Role of toll-like receptors in tissue repair and tumorigenesis

Study of TLR3, TLR4 and TLR9 in breast carcinomas and their association with metastasis

Background

Toll-like receptors (TLRs) have garnered an extraordinary amount of interest in cancer research due to their role in tumor progression. By activating the production of several biological factors, TLRs induce type I interferons and other cytokines, which drive an inflammatory response and activate the adaptive immune system. The aim of this study was to investigate the expression and clinical relevance of TLR3, 4 and 9 in breast cancer.

Methods

The expression levels of TLR3, TLR4 and TLR9 were analyzed on tumors from 74 patients with breast cancer. The analysis was performed by immunohistochemistry.

Results

Samples of carcinomas with recurrence exhibited a significant increase in the mRNA levels of TLR3, TLR4 and TLR9. Tumors showed high expression of TLRs expression levels by cancer cells, especially TLR4 and 9. Nevertheless, a significant percentage of tumors also showed TLR4 expression by mononuclear inflammatory cells (21.6%) and TLR9 expression by fibroblast-like cells (57.5%). Tumors with high TLR3 expression by tumor cell or with high TLR4 expression by mononuclear inflammatory cells were significantly associated with higher probability of metastasis. However, tumours with high TLR9 expression by fibroblast-like cells were associated with low probability of metastasis.

Conclusions

The expression levels of TLR3, TLR4 and TLR9 have clinical interest as indicators of tumor aggressiveness in breast cancer. TLRs may represent therapeutic targets in breast cancer.

Innate immunity and cancer therapy

Classical cancer immunotherapy utilizes the immune response against microbial components, and a sequence of immune responses produce antitumor effects. The identification of mammalian Toll-like receptors (TLRs), receptors for microbial components, has shed light on antigen recognition by the innate immune system and provided a molecular basis for our understanding of the relationship between innate immunity and antitumor activity. However, accumulating evidence has revealed another important role of TLRs in maintaining tissue homeostasis and has also shown that tumor cells utilize this function to create favorable conditions for growth and survival, suggesting that TLR signaling acts as a double-edged sword in cancer therapy. In this review, innate immunity-based cancer therapy will be discussed with special reference to TLR-targeting drugs.

From cytokines to toll-like receptors and beyond - current knowledge and future research needs in irritable bowel syndrome

The irritable bowel syndrome (IBS) is a complex disorder in which psychosocial, cultural and biological factors, interact. Recent knowledge in the pathophysiology of IBS, seem to combine issues such as a low grade inflammation or immune activation and dysbiosis that can trigger or exacerbate IBS. On the other hand, stress mediated through the hypothalamic-pituitary-adrenal axis can produce motility abnormalities that can modify the microbiota as well, with the subsequent immune activation in the mucosa and stimulation of nerve terminals, generating symptoms of IBS. Also, we speculate that, stress, dysbiosis or an underlying genetic predisposition, may increase the epithelial permeability leading to a contact between pathogens-associated molecular patterns and toll-like receptors in the deeper layers of the gut, developing a host immunity response and IBS generation. We believe that the role of toll-like receptors in IBS and elucidating the communication processes between the immune and the nervous system, warrant future research.

Important aspects of Toll-like receptors, ligands and their signaling pathways

Due to the rapid increase of new information on the multiple roles of Toll-like receptors (TLRs), this paper reviews several main properties of TLRs and their ligands and signaling pathways. The investigation of pathogen infections in knockout mice suggests that specific TLRs play a key role in the activation of immune responses. Although the investigation of TLR biology is just beginning, a number of important findings are emerging. This review focuses on the following seven aspects of this emerging field: (a) a history of TLR and ligand studies; (b) the molecular basis of recognition by TLRs: TLR structures, pathogen-associated molecular pattern binding sites, TLR locations and functional responses; (c) cell types in TLR expression; (d) an overview of TLRs and their ligands: expression and ligands of cell-surface TLRs and of intracellular TLRs; (e) TLR-signaling pathways; (f) discussion: TLRs control of innate and adaptive systems; the trafficking of intracellular TLRs to endolysosomes; investigation of TLRs in regulating microRNA; investigation of crystal structure of TLRs with ligand binding; incidence of infectious diseases associated with single nucleotide polymorphisms (SNPs) in TLR genes; risk of cancer related to SNPs in TLR genes; TLR-ligand mediated anti-cancer effects; and TLR-ligand induced chronic inflammation and tumorigenesis; and (g) conclusions.

