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

Abstract

The potassium ionophore nigericin induces cell death and promotes the maturation and release of IL-1b in lipopolysaccharide (LPS)-primed monocytes and macrophages, the latter depending on caspase-1 activation by an unknown mechanism. Here, we investigate the pathway that triggers cell death and activates caspase-1. We show that without LPS priming, nigericin alone triggered caspase-1 activation and IL-18 generation in THP-1 monocytic cells. Simultaneously, nigericin induced caspase-1-independent necrotic cell death, which was blocked by the cathepsin B inhibitor CA-074-Me and other cathepsin inhibitors. Cathepsin B activation after nigericin treatment was determined biochemically and corroborated by rapid lysosomal leakage and translocation of cathepsin B to the cytoplasm. IL-18 maturation was prevented by both caspase-1 and cathepsin B inhibitors in THP-1 cells, primary mouse macrophages and human blood monocytes. Moreover, IL-18 generation was reduced in THP-1 cells stably transformed either with cystatin A (an endogenous cathepsin inhibitor) or antisense cathepsin B cDNA. Collectively, our study establishes a critical role for cathepsin B in nigericin-induced caspase-1-dependent IL-18 maturation and caspase-1-independent necrosis.

P2X7 receptor polymorphism impairs extracellular adenosine 5′-triphosphate-induced interleukin-18 release from human monocytes

“…Incubation of wild-type monocytes with ATP for 60 min produced a release of IL-18 of 306752 pg/ml (n ¼ 7), while ATP incubation of homozygous monocytes produced a release of IL-18 of 138744 pg/ml (n ¼ 4), which was 44% of that observed for wild-type subjects (Po0.02; Figure 1b). In contrast, 60 min incubation of monocytes with nigericin, which can induce the release of IL-18 from monocytes, 16 resulted in a similar release of IL-18 from wild-type and homozygote monocytes (299778 pg/ml, n ¼ 6 vs 295761 pg/ml, n ¼ 3 respectively, P ¼ 0.95; Figure 1b). Thereby indicating that the impaired ATP-induced IL-18 release from homozygous monocytes was not due to differences in endogenous IL-18 levels or defects in the export mechanism responsible for IL-18 release.…”

“…4,5 In addition, the K þ ionophore, nigericin, has recently been shown to cause the release of IL-18 from human monocytes. 16 Given the central role of IL-18 in immunity and inflammation, the Glu 496 Ala polymorphism 11 and other, rarer loss-of-function polymorphisms in the P2X 7 receptor 23,24 may have clinical significance. Impaired ATPinduced release of IL-18 may play an important role in diseases where reduced or absent levels of IL-18 are known to increase susceptibility to mycobacteria and certain bacteria, and severity of septic arthritis and endotoxic shock.…”

Macrophage and microglia ontogeny in the mouse visual system can be traced by the expression of Cathepsins B and D

“…Among these, cathepsin B is involved in the degradation of cellular proteins in lysosomes and functions as an endopeptidase at neutral pH. It is also found in extralysosomal sites, such as the cytosol, plasma membrane, and pericellular spaces, where it participates in several cell processes including cancer metastasis and inflammation Hentze et al, 2003;Roshy et al, 2003). The major function of cathepsin D is the digestion of peptides and proteins within the acidic compartment of lysosomes (Dean, 1975), although it contributes to other physiological roles, such as hormone and antigen processing (Mizuochi et al, 1994;Authier et al, 1995), cell proliferation, and tissue renewal (Saftig et al, 1995), or cell differentiation (Jane et al, 2002).…”

IL‐18 associates to microvesicles shed from human macrophages by a LPS/TLR‐4 independent mechanism in response to P2X receptor stimulation

“…A decrease in the intracellular K + concentration is known to activate pro-casp-1 and accordingly high extracellular K + concentration inhibits pro-casp-1 activation [35,36]. Therefore, Figure 9C shows that stimulation of macrophages with BzATP in a high K + -containing saline solution (high K + ), low MW IL-18 (white arrowhead) was still present associated to MVs.Cathepsin B has been involved in pro-IL-18 processing [37]. Macrophages were thus incubated with LPS, rinsed, and pretreated in culture medium for 1 h with the cathepsin B inhibitor Ca-074Me.…”