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Paracatu LC, Schuettpelz LG. Contribution of Aberrant Toll Like Receptor Signaling to the Pathogenesis of Myelodysplastic Syndromes. Front Immunol 2020; 11:1236. [PMID: 32625214 PMCID: PMC7313547 DOI: 10.3389/fimmu.2020.01236] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Accepted: 05/18/2020] [Indexed: 12/12/2022] Open
Abstract
Toll like receptors (TLRs) are a family of pattern recognition receptors that play a central role in the innate immune response. These receptors are expressed on a wide variety of immune and non-immune cells, and they help shape the immune response to infection and injury through the recognition of pathogen-associated molecular patterns (PAMPs) as well as endogenous damage-associated molecular patterns (DAMPs). Accumulating evidence suggests that, in addition to regulating mature effector immune cells, TLRs can influence the immune response from the level of the hematopoietic stem cell (HSC). HSCs express TLRs, and exposure to TLR ligands influences the cycling, differentiation, and function of HSCs, with chronic TLR stimulation leading to impairment of normal HSC repopulating activity. Moreover, enhanced TLR expression and signaling is associated with myelodysplastic syndromes (MDS), a heterogenous group of HSC disorders characterized by ineffective hematopoiesis and a high risk of transformation to acute leukemias. In this review, we will discuss the role of TLR signaling in the pathogenesis of MDS, focusing on the known direct and indirect effects of this type of signaling on HSCs, the mechanisms of TLR signaling upregulation in MDS, the changes in TLR expression with disease progression, and the therapeutic implications for modulating TLR signaling in the treatment of MDS.
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Affiliation(s)
- Luana Chiquetto Paracatu
- Department of Pediatrics, Washington University School of Medicine, St. Louis, MO, United States
| | - Laura G Schuettpelz
- Department of Pediatrics, Washington University School of Medicine, St. Louis, MO, United States
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Functional Toll-Like Receptors (TLRs) Are Expressed by a Majority of Primary Human Acute Myeloid Leukemia Cells and Inducibility of the TLR Signaling Pathway Is Associated with a More Favorable Phenotype. Cancers (Basel) 2019; 11:cancers11070973. [PMID: 31336716 PMCID: PMC6678780 DOI: 10.3390/cancers11070973] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Revised: 06/26/2019] [Accepted: 07/09/2019] [Indexed: 02/06/2023] Open
Abstract
Acute myeloid leukemia (AML) is a highly heterogeneous disease with regard to biological characteristics and receptor expression. Toll-like receptors (TLRs) are upstream to the transcription factor NFκB and part of the innate immune system. They are differentially expressed on AML blasts, and during normal hematopoiesis they initiate myeloid differentiation. In this study, we investigated the response upon TLR stimulation in an AML cohort (n = 83) by measuring the increase of NFκB-mediated cytokine secretion. We observed that TLR4 is readily induced in most patients, while TLR1/2 response was more restricted. General response to TLR stimulation correlated with presence of nucleophosmin gene mutations, increased mRNA expression of proteins, which are part of the TLR signaling pathway and reduced expression of transcription-related proteins. Furthermore, signaling via TLR1/2 appeared to be linked with prolonged patient survival. In conclusion, response upon TLR stimulation, and especially TLR1/2 induction, seems to be part of a more favorable phenotype, which also is characterized by higher basal cytokine secretion and a more mature blast population.
