Mechanistic basis for nigericin-induced NLRP1 inflammasome activation in human epithelial cells

Abstract

Nigericin, an ionophore derived from Streptomyces hygroscopicus, is arguably the most commonly used tool compound to study the NLRP3 inflammasome. Recent findings, however, showed that nigericin also activates the NLRP1 inflammasome in human keratinocytes. In this study, we resolve the mechanistic basis of nigericin-driven NLRP1 inflammasome activation. In multiple non-hematopoietic cell types, nigericin rapidly and specifically inhibits the elongation stage of the ribosome cycle by depleting cytosolic potassium ions. This activates the ribotoxic stress response (RSR) sensor kinase ZAKalpha, p38 and JNK, as well as the hyperphosphorylation of the NLRP1 linker domain. As a result, nigericin-induced pyroptosis in human keratinocytes is blocked by extracellular potassium supplementation, ZAKalpha knockout or pharmacologic inhibitors of ZAKalpha and p38 kinase activities. By surveying a diverse panel of ionophores, we show that the electroneutrality of potassium efflux is essential to activate ZAKalpha-driven RSR, likely because a greater extent of K+ depletion is necessary to activate ZAKalpha-NLRP1 than NLRP3. These findings resolve the mechanism by which nigericin activates NLRP1 in nonhematopoietic cell types and demonstrate an unexpected connection between RSR, perturbations of potassium ion flux and innate immunity.

Inflammasomes in epithelial innate immunity: front line warriors

“…Once ZAKa is activated, it auto-phosphorylates itself and phosphorylates NLRP1 and MAPKs p38 and c-Jun N-terminal kinase (JNK) and downstream proteins involved in apoptosis and inflammation [151,152]. More recently, bacterial toxins, dsRNA and the NLRP3 agonist nigericin are shown to induce NLRP1 activation through ribosome stalling and activation of the ZAKa/p38 pathway, suggesting that targeting this pathway may serve as a target for a broad spectrum of diseases [154][155][156][157][158][159]. More recently, cytosolic peptide accumulation in combination with reductive stress was found to strongly activate NLRP1 activation.…”

NLRP1- A CINDERELLA STORY: a perspective of recent advances in NLRP1 and the questions they raise

“…Taken together, therefore, it may be proposed that akin to potassium efflux activation of NLRP3 as a common response mechanism to stress in myeloid cells, ribotoxic stress and the subsequent ZAKα-mediated NLRP1 activation is a common response to extrinsic stress inducers in non-myeloid cells. Intriguingly, a recent study from Zhong and colleagues report that the prototypic NLRP3 agonist nigericin activates NLRP1 in primary human skin, nasal and corneal epithelial cells 52 . NLRP1 activation by nigericin requires K + efflux-driven ribosome stalling and the ribotoxic stress response sensor, ZAKα.…”