TLR4 Activates the β-catenin Pathway to Cause Intestinal Neoplasia

Abstract

Colonic bacteria have been implicated in the development of colon cancer. We have previously demonstrated that toll-like receptor 4 (TLR4), the receptor for bacterial lipopolysaccharide (LPS), is over-expressed in humans with colitis-associated cancer. Genetic epidemiologic data support a role for TLR4 in sporadic colorectal cancer (CRC) as well, with over-expression favoring more aggressive disease. The goal of our study was to determine whether TLR4 played a role as a tumor promoter in sporadic colon cancer. Using immunofluorescence directed to TLR4, we found that a third of sporadic human colorectal cancers over-express this marker. To mechanistically investigate this observation, we used a mouse model that over-expresses TLR4 in the intestinal epithelium (villin-TLR4 mice). We found that these transgenic mice had increased epithelial proliferation as measured by BrdU labeling, longer colonic crypts and an expansion of Lgr5+ crypt cells at baseline. In addition, villin-TLR4 mice developed spontaneous duodenal dysplasia with age, a feature that is not seen in any wild-type (WT) mice. To model human sporadic CRC, we administered the genotoxic agent azoxymethane (AOM) to villin-TLR4 and WT mice. We found that villin-TLR4 mice showed an increased number of colonic tumors compared to WT mice as well as increased β-catenin activation in non-dysplastic areas. Biochemical studies in colonic epithelial cell lines revealed that TLR4 activates β-catenin in a PI3K-dependent manner, increasing phosphorylation of β-cateninSer552, a phenomenon associated with activation of the canonical Wnt pathway. Our results suggest that TLR4 can trigger a neoplastic program through activation of the Wnt/β-catenin pathway. Our studies highlight a previously unexplored link between innate immune signaling and activation of oncogenic pathways, which may be targeted to prevent or treat CRC.

Eritoran Suppresses Colon Cancer by Altering a Functional Balance in Toll-like Receptors That Bind Lipopolysaccharide

“…Our results are in agreement with previous studies showing that TLR4 is involved in colon cancer growth (5,(13)(14)(15)45). We concluded that the anticancer effect of eritoran in in vivo animal models is predominantly via direct actions on tumorous epithelial cells.…”

“…Accumulating evidence suggests that LPS receptors are involved in the dysregulation of epithelial apoptosis and proliferation that predisposes the tissue of the colon to tumorigenesis. Previous animal studies have indicated that TLR4/ MyD88 signaling causes tumor cell hyperproliferation via pathways dependent on cyclooxygenase (COX), EGFR, and b-catenin (5,(13)(14)(15). In vitro studies have shown a direct effect of LPS via TLR4/MD2 signaling on the stimulation of intestinal epithelial cell proliferation and a resistance to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis (16)(17)(18).…”

CD44 and TLR4 mediate hyaluronic acid regulation of Lgr5+ stem cell proliferation, crypt fission, and intestinal growth in postnatal and adult mice

“…This is consistent with the observation that overexpression of TLR4 in intestinal epithelial cells results in increases in Lgr5 ϩ cell number and proliferation (17). Although the role of TLR4 activation in normal small intestinal growth has not been previously addressed, TLR4 signaling is required for the enhanced colonic epithelial response seen in the repair of DSS colitis (2,6,14).…”

Toll-like receptor 2 and -4 are involved in the pathogenesis of the Guillain-Barré syndrome

“…The cell concentration was determined using the Sysmex XT-4000i hematology analyzer (Sysmex, Kobe, Japan). PBMCs were cultured in 24 well-plates and each well consisted of RPMI 1640 medium supplemented with 10% fetal calf serum (Invitrogen Life Technologies), 10 6 PBMCs and the respective agonist. Following incubation for 24 h in an SS-23062 carbon dioxide incubator (SHEL LAB, Cornelius, OR, USA) with 5% CO 2 , the supernatant was harvested, and TNF-α and IL-1β were measured using the IMMULITE 1000 immunoassay system (Siemens Healthcare Diagnostics, Erlangen, Germany) according to the manufacturer's instructions.…”

“…Each sub-type is able to recognize a specific ligand. For example, TLR2 recognizes peptidoglycan (PGN) (5) and TLR4 recognizes lipopolysaccharide (LPS) (6). After recognizing specific ligands, TLRs signal through myeloid differentiation factor (MyD)88-dependent or -independent pathways.…”