Asparagine deprivation causes a reversible inhibition of Human Cytomegalovirus acute virus replication

As obligate intracellular pathogens, viruses rely on the host cell machinery to replicateefficiently, with the host metabolism extensively manipulated for this purpose. High throughput siRNA screens provide a systematic approach for the identification of novel host-virus interactions. Here, we report a large-scale screen for host factorsimportant for human cytomegalovirus(HCMV), consisting of 6,881 siRNAs. We identified 47 proviral factors and 68 antiviral factors involved in a wide range of cellular processes including the mediator complex, proteasome function and mRNA splicing. Focused characterisation of one of the hits, asparagine synthetase(ASNS), demonstrated a strict requirement for asparaginefor HCMV replicationwhich leads to an early block in virus replicationbefore the onset of DNA amplification. This effect is specific to HCMV, as knockdown of ASNS had little effect on herpes simplex virus-1 or influenzaA virus replication, suggesting the restriction is not simply due to a failure in protein production. Remarkably, virus replicationcould be completely rescued seven days post-infection with addition of exogenous asparagine, indicating that while virus replicationis restricted at an early stage, it maintains the capacity for full replicationdays after initial infection. This study represents the most comprehensive siRNA screen for the identification of host factorsinvolved in HCMV replicationand identifies the non-essentialamino acid, asparagineas a critical factor in regulating HCMV virus replication. These results have implications for control of viral latencyand the clinical treatment of HCMV in patients.