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El-Mesery M, Seher A, Stühmer T, Siegmund D, Wajant H. MLN4924 sensitizes monocytes and maturing dendritic cells for TNF-dependent and -independent necroptosis. Br J Pharmacol 2015; 172:1222-36. [PMID: 25363690 DOI: 10.1111/bph.12998] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Revised: 10/16/2014] [Accepted: 10/21/2014] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND AND PURPOSE MLN4924 prevents the formation of active cullin-RING ubiquitin ligase complexes and thus inhibits NF-κB signalling. Here, we evaluated the effects of this compound on monocytes and dendritic cells (DCs). EXPERIMENTAL APPROACH Monocytes and DCs were challenged with TNF or LPS in the presence and absence of MLN4924. The effects of MLN4924 on cellular viability, pro-inflammatory gene induction and DC maturation were investigated using the MTT assay, elisa and FACS analysis. Mechanisms of cell death induction were evaluated by using inhibitors of caspases, RIPK1 and MLKL. KEY RESULTS MLN4924 inhibited NF-κB activation and sensitized monocytes and immature DCs (iDCs) for TNFR1-induced cell death. Neither the caspase inhibitor zVAD-fmk, the RIPK1 inhibitor necrostatin-1 (nec-1) nor the MLKL inhibitor necrosulfonamide (NSA) alone prevented TNF-induced cell death. A combination of zVAD-fmk and nec-1 or NSA, however, rescued monocytes and iDCs from MLN4924/TNF-induced cell death indicating that MLN4924 affects anti-apoptotic and anti-necrotic activities in TNFR1 signalling. MLN4924 also converted the response of iDCs to LPS from maturation to cell death. LPS-induced cell death in MLN4924-treated iDCs was again only effectively blocked by cotreatment with zVAD-fmk and nec-1 or NSA. Noteworthy, MLN4924/LPS-induced cell death was almost completely independent of endogenous TNF. MLN4924 also strongly inhibited maturation and activation of iDCs that were rescued from cell death by zVAD-fmk and nec-1. CONCLUSIONS AND IMPLICATIONS Our data reveal a strong dual suppressive effect of MLN4924 on DC activity. The targeting of NAE by MLN4924 could be a new way to treat inflammatory diseases.
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Affiliation(s)
- Mohamed El-Mesery
- Division of Molecular Internal Medicine, Department of Internal Medicine II, University Hospital Würzburg, Würzburg, Germany; Department of Biochemistry, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt
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Transcriptional and proteomic analysis reveal recombinant galectins of Haemonchus contortus down-regulated functions of goat PBMC and modulation of several signaling cascades in vitro. J Proteomics 2014; 98:123-37. [DOI: 10.1016/j.jprot.2013.12.017] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Revised: 12/05/2013] [Accepted: 12/20/2013] [Indexed: 11/22/2022]
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Conrad DP, Tsang J, Maclean M, Diallo JS, Le Boeuf F, Lemay CG, Falls TJ, Parato KA, Bell JC, Atkins HL. Leukemia cell-rhabdovirus vaccine: personalized immunotherapy for acute lymphoblastic leukemia. Clin Cancer Res 2013; 19:3832-43. [PMID: 23714728 DOI: 10.1158/1078-0432.ccr-12-3199] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE Acute lymphoblastic leukemia (ALL) remains incurable in most adults. It has been difficult to provide effective immunotherapy to improve outcomes for the majority of patients. Rhabdoviruses induce strong antiviral immune responses. We hypothesized that mice administered ex vivo rhabdovirus-infected ALL cells [immunotherapy by leukemia-oncotropic virus (iLOV)] would develop robust antileukemic immune responses capable of controlling ALL. EXPERIMENTAL DESIGN Viral protein production, replication, and cytopathy were measured in human and murine ALL cells exposed to attenuated rhabdovirus. Survival following injection of graded amounts of ALL cells was compared between cohorts of mice administered γ-irradiated rhabdovirus-infected ALL cells (iLOV) or multiple control vaccines to determine key immunotherapeutic components and characteristics. Host immune requirements were assessed in immunodeficient and bone marrow-transplanted mice or by adoptive splenocyte transfer from immunized donors. Antileukemic immune memory was ascertained by second leukemic challenge in long-term survivors. RESULTS Human and murine ALL cells were infected and killed by rhabdovirus; this produced a potent antileukemia vaccine. iLOV protected mice from otherwise lethal ALL by developing durable leukemia-specific immune-mediated responses (P < 0.0001), which required an intact CTL compartment. Preexisting antiviral immunity augmented iLOV potency. Splenocytes from iLOV-vaccinated donors protected 60% of naïve recipients from ALL challenge (P = 0.0001). Injecting leukemia cells activated by, or concurrent with, multiple Toll-like receptor agonists could not reproduce the protective effect of iLOV. Similarly, injecting uninfected irradiated viable, apoptotic, or necrotic leukemia cells with/without concurrent rhabdovirus administration was ineffective. CONCLUSION Rhabdovirus-infected leukemia cells can be used to produce a vaccine that induces robust specific immunity against aggressive leukemia.
