The Scaffolding Protein IQGAP1 Interacts with NLRC3 and Inhibits Type I IFN Production

Abstract

Sensing of cytosolic nucleotides is a critical initial step in the elaboration of type I interferon. One of several upstream receptor cGAS (cyclic-GMP-AMP synthase) binds to cytosolic DNA and generates di-cyclic nucleotides that act as secondary messengers. These secondary messengers bind directly to Stimulator of Interferon Genes (STING). STING recruits TANK binding kinase 1 (TBK1) which acts as a critical node that allows for efficient activation of interferon regulatory factors (IRFs) to drive the anti-viral transcriptome. NLRC3 is a recently characterized nucleotide-binding domain, leucine rich repeat containing protein (NLR) that negatively regulates the type I interferon pathway by inhibiting subcellular redistribution and effective signaling of STING, thus blunting the transcription of type I interferons. NLRC3 is predominantly expressed in lymphoid and myeloid cells. IQGAP1 was identified as a putative interacting partner of NLRC3 through yeast two hybrid screening. Here we show that IQGAP1 associates with NLRC3 and can disrupt the NLRC3:STING interaction in the cytosol of human epithelial cells. Furthermore, knock down of IQGAP1 in THP1 and HeLa cells causes significantly more interferon-β production in response to cytosolic nucleic acids. This result phenocopies NLRC3 deficient macrophages and fibroblasts and shRNA knock down of NLRC3 in THP1 cells. Our findings suggest IQGAP1 is a novel regulator of type I interferon production possibly via interacting with NLRC3 in human monocytic and epithelial cells.

Viral DNA Binding to NLRC3, an Inhibitory Nucleic Acid Sensor, Unleashes STING, a Cyclic Dinucleotide Receptor that Activates Type I Interferon

“…This study shows that DNA binding to NLRC3 also releases its interaction with TBK1 in a cell free system. Because of the high-affinity binding between NLRC3 and dsDNA, it is possible that this binding could liberate other NLRC3-associated proteins described in the literature, such as TNF-receptor-associated factor 6 (TRAF6) and Ras GTPase-activating-like protein IQGAP1 (Schneider et al, 2012b; Tocker et al, 2017). Given that inhibitory NLRs function as checkpoints that prevent excessive immune responses, it would be interesting to determine whether nucleic acid binding to NLRC3 casts a suppressive effect on other downstream pathways such as Lys63 (K63)-linked ubiquitination of TRAF6 and phosphoinositide 3-kinases (PI3Ks) (Karki et al, 2016; Schneider et al, 2012b).…”

Cepharanthine Prevents Estrogen Deficiency-Induced Bone Loss by Inhibiting Bone Resorption

“…As expected, the agonists partly reversed the suppressed phosphorylation of AKT and JNK, as well as inhibited osteoclast formation and reduced bone resorption. NLRC3 is a cytoplasmic sensor that regulates multiple biological functions and is known to be highly expressed in spleen and leukocyte in humans (Schneider et al, 2012 ; Karki et al, 2016 ; Tocker et al, 2017 ). It interacts with p85 subunits of PI3K, and blocks the interaction between PI3K p85 and p110α, following suppression of the activation of the PI3K-AKT signaling in cancer (Karki et al, 2016 ).…”

Negative Regulation of Cytosolic Sensing of DNA

“…NLRX1, the only mitochondrially localized member of this family, modulates sensing of dsRNA and virus-induced ROS production (Guo et al, 2016;Ma et al, 2017;Moore et al, 2008;Qin et al, 2017a;Tattoli et al, 2008). In collaboration with IQGAP1, NLRC3 suppresses DNA sensing lymphoid cells, myeloid cells, and epithelial cells through interactions with STING (Tocker et al, 2017;Zhang et al, 2014). In addition, NLRC5 can suppress TLR signaling by modulating IKK activation (Cui et al, 2010), though NLRC5 deficiency does not affect this signaling pathway (Kumar et al, 2011b).…”