title: IFN regulatory factor-2 regulates macrophage apoptosis through a STAT1/3- and caspase-1-dependent mechanism.
abstract: IFN regulatory factor (IRF)-2(-/-) mice are significantly more resistant to LPS challenge than wild-type littermates, and this was correlated with increased numbers of apoptotic Kupffer cells. To assess the generality of this observation, and to understand the role of IRF-2 in apoptosis, responses of peritoneal macrophages from IRF-2(+/+) and IRF-2(-/-) mice to apoptotic stimuli, including the fungal metabolite, gliotoxin, were compared. IRF-2(-/-) macrophages exhibited a consistently higher incidence of apoptosis that failed to correlate with caspase-3/7 activity. Using microarray gene expression profiling of liver RNA samples derived from IRF-2(+/+) and IRF-2(-/-) mice treated with saline or LPS, we identified >40 genes that were significantly down-regulated in IRF-2(-/-) mice, including Stat3, which has been reported to regulate apoptosis. Compared with IRF-2(+/+) macrophages, STAT3alpha mRNA was up-regulated constitutively or after gliotoxin treatment of IRF-2(-/-) macrophages, whereas STAT3beta mRNA was down-regulated. Phospho-Y705-STAT3, phospho-S727-STAT1, and phospho-p38 protein levels were also significantly higher in IRF-2(-/-) than control macrophages. Activation of the STAT signaling pathway has been shown to elicit expression of CASP1 and apoptosis. IRF-2(-/-) macrophages exhibited increased basal and gliotoxin-induced caspase-1 mRNA expression and enhanced caspase-1 activity. Pharmacologic inhibition of STAT3 and caspase-1 abolished gliotoxin-induced apoptosis in IRF-2(-/-) macrophages. A novel IFN-stimulated response element, identified within the murine promoter of Casp1, was determined to be functional by EMSA and supershift analysis. Collectively, these data support the hypothesis that IRF-2 acts as a transcriptional repressor of Casp1, and that the absence of IRF-2 renders macrophages more sensitive to apoptotic stimuli in a caspase-1-dependent process.
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, 600 West Baltimore Street, Baltimore, MD 21201, USA.
authors.forename: Natalia
authors.initials: N
authors.lastname: Cuesta
authors.forename: Quan M
authors.initials: QM
authors.lastname: Nhu
authors.forename: Enrique
authors.initials: E
authors.lastname: Zudaire
authors.forename: Swamy
authors.initials: S
authors.lastname: Polumuri
authors.forename: Frank
authors.initials: F
authors.lastname: Cuttitta
authors.forename: Stefanie N
authors.initials: SN
authors.lastname: Vogel
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D053148:Caspase 3 / Q000096:biosynthesis / Q000276:immunology*; D053179:Caspase 7 / Q000096:biosynthesis / Q000276:immunology*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D005912:Gliotoxin / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D050836:Interferon Regulatory Factor-2 / Q000096:biosynthesis / Q000172:deficiency / Q000276:immunology*; D007728:Kupffer Cells / Q000276:immunology* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D017737:Macrophages, Peritoneal / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011401:Promoter Regions, Genetic / Q000276:immunology; D012097:Repressor Proteins / Q000096:biosynthesis / Q000276:immunology*; D050794:STAT1 Transcription Factor / Q000096:biosynthesis / Q000276:immunology*; D050796:STAT3 Transcription Factor / Q000096:biosynthesis / Q000276:immunology*
chemical_list: D007166:Immunosuppressive Agents; D050836:Interferon Regulatory Factor-2; C494230:Irf2 protein, mouse; D008070:Lipopolysaccharides; D012097:Repressor Proteins; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D005912:Gliotoxin; C505524:Casp7 protein, mouse; D053148:Caspase 3; D053179:Caspase 7