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Affiliation(s)
- David P Conrad
- Ottawa Hospital Research Institute, Center for Cancer Therapeutics, Ottawa, Ontario, Canada
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Rhein C, Tripal P, Seebahn A, Konrad A, Kramer M, Nagel C, Kemper J, Bode J, Mühle C, Gulbins E, Reichel M, Becker CM, Kornhuber J. Functional implications of novel human acid sphingomyelinase splice variants. PLoS One 2012; 7:e35467. [PMID: 22558155 PMCID: PMC3338701 DOI: 10.1371/journal.pone.0035467] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 03/16/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Acid sphingomyelinase (ASM) hydrolyses sphingomyelin and generates the lipid messenger ceramide, which mediates a variety of stress-related cellular processes. The pathological effects of dysregulated ASM activity are evident in several human diseases and indicate an important functional role for ASM regulation. We investigated alternative splicing as a possible mechanism for regulating cellular ASM activity. METHODOLOGY/PRINCIPAL FINDINGS We identified three novel ASM splice variants in human cells, termed ASM-5, -6 and -7, which lack portions of the catalytic- and/or carboxy-terminal domains in comparison to full-length ASM-1. Differential expression patterns in primary blood cells indicated that ASM splicing might be subject to regulatory processes. The newly identified ASM splice variants were catalytically inactive in biochemical in vitro assays, but they decreased the relative cellular ceramide content in overexpression studies and exerted a dominant-negative effect on ASM activity in physiological cell models. CONCLUSIONS/SIGNIFICANCE These findings indicate that alternative splicing of ASM is of functional significance for the cellular stress response, possibly representing a mechanism for maintaining constant levels of cellular ASM enzyme activity.
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Affiliation(s)
- Cosima Rhein
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Philipp Tripal
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Angela Seebahn
- Institute of Biochemistry, Emil-Fischer-Centre, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Alice Konrad
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Marcel Kramer
- Leibniz Institute for Age Research – Fritz Lipmann Institute and Center for Sepsis Control and Care at Jena University Hospital, Jena, Germany
| | - Christine Nagel
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Jonas Kemper
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Jens Bode
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Christiane Mühle
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Erich Gulbins
- Department of Molecular Biology, University of Duisburg-Essen, Essen, Germany
| | - Martin Reichel
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Cord-Michael Becker
- Institute of Biochemistry, Emil-Fischer-Centre, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Johannes Kornhuber
- Department of Psychiatry and Psychotherapy, University Hospital, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
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Abstract
Interferon-α (IFN-α), a type I IFN, is a well-known antitumoral agent. The investigation of its clinical properties in acute myeloid leukemia (AML) has been prompted by its pleiotropic antiproliferative and immune effects. So far, integration of IFN-α in the therapeutic arsenal against AML has been modest in view of the divergent results of clinical trials. Recent insights into the key pharmacokinetic determinants of the clinical efficacy of IFN along with advances in its pharmaceutical formulation, have sparked renewed interest in its use. This paper reviews the possible applicability of IFN-α in the treatment of AML and provides a rational basis to re-explore its efficacy in clinical trials.
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Berthon C, Driss V, Liu J, Kuranda K, Leleu X, Jouy N, Hetuin D, Quesnel B. In acute myeloid leukemia, B7-H1 (PD-L1) protection of blasts from cytotoxic T cells is induced by TLR ligands and interferon-gamma and can be reversed using MEK inhibitors. Cancer Immunol Immunother 2010; 59:1839-49. [PMID: 20814675 PMCID: PMC2945474 DOI: 10.1007/s00262-010-0909-y] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Accepted: 08/16/2010] [Indexed: 12/15/2022]
Abstract
B7-H1 (PD-L1) is a B7-related protein that inhibits T-cell responses. B7-H1 participates in the immunoescape of cancer cells and is also involved in the long-term persistence of leukemic cells in a mouse model of leukemia. B7-H1 can be constitutively expressed by cancer cells, but is also induced by various stimuli. Therefore, we examined the constitutive and inducible expression of B7-H1 and the consequences of this expression in human acute myeloid leukemia (AML). We analyzed B7-H1 expression in a cohort of 79 patients with AML. In addition, we studied blast cells after incubation with interferon-gamma or toll-like receptors (TLR) ligands. Finally, we evaluated functionality of cytotoxic T-cell activity against blast cells. Expression of B7-H1 upon diagnosis was high in 18% of patients. Expression of TLR2, 4 and 9 was detected in one-third of AML samples. Expression of TLR2 and TLR4 ligands or IFN-γ induced by B7-H1 was found to protect AML cells from CTL-mediated lysis. Spontaneous B7-H1 expression was also found to be enhanced upon relapse in some patients. MEK inhibitors, including UO126 and AZD6244, reduced B7-H1 expression and restored CTL-mediated lysis of blast cells. In AML, B7-H1 expression by blasts represents a possible immune escape mechanism. The inducibility of B7-H1 expression by IFN-γ or TLR ligands suggests that various stimuli, either produced during the immune response against leukemia cells or released by infectious microorganisms, could protect leukemic cells from T cells. The efficacy of MEK inhibitors against B7-H1-mediated inhibition of CTLs suggests a possible cancer immunotherapy strategy using targeted drugs.
