title: Pseudomonas aeruginosa delays Kupffer cell death via stabilization of the X-chromosome-linked inhibitor of apoptosis protein.
abstract: Kupffer cells are important for bacterial clearance and cytokine production during infection. We have previously shown that severe infection with Pseudomonas aeruginosa ultimately results in loss of Kupffer cells and hepatic bacterial clearance. This was associated with prolonged hepatic inflammation. However, there is a period of time during which there is both preserved hepatic bacterial clearance and increased circulating TNF-alpha. We hypothesized that early during infection, Kupffer cells are protected against TNF-alpha-induced cell death via activation of survival pathways. KC13-2 cells (a clonal Kupffer cell line) were treated with P. aeruginosa (strain PA103), TNF-alpha, or both. At early time points, TNF-alpha induced caspase-mediated cell death, but PA103 did not. When we combined the two exposures, PA103 protected KC13-2 cells from TNF-alpha-induced cell death. PA103, in the setting of TNF exposure, stabilized the X-chromosome-linked inhibitor of apoptosis protein (XIAP). Stabilization of XIAP can occur via PI3K and Akt. We found that PA103 activated Akt and that pretreatment with the PI3K inhibitor, LY294002, prevented PA103-induced protection against TNF-alpha-induced cell death. The effects of LY294002 included decreased levels of XIAP and increased amounts of cleaved caspase-3. Overexpression of Akt mimicked the effects of PA103 by protecting cells from TNF-alpha-induced cell death and XIAP cleavage. Transfection with a stable, nondegradable XIAP mutant also protected cells against TNF-alpha-induced cell death. These studies demonstrate that P. aeruginosa delays TNF-alpha-induced Kupffer cell death via stabilization of XIAP.
authors.affiliation: Division of Pulmonary, Critical Care, and Occupational Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, 200 Hawkins Drive, Iowa City, IA 52242, USA. alix-ashare@uiowa.edu
authors.forename: Alix
authors.initials: A
authors.lastname: Ashare
authors.forename: Martha M
authors.initials: MM
authors.lastname: Monick
authors.forename: Amanda B
authors.initials: AB
authors.lastname: Nymon
authors.forename: John M
authors.initials: JM
authors.lastname: Morrison
authors.forename: Matthew
authors.initials: M
authors.lastname: Noble
authors.forename: Linda S
authors.initials: LS
authors.lastname: Powers
authors.forename: Timur O
authors.initials: TO
authors.lastname: Yarovinsky
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Yahr
authors.forename: Gary W
authors.initials: GW
authors.lastname: Hunninghake
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D016470:Bacteremia / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D061945:Caspase Inhibitors; D002460:Cell Line; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D002999:Clone Cells; D006801:Humans; D007728:Kupffer Cells / Q000166:cytology / Q000201:enzymology / Q000378:metabolism* / Q000382:microbiology*; D008099:Liver / Q000166:cytology / Q000382:microbiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis / Q000235:genetics; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
chemical_list: D061945:Caspase Inhibitors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; D051057:Proto-Oncogene Proteins c-akt