Proteasomes are large, multisubunit complexes that support normal cellular activities by executing the bulk of
protein turnover. During
infection, many viruses have been shown to promote viral replication by using proteasomes to degrade cellular factors that restrict viral replication. For example, the human cytomegalovirus (HCMV) pp71
protein induces the proteasomal degradation of Daxx, a cellular transcriptional repressor that can silence viral immediate early (IE) gene expression. We previously showed that this degradation requires both the
proteasome catalytic 20S core particle (CP) and the 19S regulatory particle (RP). The 19S RP associates with the 20S CP to facilitate protein degradation but also plays a 20S CP-independent role promoting transcription. Here, we present a nonproteolytic role of the 19S RP in HCMV IE gene expression. We demonstrate that 19S RP subunits are recruited to the major immediate early promoter (MIEP) that directs IE transcription. Depletion of 19S RP subunits generated a defect in
RNA polymerase II elongation through the MIE locus during HCMV
infection. Our results reveal that HCMV commandeers
proteasome components for both proteolytic and nonproteolytic roles to promote HCMV lytic
infection. Importance:
Proteasome inhibitors decrease or eliminate 20S CP activity and are garnering increasing interest as chemotherapeutics. However, an increasing body of evidence implicates 19S RP subunits in important proteolytic-independent roles during transcription. Thus, pharmacological inhibition of the 20S CP as a means to modulate
proteasome function toward
therapeutic effect is an incomplete capitalization on the potential of this approach. Here, we provide an additional example of nonproteolytic 19S RP function in promoting HCMV transcription. These data provide a novel system with which to study the roles of different
proteasome components during transcription, a rationale for previously described shifts in 19S RP subunit localization during HCMV
infection, and a potential therapeutic intervention point at a pre-immediate early stage for the inhibition of HCMV
infection.