Divergent expression of bacterial wall sensing Toll-like receptors 2 and 4 in colorectal cancer

Toll-like receptors in health and disease

Toll-like receptors (TLRs) are inflammatory triggers and belong to a family of pattern recognition receptors (PRRs) that are central to the regulation of host protective adaptive immune responses. Activation of TLRs in innate immune myeloid cells directs lymphocytes to produce the most appropriate effector responses to eliminate infection and maintain homeostasis of the body's internal environment. Inappropriate TLR stimulation can lead to the development of general autoimmune diseases as well as chronic and acute inflammation, and even cancer. Therefore, TLRs are expected to be targets for therapeutic treatment of inflammation-related diseases, autoimmune diseases, microbial infections, and human cancers. This review summarizes the recent discoveries in the molecular and structural biology of TLRs. The role of different TLR signaling pathways in inflammatory diseases, autoimmune diseases such as diabetes, cardiovascular diseases, respiratory diseases, digestive diseases, and even cancers (oral, gastric, breast, colorectal) is highlighted and summarizes new drugs and related clinical treatments in clinical trials, providing an overview of the potential and prospects of TLRs for the treatment of TLR-related diseases.

Dietary fiber as a wide pillar of colorectal cancer prevention and adjuvant therapy

Colorectal cancer is the third most incident and second most lethal type of cancer worldwide. Lifestyle and dietary patterns are the key factors for higher disease development risk. The dietary fiber intake from fruits and vegetables, mainly formed by food hydrocolloids, can help to lower the incidence of this type of neoplasia. Different food polysaccharides have applications in anti-tumoral therapy, such as coadjuvant to mainstream drugs, carriage-like properties, or direct influence on tumoral cells. Some classes include inulin, β-glucans, pectins, fucoidans, alginates, mucilages, and gums. Therefore, it is fundamental to discuss colorectal cancer mechanisms and the roles played by different polysaccharides in intestinal health. Genetic, environmental, and immunological modulation of mutated pathways regarding colorectal cancer has been explored before. Microbial diversity, byproduct formation (primarily short-chain fatty acids), inflammatory profile control, and tumoral mutated pathways regulation are thoroughly explored mechanisms by which dietary fiber sources influence a healthy gut ambiance.

Comprehensive Bioinformatics Analysis of Toll-Like Receptors (TLRs) in Pan-Cancer

Background

To conduct a comprehensive bioinformatics analysis on the transcriptome signatures of Toll-like receptors (TLRs) in pan-cancer. Materials and methods. A total of 11,057 tissues consisting of 33 types of carcinoma in The Cancer Genome Atlas (TCGA) were retrieved, and then we further explored the correlation between TLRs' expression with tumorigenesis, immune infiltration, and drug sensitivity. We conducted a comprehensive bioinformatics analysis on TLR1 to 10 in pan-cancer, including differential expression analysis between normal and tumor tissues, differential immune subtype correlation, survival analysis, tumor immune infiltration estimating, stemness indices correlation, and drug responses correlation.

Results

TLR2 was highly expressed in most types of tumors. TLR9 was hardly expressed compared to other TLR genes, which lead to TLR9 showing less correlation with both immune-estimate scores and stromal-estimate scores. All the TLRs were related with immune subtype of tumor samples that all of them were differentially expressed in differential immune subtype samples. The expression of TLRs was positively related with immune-estimate scores and stromal-estimate scores in almost all types of tumor. The expression of TLRs was negatively correlated with mRNA expression-based stemness scores (RNAss) in nearly almost type of tumors except kidney renal clear cell carcinoma (KIRC) and also negatively correlated with DNA methylation-based stemness scores (DNAss) in many types of tumors except adrenocortical carcinoma (ACC), cholangiocarcinoma (CHOL), KIRC, acute myeloid leukemia (LAML), low-grade glioma (LGG), testicular germ cell tumors (TGCT), thyroid carcinoma (THCA), thymoma (THYM), and uveal melanoma (UVM). The expression of TLR9 was significantly positively correlated with the drug sensitivity of fluphenazine, alectinib, carmustine, and 7−hydroxystaurosporine. TLR7 was significantly positively correlated with the drug sensitivity of alectinib.

