ID: 219: DAPK1: A novel regulator of RIG-I identified by Kinome-Wide siRNA screening

The pattern recognition receptor RIG-I is a pivotal sensor of viral infections. Its activation by 5′-triphosphorylated- or double-stranded-RNA leads to subsequent signaling via MAVS, TBK1 and IKK epsilon resulting in IRF3 nuclear translocation. Activated IRF3 induces transcription of type I and type III interferons and several interferon stimulated genes. Despite intensive investigations on the RIG-I signaling pathway, its regulatory network still remains largely elusive. To gain more insight into the complex regulation of this pathway a kinome-wide siRNA screen was performed. The primary screen revealed over 100 siRNAs that significantly altered the translocation of IRF3 to the nucleus upon RIG-I stimulation. The top 50 candidates were further analyzed in three independent validation screens based on IRF3-sensitive promoter reporter assays or Rift-valley-fever virus replication. Taking all three validation screens into account, 21 novel regulators of the RIG-I signaling pathway could be identified. Relevance of the identified hits in regulating the host-cell antiviral defense was demonstrated by analyzing cytokine profiles and the impact on Influenza A virus replication. In the course of this screen, DAPK1 was identified as an inhibitor of RIG-I mediated IRF3 activation. Extensive mapping experiments revealed a minimal construct, including the kinase domain, to be sufficient for inhibiting IRF3 reporter activation in over-expression experiments. Furthermore, interaction studies revealed binding of DAPK1 to ligand-activated RIG-I, suggesting that a DAPK1 mediated phosphorylation of RIG-I inhibits its activity. In fact, in an in vitro kinase assays we could demonstrate that RIG-I is a substrate of DAPK1.