Inflammation and colon cancer

The connection between inflammation and tumorigenesis is well-established and in the last decade has received a great deal of supporting evidence from genetic, pharmacological, and epidemiological data. Inflammatory bowel disease is an important risk factor for the development of colon cancer. Inflammation is also likely to be involved with other forms of sporadic as well as heritable colon cancer. The molecular mechanisms by which inflammation promotes cancer development are still being uncovered and could differ between colitis-associated and other forms of colorectal cancer. Recent work has elucidated the role of distinct immune cells, cytokines, and other immune mediators in virtually all steps of colon tumorigenesis, including initiation, promotion, progression, and metastasis. These mechanisms, as well as new approaches to prevention and therapy, are discussed in this review.

Toll-like receptors and B-cell receptors synergize to induce immunoglobulin class-switch DNA recombination: relevance to microbial antibody responses

Differentiation of naïve B cells, including immunoglobulin class-switch DNA recombination, is critical for the immune response and depends on the extensive integration of signals from the B-cell receptor (BCR), tumor necrosis factor (TNF) family members, Toll-like receptors (TLRs), and cytokine receptors. TLRs and BCR synergize to induce class-switch DNA recombination in T cell-dependent and T cell-independent antibody responses to microbial pathogens. BCR triggering together with simultaneous endosomal TLR engagement leads to enhanced B-cell differentiation and antibody responses. Te requirement of both BCR and TLR engagement would ensure appropriate antigen-specific activation in an infection. Co-stimulation of TLRs and BCR likely plays a significant role in anti-microbial antibody responses to contain pathogen loads until the T cell-dependent antibody responses peak. Furthermore, the temporal sequence of different signals is also critical for optimal B cell responses, as exemplified by the activation of B cells by initial TLR engagement, leading to the up-regulation of co-stimulatory CD80 and MCH-II receptors, which result in more efficient interactions with T cells, thereby enhancing the germinal center reaction and antibody affinity maturation. Overall, BCR and TLR stimulation and the integration with signals from the pathogen or immune cells and their products determine the ensuing B-cell antibody response.

Hypoxic stress up-regulates the expression of Toll-like receptor 4 in macrophages via hypoxia-inducible factor

Toll-like receptors (TLRs) are germline-encoded innate immune receptors that recognize invading micro-organisms and induce immune and inflammatory responses. Deregulation of TLRs is known to be closely linked to various immune disorders and inflammatory diseases. Cells at sites of inflammation are exposed to hypoxic stress, which further aggravates inflammatory processes. We have examined if hypoxic stress modulates the TLR activity of macrophages. Hypoxia and CoCl(2) (a hypoxia mimetic) enhanced the expression of TLR4 messenger RNA and protein in macrophages (RAW264.7 cells), whereas the messenger RNA of other TLRs was not increased. To determine the underlying mechanism, we investigated the role of hypoxia-inducible factor 1 (HIF-1) in the regulation of TLR4 expression. Knockdown of HIF-1alpha expression by small interfering RNA inhibited hypoxia-induced and CoCl(2)-induced TLR4 expression in macrophages, while over-expression of HIF-1alpha potentiated TLR4 expression. Chromatin immunoprecipitation assays revealed that HIF-1alpha binds to the TLR4 promoter region under hypoxic conditions. In addition, deletion or mutation of a putative HIF-1-binding motif in the TLR4 promoter greatly attenuated HIF-1alpha-induced TLR4 promoter reporter expression. Up-regulation of TLR4 expression by hypoxic stress enhanced the response of macrophages to lipopolysaccharide, resulting in increased expression of cyclooxygenase-2, interleukin-6, regulated on activation normal T cell expressed and secreted, and interferon-inducible protein-10. These results demonstrate that TLR4 expression in macrophages is up-regulated via HIF-1 in response to hypoxic stress, suggesting that hypoxic stress at sites of inflammation enhances susceptibility to subsequent infection and inflammatory signals by up-regulating TLR4.