Conclusions

Our study reveals the significant role of TLRs family in pan-cancer and provides potential therapeutic strategies of cancer.

Inhibition of TLR7 and TLR9 Reduces Human Cholangiocarcinoma Cell Proliferation and Tumor Development

BACKGROUND

Toll-like receptors (TLRs) are key players in innate immunity and modulation of TLR signaling has been demonstrated to profoundly affect proliferation and growth in different types of cancer. However, the role of TLRs in human intrahepatic cholangiocarcinoma (ICC) pathogenesis remains largely unexplored.

AIMS

We set out to determine if TLRs play any role in ICCs which could potentially make them useful treatment targets.

METHODS

Tissue microarrays containing samples from 9 human ICCs and normal livers were examined immunohistochemically for TLR4, TLR7, and TLR9 expression. Proliferation of human ICC cell line HuCCT1 was measured by MTS assay following treatment with CpG-ODN (TLR9 agonist), imiquimod (TLR7 agonist), chloroquine (TLR7 and TLR9 inhibitor) and IRS-954 (TLR7 and TLR9 antagonist). The in vivo effects of CQ and IRS-954 on tumor development were also examined in a NOD-SCID mouse xenograft model of human ICC.

RESULTS

TLR4 was expressed in all normal human bile duct epithelium but absent in the majority (60%) of ICCs. TLR7 and TLR9 were expressed in 80% of human ICCs. However, TLR7 was absent in all cases of normal human bile duct epithelium and only one was TLR9 positive. HuCCT1 cell proliferation in vitro significantly increased following IMQ or CpG-ODN treatment (P < 0.03 and P < 0.002, respectively) but decreased with CQ (P < 0.02). In the mouse xenograft model there was significant reduction in size of tumors from CQ and IRS-954 treated mice compared to untreated controls.

CONCLUSION

TLR7 and TLR9 should be further explored for their potential as actionable targets in the treatment of ICC.

Protein overexpression of toll-like receptor 4 and myeloid differentiation factor 88 in oral squamous cell carcinoma and clinical significance

Oral squamous cell carcinoma (OSCC) is the most common type of malignancy of the head and neck. In the present study, the expression of Toll-like receptor 4 (TLR4) and myeloid differentiation primary response gene 88 (MyD88) was evaluated in 55 OSCC tissues and their corresponding adjacent tissues using immunohistochemistry and reverse-transcription quantitative PCR. The results indicated that TLR4 and MyD88 were overexpressed in OSCC. Furthermore, high expression of MyD88 was negatively associated with a poor degree of differentiation, recurrence and metastasis of the tumor and was positively associated with underlying disease, including hypertension, heart disease and diabetes mellitus. Furthermore, high expression of TLR4 was positively associated with a long growth time of the tumor. In conclusion, the present study evaluated the expression levels of TLR4 and MyD88 in OSCC, as well as the association between them and clinicopathological factors, to provide markers for the prognosis and treatment of OSCC. These two genes may serve as biomarkers to optimize OSCC treatment, setting a new direction for stratifying patients and developing precise and personalized treatment regimens; the TLR4/MyD88 pathway may serve as a potential therapeutic target in the future.

The Relationship between the Tissue Expression of TLR2, TLR4, TLR5, and TLR7 and Systemic Inflammatory Responses in Colorectal Cancer Patients

BACKGROUND

Colorectal cancer (CRC) is the third most commonly diagnosed malignancy globally. CRC patients with elevated plasma C-reactive protein (CRP) levels exhibit compromised prognoses. Toll-like receptors (TLRs), activating the innate and adaptive immune systems, may contribute to pro- and antitumorigenic inflammatory responses. We aimed to identify a possible link between local and systemic inflammatory responses in CRC patients by investigating the association between tissue TLRs and plasma CRP.

