Human Procaspase-1 Variants with Decreased Enzymatic Activity Are Associated with Febrile Episodes and May Contribute to Inflammation via RIP2 and NF-κB Signaling

Abstract

The proinflammatory enzyme caspase-1 plays an important role in the innate immune system and is involved in a variety of inflammatory conditions. Rare naturally occurring human variants of the caspase-1 gene (CASP1) lead to different protein expression and structure and to decreased or absent enzymatic activity. Paradoxically, a significant number of patients with such variants suffer from febrile episodes despite decreased IL-1β production and secretion. In this study, we investigate how variant (pro)caspase-1 can possibly contribute to inflammation. In a transfection model, such variant procaspase-1 binds receptor interacting protein kinase 2 (RIP2) via Caspase activation and recruitment domain (CARD)/CARD interaction and thereby activates NF-κB, whereas wild-type procaspase-1 reduces intracellular RIP2 levels by enzymatic cleavage and release into the supernatant. We approach the protein interactions by coimmunoprecipitation and confocal microscopy and show that NF-κB activation is inhibited by anti–RIP2-short hairpin RNA and by the expression of a RIP2 CARD-only protein. In conclusion, variant procaspase-1 binds RIP2 and thereby activates NF-κB. This pathway could possibly contribute to proinflammatory signaling.

Enzymatically Inactive Procaspase 1 stabilizes the ASC Pyroptosome and Supports Pyroptosome Spreading during Cell Division

“…Enhanced interaction between caspase-1 and ASC in cells carrying Ch-C284A compared with Ch-WT cells, which we determined through co-immunoprecipitation and FLIM-FRET, supports this hypothesis. Previously, a similar mechanism was suggested for the interaction between procaspase-1 and RIP2 (14).…”

“…Numerous pro-inflammatory proteins, including PYPAF1, PYPAF5, PYPAF7, and pyrin, may interact with ASC or procaspase-1 either through their CARD or pyrin domain (48 -51). In support of this hypothesis, procaspase-1 variants with disturbed enzymatic activity have been shown to enhance RIP2-mediated NF-B responses in HEK293T cells (14). Caspase-1/RIP2 interactions, however, have been suggested to occur prior to inflammasome assembly (51).…”

“…Cells were lysed and processed as reported previously (14,51). Concentrations of mature IL-1␤ in the supernatant were determined by cytometric bead arrays from BD Biosciences.…”

“…Thus, systemic inflammation in these patients most likely results from the induction of alternative pro-inflammatory pathways. Indeed, enzymatically inactive procaspase-1 variants were documented to maintain prolonged interactions with receptor-interacting protein kinase 2 (RIP2) through its CARD, which results in enhanced NF-B activation, resembling an alternative pro-inflammatory pathway (14).…”

RIP kinases: key decision makers in cell death and innate immunity

“…Intriguingly, some patients with variants of the caspase 1 gene, which encode for forms of procaspase 1 with greatly reduced or absent enzymatic activity, frequently exhibit fever even though levels of IL-1b are low. 183 The latter study demonstrated that the CARD domain of these procaspase 1 variants binds to the CARD of RIP2 to trigger activation of NFkB and presumably downstream inflammatory responses that underpin the regular febrile episodes.…”