The single IgG IL-1-related receptor controls TLR responses in differentiated human intestinal epithelial cells.
Intestinal epithelial cells (IECs) are constantly exposed to enteric microbes. Although IECs express TLRs that recognize bacterial products, the activation of these TLRs is strictly controlled through poorly understood mechanisms, producing a state of hyporesponsiveness and preventing unwanted inflammation. The single IgG IL-1-related receptor (Sigirr) is a negative regulator of TLRs that is expressed by IECs and was recently shown to inhibit experimental colitis. However, the importance of Sigirr in IEC hyporesponsiveness and its distribution within the human colon is unknown. In this study, we investigated the role of Sigirr in regulating epithelial-specific TLR responses and characterized its expression in colonic biopsy specimens. Transformed and nontransformed human IECs were cultured as monolayers. Transient gene silencing and stable overexpression of Sigirr was performed to assess innate IEC responses. Sigirr expression in human colonic biopsy specimens was examined by immunohistochemistry. Bacterial infection of IECs and exposure to flagellin transiently decreased Sigirr protein expression, concurrent with secretion of the neutrophil chemokine IL-8. Sigirr gene silencing augmented chemokine responses to bacterial flagellin, Pam3Cys, and the cytokine IL-1beta. Conversely, stable overexpression of Sigirr diminished NF-kappaB-mediated IL-8 responses to TLR ligands. We also found that Sigirr expression increased as IECs differentiated in culture. This observation was confirmed in biopsy sections, in which Sigirr expression within colonic crypts was prominent in IECs at the apex and diminished at the base. Our findings show that Sigirr broadly regulates innate responses in differentiated human IECs; therefore, it may modulate epithelial involvement in infectious and inflammatory bowel diseases.
Division of Pediatric Gastroenterology, BC Children's Hospital, Vancouver, British Columbia V6H 3V4,Canada.
Mohammed A
MA
Khan
Theodore S
TS
Steiner
Ho Pan
HP
Sham
Kirk S
KS
Bergstrom
Jingtian T
JT
Huang
Kiran
K
Assi
Bill
B
Salh
Isabella T
IT
Tai
Xiaoxia
X
Li
Bruce A
BA
Vallance
D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D018938:Caco-2 Cells; D002454:Cell Differentiation; D002460:Cell Line; D003106:Colon / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D004847:Epithelial Cells / Q000378:metabolism* / Q000382:microbiology; D005408:Flagellin / Q000235:genetics / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D019073:HT29 Cells; D006801:Humans; D007150:Immunohistochemistry; D016209:Interleukin-8 / Q000378:metabolism; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D034622:RNA Interference; D017472:Receptors, Interleukin-1 / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051193:Toll-Like Receptors / Q000235:genetics / Q000378:metabolism*
D016209:Interleukin-8; D016328:NF-kappa B; D017472:Receptors, Interleukin-1; C546891:SIGIRR protein, human; D051193:Toll-Like Receptors; D005408:Flagellin