Increased Mature Interleukin-1β (IL-1β) Secretion from THP-1 Cells Induced by Nigericin Is a Result of Activation of p45 IL-1β-converting Enzyme Processing

Abstract

By contrast, dexamethasone, cycloheximide, and the Na ؉ /H ؉ antiporter inhibitor, 5-(N-ethyl-N-isopropyl)-amiloride, had no effect on nigericin-induced release of IL-1␤. We have therefore shown conclusively, for the first time, that nigericin-induced release of IL-1␤ is dependent upon activation of p45 ICE processing. So far, the mechanism by which reduced intracellular potassium ion concentration triggers p45 ICE processing is not known, but further investigation in this area could lead to the discovery of novel molecular targets whereby control of IL-1␤ production might be effected. Interleukin-1␤ (IL-1␤)1 is produced as an inactive 31-kDa precursor protein through the enzymatic cleavage of IL-1␤-converting enzyme (ICE), which cleaves the IL-1␤ precursor between Asp-116 and Ala-117 (1). ICE itself is produced as a 45-kDa precursor, which has recently been shown to be converted autocatalytically to an active p10/p20 heterodimer (2). The physiological control of ICE processing, and hence IL-1␤ conversion and secretion, is still unknown. Studies by Perregaux et al. (3,4) suggest that IL-1␤ processing is controlled by intracellular potassium ion concentration. Mouse peritoneal macrophages stimulated with LPS produce massive amounts of cell-associated, 31-kDa IL-1␤. Upon addition of the K ϩ /H ϩ ionophore, nigericin, rapid and complete processing of intracellular IL-1␤ occurred with the appearance of mature 17-kDa IL-1␤ in the medium. Similar effects were reported using human peripheral blood monocytes. Although in these studies marked leakage of the cytoplasmic enzyme, lactic acid dehydrogenase (LDH) occurred, suggesting substantial cell damage, it was argued that the effect of nigericin was not due simply to lysis, inasmuch as, unlike the effects of hypotonic shock, at no time were significant levels of proIL-1␤ detected in the culture medium. Furthermore, the nigericin-induced 17-kDa IL-1␤ was shown to have the expected N-terminal sequence. These results, together with studies by Walev et al. (5) showing that high extracellular concentrations of K ϩ or combinations of K ϩ -channel blockers prevented the physiological release of IL-1␤, suggest that a net reduction of intracellular K ϩ ion concentration is necessary for the processing of proIL-1␤. Both Perregaux et al.

Intracellular type III secretion by cytoplasmic Shigella flexneri promotes caspase-1-dependent macrophage cell death

“…The K + /H + antiport ionophore nigericin even increased Shigella cytotoxicity approximately twofold. This result corresponds to reports that nigericin and other treatments leading to potassium depletion in macrophages trigger apoptosis and the release of mature IL-1b by activating caspase-1 (Cheneval et al, 1998;Perregaux & Gabel, 1994;Walev et al, 1995). Thus, in S. flexneriinfected macrophages treated with nigericin, the bacteria and the ionophore seem to synergistically activate caspase-1 and cell death.…”

Kinetics and Mechanism of ATP-Dependent IL-1β Release from Microglial Cells

“…concentration, either by means of selective K ϩ ionophores or inhibitors of plasma membrane K ϩ channels, caused strong activation of IL-1␤ release in its mature form. However, it was not until 1998 that formal demonstration was provided that reducing the K ϩ concentration led to ICE/caspase 1 cleavage (27). The activatory effect of low K ϩ could also be shown on the isolated recombinant enzyme.…”

Critical role for cathepsin B in mediating caspase-1-dependent interleukin-18 maturation and caspase-1-independent necrosis triggered by the microbial toxin nigericin

“…11,12,14,31,44 The LPS-priming step allows S-methionine-labeled caspases 1, 4, 5 and 11 were incubated with purified human cathepsin B in cleavage buffer at the indicated pH. The resulting cleavage products were analyzed by SDS-PAGE and autoradiography.…”

“…[10][11][12][13] Nigericin is a potassium ionophore and thus induces potassium efflux and intracellular acidification, and potassium depletion has been shown to be crucial for enhancing IL-1b processing. 12,13 Recent studies suggested that both ATP and nigericin induce caspase-1 activation in LPS-stimulated cells, 14,15 and ionophore toxins of microbial origin have been shown to induce cell death in certain cell types.…”