Pleiotropic roles of the ubiquitin-proteasome system during viral propagation

Protein ubiquitination is a highly conserved post-translational modification affecting various biological processes including viral propagation. Ubiquitination has multiple effects on viral propagation, including viral genome uncoating, viral replication, and immune evasion. Ubiquitination of viral proteins is triggered by the ubiquitin-proteasome system (UPS). This involves the covalent attachment of the highly conserved 76 amino acid residue ubiquitin protein to target proteins by the consecutive actions of E1, E2 and E3 enzymes, and the 26S proteasome that together form a multiprotein complex that degrades target proteins. The UPS is the primary cytosolic proteolytic machinery for the selective degradation of various forms of proteins including viral proteins, thereby limiting viral growth in host cells. To combat this host anti-viral machinery, viruses have evolved the ability to employ or subvert the UPS to inactivate or degrade cellular proteins to favour viral propagation. This review highlights our current knowledge on the different roles of the UPS during viral propagation.