Innate immune signaling by Toll-like receptor-4 (TLR4) shapes the inflammatory microenvironment in colitis-associated tumors.
BACKGROUND
Patients with ulcerative colitis are at increased risk for developing colorectal cancer. We have shown that Toll-like receptor-4 (TLR4) is overexpressed in human colitis-associated cancer (CAC) and that mice deficient in TLR4 are markedly protected against colitis-associated neoplasia. We wished to elucidate the specific contributions of TLR4 signaling by myeloid cells and colonic epithelial cells (CEC) in colitis-associated tumorigenesis.


METHODS
TLR4-deficient mice or wildtype littermates (WT) were transplanted with bone marrow (BM) cells: TLR4(-/-) BM-->WT mice (TLR4-expressing CEC) and WT BM-->TLR4(-/-) mice (TLR4-expressing myeloid cells). Colitis-associated neoplasia was induced by azoxymethane (AOM 7.3 mg/kg) injection and 2 cycles of dextran sodium sulfate (DSS) treatment.


RESULTS
The number and size of dysplastic lesions were greater in TLR4(-/-) BM-->WT mice than in WT BM-->TLR4(-/-) mice (P < 0.005). Histologically, TLR4(-/-) BM-->WT mice had greater numbers of mucosal neutrophils and macrophages compared to WT BM-->TLR4(-/-) mice. The chemokines KC and CCL2, important in recruitment of neutrophils and macrophages, respectively, were induced in mice expressing TLR4 in CEC rather than the myeloid compartment. The lamina propria infiltrate of mice expressing TLR4 in CEC was characterized by macrophages expressing Cox-2. Moreover, mice expressing TLR4 in CEC rather than the myeloid compartment had increased production of amphiregulin and EGFR activation.


CONCLUSIONS
These findings indicate that TLR4 signaling on CEC is necessary for recruitment and activation of Cox-2-expressing macrophages and increasing the number and size of dysplastic lesions. Our results implicate innate immune signaling on CEC as a key regulator of a tumor-promoting microenvironment.
Fukata
Masayuki
M
Division of Gastroenterology, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida 33101, USA.
Hernandez
Yasmin
Y
Conduah
Daisy
D
Cohen
Jason
J
Chen
Anli
A
Breglio
Keith
K
Goo
Tyralee
T
Hsu
David
D
Xu
Ruliang
R
Abreu
Maria T
MT
D000818:Animals; D016026:Bone Marrow Transplantation; D003093:Colitis, Ulcerative / Q000453:epidemiology / Q000276:immunology* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000276:immunology* / Q000473:pathology; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000276:immunology; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008264:Macrophages / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D012307:Risk Factors; D015398:Signal Transduction / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
D036341:Intercellular Signaling Peptides and Proteins; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D051546:Cyclooxygenase 2; D015232:Dinoprostone