METHODS

Tissue expressions of TLR2, TLR4, TLR5, and TLR7 were assessed using immunohistochemistry of tissue microarray slides from 549 CRC patients surgically treated between 1998 and 2005. Blood samples were drawn preoperatively, centrifuged, aliquoted, and stored at -80°C until analysis. Plasma CRP was determined through high-sensitivity time-resolved immunofluorometric assay. We investigated the association of TLRs to clinicopathologic variables, plasma CRP, and survival.

RESULTS

High TLR2 expression (hazard ratio [HR] 0.59; 95% confidence interval [CI] 0.41-0.85; p = 0.005), high TLR5 expression (HR 0.60; 95% CI 0.45-0.83; p = 0.002), positive TLR7 expression (HR 0.49; 95% CI 0.33-0.72; p < 0.001), and low CRP (HR 1.48; 95% CI 1.08-2.11; p = 0.017) were associated with a better prognosis. A high TLR2 immunoexpression was associated with a better prognosis among low-CRP patients (HR 0.53; 95% CI 0.35-0.80; p = 0.002), high TLR4 expression among high-CRP patients (HR 2.04; 95% CI 1.04-4.00; p = 0.038), high TLR5 expression among low-CRP patients (HR 0.059; 95% CI 0.37-0.92; p = 0.021), and positive TLR7 expression among low-CRP patients (HR 0.53; 95% CI 0.28-1.00; p = 0.049). In multivariate analyses, no biomarkers emerged as significant independent variables.

CONCLUSIONS

High tissue TLR2, TLR5, and TLR7 levels were associated with a better prognosis. Among low-CRP patients, those with high TLR2, TLR5, and TLR7 immunoexpressions exhibited a better prognosis. Among high CRP patients, a high TLR4 immunoexpression was associated with a better prognosis.

The association of immunosurveillance and distant metastases in colorectal cancer

Background

Colorectal cancer (CRC) is the third most common malignancy worldwide, but the key driver to distant metastases is still unknown. This study aimed to elucidate the link between immunosurveillance and organotropism of metastases in CRC by evaluating different gene signatures and pathways.

Material and methods

CRC patients undergoing surgery at the Department of General, Visceral and Transplantation Surgery at the Ludwig-Maximilian University Hospital Munich (Munich, Germany) were screened and categorized into M0 (no distant metastases), HEP (liver metastases) and PER (peritoneal carcinomatosis) after a 5-year follow-up. Six patients of each group were randomly selected to conduct a NanoString analysis, which includes 770 genes. Subsequently, all genes were further analyzed by gene set enrichment analysis (GSEA) based on seven main cancer-associated databases.

Results

Comparing HEP vs. M0, the gene set associated with the Toll-like receptor (TLR) cascade defined by the Reactome database was significantly overrepresented in HEP. HSP90B1, MAPKAPK3, PPP2CB, PPP2R1A were identified as the core enrichment genes. The immunologic signature pathway GSE6875_TCONV_VS_FOXP3_KO_TREG_DN with FOXP3 as downstream target was significantly overexpressed in M0. RB1, TMEM 100, CFP, ZKSCAN5, DDX50 were the core enrichment genes. Comparing PER vs. M0 no significantly differentially expressed gene signatures were identified.

Conclusion

Chronic inflammation might enhance local tumor growth. This is the first study identifying immune related gene sets differentially expressed between patients with either liver or peritoneal metastases. The present findings suggest that the formation of liver metastases might be associated with TLR-associated pathways. In M0, a high expression of FOXP3 + tumor infiltrating lymphocytes (TILs) seemed to prevent at least in part metastases. Thus, these correlative findings lay the cornerstone to further studies elucidating the underlying mechanisms of organotropism of metastases.

