ArfGAP Domain-Containing Protein 2 (ADAP2) Integrates Upstream and Downstream Modules of RIG-I Signaling and Facilitates Type I Interferon Production

Abstract

Transcription of type I interferon genes during RNA virus infection requires signal communication between several pattern recognition receptor (PRR)-adaptor complexes located at distinct subcellular membranous compartments and a central cytoplasmic TBK1-interferon regulatory factor 3 (IRF3) kinase-transcription factor module. However, how the cell integrates signal transduction through spatially distinct modules of antiviral signaling pathways is less defined. RIG-I is a major cytosolic PRR involved in the control of several RNA viruses. Here we identify ArfGAP domain-containing protein 2 (ADAP2) as a key novel scaffolding protein that integrates different modules of the RIG-I pathway, located at distinct subcellular locations, and mediates cellular antiviral type I interferon production. ADAP2 served to bridge the mitochondrial membrane-bound upstream RIG-I adaptor MAVS and the downstream cytosolic complex of NEMO (regulatory subunit of TBK1), TBK1, and IRF3, leading to IRF3 phosphorylation. Furthermore, independently, ADAP2 also functioned as a major orchestrator of the interaction of TBK1 with NEMO and IRF3. Mutational and cell-free reconstituted RIG-I signaling assay-based analyses identified that the ArfGAP domain of ADAP2 mediates the interferon response. TRAF3 acted as a trigger for ADAP2 to recruit RIG-I pathway component proteins into a single macromolecular complex. This study provides important novel insights into the assembly and integration of different modules of antiviral signaling cascades.

TANK-binding kinase 1 as a novel therapeutic target for viral diseases

“…As a result, TRIM26 bridges interaction between TBK1 with NEMO and facilitates the activation of the antiviral immune response [68]. In addition, varieties of molecules facilitate the formation of TBK1-containing complexes to enhance antiviral responses by directly binding to TBK1, such as ArfGAP domain-containing protein 2 (ADAP2) [69], muscle segment homeobox1 (MSX1) [70], ERassociated protein ZDHHC1 [71], downstream of kinase 3 (DOK3) [72], translocases of outer membrane 70 (Tom70) heat-shock protein of 90 KDa (HSP90) complex [73], IFNinduced TPR protein IFIT3 [74] and phosphatidylserinespecific phospholipase PLA1A [75].…”

Recent advances in antiviral interferon-stimulated gene biology

“…Notably, ADAP2-mediated inhibition of viral infection still occurred after mitochondrial antiviral-signaling protein knockdown, indicating a RIG-I-like receptor-independent function. In contrast, in a cell culture model of either poly-IC transfection or pattern recognition receptor overexpression, ADAP2 positively regulated IFN responses 29 . Additional studies are needed to determine whether this phenotype is linked to ADAP2-induced macropinocytosis.…”

Lessons in self-defence: inhibition of virus entry by intrinsic immunity

“…These results indicate that ADAP2 selectively blocks virus entry occurring in endosomes, particularly late endosomes. Furthermore, the antiviral activity of ADAP2 does not result from its influence on the expression of other interferon-stimulated genes 143 , as restriction still occurred in cells in which the gene encoding mitochondrial antiviral signalling protein (MAVS) was knocked out 141 .…”