MCC950 directly targets the NLRP3 ATP-hydrolysis motif for inflammasome inhibition

Interleukin-1β (IL-1β) is a cytokine whose bioactivity is controlled by activation of the inflammasome. However, in response to lipopolysaccharide, human monocytes secrete IL-1β independently of classical inflammasome stimuli. Here, we report that this constituted a species-specific response that is not observed in the murine system. Indeed, in human monocytes, lipopolysaccharide triggered an "alternative inflammasome" that relied on NLRP3-ASC-caspase-1 signaling, yet was devoid of any classical inflammasome characteristics including pyroptosome formation, pyroptosis induction, and K(+) efflux dependency. Genetic dissection of the underlying signaling pathway in a monocyte transdifferentiation system revealed that alternative inflammasome activation was propagated by TLR4-TRIF-RIPK1-FADD-CASP8 signaling upstream of NLRP3. Importantly, involvement of this signaling cascade was limited to alternative inflammasome activation and did not extend to classical NLRP3 activation. Because alternative inflammasome activation embraces both sensitivity and promiscuity of TLR4, we propose a pivotal role for this signaling cascade in TLR4-driven, IL-1β-mediated immune responses and immunopathology in humans.

The NLRP3 inflammasome responds to microbes and danger signals by processing and activating proinflammatory cytokines including IL-1β and IL-18. We show that NLRP3 inflammasome activation is restricted to interphase of the cell cycle by NEK7, a serine/threonine kinase previously implicated in mitosis. NLRP3 inflammasome activation requires NEK7, which binds to the NLRP3 leucine-rich repeat domain in a kinase-independent manner downstream from the induction of mitochondrial ROS. This interaction is necessary for NLRP3-ASC complex formation, ASC oligomerization, and caspase-1 activation. NEK7 promotes the NLRP3-dependent cellular inflammatory response to intraperitoneal monosodium urate challenge, and the development of experimental autoimmune encephalitis in mice. Our findings suggest NEK7 serves as a cellular switch that enforces mutual exclusivity between the inflammasome response and cell division.

Identifying the molecular targets for the beneficial or detrimental effects of small-molecule drugs is an important and currently unmet challenge. We have developed a method, drug affinity responsive target stability (DARTS), which takes advantage of a reduction in the protease susceptibility of the target protein upon drug binding. DARTS is universally applicable because it requires no modification of the drug and is independent of the mechanism of drug action. We demonstrate use of DARTS to identify known small-molecule-protein interactions and to reveal the eukaryotic translation initiation machinery as a molecular target for the longevity-enhancing plant natural product resveratrol. We envisage that DARTS will also be useful in global mapping of protein-metabolite interaction networks and in label-free screening of unlimited varieties of compounds for development as molecular imaging agents.