Ginsenoside Rd Inhibits Glioblastoma Cell Proliferation by Up-Regulating the Expression of miR-144-5p

miR-144-5p exhibits anti-tumor activities in various cancers. Although treatment for glioblastoma has progressed rapidly, novel targets for glioblastoma are insufficient, particularly those used in precision medicine. In the current study, we found that ginsenoside Rd reduced the proliferation and migration of glioblastoma cells. Ginsenoside Rd up-regulated the tumor-suppressive miR-144-5p in glioblastoma cells. Moreover, Toll-like receptor 2, which is a target of miR-144-5p, was down-regulated. After inhibition of miR-144-5p, the effect of Ginsenoside Rd on proliferation inhibition and down-regulation of Toll-like receptor 2 was reduced. These data demonstrated the ginsenoside Rd/miR-144-5p/Toll-like receptor 2 regulatory nexus that controls the glioblastoma pathogenesis of glioblastoma. Our work provided novel targets for glioblastoma diagnosis and treatment.

Toll-Like Receptor 2 at the Crossroad between Cancer Cells, the Immune System, and the Microbiota

Toll-like receptor 2 (TLR2) expressed on myeloid cells mediates the recognition of harmful molecules belonging to invading pathogens or host damaged tissues, leading to inflammation. For this ability to activate immune responses, TLR2 has been considered a player in anti-cancer immunity. Therefore, TLR2 agonists have been used as adjuvants for anti-cancer immunotherapies. However, TLR2 is also expressed on neoplastic cells from different malignancies and promotes their proliferation through activation of the myeloid differentiation primary response protein 88 (MyD88)/nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) pathway. Furthermore, its activation on regulatory immune cells may contribute to the generation of an immunosuppressive microenvironment and of the pre-metastatic niche, promoting cancer progression. Thus, TLR2 represents a double-edge sword, whose role in cancer needs to be carefully understood for the setup of effective therapies. In this review, we discuss the divergent effects induced by TLR2 activation in different immune cell populations, cancer cells, and cancer stem cells. Moreover, we analyze the stimuli that lead to its activation in the tumor microenvironment, addressing the role of danger, pathogen, and microbiota-associated molecular patterns and their modulation during cancer treatments. This information will contribute to the scientific debate on the use of TLR2 agonists or antagonists in cancer treatment and pave the way for new therapeutic avenues.

The prognostic role of tissue TLR2 and TLR4 in colorectal cancer

Colorectal cancer (CRC), the second most common cancer globally, resulted in 881,000 deaths in 2018. Toll-like receptors (TLRs) are crucial to detecting pathogen invasion and inducing the host’s immune response. This study aimed to explore the prognostic value of TLR2 and TLR4 tumor expressions in colorectal cancer patients. We studied the immunohistochemical expressions of TLR2 and TLR4 using tissue microarray specimens from 825 patients undergoing surgery in the Department of Surgery, Helsinki University Hospital, between 1982 and 2002. We assessed the relationships between TLR2 and TLR4 expressions and clinicopathological variables and patient survival. We generated survival curves using the Kaplan-Meier method, determining significance with the log-rank test. Among patients with lymph node–positive disease and no distant metastases (Dukes C), a strong TLR2 immunoactivity associated with a better prognosis (p < 0.001). Among patients with local Dukes B disease, a strong TLR4 immunoactivity associated with a worse disease-specific survival (DSS; p = 0.017). In the multivariate survival analysis, moderate TLR4 immunoactivity compared with strong TLR4 immunoactivity (hazard ratio (HR) 0.66, 95% confidence interval (CI) 0.49–0.89, p = 0.007) served as an independent prognostic factor. In the multivariate analysis for the Dukes subgroups, moderate TLR2 immunoactivity (HR 2.63, 95% CI 1.56–4.44, p < 0.001) compared with strong TLR2 immunoactivity served as an independent negative prognostic factor in the Dukes C subgroup. TLR2 and TLR4 might be new prognostic factors to indicate which CRC patients require adjuvant therapy and which could spare from an unnecessary follow-up, but further investigations are needed.

