Infection of human intestinal epithelial cells by invasive bacteria activates NF-κB and increases ICAM-1 expression through NOD₁

Background/Aims: Nucleotide-binding oligomerization domain ${\text\tiny{1}}$($NOD{\text\tiny{1}}$) is required for primary intestinal epithelial cells (IECs) to respond to natural mucopeptides secreted by gram-negative bacteria. Infection of human IECs with invasive bacteria up-regulates intercellular adhesion $molecule-{\text\tiny{1}}$ ($ICAM-{\text\tiny{1}}$) expression. However, the role of NOD family members in host defense has been largely unknown. The aim of this study was to determine whether there is a functional role for $NOD{\text\tiny{1}}$ in the up-regulation of $ICAM-{\text\tiny{1}}$ expression in invasive bacteria-infected IECs. Methods: $ICAM-{\text\tiny{1}}$ mRNA expression was compared between controls, $Caco-{\text\tiny{2}}$ or $HT{\text\tiny{29}}$ cells transfected with an empty vector, and IECs stably transfected with a dominant-negative (DN) $NOD{\text\tiny{1}}$. Expression was compared using qualitative reverse transcription polymerase chain reaction (RT-PCR), real-time RT-PCR, and flow cytometry after infection with enteroinvasive Escherichia coli $O{\text\tiny{29}}$:NM or Shigella flexneri. Nuclear factor ${\kappa}B$ ($NF-{\kappa}B$) activation was determined by electrophoretic mobility shift assays. Results: DN $NOD{\text\tiny{1}}$ significantly inhibited the up-regulation of $ICAM-{\text\tiny{1}}$ expression in response to an enteroinvasive bacterial infection. The $Caco-{\text\tiny{2}}$ cells transfected with DN $NOD{\text\tiny{1}}$ manifested marked inhibition of $NF-{\kappa}B$ activation in response to E. coli $O{\text\tiny{29}}$:NM infection. Conclusions: Signaling through $NOD{\text\tiny{1}}$ may play an essential role in neutrophil trafficking following infection with enteroinvasive bacteria.