Escherichia coli Rho GTPase-activating toxin CNF1 mediates NLRP3 inflammasome activation via p21-activated kinases-1/2 during bacteraemia in mice

Abstract

Summary Inflammasomes are signaling platforms that are assembled in response to infection or sterile inflammation by cytosolic pattern recognition receptors (PRRs). The consequent inflammasome-triggered Caspase-1 activation is critical for the host defense against pathogens. During infection, NLRP3, a PRR also called Cryopyrin, triggers the assembly of an inflammasome activating Caspase-1 via the recruitment of ASC and Nek7. The NLRP3 inflammasome activation is tightly controlled both transcriptionally and post-translationally. Despite the importance of the NLRP3 inflammasome regulation in autoinflammatory and infectious diseases, little is known about the mechanism controlling the NLRP3 activation and the upstream signaling that regulates the NLRP3 inflammasome assembly. We have previously shown that the RhoGTPases-activating toxin from Escherichia coli , CNF1, activates Caspase-1, but the upstream mechanism is unclear. Here we provide evidence of the role of the NLRP3 inflammasome in sensing the activity of bacterial toxins and virulence factors that activate host RhoGTPases. We demonstrate that this activation relies on monitoring of the toxin’s activity on the RhoGTPase Rac2. We also show that the NLRP3 inflammasome is activated by a signaling cascade involving the P21 activated kinases (Pak) 1/2 and the Pak1-mediated phosphorylation of Threonine 659 of NLRP3, which is necessary for the NLRP3-Nek7 interaction, the inflammasome activation and the IL-1ß cytokine maturation. Furthermore, inhibition of the Pak-NLRP3 axis diminishes the bacterial clearance of CNF1-expressing UTI89 E . coli during bacteremia in mice. Altogether, our results establish Pak1/2 as critical regulators of the NLRP3 inflammasome and reveal the role of the Pak-NLRP3 signaling axis in vivo during bacteremia in mice.

Impact of thermogenesis induced by chronic β3-adrenergic receptor agonist treatment on inflammatory and infectious response during bacteremia in mice

“…Interestingly, even if rectal temperature was different before infection ( Fig 1A ), the fever measured 4 hours after bacterial infection was equivalent between NaCl- and CL316,243-treated mice. As expected, the bacteremia was decreased at 24 hours and completely resolved after 48 hours, demonstrating bacteria clearance by mice ( Fig 3B ) [ 22 ]. Activation of brown and brite adipocytes did not modify this response to infection ( Fig 3B ).…”

“…At the end of this treatment, half of the mice of each group were infected with E . coli and monitored 48 hours as previously described [ 22 ]. While bacteria induced a decrease of body weight in NaCl treated mice, no additive effect was found in CL316,243 treated mice ( Fig 1B ).…”

“…For infection, treatment with CL316,243 was stopped after 7 day, then mice were injected with E . coli (UTI89 strain, 1.71x10 7 CFU/mouse in phosphate-buffered saline solution (PBS), caudal intra-venous injection) and monitored for 48 hours before sacrifice [ 22 ]. At 0, 4, 24 and 48 hours after bacterial infection rectal temperature was recorded with a digital thermometer.…”

NEK7-Mediated Activation of NLRP3 Inflammasome Is Coordinated by Potassium Efflux/Syk/JNK Signaling During Staphylococcus aureus Infection

“…In agreement with the in vivo results, our in vitro data showed that the expression of NEK7 in both types of macrophages was decreased during S. aureus infection, simultaneously, the formation of NEK7 and NLRP3 complexes was increased ( Figures 2A–C ). Consistently, some studies reported that the expression of NEK7 was decreased with the enhanced interaction of NEK7-NLRP3 under the stimulation of LPS and ATP ( 25 ), LPS and cytotoxic necrosis factor (CNF1) ( 26 ) or LPS and IgA ICs ( 27 ). Furthermore, S. aureus infection-induced expression of NLRP3 inflammasome-associated molecules were significantly decreased by NEK7-siRNA pretreatment ( Figures 2D–F ), suggesting that NEK7 participated in NLRP3 inflammasome activation.…”

Optineurin links Hace1-dependent Rac ubiquitylation to integrin-mediated mechanotransduction to control bacterial invasion and cell division

“…Thus, Rac1 influences the mechanical response/adaptation of cells via the aforementioned functions. It is now important to define how to position Rac-mediated control of cell functions in the context of mechanosensing, given that ECM stiffening and abnormal responses to mechanical cues of the ECM are associated with a large spectrum of human diseases, including cancer and chronic inflammation [41][42][43][44][45] , and that Rac1 plays a critical role in the control of cell-extracellular matrix (ECM) adhesion, transcriptional responses, and cell division [46][47][48] and is frequently highjacked by invasive pathogens during infectious processes [49][50][51][52][53] .…”