Role of toll-like receptor 4 in colorectal carcinogenesis: a meta-analysis

Interactions between toll-like receptors signaling pathway and gut microbiota in host homeostasis

BACKGROUND

Toll-like receptors (TLRs) are a family of fundamental pattern recognition receptors in the innate immune system, constituting the first line of defense against endogenous and exogenous antigens. The gut microbiota, a collection of commensal microorganisms in the intestine, is a major source of exogenous antigens. The components and metabolites of the gut microbiota interact with specific TLRs to contribute to whole-body immune and metabolic homeostasis.

OBJECTIVE

This review aims to summarize the interaction between the gut microbiota and TLR signaling pathways and to enumerate the role of microbiota dysbiosis-induced TLR signaling pathways in obesity, inflammatory bowel disease (IBD), and colorectal cancer (CRC).

RESULTS

Through the recognition of TLRs, the microbiota facilitates the development of both the innate and adaptive immune systems, while the immune system monitors dynamic changes in the commensal bacteria to maintain the balance of the host-microorganism symbiosis. Dysbiosis of the gut microbiota can induce a cascade of inflammatory and metabolic responses mediated by TLR signaling pathways, potentially resulting in various metabolic and inflammatory diseases.

CONCLUSION

Understanding the crosstalk between TLRs and the gut microbiota contributes to potential therapeutic applications in related diseases, offering new avenues for treatment strategies in conditions like obesity, IBD, and CRC.

Exploring TLR signaling pathways as promising targets in cervical cancer: The road less traveled

Cervical cancer is the leading cause of cancer-related deaths for women globally. Despite notable advancements in prevention and treatment, the identification of novel therapeutic targets remains crucial for cervical cancer. Toll-like receptors (TLRs) play an essential role in innate immunity as pattern-recognition receptors. There are several types of pathogen-associated molecular patterns (PAMPs), including those present in cervical cancer cells, which have the ability to activate toll-like receptors (TLRs). Recent studies have revealed dysregulated toll-like receptor (TLR) signaling pathways in cervical cancer, leading to the production of inflammatory cytokines and chemokines that can facilitate tumor growth and metastasis. Consequently, TLRs hold significant promise as potential targets for innovative therapeutic agents against cervical cancer. This book chapter explores the role of TLR signaling pathways in cervical cancer, highlighting their potential for targeted therapy while addressing challenges such as tumor heterogeneity and off-target effects. Despite these obstacles, targeting TLR signaling pathways presents a promising approach for the development of novel and effective treatments for cervical cancer.

Gut Microbiota, Inflammatory Bowel Disease, and Cancer: The Role of Guardians of Innate Immunity

Inflammatory bowel diseases (IBDs) are characterized by a persistent low-grade inflammation that leads to an increased risk of colorectal cancer (CRC) development. Several factors are implicated in this pathogenetic pathway, such as innate and adaptive immunity, gut microbiota, environment, and xenobiotics. At the gut mucosa level, a complex interplay between the immune system and gut microbiota occurs; a disequilibrium between these two factors leads to an alteration in the gut permeability, called 'leaky gut'. Subsequently, an activation of several inflammatory pathways and an alteration of gut microbiota composition with a proliferation of pro-inflammatory bacteria, known as 'pathobionts', take place, leading to a further increase in inflammation. This narrative review provides an overview on the principal Pattern Recognition Receptors (PRRs), including Toll-like receptors (TLRs) and NOD-like receptors (NLRs), focusing on their recognition mechanisms, signaling pathways, and contributions to immune responses. We also report the genetic polymorphisms of TLRs and dysregulation of NLR signaling pathways that can influence immune regulation and contribute to the development and progression of inflammatory disease and cancer.

Microbial sensing in the intestine

The gut microbiota plays a key role in host health and disease, particularly through their interactions with the immune system. Intestinal homeostasis is dependent on the symbiotic relationships between the host and the diverse gut microbiota, which is influenced by the highly co-evolved immune-microbiota interactions. The first step of the interaction between the host and the gut microbiota is the sensing of the gut microbes by the host immune system. In this review, we describe the cells of the host immune system and the proteins that sense the components and metabolites of the gut microbes. We further highlight the essential roles of pattern recognition receptors (PRRs), the G protein-coupled receptors (GPCRs), aryl hydrocarbon receptor (AHR) and the nuclear receptors expressed in the intestinal epithelial cells (IECs) and the intestine-resident immune cells. We also discuss the mechanisms by which the disruption of microbial sensing because of genetic or environmental factors causes human diseases such as the inflammatory bowel disease (IBD).

