Abstract
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 ApcMin/+ (multiple intestinal neoplasia) model mouse is a well‐utilized model of FAP, an inherited form of intestinal cancer. In this study, ApcMin/+ 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 ApcMin/+ WT and ApcMin/+ 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 ApcMin/+ TLR4−/− mice compared with ApcMin/+ 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.
Highlights
Colorectal cancer (CRC) has become the second leading cause of cancer‐related death in developed countries
The results revealed that the mean proportion of megakaryocyte‐erythroid progenitors (MEP) in bone marrow cells (BMCs) was 6.35% in ApcMin/+ WT mice, which was lower than 9.2% in ApcMin/+Toll‐like receptor 4 (TLR4)−/− mice (P < .05) (Figure 2A,B)
ApcMin/+ intestinal adenoma mice were generated on TLR4‐sufficient and TLR4‐deficient backgrounds to investigate the carcinogenic effect of TLR4 by comparing mice survival, peripheral blood cells, bone marrow haematopoietic precursor cells and numbers of polyps in the guts of ApcMin/+ WT and ApcMin/+ TLR4 mice
Summary
Colorectal cancer (CRC) has become the second leading cause of cancer‐related death in developed countries. Along with axin and glycogen synthase kinase 3b (GSK3b), assembles a protein complex that targets β‐catenin for degradation, which is regulated by Wnt signalling.[5] This is the main mechanism of Apc mutation leading to tumorigenesis, as the resulting increased availability of β‐catenin causes changes in the transcriptional process to decrease the amount of cell differentiation.[6]. It has been reported that TLR4‐deficient C3H/HeJ mice developed more tumours relative to TLR4‐normal C3H/HeN mice.[15] This suggests that TLR4 may have a role in inhibiting tumorigenesis. High‐throughput sequencing was used to screen out the production of TLR4 signalling downstream genes and validate them in a variety of ways These data may provide an insight into the role of TLR4 in intestinal tumorigenesis. The suspensions were mixed well and incubated for 20 min at room temperature in the dark; PBS was added to mix and dilute, and flow cytometry (Beckman Coulter, USA) was used for testing.[18,19]
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