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-α. We hypothesized that early during infection, Kupffer cells are protected against TNF-α-induced cell death via activation of survival pathways. KC13-2 cells (a clonal Kupffer cell line) were treated with P. aeruginosa (strain PA103), TNF-α, or both. At early time points, TNF-α induced caspase-mediated cell death, but PA103 did not. When we combined the two exposures, PA103 protected KC13-2 cells from TNF-α-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-α-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-α-induced cell death and XIAP cleavage. Transfection with a stable, nondegradable XIAP mutant also protected cells against TNF-α-induced cell death. These studies demonstrate that P. aeruginosa delays TNF-α-induced Kupffer cell death via stabilization of XIAP.

Inactivation of Host Akt/Protein Kinase B Signaling by Bacterial Pore-forming Toxins

“…Some bacterial pathogens are known to actively modulate Akt signaling by secreting effector proteins into target host cells (Edwards and Apicella, 2006;Knodler et al, 2005;Pendaries et al, 2006;Ashare et al, 2007). To address this possibility with UPEC, we infected 5637 bladder cells with either live or gentamicin-killed UTI89.…”

“…Similarly, cytotoxic necrotizing factor 1 (CNF1), a secreted toxin encoded by a number of E. coli pathogens, including some UPEC isolates, can prevent host cell apoptosis by the stimulation of Akt and subsequent NF B activation (Miraglia et al, 2007). Pseudomonas aeruginosa can also protect target host cells from death, apparently via stabilization of the X-chromosome-linked inhibitor of apoptosis protein, downstream of Akt activation by as-yet unidentified bacterial factor(s) (Ashare et al, 2007). Interestingly, P. aeruginosa not only stimulates Akt phosphorylation but also requires Akt activation to effectively invade target host cells, as does N. gonorrhoeae (Kierbel et al, 2005;Edwards and Apicella, 2006).…”

“…UTI89 caused a marked decline in S473 phosphorylation by 90 min after infection, whereas infection with AAEC185/pSH2 did not ( Figure 1A). These results were quantified and normalized by dividing pAkt S473 levels by total Akt1 levels, as shown in the graph in Figure 1A.Some bacterial pathogens are known to actively modulate Akt signaling by secreting effector proteins into target host cells (Edwards and Apicella, 2006;Knodler et al, 2005;Pendaries et al, 2006;Ashare et al, 2007). To address this possibility with UPEC, we infected 5637 bladder cells with either live or gentamicin-killed UTI89.…”

Hyperglycemia induces apoptosis in rat liver through the increase of hydroxyl radical: new insights into the insulin effect

“…This is the first study to show that insulin has anti-apoptotic action, at least in part, through XIAP induction in rat liver. Other authors had reported that XIAP is stabilized via the activation of AKT in Kupffer cells (Ashare et al 2007). Moreover, XIAP is known to be phosphorylated at serine 87 by Akt, and this phosphorylation stabilizes the protein (Dan et al 2004).…”

Molecular Mechanisms of Host-Pathogen Interactions and their Potential for the Discovery of New Drug Targets

“…Pseudomonas aeruginosa is an important human pathogen that inhibits TNF-α induced macrophage cell death [104] and infection-induced cell death in corneal epithelial cells [105]. In the related plant pathogen P. syringae secreted protein AvrPtoB has been demonstrated to have E3 ubiquitin ligase activity and that this activity is necessary to inhibit host cell apoptosis [106,107].…”