Rad50-CARD9 interactions link cytosolic DNA sensing to IL-1β production

Abstract

Double-stranded DNA (dsDNA) in the cytoplasm triggers interleukin-1β (IL-1β) production as an anti-viral host response, and deregulation of the pathways involved can promote inflammatory disease. Here we report a direct cytosolic interaction between the DNA-damage sensor Rad50 and the innate immune adapter CARD9. Dendritic cell transfection with dsDNA or infection with a DNA virus induces the formation of dsDNA-Rad50-CARD9 signaling complexes for NF-κB activation and pro-IL-1β generation. Primary cells conditionally deficient for Rad50 or lacking CARD9 consequently exhibit defective DNA-induced IL-1β production, and Card9−/− mice have impaired inflammatory responses upon DNA virus infection in vivo. These results define a cytosolic DNA recognition pathway for inflammation and a physical and functional connection between a conserved DNA-damage sensor and the innate immune response to pathogens.

Cellular and molecular regulation of innate inflammatory responses

“…RIG-I 11 and melanoma differentiation-associated protein 5 (MDA5) 12 can recognize viral dsRNA and recruit the CARD containing adaptor protein MAVS (also known as IPS-1, CARDIF or VISA), leading to IRF activation and the production of type I IFN. In addition to RLRs, a group of cytosolic DNA sensors such as cyclic GMP-AMP synthase (cGAS), [13][14][15] absent in melanoma 2 (AIM2), 16,17 DDX41, 18,19 Rad50, 20,21 LRRFIP1, 22 DNA-dependent activator of IRFs (DAI), 23 as well as various RNA sensors such as IFN-induced protein with tetratricopeptide repeats 1 (IFIT1) 24 also play potent roles in inducing antiviral immune response, respectively via the adaptor protein stimulator of interferon genes (STING, also known as MITA, ERIS or MPYS) or the MAVS pathway. cGAS, which was previously thought to recognize cytoplasmic dsDNA over 40 bp in a sequence-independent manner, is recently shown to recognize unpaired guanosines flanking short (12-20 bp) dsDNA (Y-form DNA) found in human immunodeficiency virus type 1 to induce type I IFN production.…”

When our genome is targeted by pathogenic bacteria

“…IFN primes the pattern recognition receptor system (PRR) [73] for amplified antimicrobial response through the production of cytokines and chemokines, and the recruitment of phagocytic cells [77]. Similarly, Rad50 forms a complex with cytosolic dsDNA and the innate immune system adaptor CARD9 (caspase recruitment domain family 9), resulting in the production of the highly proinflammatory Interleukin lβ after NF-κB pathway activation [78]. Moreover, ATM and DNA-PK have also been shown to be associated with cytoplasmic PRR.…”

Innate immune activation of NFκB and its antagonism by poxviruses

“…However, DNA-PK sensing of MVA did not lead to NFkB activation. A rare to date clear example of how cytosolic DNA sensing of poxviruses can cause NFkB activation was recently provided by Roth et al [90]. This involved detection of cowpox and VACV DNA in murine DCs by direct binding to the DNA damage sensor Rad50, which somehow relocated from the nucleus to the cytoplasm in response to poxviral infection.…”

“…This involved detection of cowpox and VACV DNA in murine DCs by direct binding to the DNA damage sensor Rad50, which somehow relocated from the nucleus to the cytoplasm in response to poxviral infection. Rad50 then recruited the innate immune signalling adaptor caspase-associated recruitment domain 9 (CARD9), which activated the IKK complex via Bcl-10, leading to induction of NFkB-dependent genes including TNFa and pro-IL-1b [90]. Importantly, Rad50/CARD9 sensing of poxviruses was also shown to operate in vivo.…”