Abstract
Viruses and hosts are situated in a molecular arms race. To avoid morbidity and mortality, hosts evolved antiviral restriction factors. These restriction factors exert selection pressure on the viruses and drive viral evolution toward increasingly efficient immune antagonists. Numerous viruses exploit cellular DNA damage-binding protein 1 (DDB1)-containing Cullin RocA ubiquitin ligases (CRLs) to induce the ubiquitination and subsequent proteasomal degradation of antiviral factors expressed by their hosts. To establish a comprehensive understanding of the underlying protein interaction networks, we performed immuno-affinity precipitations for a panel of DDB1-interacting proteins derived from viruses such as mouse cytomegalovirus (MCMV, Murid herpesvirus [MuHV] 1), rat cytomegalovirus Maastricht MuHV2, rat cytomegalovirus English MuHV8, human cytomegalovirus (HCMV), hepatitis B virus (HBV), and human immunodeficiency virus (HIV). Cellular interaction partners were identified and quantified by mass spectrometry (MS) and validated by classical biochemistry. The comparative approach enabled us to separate unspecific interactions from specific binding partners and revealed remarkable differences in the strength of interaction with DDB1. Our analysis confirmed several previously described interactions like the interaction of the MCMV-encoded interferon antagonist pM27 with STAT2. We extended known interactions to paralogous proteins like the interaction of the HBV-encoded HBx with different Spindlin proteins and documented interactions for the first time, which explain functional data like the interaction of the HIV-2-encoded Vpr with Bax. Additionally, several novel interactions were identified, such as the association of the HIV-2-encoded Vpx with the transcription factor RelA (also called p65). For the latter interaction, we documented a functional relevance in antagonizing NF-κB-driven gene expression. The mutation of the DDB1 binding interface of Vpx significantly impaired NF-κB inhibition, indicating that Vpx counteracts NF-κB signaling by a DDB1- and CRL-dependent mechanism. In summary, our findings improve the understanding of how viral pathogens hijack cellular DDB1 and CRLs to ensure efficient replication despite the expression of host restriction factors.
Highlights
In response to viral infections, host cells have evolved a plethora of so-called restriction factors that inhibit specific steps of the viral replication cycle, thereby limiting the damage caused by infections
Based on the finding that the MCMV-encoded accessory protein pM27 exploits Cul4A and DNA damage-binding protein 1 (DDB1) to induce ubiquitination and proteasomal degradation of STAT2, we studied pM27, its HCMV-derived homolog pUL27 as well as pE27 and pR27 of Murid herpesvirus (MuHV) 8 and MuHV2, respectively
Since Cullin RocA ubiquitin ligases (CRLs) became amenable for pharmacologic intervention using drugs such as MLN4924 and since CRL activity is essential for replication of several human-pathogenic viruses [21, 72], viral CRL exploitation may be turned into therapeutic approaches
Summary
In response to viral infections, host cells have evolved a plethora of so-called restriction factors that inhibit specific steps of the viral replication cycle, thereby limiting the damage caused by infections. Several of these restriction factors are encoded by interferon (IFN)-stimulated genes (ISG) [1, 2]. Viruses inducing the proteasomal degradation of host restriction factors via ubiquitination [6, 7] often lose their replication capacity, if the Ub conjugation machinery or the proteasome is inactivated [8,9,10,11,12]. A specific inhibition of individual Ub ligases might limit side effects to levels tolerable in the context of antiviral therapies
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call