Pathomorphological Manifestations and the Course of the Cervical Cancer Disease Determined by Variations in the TLR4 Gene

Cervical cancer (CC) is often associated with human papillomavirus (HPV). Chronic inflammation has been described as one of the triggers of cancer. The immune system fights diseases, including cancer. The genetic polymorphism of pathogen recognition receptors potentially influences the infectious process, development, and disease progression. Many candidate genes SNPs have been contradictory demonstrated to be associated with cervical cancer by association studies, GWAS. TLR4 gene activation can promote antitumor immunity. It can also result in immunosuppression and tumor growth. Our study aimed to investigate eight selected polymorphisms of the TLR4 gene (rs10759932, rs1927906, rs11536898, rs11536865, rs10983755, rs4986790, rs4986791, rs11536897) and to determine the impact of polymorphisms in genotypes and alleles on the pathomorphological characteristics and progression in a group of 172 cervical cancer subjects with stage I-IV. Genotyping was performed by RT-PCR assay. We detected that the CA genotype and A allele of rs11536898 were significantly more frequent in patients with metastases (p = 0.026; p = 0.008). The multivariate logistic regression analysis confirmed this link to be significant. The effect of rs10759932 and rs11536898 on progression-free survival (PFS) and overall survival (OS) has been identified as important. In univariate and multivariate Cox analyses, AA genotype of rs11536898 was a negative prognostic factor for PFS (p = 0.024; p = 0.057, respectively) and OS (p = 0.008; p = 0.042, respectively). Rs11536898 C allele predisposed for longer PFS (univariate and multivariate: p = 0.025; p = 0.048, respectively) and for better OS (univariate and multivariate: p = 0.010; p = 0.043). The worse prognostic factor of rs10759932 in a univariate and multivariate Cox analysis for survival was CC genotype: shorter PFS (p = 0.032) and increased risk of death (p = 0.048; p = 0.015, respectively). The T allele of rs10759932 increased longer PFS (univariate and multivariate: p = 0.048; p = 0.019, respectively) and longer OS (univariate and multivariate: p = 0.037; p = 0.009, respectively). Our study suggests that SNPs rs10759932 and rs11536898 may have the potential to be markers contributing to the assessment of the cervical cancer prognosis. Further studies, preferably with larger groups of different ethnic backgrounds, are needed to confirm the results of the current study.

An updated systematic review of the association between the TLR4 polymorphism rs4986790 and cancers risk

BACKGROUND

Toll-like receptor 4 (TLR4) is a lipopolysaccharide receptor that may influence tumor progression through inflammatory response and immune response. This complex process mainly occurs within cells. The correlation between TLR4 and neoplasms has been of great interest, but discrepancies remain.

METHODS

We analyze the literature retrieved from five databases (Web of Science, PubMed, Embase, CNKI, and Wan Fang) to assess the intensity of association using odds ratio (ORs) and 95% confidence intervals (95% CI). Meta-regression and subgroup analysis were utilized to find sources of heterogeneity. Publication bias is estimated using contour-enhanced funnel plots, Begg's test, and Egger's test, and we implemented sensitivity analysis to clarify the reliability of the outcomes. We also conducted an evaluation of the sample size using trial sequential analysis (TSA) method.

RESULTS

We found a significant association between rs4986790 and tumors (dominant model: OR [95% CI] = 1.25 [1.11-1.42]; heterozygous model OR [95% CI] = 1.25 [1.11-1.41]; and additive model: OR [95% CI] = 1.25 [1.10-1.41]. Specifically, the rs4986790 minor allele G may increase the risk of gastric cancer (dominant model: OR [95% CI] = 1.62 [1.3-2.03]; heterozygous model: OR [95% CI] = 1.57 [1.24-1.97]; additive model: OR [95% CI] = 1.64 [1.31-2.05] and other tumors (dominant model: OR [95% CI] = 1.36 [1.17-1.57]; heterozygous model: OR [95% CI] = 1.43 [1.25-1.63]; additive model: OR [95% CI] = 1.35 [1.18-1.55]. Further subgroup analysis showed that this association are both present in Caucasian and Asian.

CONCLUSION

The outcomes of our systemic review proved that the TLR4 polymorphism rs4986790 is associated with cancer, especially with gastric cancer, and this strong correlation are evident in Caucasians and Asian.

Toll-Like Receptors (TLRs): Structure, Functions, Signaling, and Role of Their Polymorphisms in Colorectal Cancer Susceptibility

Toll-like receptors (TLRs) are the important mediators of inflammatory pathways in the gut which play a major role in mediating the immune responses towards a wide variety of pathogen-derived ligands and link adaptive immunity with the innate immunity. Numerous studies in different populations across the continents have reported on the significant roles of TLR gene polymorphisms in modulating the risk of colorectal cancer (CRC). CRC is one of the major malignancies affecting the worldwide population and is currently ranking the third most common cancer in the world. In this review, we have attempted to discuss the structure, functions, and signaling of TLRs in comprehensive detail together with the role played by various TLR gene SNPs in CRC susceptibility.