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Affiliation(s)
- Céline Berthon
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
- Service des Maladies du Sang, Centre Hospitalier et Universitaire de Lille, Rue Polonovski, 59037 Lille, France
| | - Virginie Driss
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
| | - Jizhong Liu
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
| | - Klaudia Kuranda
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
| | - Xavier Leleu
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
- Service des Maladies du Sang, Centre Hospitalier et Universitaire de Lille, Rue Polonovski, 59037 Lille, France
| | - Nathalie Jouy
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
| | - Dominique Hetuin
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
| | - Bruno Quesnel
- INSERM, unit 837, Institut de Recherche sur le Cancer de Lille, Lille, France
- Université Nord de France, Institut Fédératif de Recherche 114, Lille, France
- Service des Maladies du Sang, Centre Hospitalier et Universitaire de Lille, Rue Polonovski, 59037 Lille, France
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Park JH, Yoon HE, Kim DJ, Kim SA, Ahn SG, Yoon JH. Toll-like receptor 5 activation promotes migration and invasion of salivary gland adenocarcinoma. J Oral Pathol Med 2010; 40:187-93. [DOI: 10.1111/j.1600-0714.2010.00929.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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Hanafi LA, Bolduc M, Gagné MEL, Dufour F, Langelier Y, Boulassel MR, Routy JP, Leclerc D, Lapointe R. Two distinct chimeric potexviruses share antigenic cross-presentation properties of MHC class I epitopes. Vaccine 2010; 28:5617-26. [PMID: 20600515 DOI: 10.1016/j.vaccine.2010.06.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Accepted: 06/07/2010] [Indexed: 11/29/2022]
Abstract
Chimeric VLPs made of papaya mosaic virus (PapMV) trigger a CTL response through antigenic presentation of epitopes on MHC class I. Here, a chimeric VLP composed of malva mosaic virus (MaMV) was shown to share similar properties. We demonstrated the capacity of both VLPs to enter human APCs. The chimeric constructions were cross-presented in CD40-activated B lymphocytes leading to in vitro expansion of antigen-specific T lymphocytes. We showed that high concentrations of chimeric MaMV induced cell death, suggesting that some modifications can trigger collateral effects in vitro. Results suggest that potexvirus VLPs are an attractive vaccine platform for inducing a CTL response.
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Affiliation(s)
- Laïla-Aïcha Hanafi
- Research Centre, Centre hospitalier de l'Université de Montréal (CRCHUM) - Hôpital Notre-Dame, Université de Montréal and Institut du Cancer de Montréal, Montréal, Québec, Canada
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Li X, Jiang S, Tapping RI. Toll-like receptor signaling in cell proliferation and survival. Cytokine 2009; 49:1-9. [PMID: 19775907 DOI: 10.1016/j.cyto.2009.08.010] [Citation(s) in RCA: 221] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Accepted: 08/25/2009] [Indexed: 02/06/2023]
Abstract
Toll-like receptors (TLRs) are important sensors of foreign microbial components as well as products of damaged or inflamed self tissues. Upon sensing these molecules, TLRs initiate a series of downstream signaling events that drive cellular responses including the production of cytokines, chemokines, and other inflammatory mediators. This outcome results from the intracellular assembly of protein complexes that drive phosphorylation and other signaling cascades ultimately leading to chromatin remodeling and transcription factor activation. In addition to driving inflammatory responses, TLRs also regulate cell proliferation and survival which serves to expand useful immune cells and integrate inflammatory responses and tissue repair processes. In this context, central TLR signaling molecules, such as the mitogen-activated protein kinases (MAPK) and phosphoinositide 3-kinase (PI3K), play key roles. In addition, four major groups of transcription factors which are targets of TLR activation also control cell fate. This review focuses on the role of TLR signaling as it relates to cell proliferation and survival. This topic not only has important implications for understanding host defense and tissue repair, but also cancer which is often associated with conditions of chronic inflammation.
