Human Genome-Wide RNAi Screen Identifies an Essential Role for Inositol Pyrophosphates in Type-I Interferon Response

The pattern recognition receptor rig-i is critical for type-i interferon production. however,the global regulation of rig-i signaling is only partially understood. using a human genome-wide rnai-screen,we identified 226 novel regulatory proteins of rig-i mediated interferon-β production. furthermore,the screen identified a metabolic pathway that synthesizes the inositol pyrophosphate 1-ip7 as a previously unrecognized positive regulator of interferon production. detailed genetic and biochemical experiments demonstrated that the kinase activities of ippk,ppip5k1 and ppip5k2 (which convert ip5 to1-ip7) were critical for both interferon induction,and the control of cellular infection by sendai and influenza a viruses. conversely,ectopically expressed inositol pyrophosphate-hydrolases dipps attenuated interferon transcription. mechanistic experiments in intact cells revealed that the expression of ippk,ppip5k1 and ppip5k2 was needed for the phosphorylation and activation of irf3,a transcription factor for interferon. the addition of purified individual inositol pyrophosphates to a cell free reconstituted rig-i signaling assay further identified 1-ip7 as an essential component required for irf3 activation. the inositol pyrophosphate may act by β-phosphoryl transfer,since its action was not recapitulated by a synthetic phosphonoacetate analogue of 1-ip7. this study thus identified several novel regulators of rig-i,and a new role for inositol pyrophosphates in augmenting innate immune responses to viral infection that may have therapeutic applications.