TLR4 signaling in the development of colitis-associated cancer and its possible interplay with microRNA-155

Ulcerative colitis (UC) has closely been associated with an increased risk of colorectal cancer. However, the exact mechanisms underlying colitis-associated cancer (CAC) development remain unclear. As a classic pattern-recognition receptor, Toll like receptor (TLR)4 is a canonical receptor for lipopolysaccharide of Gram-negative bacteria (including two CAC-associated pathogens Fusobacterium nucleatum and Salmonella), and functions as a key bridge molecule linking oncogenic infection to colonic inflammatory and malignant processes. Accumulating studies verified the overexpression of TLR4 in colitis and CAC, and the over-expressed TLR4 might promote colitis-associated tumorigenesis via facilitating cell proliferation, protecting malignant cells against apoptosis, accelerating invasion and metastasis, as well as contributing to the creation of tumor-favouring cellular microenvironment. In recent years, considerable attention has been focused on the regulation of TLR4 signaling in the context of colitis-associated tumorigenesis. MicroRNA (miR)-155 and TLR4 exhibited a similar dynamic expression change during CAC development and shared similar CAC-promoting properties. The available data demonstrated an interplay between TLR4 and miR-155 in the context of different disorders or cell lines. miR-155 could augment TLR4 signaling through targeting negative regulators SOCS1 and SHIP1; and TLR4 activation would induce miR-155 expression via transcriptional and post-transcriptional mechanisms. This possible TLR4-miR-155 positive feedback loop might result in the synergistic accelerating effect of TLR4 and miR-155 on CAC development.

TLR-4 Signaling vs. Immune Checkpoints, miRNAs Molecules, Cancer Stem Cells, and Wingless-Signaling Interplay in Glioblastoma Multiforme-Future Perspectives

Toll-like-receptor (TLR) family members were detected in the central nervous system (CNS). TLR occurrence was noticed and widely described in glioblastomamultiforme (GBM) cells. After ligand attachment, TLR-4 reorients domains and dimerizes, activates an intracellular cascade, and promotes further cytoplasmatic signaling. There is evidence pointing at a strong relation between TLR-4 signaling and micro ribonucleic acid (miRNA) expression. The TLR-4/miRNA interplay changes typical signaling and encourages them to be a target for modern immunotherapy. TLR-4 agonists initiate signaling and promote programmed death ligand-1 (PD-1L) expression. Most of those molecules are intensively expressed in the GBM microenvironment, resulting in the autocrine induction of regional immunosuppression. Another potential target for immunotreatment is connected with limited TLR-4 signaling that promotes Wnt/DKK-3/claudine-5 signaling, resulting in a limitation of GBM invasiveness. Interestingly, TLR-4 expression results in bordering proliferative trends in cancer stem cells (CSC) and GBM. All of these potential targets could bring new hope for patients suffering from this incurable disease. Clinical trials concerning TLR-4 signaling inhibition/promotion in many cancers are recruiting patients. There is still a lot to do in the field of GBM immunotherapy.

Study of Toll‑Like Receptor 4 Gene Polymorphisms in Colorectal Cancer: Correlation with Clinicopathological Features

Polymorphisms of Toll-like receptor 4 (TLR4) as a key player in cell proliferation, apoptosis, and angiogenesis have been linked to colorectal cancer (CRC) in different populations. We aimed in this study to determine genetic associations of TLR4 variants with CRC progression in Egyptian patients. Genotype and allelic frequencies of Asp299Gly (rs4986790) and Thr399Ile (rs4986791) were compared between 127 CRC patients and 141 healthy Egyptians using restriction fragment length polymorphism, and were correlated to clinicopathological findings. Results revealed that the variant alleles (G of Asp299Gly) and (T of Thr399Ile) were significantly associated with CRC among Egyptians. Confirmed by haplotype analysis, AT and GT haplotypes were more frequent in CRC patients than controls with increased CRC odds (OR = 3.54 and 3.45, 95% CI = 1.48-8.48 and 1.09-10.83, respectively). In addition, the G allele of Asp299Gly SNP was observed to be significantly associated with progressive CRC, including stage IV (P = .001), grade III (P = .025), N2 lymph nodes (P = .020), and metastasis (P = .001). On the other hand, Thr399Ile variant did not show any association with tumor behavior. Taken together, we conclude a significant association of Asp299Gly and Thr399Ile variants with the risk of development of CRC in Egypt. Asp299Gly variant, but not the Thr399Ile variant, may serve as a biomarker of this disease progression in Egyptian population.

