Uropathogenic Escherichia coli Potentiates Type 1 Pilus-Induced Apoptosis by Suppressing NF-κB

Abstract

Urinary tract infections (UTIs) are among the most common inflammatory diseases. Acute UTIs are typically caused by type 1-piliated Escherichia coli and result in urothelial apoptosis, local cytokine release, and neutrophil infiltration. To examine the urothelial apoptotic response, a human urothelial cell line was incubated with various E. coli isolates and was then characterized by flow cytometry. Uropathogenic E. coli (UPEC) induced rapid urothelial apoptosis that was strictly dependent upon interactions mediated by type 1 pili. Interestingly, nonpathogenic HB101 E. coli expressing type 1 pili induced apoptosis at approximately 50% of the level induced by UPEC, suggesting that pathogenic strains contribute to apoptosis by pilus-independent mechanisms. Consistent with this possibility, UPEC blocked activity of an NF-B-dependent reporter in response to inflammatory stimuli, yet this effect was independent of functional type 1 pili and was not mediated by laboratory strains of E. coli. UPEC suppressed NF-B by stabilizing IB␣, and UPEC rapidly altered cellular signaling pathways. Finally, blocking NF-B activity increased the level of piliated HB101-induced apoptosis to the level of apoptosis induced by UPEC. These results suggest that UPEC blocks NF-B and thereby enhances type 1 pili-induced apoptosis as a component of the uropathogenic program.Urinary tract infections (UTIs) are among the most common infectious diseases, resulting in over 7 million clinic visits annually in the United States alone (7) and causing significant morbidity and mortality. The majority of UTIs are due to ascending infections of the urinary bladder (cystitis) by Escherichia coli that expresses type 1 pili, fibrous organelles that mediate attachment to mannosylated host cell proteins (reviewed in reference 19). The infection process results in bladder inflammation that causes symptoms such as pain and frequent or urgent voiding. Given the emergence of antibiotic-resistant strains of uropathogenic E. coli (UPEC) (A. J. Schaeffer, Editorial, Curr. Opin. Urol. 10:23-24, 2000), a more thorough understanding of pathogenic mechanisms is necessary to identify novel therapeutic targets for the treatment and prevention of UTIs.A key feature of inflammation during UTIs is a disruption of the urothelial integrity due to the exfoliation and subsequent excretion of superficial urothelial cells (4). Studies with mice have shown that UPEC induces a rapid loss of superficial urothelial cells, and the sloughing of superficial cells is due to the induction of apoptosis (12). This apoptotic process is dependent upon the expression of intact type 1 pili, since fimH mutant UPEC strains lacking the adhesin subunit FimH that forms the pilus tip fail to induce apoptosis, yet laboratory strains of E. coli induce apoptosis if they express intact type 1 pili. As a result of the urothelial apoptotic response, clearance of a majority of UPEC from the bladder occurs during voiding of urine. Thus, urothelial apoptosis is considered to be an important host defense in r...

Role of biofilm in catheter-associated urinary tract infection☆

“…[6][7][8][9] Both processes contribute to clearance of the bacteria from the mucosal surface. In contrast, catheter surfaces have no inherent defense mechanisms.…”

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

“…During the course of an infection, UPEC can stimulate a number of antimicrobial, proinflammatory, prodifferentiation, proliferation, and host cell death pathways (Mulvey, 2002;Mysorekar et al, 2002). In some cases, UPEC can reportedly modulate these signaling events, causing attenuation of host inflammatory responses and potentiating host apoptotic cascades (Klumpp et al, 2001(Klumpp et al, , 2006Hunstad et al, 2005;Billips et al, 2007). These phenomena have been linked in part to the suppression of nuclear factor-B (NF B) activation and downstream signaling by unknown factors associated with UPEC (Klumpp et al, 2001;Hunstad et al, 2005).…”

“…In some cases, UPEC can reportedly modulate these signaling events, causing attenuation of host inflammatory responses and potentiating host apoptotic cascades (Klumpp et al, 2001(Klumpp et al, , 2006Hunstad et al, 2005;Billips et al, 2007). These phenomena have been linked in part to the suppression of nuclear factor-B (NF B) activation and downstream signaling by unknown factors associated with UPEC (Klumpp et al, 2001;Hunstad et al, 2005). By hindering host cytokine expression and ensuing inflammatory responses, UPEC may be better able to establish itself and multiply within the cells and tissues of the urinary tract.…”

Characterization of tight junction proteins in cultured human urothelial cells

“…TEU-2 cells were generated by immortalization of normal human ureteral cells with human papillomavirus type 16E6E7 (Klumpp et al 2001). Cultures were grown in EpiLife ® .…”

“…TEU-2 cells are an immortalized cell line derived from normal human ureter (Klumpp et al 2001) that form a stratified epithelium in vitro and thus provide a potential model for studies on the presence, distribution and junctional properties of TJs. Our observations characterize the presence and distribution of specific TJ elements in cultured urothelial cells and provide reference data for future studies on the involvement of TJs in pathological conditions of the urinary system.…”