Induction of Guanylate Binding Protein 5 by Gamma Interferon Increases Susceptibility toSalmonella entericaSerovar Typhimurium-Induced Pyroptosis in RAW 264.7 Cells

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Abstract
The regulation of caspase-1 activation in macrophages plays a central role in host defense against bacterial pathogens. The activation of caspase-1 by the detection of bacterial products through Nod-like receptors leads to the secretion of mature interleukin-1β (IL-1β) and IL-18 and the induction of rapid host cell death (pyroptosis). Here, we report that pyroptosis induced bySalmonella entericaserovar Typhimurium can be positively regulated by prior gamma interferon (IFN-γ) stimulation of RAW 264.7 cells. This increase in cell death is dependent on both caspase-1 activation and, in part,Salmonellapathogenicity island 1 (SPI-1) expression bySalmonella. Furthermore, the exogenous expression of the IFN-γ-induced protein guanylate binding protein 5 (GBP-5) is sufficient to induce a heightened susceptibility of RAW 264.7 cells toSalmonella-induced pyroptosis, and the endogenous expression of GBP-5 is important for this phenomenon. RAW 264.7 cells with decreased expression of GBP-5 mRNA (inhibited by short hairpin RNA against GBP-5) release twofold less lactate dehydrogenase (a marker of membrane permeability) upon infection by invasiveS. entericaserovar Typhimurium than do infected control cells. Importantly, 3× FLAG-tagged GBP-5 is localized to membrane ruffles, which contact invasiveSalmonella, and is found on the membranes of spacious phagosomes containingSalmonella(although it is also found in the cytoplasm and on other cellular membranes), placing 3× FLAG GBP-5 at the interface of secreted SPI-1 effectors and host protein machinery. The regulation of pyroptosis by the IFN-γ-induced protein GBP-5 may play an important role in the host defense againstSalmonella entericaserovar Typhimurium and perhaps other invasive bacterial pathogens.