Distinct Roles of the Antiapoptotic Effectors NleB and NleF from Enteropathogenic Escherichia coli

Infect Immun. 2017 Mar 23;85(4):e01071-16. doi: 10.1128/IAI.01071-16. Print 2017 Apr.

Abstract

During infection, enteropathogenic Escherichia coli (EPEC) translocates effector proteins directly into the cytosol of infected enterocytes using a type III secretion system (T3SS). Once inside the host cell, these effector proteins subvert various immune signaling pathways, including death receptor-induced apoptosis. One such effector protein is the non-locus of enterocyte effacement (LEE)-encoded effector NleB1, which inhibits extrinsic apoptotic signaling via the FAS death receptor. NleB1 transfers a single N-acetylglucosamine (GlcNAc) residue to Arg117 in the death domain of Fas-associated protein with death domain (FADD) and inhibits FAS ligand (FasL)-stimulated caspase-8 cleavage. Another effector secreted by the T3SS is NleF. Previous studies have shown that NleF binds to and inhibits the activity of caspase-4, -8, and -9 in vitro Here, we investigated a role for NleF in the inhibition of FAS signaling and apoptosis during EPEC infection. We show that NleF prevents the cleavage of caspase-8, caspase-3, and receptor-interacting serine/threonine protein kinase 1 (RIPK1) in response to FasL stimulation. When translocated into host cells by the T3SS or expressed ectopically, NleF also blocked FasL-induced cell death. Using the EPEC-like mouse pathogen Citrobacter rodentium, we found that NleB but not NleF contributed to colonization of mice in the intestine. Hence, despite their shared ability to block FasL/FAS signaling, NleB and NleF have distinct roles during infection.

Keywords: EPEC; FasL signaling; NleB1; NleF; caspase inhibitor; cell death.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis*
  • Caspases / metabolism
  • Cell Line
  • Ectopic Gene Expression
  • Enteropathogenic Escherichia coli / physiology*
  • Escherichia coli Infections / metabolism*
  • Escherichia coli Infections / microbiology*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Fas Ligand Protein / metabolism
  • Genetic Complementation Test
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Mutation
  • Signal Transduction
  • Virulence Factors / genetics
  • Virulence Factors / metabolism*
  • fas Receptor / metabolism

Substances

  • Escherichia coli Proteins
  • Fas Ligand Protein
  • NleB protein, E coli
  • NleF protein, E coli
  • Virulence Factors
  • fas Receptor
  • Caspases