title: Nod1 mediates cytoplasmic sensing of combinations of extracellular bacteria.
abstract: During mucosal colonization, epithelial cells are concurrently exposed to numerous microbial species. Epithelial cytokine production is an early component of innate immunity and contributes to mucosal defence. We have previously demonstrated a synergistic response of respiratory epithelial cells to costimulation by two human pathogens, Streptococcus pneumoniae and Haemophilus influenzae. Here we define a molecular mechanism for the synergistic activation of epithelial signalling during polymicrobial colonization. H. influenzae peptidoglycan synergizes with the pore-forming toxin pneumolysin from S. pneumoniae. Radiolabelled peptidoglycan enters epithelial cells more efficiently in the presence of pneumolysin, consistent with peptidoglycan gaining access to the cytoplasm via toxin pores. Other pore-forming toxins (including anthrolysin O from Bacillus anthracis and Staphylococcus aureus alpha-toxin) can substitute for pneumolysin in the generation of synergistic responses. Consistent with a requirement for pore formation, S. pneumoniae expressing pneumolysin but not an isogenic mutant expressing a non-pore-forming toxoid prime epithelial responses. Nod1, a host cytoplasmic peptidoglycan-recognition molecule, is crucial to the epithelial response. Taken together, these findings demonstrate a role for cytosolic recognition of peptidoglycan in the setting of polymicrobial epithelial stimulation. We conclude that combinations of extracellular organisms can activate innate immune pathways previously considered to be reserved for the detection of intracellular microorganisms.
authors.affiliation: Departments of Microbiology and Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA. ar127@columbia.edu
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Ratner
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Aguilar
authors.forename: Mikhail
authors.initials: M
authors.lastname: Shchepetov
authors.forename: Elena S
authors.initials: ES
authors.lastname: Lysenko
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Weiser
mesh_terms: D001419:Bacteria / Q000254:growth & development* / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D004847:Epithelial Cells / Q000378:metabolism / Q000382:microbiology; D006193:Haemophilus influenzae / Q000254:growth & development / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000494:pharmacology; D053474:Nod1 Signaling Adaptor Protein / Q000235:genetics / Q000378:metabolism*; D010457:Peptidoglycan / Q000378:metabolism / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D013296:Streptococcus pneumoniae / Q000254:growth & development / Q000378:metabolism; D013301:Streptolysins / Q000378:metabolism / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D016209:Interleukin-8; D008562:Membrane Glycoproteins; C119067:NOD1 protein, human; D053474:Nod1 Signaling Adaptor Protein; D010457:Peptidoglycan; D034741:RNA, Small Interfering; D013301:Streptolysins; C498000:anthrolysin O, Bacillus anthracis; C032290:plY protein, Streptococcus pneumoniae; D010738:Type C Phospholipases