title: ELMO1 has an essential role in the internalization ofSalmonellaTyphimurium into enteric macrophages that impacts disease outcome.
abstract: OBJECTIVE
  4-6 million people die of enteric infections each year. After invading intestinal epithelial cells, enteric bacteria encounter phagocytes. However, little is known about how phagocytes internalize the bacteria to generate host responses. Previously, we have shown that BAI1 (Brain Angiogenesis Inhibitor 1) binds and internalizes Gram-negative bacteria through an ELMO1 (Engulfment and cell Motility protein 1)/Rac1-dependent mechanism. Here we delineate the role of ELMO1 in host inflammatory responses following enteric infection.
  
  
  METHODS
  ELMO1-depleted murine macrophage cell lines, intestinal macrophages and ELMO1 deficient mice (total or myeloid-cell specific) was infected withSalmonellaenterica serovar Typhimurium. The bacterial load, inflammatory cytokines and histopathology was evaluated in the ileum, cecum and spleen. The ELMO1 dependent host cytokines were detected by a cytokine array. ELMO1 mediated Rac1 activity was measured by pulldown assay.
  
  
  RESULTS
  The cytokine array showed reduced release of pro-inflammatory cytokines, including TNF-α and MCP-1, by ELMO1-depleted macrophages. Inhibition of ELMO1 expression in macrophages decreased Rac1 activation (~6 fold) and reduced internalization ofSalmonella. ELMO1-dependent internalization was indispensable for TNF-α and MCP-1. Simultaneous inhibition of ELMO1 and Rac function virtually abrogated TNF-α responses to infection. Further, activation of NF-κB, ERK1/2and p38 MAP kinases were impaired in ELMO1-depleted cells. Strikingly, bacterial internalization by intestinal macrophages was completely dependent on ELMO1.Salmonellainfection of ELMO1-deficient mice resulted in a 90% reduction in bacterial burden and attenuated inflammatory responses in the ileum, spleen and cecum.
  
  
  CONCLUSIONS
  These findings suggest a novel role for ELMO1 in facilitating intracellular bacterial sensing and the induction of inflammatory responses following infection withSalmonella.
authors.affiliation: Dept of Pathology, University of California San Diego.
authors.forename: Soumita
authors.initials: S
authors.lastname: Das
authors.affiliation: Dept of Pathology, University of California San Diego.
authors.forename: Arup
authors.initials: A
authors.lastname: Sarkar
authors.affiliation: Dept of Pathology, University of California San Diego.
authors.forename: Sarmistha Sinha
authors.initials: SS
authors.lastname: Choudhury
authors.affiliation: Dept of Cell Biology, University of Virginia, Charlottesville.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Owen
authors.affiliation: Dept of Pathology, University of California San Diego.
authors.forename: Victoria
authors.initials: V
authors.lastname: Castillo
authors.affiliation: Dept of Pathology, University of California San Diego.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fox
authors.affiliation: Dept of Medicine, University of California San Diego.
authors.forename: Lars
authors.initials: L
authors.lastname: Eckmann
authors.affiliation: Dept of Microbiology and Immunology, University of Rochester School of Medicine.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Elliott
authors.affiliation: Dept of Cell Biology, University of Virginia, Charlottesville.
authors.forename: James E
authors.initials: JE
authors.lastname: Casanova
authors.affiliation: Dept of Pathology, University of California San Diego.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Ernst
keywords: Engulfment pathway; Enteric infection; Host cellular responses; Intestinal inflammation; Salmonella