The significance of toll-like receptors in human diseases

Toll-like receptors (TLRs) are a family of transmembrane receptors that have been preserved throughout evolution and which selectively recognize a broad spectrum of microbial components and endogenous molecules released by injured tissue. Identification of these ligands by TLRs triggers signalling pathways which lead to the expression of numerous genes involved in a defensive response. In mammals, the products of these genes initiate inflammation, coordinate the effector functions of innate immunity, instruct and modulate adaptive immunity and initiate tissue repair and regeneration. Different mutations and experimental models which alter TLR function have revealed the significance of these receptors in susceptibility to infection and their involvement in the pathogenesis of a large number of non-infective inflammatory disorders such as cancer, allergy, autoimmunity, inflammatory bowel disease, or atherosclerosis. TLRs are currently viewed as important targets for the development of new vaccines and innovative therapies to prevent and treat human diseases.

Hyperactivated B cells in human inflammatory bowel disease

IBD is characterized by a chronic, dysregulated immune response to intestinal bacteria. Past work has focused on the role of T cells and myeloid cells in mediating chronic gastrointestinal and systemic inflammation. Here, we show that circulating and tissue B cells from CD patients demonstrate elevated basal levels of activation. CD patient B cells express surface TLR2, spontaneously secrete high levels of IL-8, and contain increased ex vivo levels of phosphorylated signaling proteins. CD clinical activity correlates directly with B cell expression of IL-8 and TLR2, suggesting a positive relationship between these B cell inflammatory mediators and disease pathogenesis. In contrast, B cells from UC patients express TLR2 but generally do not demonstrate spontaneous IL-8 secretion; however, significant IL-8 production is inducible via TLR2 stimulation. Furthermore, UC clinical activity correlates inversely with levels of circulating TLR2+ B cells, which is opposite to the association observed in CD. In conclusion, TLR2+ B cells are associated with clinical measures of disease activity and differentially associated with CD- and UC-specific patterns of inflammatory mediators, suggesting a formerly unappreciated role of B cells in the pathogenesis of IBD.

The TIR/BB-loop mimetic AS-1 protects the myocardium from ischaemia/reperfusion injury

AIMS

Innate immune and inflammatory responses are involved in myocardial ischaemia/reperfusion (I/R) injury. The interleukin-1 receptor (IL-1R)-mediated, MyD88-dependent nuclear factor kappa B (NF-kappaB) activation pathway plays an important role in the induction of innate immunity and inflammation. However, the role of the IL-1R-MyD88 pathway in myocardial I/R injury has not been thoroughly investigated. We hypothesized that inhibition of the interaction of IL-1R with MyD88 will attenuate myocardial ischaemic injury through reducing inflammatory responses.

METHODS AND RESULTS

Male C57BL/6 mice were subjected to myocardial ischaemia (45 min) followed by reperfusion (4 h). In the treatment group, after mice were subjected to ischaemia (45 min), the TIR/BB-loop mimetic (AS-1), which inhibits the interaction of IL-1R with MyD88, was administered immediately before reperfusion. Hearts were harvested and cellular proteins were isolated for immunoprecipitation and immunoblotting. AS-1 administration significantly decreased infarct size by 32.92% compared with the untreated I/R group. Ejection fraction and fractional shortening in AS-1-treated mice were also significantly increased by 18.0 and 25.6%, respectively, compared with the untreated I/R group. AS-1 administration significantly decreased the I/R-increased interaction between IL-1R and MyD88, attenuated the I/R-increased NF-kappaB binding activity, and reduced levels of inflammatory cytokines and adhesion molecules in the myocardium compared with the untreated I/R group. In addition, AS-1 administration significantly decreased myocardial myeloperoxidase activity by 23.6% and neutrophil infiltration in the myocardium compared with the untreated I/R group.

CONCLUSION

The results demonstrated an important role for the IL-1R-mediated MyD88-dependent signalling pathway in myocardial I/R injury. The data suggest that modulation of the IL-1R/MyD88 interaction could be a strategy for reducing myocardial ischaemic injury.