Uropathogenic <i>Escherichia coli</i> Toxins Induce Caspase-Independent Apoptosis in Renal Proximal Tubular Cells via ERK Signaling

Abstract

Background: Pyelonephritis is a risk factor for renal tubular epithelial cell damage. Recent studies have shown that Escherichia coli and/or its toxins may stimulate apoptotic cell death in renal tubular cells, but the underlying molecular mechanisms remain to be elucidated. Methods: Confluent LLC-PK₁ cells were exposed to E. coli toxins from overnight cultures of the uropathogenic O6K13H1 (O6) and the nonpathogenic W3110. The cell death was studied with morphological and biological assay. Results:E. coli soluble toxins from uropathogenic O6:K13:H1(O6) strain were found to induce apoptosis in a dose- and time-dependent manner in LLC-PK1 cells. The expression of FasR and the phosphorylation of ERK1/2 were significantly upregulated by O6 soluble toxins in a time-dependent manner. Cell death was completely inhibited by two specific ERK1/2 inhibitors, but not by a broad caspase inhibitor, zVAD-fmk, implicating a caspase-independent pathway via ERK. Moreover, we found that lysophosphatidic acid could trigger a survival signal through G-proteins and PI3K. Conclusion: We demonstrate that apoptosis induced by uropathogenic E. coli toxins is dependent on ERK1/2. Caspases, although being activated, are not necessary for cell death, and they act after the ERK signaling at which point cells become committed to cell death or can be rescued.

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

“…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. At the same time, UPEC-induced death of bladder and renal epithelial cells can compromise mucosal barriers, and it may thereby facilitate bacterial dissemination and persistence within the urinary tract (Mulvey et al, 1998Chen et al, 2003a;Bower et al, 2005;Eto et al, 2006;Mansson et al, 2007b).…”

“…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. At the same time, UPEC-induced death of bladder and renal epithelial cells can compromise mucosal barriers, and it may thereby facilitate bacterial dissemination and persistence within the urinary tract (Mulvey et al, 1998Chen et al, 2003a;Bower et al, 2005;Eto et al, 2006;Mansson et al, 2007b).A key regulator of host cell survival pathways is Akt (also known as protein kinase B, PKB; for recent reviews, see Fayard et al, 2005;Song et al, 2005;Manning and Cantley, 2007). This serine/threonine kinase is able to inhibit apoptosis, and it can help control cell cycle and metabolic pathways, endocytosis and vesicular trafficking, and host inflammatory responses, including the activation of NF B. Akt is activated downstream of phosphoinositide 3-kinase (PI3-kinase), which itself is activated by integrin signaling, the engagement of G protein-coupled receptors, or the stimulation of receptor tyrosine kinases by insulin or other growth factors (Vanhaesebroeck et al, 2001).…”

Apoptosis-Inducing Factor Participation in Bovine MacrophageMycobacterium bovis-Induced Caspase-Independent Cell Death

“…In addition, data from a different study demonstrated that BH3 domain-only molecules kill cells deficient in the downstream effectors Apaf-1, caspase 9, and caspase 3 by a caspase-independent process of mitochondrial dysfunction (9). CICD has also been associated with hostpathogen interactions; for instance, it has been reported that soluble toxins of Escherichia coli activated CD via extracellular signal-regulated kinase (ERK) signaling in renal proximal tubular epithelial cells without caspase involvement (8). Additionally, Salmond et al (36) demonstrated that the B subunit of E. coli heat-labile enterotoxin (EtxB) induced a rapid loss of mitochondrial membrane potential and cell viability, which were not affected by caspase inhibitors, in CD8 ϩ T cells.…”

Mannheimia haemolytica Leukotoxin Induces Apoptosis of Bovine Lymphoblastoid Cells (BL-3) via a Caspase-9-Dependent Mitochondrial Pathway

“…Several bacteria and their products are known to activate this process by different pathways. For example, the uropathogenic Escherichia coli toxin complex is known to induce apoptosis in a caspase-independent manner, using the extracellular signal-regulated kinase pathway (10). Other examples include activation of p38 mitogen-activated protein kinases in macrophages by anthrax lethal factor and caspase activation in human fibroblast cells incubated with Shiga toxin (27,33,36).…”