the Rho-GTPase Rac1, the serine/threonine kinase PAK1, and the actin-nucleating protein Arp2 as key players in the formation of these membranous extensions. To further elucidate the underlying mechanisms, we analyzed the nsP1 interactome through mass spectrometry. Among the identified cellular partners, we demonstrated the functional role of HAX1 and SCRIB proteins, which are also involved in regulating the Rac1-PAK-Arp2 signaling pathway.Beyond their critical role in filopodia formation, these nsP1 partners were found to be essential for the replication of CHIKV and related Alphavirus genomes in infected cells. These findings highlight the existence of common mechanisms between nsP1-induced membrane deformations and viral replication.