β-arrestin-2 up-regulates toll-like receptor 2 signaling and inhibits apoptosis in human endometrial cancer heterotransplants in nude mice

BACKGROUND

β-arrestin-2(Arr2) functions as an anti-apoptotic factor and affects cell proliferation, but its downstream molecular pathway in endometrial carcinoma (EC) is still unclear. This study aimed to investigate the effects of the stable overexpression of Arr2 on the proliferation and apoptosis of human EC heterotransplants and the expression of associated molecules, including Toll-like receptor 2(TLR2), serine-threonine kinase Akt (Akt), glycogen synthase kinase-3β(GSK3β) and some typical inflammatory cytokines such as NF-κB p56, TNF-α and IL-6 & IL-8.

METHODS

Human EC cell line Ishikawa, stably transfected with Arr2 full-length plasmid, was injected subcutaneously into nude mice. They were treated with 0, 10, 20 mg/kg paclitaxel and the volume and weight of the tumor tissue were measured and calculated. The necrotic index were assessed by H&E staining and microscopic observation. The levels of caspase-3, caspase-9, TLR2, NF-κB p56, Akt, GSK3β were measured by western blot, and the levels of TNF-α, IL-6, IL-8 were measured by real-time PCR.

RESULTS

We found that Arr2 overexpression promoted the growth of human EC heterotransplants. Arr2 attenuated the promotion of caspase-3 and caspase-9 by paclitaxel and mediated the increase of TLR2 and several inflammatory cytokines. The levels of Akt and GSK3β were not affected.

CONCLUSION

Arr2 overexpression was associated with the increase of TLR2 and several inflammatory factors, meanwhile inhibited paclitaxel-induced anti-tumor effect on human EC heterotransplants.

Serum TLR2 and TLR4 levels in colorectal cancer and their association with systemic inflammatory markers, tumor characteristics, and disease outcome

Toll-like receptors (TLRs) are involved in colorectal cancer (CRC) pathogenesis. However, the significance of serum TLR concentrations in CRC is unknown. We analyzed serum TLR2 and TLR4 concentrations with ELISA in preoperative samples from 118 patients with CRC and 88 matched controls. We also assessed tissue TLR expression with immunohistochemistry and by detecting serum determinants of systemic inflammation. Most participants (>70%) had undetectable serum TLR2. The mean serum TLR4 levels were lower in patients than in controls (1.1 vs 1.8 ng/mL; p = 0.015). Undetectable TLR4 was more common in stage I (39%) than in stages II-IV (11%, p < 0.001). TLR2 or TLR4 expression in tumor cells did not correlate with serum levels, but abundant TLR2 expression in normal colon epithelium was associated with detectable serum TLR2 (p = 0.034). Undetectable serum TLR2 was linked to high modified Glasgow prognostic scores (p = 0.010), high CRP levels (p = 0.013), blood vessel invasion (p = 0.013), and tended to be associated with worse 5-year survival (p = 0.052). In conclusion, serum TLR2 levels were inversely associated with systemic inflammation in patients with CRC. Moreover, serum TLR2 levels might depend more on normal colorectal mucosa contributions than on tumor tissue contributions. Further studies are required to assess the prognostic value of serum TLR2.

