BTK operates a phospho-tyrosine switch to regulate NLRP3 inflammasome activity

Abstract

Activity of the NLRP3 inflammasome, a critical mediator of inflammation, is controlled by accessory proteins, posttranslational modifications, cellular localization, and oligomerization. How these factors relate is unclear. We show that a well-established drug target, Bruton’s tyrosine kinase (BTK), affects several levels of NLRP3 regulation. BTK directly interacts with NLRP3 in immune cells and phosphorylates four conserved tyrosine residues upon inflammasome activation, in vitro and in vivo. Furthermore, BTK promotes NLRP3 relocalization, oligomerization, ASC polymerization, and full inflammasome assembly, probably by charge neutralization, upon modification of a polybasic linker known to direct NLRP3 Golgi association and inflammasome nucleation. As NLRP3 tyrosine modification by BTK also positively regulates IL-1β release, we propose BTK as a multifunctional positive regulator of NLRP3 regulation and BTK phosphorylation of NLRP3 as a novel and therapeutically tractable step in the control of inflammation.

PHOrming the inflammasome: phosphorylation is a critical switch in inflammasome signalling

“…Recent research has highlighted how the subcellular localisation of inflammasome proteins is essential for complex formation and is also regulated by phosphorylation. For example, NLRP3 localisation to the trans -Golgi network appears to be regulated by PKD and BTK [ 26 , 38 ]. While our knowledge of inflammasome pathway phosphorylation has expanded, it is difficult to reconcile the numerous phosphorylation and dephosphorylation events that have been reported.…”

“…Both groups observed that BTK could directly interact with NLRP3 and ASC, but whether BTK could directly phosphorylate NLRP3 was unknown [ 36 , 37 ]. A recent study from Bittner et al [ 38 ] identified direct BTK-mediated phosphorylation of NLRP3 and linked this to the subcellular location of NLRP3. A polybasic motif in the linker region between the PYD and NACHT of NLRP3 is critical for binding to phosphatidylinositol-4-phosphate on the trans-Golgi network and subsequent inflammasome activation [ 27 ].…”

“…Stimulation of NLRP3 with nigericin induces BTK-mediated phosphorylation of NLRP3 that weakens the interaction between NLRP3 and the Golgi. NLRP3 is consequently released, allowing NLRP3 oligomerisation and inflammasome formation in the cytosol [ 38 ]. However, as discussed above in relation to Ser5, Mao et al [ 20 ] have characterised BTK as a negative regulator of NLRP3.…”

The Role of Inflammasomes in Osteoarthritis and Secondary Joint Degeneration Diseases

“…Considering the indirect inhibitors of NLRP3, Bruton’s tyrosine kinase (BTK) inhibitors, such as ibrutinib and evobrutinib, are being explored for the treatment of autoimmune diseases [ 152 ]. BTK was shown to be directly involved in NLRP3 inflammasome activation [ 153 , 154 , 155 ]. Fenebrutinib has successfully passed a phase II clinical trial as a selective, reversible BTK inhibitor for the treatment of patients with RA who have a poor response to methotrexate therapy [ 156 ].…”

Posttranslational Regulation of Inflammasomes, Its Potential as Biomarkers and in the Identification of Novel Drugs Targets

“…BTK kinase activity inhibits PP2A function and thereby lead to inhibition of NLRP3 de-phosphorylation of Ser5 of NLRP3 in PYD domain preventing its oligomerization ( Mao et al, 2020 ). Recently, four tyrosine residues have been identified by Bittner et al (2021) as direct BTK phosphorylation upon in vitro and in vivo inflammasome activation. These sites are Tyr136, Tyr140, Tyr143, and Tyr164, that are situated in the polybasic linker between PYD and NACHT domains, which is critical for interaction with negatively charged phosphatidylinositol phosphates (PIPs) at organelles, such as the Golgi.…”