Uropathogenic Escherichia coli induces extrinsic and intrinsic cascades to initiate urothelial apoptosis

David J. Klumpp*, Matthew T. Rycyk, Michael C. Chen, Praveen Thumbikat, Shomit Sengupta, Anthony J. Schaeffer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

61 Scopus citations

Abstract

A murine model of urinary tract infection identified urothelial apoptosis as a key event in the pathogenesis mediated by uropathogenic Escherichia coli (UPEC), yet the mechanism of this important host response is not well characterized. We employed a culture model of UPEC-urothelium interactions to examine the biochemical events associated with urothelial apoptosis induced by the UPEC strain NU14. NU14 induced DNA cleavage within 5 h that was inhibited by the broad caspase inhibitor ZVAD, and urothelial caspase 3 activity was induced within 3 h of exposure to type 1 piliated NU14 and was dependent upon interactions mediated by the type 1 pilus adhesin FimH. Flow cytometry experiments using chloromethyl-X-rosamine and Indo-1 revealed FimH-dependent mitochondrial membrane depolarization and elevated [Ca2+] in, respectively, indicating activation of the intrinsic apoptotic pathway. Consistent with this possibility, overexpression of BclXL inhibited NU14 activation of caspase 3. Immunoblotting, caspase inhibitors, and caspase activity assays implicated both caspase 2 and caspase 8 in apoptosis, suggesting the involvement of the intrinsic and extrinsic apoptotic cascades. To reconcile the apparent activation of both extrinsic and intrinsic pathways, we examined Bid-green fluorescent protein localization and observed translocation from the cytosol to mitochondria in response to either NU14 or purified FimH. These data suggest that FimH acts as a tethered toxin of UPEC that activates caspase-dependent urothelial apoptosis via direct induction of the extrinsic pathway and that the intrinsic pathway is activated indirectly as a result of coupling by caspase 8-mediated Bid cleavage.

Original languageEnglish (US)
Pages (from-to)5106-5113
Number of pages8
JournalInfection and immunity
Volume74
Issue number9
DOIs
StatePublished - Sep 2006

ASJC Scopus subject areas

  • Parasitology
  • Microbiology
  • Immunology
  • Infectious Diseases

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