Many viruses have been implicated in utilizing or modulating the
Ubiquitin Proteasome System (UPS) to enhance viral multiplication and/or to sustain a
persistent infection. The mosquito-borne Venezuelan equine encephalitis virus (VEEV) belongs to the Togaviridae family and is an important biodefense pathogen and select agent. There are currently no approved
vaccines or
therapies for VEEV
infections; therefore, it is imperative to identify novel targets for therapeutic development. We hypothesized that a functional UPS is required for efficient VEEV multiplication. We have shown that at non-toxic concentrations
Bortezomib, a FDA-approved inhibitor of the
proteasome, proved to be a potent inhibitor of VEEV multiplication in the human
astrocytoma cell line U87MG.
Bortezomib inhibited the virulent Trinidad donkey (TrD) strain and the attenuated TC-83 strain of VEEV. Additional studies with virulent strains of Eastern equine encephalitis virus (EEEV) and Western equine encephalitis virus (WEEV) demonstrated that
Bortezomib is a broad spectrum inhibitor of the New World alphaviruses. Time-of-addition assays showed that
Bortezomib was an effective inhibitor of viral multiplication even when the
drug was introduced many hours post exposure to the virus. Mass spectrometry analyses indicated that the VEEV
capsid protein is ubiquitinated in infected cells, which was validated by confocal microscopy and immunoprecipitation assays. Subsequent studies revealed that capsid is ubiquitinated on K48 during early stages of
infection which was affected by
Bortezomib treatment. This study will aid future investigations in identifying host
proteins as potential broad spectrum therapeutic targets for treating
alphavirus infections.