Cullin E3 ligases and their rewiring by viral factors

The ability of viruses to subvert host pathways is central in disease pathogenesis. Over the past decade, a critical role for the Ubiquitin Proteasome System (UPS) in counteracting host immune factors during viral infection has emerged. This counteraction is commonly achieved by the expression of viral proteins capable of sequestering host ubiquitin E3 ligases and their regulators. In particular, many viruses hijack members of the Cullin-RING E3 Ligase (CRL) family. Viruses interact in many ways with CRLs in order to impact their ligase activity; one key recurring interaction involves re-directing CRL complexes to degrade host targets that are otherwise not degraded within host cells. Removal of host immune factors by this mechanism creates a more amenable cellular environment for viral propagation. To date, a small number of target host factors have been identified, many of which are degraded via a CRL-proteasome pathway. Substantial effort within the field is ongoing to uncover the identities of further host proteins targeted in this fashion and the underlying mechanisms driving their turnover by the UPS. Elucidation of these targets and mechanisms will provide appealing anti-viral therapeutic opportunities. This review is focused on the many methods used by viruses to perturb host CRLs, focusing on substrate sequestration and viral regulation of E3 activity.