Investigating the Role of Sphingosine Kinases During Alphavirus Infection
2022 Copyright, the authors
Several alphaviruses, critical human pathogens, have re-emerged in recent years. Alphaviruses are found on all continents and infect both invertebrates and vertebrates, including some aquatic animals. They are classified as arboviruses because hematophagous arthropods transmit them. Based on the symptoms they cause, alphaviruses are classified as either arthritogenic or encephalitic.
Rising global travel has led to outbreaks of infections in new regions, increasing the geographical ranges of alphaviruses and causing new infections in susceptible hosts. Currently, there are no approved prophylactic or therapeutic measures to prevent or treat alphavirus infections; prevention measures have focused on vector control. These measures are insufficient, however, as mutations that enable more efficient viral transmission or increase susceptible vector range have been observed with alphaviruses. Thus, there is an urgent need to develop therapies that can target the infection cycle in hosts.
Studies investigating host factors utilized by alphaviruses are vital to developing therapies for treatment. As obligate intracellular pathogens, viruses require host factors for successful infection. These host factors play specific roles in different stages of the viral lifecycle – entry, replication, translation, assembly, and exit. Of particular interest to this study is the viral nonstructural protein, nsP3, described in several reports as an enigma, which is a hub for host-alphavirus interactions. Understanding the mechanisms that underpin these interactions and how they affect viral replication and infection success will be valuable in developing effective therapies.
In the following studies, we characterize the role of sphingosine kinases (SphKs) during alphavirus infection. Using localization and inhibitor studies, we investigate kinase effects on arthritogenic and encephalitic alphavirus infection. These experiments revealed that SphK1 was necessary for infection by the prototypical encephalitic alphavirus, Venezuelan equine encephalitis virus (VEEV). Arthritogenic alphaviruses preferentially utilized SphK2 during infection.
Furthermore, a novel potent SphK inhibitor blocked infection of Chikungunya virus (CHIKV), an arthritogenic alphavirus, decreasing viral replication, and infectious progeny production. Finally, host-virus protein-protein interactions were explored using CHIKV nsP3 mutants. We found the hypervariable domain (HVD) of nsP3 to be essential for CHIKV colocalization with SphK2. The data from these studies point to a role for the sphingosine kinases in alphavirus infection.