Virus-host interactions in the chikungunya virus replication cycle

The prevalence of arthropod-borne viruses (arboviruses) dramatically increased in the last decade in diseased-endemic countries and the viruses have and are arriving in previously unaffected countries. The dispersal of these arboviruses is progressively being facilitated by climate change and increased transcontinental movements. Arboviruses are capable of efficiently replicating in both their vertebrate host and invertebrate vectors. Chikungunya virus (CHIKV), member of the Alphavirus genus, is such a re-emerging arbovirus which has increasingly affected public health on all inhabited continents.

Generally, viruses are dependent on their host cell to complete all steps in the viral replication cycle. In order to do so, many virus-host protein-protein interactions are necessary. To date the virus-host and virus-vector interactome for CHIKV is poorly understood. So far, multiple attachment factors used for CHIKV entry have been identified but the whole picture remains incomplete. We applied an affinity-based purification approach coupled to mass spectrometry analysis (AP-MS) to identify protein-protein interactions that facilitate the entry of CHIKV in both human and mosquito cells. We were able to identify and validate the involvement of the CD147 protein complex in the entry of CHIKV in human but not mosquito cells. Our AP-MS strategy further identified seven attachment candidates for CHIKV in mosquito cells whereof two proteins (ATPB and RPSA) were previously described as attachment factors for CHIKV and/or related alphaviruses in mosquito cells. Our results add to current knowledge on alphaviral entry and indicate that this process is a versatile multi-route step where various attachment factors and endocytic pathways are used.

CHIKV has a broad cellular tropism, however one marked exception is the resistance of the A549 cell line to CHIKV infection. This resistance could indicate the presence of a restrictive mechanism for CHIKV in A549 cells and understanding the viral and host proteins involved would be of great interest. We used the high genomic plasticity of CHIKV to adapt the virus to efficient growth in this restrictive cell line. We identified four adaptive mutations after serially passaging CHIKV, two in the structural and two in the non-structural proteins and assessed their contribution to the increased viral replication in A549 cells. While the adaptive mutations in the non-structural proteins also stimulate viral replication in Vero cells, the mutations in the structural proteins negatively impact viral replication in Vero cells. Further identification of this natural block to CHIKV in A549 cells is subject of future research.

In conclusion, the work presented in this thesis adds to a better general understanding of the CHIKV replication cycle but many unknowns remain.