Expanded Expression of Toll-Like Receptor 2 in Proliferative Verrucous Leukoplakia

Proliferative verrucous leukoplakia (PVL) is a premalignant condition of the oral mucosa with > 70% chance of progression to squamous cell carcinoma (SCC), while lacking the common risks and behavior seen in non-PVL oral squamous carcinogenesis. PVL follows a multi-stage slow, relentless and usually multifocal expansion of surface epithelial thickening that over time takes on a verrucous architecture, eventually leading to verrucous carcinoma and/or dysplasia followed by "conventional" SCC, a process that takes years and is notoriously difficult to manage. As mucosal surfaces and carcinomas arising at these sites, are colonized by microorganisms, host receptors for microbial products have received attention as potential contributors to carcinogenesis. Studies show that microbial pattern recognition toll-like receptor (TLR)2 in various epithelial cells is upregulated in premalignant lesions and in malignant cells and can activate oncogenic pathways. Because of the highly progressive nature of PVL, we examined TLR2 expression in well-characterized PVL samples by immunohistochemistry. We found that, similar to epithelial dysplasia and SCC, PVL keratinocytes throughout the epithelial thickness showed diffuse TLR2 expression even in early stage lesions prior to onset of dysplasia. In contrast, oral mucosal samples in the absence of hyperorothokeratosis or dysplasia, expressed TLR2 primarily in the basal and parabasal layers. Given the high rates of PVL transformation and the previously established pro-cancer role of high TLR2 expression in malignant oral squamous cells, it is important to determine how its' expression and functions are regulated in the oral squamous epithelium, and what is the specific TLR2 role in carcinogenesis.

TLR4 Polymorphisms and Expression in Solid Cancers

Toll-like receptors (TLRs) are a type of pattern-recognition receptor (PRR) that are part of the innate immune system known to recognize pathogen-associated molecular patterns and thereby play a crucial role in host immune response. Among the various known TLRs, TLR4 is one of the most extensively studied PRRs expressed by immune, certain nonimmune, and tumor cells. When TLR4 binds with the bacterial lipopolysaccharide, it induces production of proinflammatory cytokines, chemokines, and effector molecules as part of the immune response. Continuous exposure to pathogens and TLR4 signaling results in chronic inflammation that may further lead to malignant transformation. TLR4 is a highly polymorphic gene, and genetic variations are known to influence host immune response, leading to dysregulation of signaling pathway, which may affect an individual's susceptibility to various diseases, including cancer. Furthermore, TLR4 expression in different tumor types may also serve as a marker for tumor proliferation, differentiation, metastasis, prognosis, and patient survival. This review aims to summarize various reports related to TLR4 polymorphisms and expression patterns and their influences on different cancer types with a special focus on solid tumors.

Butyrate upregulates the TLR4 expression and the phosphorylation of MAPKs and NK-κB in colon cancer cell in vitro

Microbiota and its induced inflammation in colorectal mucosa have been considered risk factors for the development of colorectal carcinogenesis. Previous studies demonstrated that the coexisting elements of microbiota in the gut, such as short chain fatty acids (SCFAs) and lipopolysaccharides (LPS), which exhibited regulatory effects on the intestinal epithelial cells individually. Unfortunately, the association between butyrate and the toll-like receptor (TLR) signaling pathway in the development of colon cancer is not fully elucidated. In the present study, by culturing human colon cancer SW480 cells or mouse colon cancer CT26 cells with butyrate and/or TLR4 ligand LPS in vitro, it was identified that butyrate suppressed the growth and promoted apoptosis of these cancer cells. Notably, the expression levels of TLR4 and CD14 were markedly increased on these butyrate-treated cells, but not on LPS-alone treated cells. Additionally, butyrate treatment induced the phosphorylation of extracellular signal-regulated kinase, tumor protein 38, c-Jun NH2-terminal kinase and nuclear factor-κB (NF-κB) p65, and then promoted the pro-inflammatory cytokine tumor necrosis factor-α, but not interleukin 6 secretion in SW480 and CT26 cells. Therefore, butyrate treatment regulates the expression of TLR4, mitogen-activated protein kinase and NF-κB signal pathway activation and pro-inflammatory response in vitro. Although the exact mechanisms have not been fully explored, these results suggested that butyrate and LPS-TLR4 signaling mediated innate immunity in colon cancer cells through two distinct but inter-regulated pathways. Thus, butyrate can further initiate innate immunity against tumor cells by upregulating the TLR4 expression and activation to preserve intestinal homeostasis.