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Affiliation(s)
- Xinyan Li
- Department of Microbiology, University of Illinois at Urbana-Champaign, USA
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Yusuf N, Nasti TH, Meleth S, Elmets CA. Resveratrol enhances cell-mediated immune response to DMBA through TLR4 and prevents DMBA induced cutaneous carcinogenesis. Mol Carcinog 2009; 48:713-23. [PMID: 19142898 DOI: 10.1002/mc.20517] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Toll-like receptors (TLRs) activate signals that are critically involved in innate immune responses and that contribute to the initiation of adaptive immune responses. Resveratrol (trans-3,5,4-trihydroxystilbene), a polyphenol found in red grapes and in several other plant sources, is an effective chemopreventive agent in cutaneous chemical carcinogenesis. In this study, we investigated whether TLR4 was required for the chemopreventive action of resveratrol in DMBA skin carcinogenesis. For this purpose, mice with normal and deficient TLR4 function were compared when pretreated with resveratrol and then subjected to a DMBA-induced skin carcinogenesis protocol. There were fewer tumors/group (P < 0.001) in resveratrol treated TLR4 competent C3H/HeN mice than in TLR4 deficient C3H/HeJ mice. In addition, the size of tumors in C3H/HeN mice was reduced in vivo and their survival in vitro was inhibited by resveratrol to a significantly greater extent than in C3H/HeJ mice. Resveratrol inhibited angiogenesis to a much greater extent in the TLR4 competent mice than in TLR4 deficient mice. IFN-gamma and IL-12 levels were also increased in TLR4 competent mice compared to TLR4 deficient mice, and TLR4 competent C3H/HeN mice exhibited a greater increase in the cell-mediated immune response to DMBA. The results of this study indicate that TLR4 is an important mediator of resveratrol chemoprevention in DMBA skin tumorigenesis.
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Affiliation(s)
- Nabiha Yusuf
- Department of Dermatology, Skin Diseases Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294-0019, USA
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Toll-like receptors and their role in carcinogenesis and anti-tumor treatment. Cell Mol Biol Lett 2008; 14:248-72. [PMID: 19096763 PMCID: PMC6275910 DOI: 10.2478/s11658-008-0048-z] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2008] [Accepted: 12/09/2008] [Indexed: 01/07/2023] Open
Abstract
Toll-like receptors (TLRs) have been described as major components of the innate immune system, recognizing the conserved molecular structures found in the large groups of pathogens called pathogen-associated molecular patterns (PAMPs). TLR expression is ubiquitous, from epithelial to immunocompetent cells. TLR ligation triggers several adapter proteins and downstream kinases, leading to the induction of key pro-inflammatory mediators but also anti-inflammatory and anti-tumor cytokines. The result of this activation goes beyond innate immunity to shape the adaptive responses against pathogens and tumor cells, and maintains host homeostasis via cell debris utilization. TLRs have already become potent targets in infectious disease treatment and vaccine therapy and in neoplastic disease treatment, due to their ability to enhance antigen presentation. However, some studies show the dual effect of TLR stimulation on malignant cells: they can be proapoptotic or promote survival under different conditions. It is therefore crucial to design further studies assessing the biology of these receptors in normal and transformed cells. The established role of TLRs in human disease therapy is based on TLR7 and TLR4 agonists, respectively for the novel treatment of some types of skin cancer and for the anti-hepatitis B virus vaccine. Some clinical trials involving TLR agonists as potent enhancers of the anti-tumor response in solid tumors have begun.
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