DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis

Abstract

Val-boroPro (talabostat, PT-100), a nonselective inhibitor of post-proline cleaving serine proteases, stimulates mammalian immune systems through an unknown mechanism of action. Despite this lack of mechanistic understanding, Val-boroPro has attracted significant interest as a potential anticancer agent, reaching Phase III trials in humans. Here we show that Val-boroPro stimulates the immune system by triggering a proinflammatory form of cell death in monocytes and macrophages known as pyroptosis. We demonstrate that the inhibition of two serine proteases, DPP8 and DPP9, activates the proprotein form of caspase-1 independent of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β, but does cleave and activate gasdermin D to induce pyroptosis. Mice lacking caspase-1 do not show immune stimulation after treatment with Val-boroPro. Our data identifies the first small molecule that induces pyroptosis and reveals a new checkpoint that controls the activation of the innate immune system.

Pyroptosis and Apoptosis Pathways Engage in Bidirectional Crosstalk in Monocytes and Macrophages

“…Similar to the results in RAW 264.7 macrophages, we observed that Val-boroPro treatment of GSDMD −/− THP-1 cells (Okondo, et al, 2017), but not control or CASP1 −/− cells, induced PARP cleavage (Fig. 2A, Fig.…”

“…We previously showed that knockout of GSDMD delayed, but did not entirely prevent, DPP8/9 inhibitor-induced cell death in human THP-1 macrophages (Okondo, et al, 2017). To confirm that Gsdmd is similarly not essential for DPP8/9 inhibitor-induced cell death in mouse macrophages, we generated several Gsdmd −/− RAW 264.7 macrophage cell lines using CRISPR/Cas9 gene editing technology (Fig.…”

“…First, in the absence of ASC, the NAIP-NLRC4 and Nlrp1b scaffolds can directly activate pro-caspase-1 without inflammasome complex formation or autoproteolysis (Broz, et al, 2010; Guey, et al, 2014; Van Opdenbosch, et al, 2014). Second, small molecule inhibitors of the cytosolic host serine proteases DPP8 and DPP9, including Val-boroPro (Figure 1A) and L- allo -Ile-isoindoline, can induce pyroptosis via activation of pro-caspase-1 without autoproteolysis through a still unknown mechanism (Okondo, et al, 2017). In both cases, activated pro-caspase-1 cleaves GSDMD and induces pyroptosis, but does not efficiently cleave IL-1β or IL-18.…”

“…Unlike the cell death responses to these microbial stimuli, programmed cell death induced by DPP8/9 inhibitors is entirely dependent on caspase-1 (Okondo, et al, 2017). As such, DPP8/9 inhibitors can serve as useful tools to exclusively activate caspase-1 in cells.…”

Monogenic autoinflammatory disorders: beyond the periodic fever

“…60 PAPA syndrome is caused by heterozygous mutations in PSTPIP1 and although it is understood that the inflammatory manifestations in PAPA syndrome are pyrin dependent, 61,62 the exact mechanism of disease is unclear. [66][67][68][69] An autosomal recessive form of generalised pustular psoriasis has also been described. 63 Two rare dermatological conditions, multiple selfhealing palmoplantar carcinoma and familial keratosis lichenoides chronica, have recently been linked to activating heterozygous mutations in NLRP1.…”