Roles of Host Immunity in Viral Myocarditis and Dilated Cardiomyopathy

The pathogenesis of viral myocarditis includes both the direct damage mediated by viral infection and the indirect lesion resulted from host immune responses. Myocarditis can progress into dilated cardiomyopathy that is also associated with immunopathogenesis. T cell-mediated autoimmunity, antibody-mediated autoimmunity (autoantibodies), and innate immunity, working together, contribute to the development of myocarditis and dilated cardiomyopathy.

Toll-like receptor 2 stimulation promotes colorectal cancer cell growth via PI3K/Akt and NF-κB signaling pathways

Toll-like receptor (TLR) 2 is a key regulator of innate immune responses and has been shown to play an important role in inflammation-associated cancers. In this study, we aimed to evaluate the role of TLR2 in colorectal cancer (CRC). We demonstrated that TLR2 mRNA and protein expression was significantly upregulated in tumors from CRC patients and indicated poor prognosis. Using the TLR2 agonist Pam3Cys (P3C) to activate TLR2 signaling in human CRC cell lines, we showed that TLR2 drives cellular proliferation, which was dependent upon PI3K/Akt and NF-κB signaling pathways and was associated with the upregulation of anti-apoptotic genes BCL2A1, WISP1 and BIRC3. Likewise, pharmacological blockade of PI3K/Akt and NF-κB pathways mitigated the CRC pro-survival effects of TLR2 stimulation. Furthermore, genetic ablation of TLR2 using CRISPR/Cas9 suppressed CRC cell proliferation, invasion and migration. Taken together, these findings demonstrate that TLR2 plays an important role in colorectal tumorigenesis and may represent a promising therapeutic target in CRC.

MicroRNA-6869-5p acts as a tumor suppressor via targeting TLR4/NF-κB signaling pathway in colorectal cancer

Many studies have implicated that microRNAs (miRNAs), as non-coding RNAs, play important roles in the development and progression of colorectal cancer (CRC). However, little is known about the role of a newly identified miRNA, miR-6869-5p, in CRC. We aim to investigate the modifying effects and underlying mechanisms of miR-6869-5 in colorectal carcinogenesis and progression. Significantly reduced levels of miR-6869-5p were observed in both serum exosomes tumor tissue samples from patients with CRC. The prediction of targets of miR-6869-5p in databases of targetscan, microRNA. ORG and miRDBA revealed that toll-like receptor 4 (TLR4) is a potential target for this miRNA. MiR-6869-5p could inhibit cell proliferation and the production of inflammatory cytokines (TNF-α and IL-6) in CRC cells via directly targeting TLR4. The protective effect of miR-6869-5p from colorectal carcinogenesis was dependent on TLR4/NF-κB signaling pathway. In addition, the 3-year survival was poor among CRC patients with decreased levels of miR-6869-5p in serum exosomes. Thus, miR-6869-5p may serve as a tumor suppressor in CRC, and serum exosomal miR-6869-5p is a promising circulating biomarker for the prediction of CRC prognosis.

Toll like receptor signaling pathway as a potential therapeutic target in colorectal cancer

Toll like receptor (TLR) signaling is involved in activating innate and adaptive immune responses and plays a critical role in inflammation-induced diseases such as colorectal cancer (CRC). Dysregulation of this signaling pathway can result in disturbance of epithelial layer hemostasis, chronic inflammatory, excessive repair responses, and development of CRC. There is now substantial evidence for the benefit of targeting of this pathway in cancer treatment, and several agents have been approved, such as BCG (Bacillus Calmette Guérin), MPL (monophosphoryl lipid A) and imiquimod. This review summarizes the current knowledge about the different functions of TLRs on tumor cells and their application in cancer therapy with particular emphasis on recent preclinical and clinical research in treatment of CRC.