Toll-like receptor 4 regulates spontaneous intestinal tumorigenesis by up-regulating IL-6 and GM-CSF

Inflammation is as an important component of intestinal tumorigenesis. The activation of Toll-like Receptor 4 (TLR4) signalling promotes inflammation in colitis of mice, but the role of TLR4 in intestinal tumorigenesis is not yet clear. About 80%-90% of colorectal tumours contain inactivating mutations in the adenomatous polyposis coli (APC) tumour suppressor, and intestinal adenoma carcinogenesis in familial adenomatous polyposis (FAP) is also closely related to the germline mutations in APC. The APC^Min/+ (multiple intestinal neoplasia) model mouse is a well-utilized model of FAP, an inherited form of intestinal Cancer. In this study, APC^Min/+ intestinal adenoma mice were generated on TLR4-sufficient and TLR4-deficient backgrounds to investigate the carcinogenic effect of TLR4 in mouse gut by comparing mice survival, peripheral blood cells, bone marrow haematopoietic precursor cells and numbers of polyps in the guts of APC^Min/+ WT and APC^Min/+ TLR4^-/- mice. The results revealed that TLR4 had a critical role in promoting spontaneous intestinal tumorigenesis. Significant differential genes were screened out by the high-throughput RNA-Seq method. After combining these results with KEGG enrichment data, it was determined that TLR4 might promote intestinal tumorigenesis by activating cytokine-cytokine receptor interaction and pathways in Cancer signalling pathways. After a series of validation experiments for the concerned genes, it was found that IL6, GM-CSF (CSF2), IL11, CCL3, S100A8 and S100A9 were significantly decreased in gut tumours of APC^Min/+ TLR4^-/- mice compared with APC^Min/+ WT mice. In the functional study of core down-regulation factors, it was found that IL6, GM-CSF, IL11, CCL3 and S100A8/9 increased the viability of colon Cancer cell lines and decreased the Apoptosis rate of colon Cancer cells with irradiation and chemical treatment.