Hyaluronic Acid Binding to TLR4 Promotes Proliferation and Blocks Apoptosis in Colon Cancer

Hyaluronic acid (HA), a constituent of the extracellular matrix, promotes colorectal cancer growth. CD44 is a relevant HA receptor in this context. However, HA is also a ligand for TLR4, a receptor of significance in colorectal cancer. In this study, we examine the relative contribution of HA interactions with CD44 and TLR4 in colon tumorigenesis. Colorectal cancer models included Apc^Min/+ mice, azoxymethane/dextran sodium sulfate (AOM-DSS), and CT26 tumor isografts. We used knockout mice and CT26 colorectal cancer cells with CRISPR knockdown of CD44 and TLR4. HA activity was modulated by PEP1 (a 12-mer peptide that blocks HA from binding its receptors), hyaluronidase (which promotes HA degradation), or 4-MU (HA synthesis inhibitor). Blockade of HA binding via PEP1 decreased growth in all colorectal cancer models and in cell culture. The effects were significant in WT and with CD44 deletion, but not with TLR4 deletion. In the AOM-DSS model, mice deficient in CD44 or TLR4 had fewer tumors. CD44- and TLR4-deficient CT26 isografts grew more slowly, exhibiting decreased tumor cell proliferation and increased apoptosis. In vitro, endogenous HA blocked LPS binding to TLR4 suggesting that HA is a relevant TLR4 ligand in colon cancer. Finally, PEP1 enhanced tumor radiation sensitivity in the isograft model. Together, these results indicate that HA binding to TLR4, as well as CD44, plays a key role in colon tumorigenesis. These findings also raise the possibility that an agent that blocks HA binding, such as PEP1, may be useful as an adjuvant therapy in colon cancer.

The association between phospholipase C epsilon gene (PLCE1) polymorphisms and colorectal cancer risk in a Chinese Han population: a case-control study

BACKGROUND

Heritable factors contribute to the development of colorectal cancer (CRC). We investigated the association between single nucleotide polymorphisms in phospholipase C epsilon 1 (PLCE1) and CRC susceptibility.

METHODS

We selected eight tag single nucleotide polymorphisms (tSNPs) and investigated whether they were associated with CRC in Chinese Han population. In this study, we used Sequenom MassARRAY technology and genotyped 276 CRC cases and 385 controls. The effects of the polymorphisms on the risk of CRC were expressed as odds ratios (ORs) with 95% confidence intervals (95% CIs), evaluated by different genetic models using unconditional logistic regression analysis adjusted for age and gender. We also analyzed the risk of the eight PLCE1 tSNPs in different histology of CRC.

RESULTS

Based on x(2) tests, rs753724 (OR = 1.49, 95% CI: 1.10-2.03, P = 0.010) and rs10882424 (OR = 1.32, 95% CI: 1.02-1.70, P = 0.037) in PLCE1 were associated with CRC. In genetic model analyses, we found that rs753724 in PLCE1 may increase CRC risk (OR = 1.48, 95% CI: 1.09-2.03, P = 0.013) in the log-additive model, and rs11187842 in PLCE1 may increase CRC risk (OR = 3.09, 95% CI: 1.17-8.14, P = 0.018) in the recessive model. Rs753724 TT (OR = 4.31, P = 0.010), rs11187842 TT (OR = 5.78, P = 0.003), and rs10882424 GG (OR = 2.64, P = 0.022) in PLCE1 may increase rectal cancer in a recessive model.

CONCLUSIONS

Our results suggest that PLCE1 may be associated with CRC in Han Chinese population.

Multiple roles of toll-like receptor 4 in colorectal cancer

Toll-like receptor (TLR) signaling has been implicated in the inflammatory responses in intestinal epithelial cells (IECs). Such inflammatory signals mediate complex interactions between commensal bacteria and TLRs and are required for IEC proliferation, immune response, repair, and homeostasis. The upregulation of certain TLRs in colorectal cancer (CRC) tissues suggests that TLRs may play an essential role in the prognosis of chronic and inflammatory diseases that ultimately culminate in CRC. Here, we provide a comprehensive review of the literature on the involvement of the TLR pathway in the initiation, progression, and metastasis of CRC, as well as inherited genetic variation and epigenetic regulation. The differential expression of TLRs in epithelial cells has also been discussed. In particular, we emphasize the physiological role of TLR4 in CRC development and pathogenesis, and propose novel and promising approaches for CRC therapeutics with the aid of TLR ligands.