Having connected ER stress to production of TXNIP, we specifically tested whether ER stress also causes production of IL-1β. Indeed, we find that Tg causes robust IL-1β secretion, as occurs during hyperglycemia in pancreatic islets (Figure 6A); or extracellular ATP, a well-known DAMP and NLRP3 inflammasome activator, in THP-1 macrophage cell lines (Figure 6B). We further tested known signaling events linking activation of the NLRP3 inflammasome to IL-1β production by DAMPs, and found that ER stress causes Caspase-1 cleavage from its zymogen form, as occurs with ATP (Figure 6C). The effects of ER stress on IL-1β appear to be largely post-transcriptional as only modest increases of IL-1β mRNA occur with Tg (Figure S7G). Furthermore, shRNA knock-down of the NLRP3 inflammasome abrogates Caspase-1 cleavage, and IL-1β production, under ER stress (Figure 6D and E), as does a specific inhibitor of Caspase-1, Z-YVAD-FMK (Figure S7H,I).
