Mutational analysis identifies residues crucial for homodimerization of myeloid differentiation factor 88 (MyD88) and for its function in immune cells.

Myeloid differentiation factor 88 (MyD88) is an adaptor protein that transduces intracellular signaling pathways evoked by the Toll-like receptors (TLRs) and interleukin-1 receptors (IL-1Rs). MyD88 is composed of an N-terminal death domain (DD) and a C-terminal Toll/IL-1 receptor (TIR) domain, separated by a short region. Upon ligand binding, TLR/IL-1Rs hetero- or homodimerize and recruit MyD88 through their respective TIR domains. Then, MyD88 oligomerizes via its DD and TIR domain and interacts with the interleukin-1 receptor-associated kinases (IRAKs) to form the Myddosome complex. We performed site-directed mutagenesis of conserved residues that are located in exposed regions of the MyD88-TIR domain and analyzed the effect of the mutations on MyD88 signaling. Our studies revealed that mutation of Glu(183), Ser(244), and Arg(288) impaired homodimerization of the MyD88-TIR domain, recruitment of IRAKs, and activation of NF-κB. Moreover, overexpression of two green fluorescent protein (GFP)-tagged MyD88 mini-proteins (GFP-MyD88151-189 and GFP-MyD88168-189), comprising the Glu(183) residue, recapitulated these effects. Importantly, expression of these dominant negative MyD88 mini-proteins competed with the function of endogenous MyD88 and interfered with TLR2/4-mediated responses in a human monocytic cell line (THP-1) and in human primary monocyte-derived dendritic cells. Thus, our studies identify novel residues of the TIR domain that are crucially involved in MyD88 homodimerization and TLR signaling in immune cells.

Anti-proliferative effect of a triazole derivative (ST1959) on LNCaP human prostate cancer cells through down-regulation of cyclin and androgen receptor expression.

BACKGROUND: Previous studies demonstrated that ST1959, a triazole derivative endowed with immunomodulatory activities, also exerts inhibitory effects on proliferation and survival of a panel of tumor cells. In this study, we sought to ascertain the effects of ST1959 on the growth of androgen-dependent and androgen-independent prostate cancer (PCa) cells. METHODS: The growth of androgen-dependent (LNCaP) and androgen-independent (PC3, DU-145) cells was analyzed in vitro both in the presence and absence of ST1959. Modulation of cyclin and androgen receptor (AR) expression following treatment with ST1959 was analyzed by Western blot and cytofluorimetric analysis. RESULTS: We observed that ST1959 causes a significant growth inhibition of LNCaP cells without affecting proliferation of androgen-insensitive DU-145 and PC3 cell lines. These effects were associated with G0/G1 cell cycle arrest and down-regulation of cyclin D1, A and B and AR expression. CONCLUSIONS: Our present findings indicate that the anti-proliferative activity of ST1959 on cell growth of androgen-dependent LNCaP PCa cells may be brought about by decreasing expression of functional AR and selected cyclins, ultimately leading to cell growth inhibition.

Identification of critical residues of the MyD88 death domain involved in the recruitment of downstream kinases.

MyD88 couples the activation of the Toll-like receptors and interleukin-1 receptor superfamily with intracellular signaling pathways. Upon ligand binding, activated receptors recruit MyD88 via its Toll-interleukin-1 receptor domain. MyD88 then allows the recruitment of the interleukin-1 receptor-associated kinases (IRAKs). We performed a site-directed mutagenesis of MyD88 residues, conserved in death domains of the homologous FADD and Pelle proteins, and analyzed the effect of the mutations on MyD88 signaling. Our studies revealed that mutation of residues 52 (MyD88(E52A)) and 58 (MyD88(Y58A)) impaired recruitment of both IRAK1 and IRAK4, whereas mutation of residue 95 (MyD88(K95A)) only affected IRAK4 recruitment. Since all MyD88 mutants were defective in signaling, recruitment of both IRAKs appeared necessary for activation of the pathway. Moreover, overexpression of a green fluorescent protein (GFP)-tagged mini-MyD88 protein (GFP-MyD88-(27-72)), comprising the Glu(52) and Tyr(58) residues, interfered with recruitment of both IRAK1 and IRAK4 by MyD88 and suppressed NF-kappaB activation by the interleukin-1 receptor but not by the MyD88-independent TLR3. GFP-MyD88-(27-72) exerted its effect by titrating IRAK1 and suppressing IRAK1-dependent NF-kappaB activation. These experiments identify novel residues of MyD88 that are crucially involved in the recruitment of IRAK1 and IRAK4 and in downstream propagation of MyD88 signaling.

Pharmacological inhibition of TLR9 activation blocks autoantibody production in human B cells from SLE patients.

OBJECTIVES: Toll-like receptor 9 (TLR9), which recognizes hypomethylated DNA [cytosine-phosphate-guanine (CpG)], plays a role in the maintenance of serological memory and has been recently implicated in the pathogenesis of SLE. We previously reported that in vitro TLR9 triggers memory B-cell differentiation into antibody-producing cells, and that the MyD88-inhibitor ST2825 blocks TLR9-induced plasma cell (PC) generation. Here, we investigated whether memory B cells produce autoantibodies in SLE patients with active disease or in clinical remission, and whether ST2825 could inhibit PC generation in SLE patients. METHODS: Peripheral blood mononuclear cells from 10 SLE patients in clinical remission and 2 with active SLE were cultured in the presence of CpG with or without ST2825. Phenotypical analysis of CpG-stimulated cells was performed by flow cytometry. Supernatants were collected to measure antibody production by ELISA and to detect autoantibodies by IF. RESULTS: CpG-induced TLR9 stimulation caused autoantibody secretion in patients with active disease and in the majority of patients in clinical remission. Inhibition of MyD88 completely blocked the de novo generation of PCs and the secretion of autoantibodies. CONCLUSIONS: Autoreactive B cells persist in SLE patients during disease remission in the circulating B-cell memory pool. TLR9-dependent activation of memory B cells by pathogens could be one of the mechanisms triggering relapses in SLE. Compounds targeting the TLR/MyD88 pathway may be used as novel therapeutic tools to treat acute disease and to prevent relapses in SLE patients.

Targeting TLR/IL-1R signalling in human diseases.

The members of Toll-like receptor/interleukin (IL)-1 receptor (TLR/IL-1R) superfamily play a fundamental role in the immune response. These receptors detect microbial components and trigger complex signalling pathways that result in increased expression of multiple inflammatory genes. On the other hand, an aberrant activation of TLR/IL-1R signalling can promote the onset of inflammatory and autoimmune diseases, raising the interest in the development of therapeutic strategies for the control of their function. In this review, we illustrate the structural and functional features of TLR/IL-1R proteins and discuss some recent advances in the approaches undertaken to develop anti-inflammatory therapeutic drugs. In particular, we will focus on inhibitors, such as decoy peptides and synthetic mimetics, that interfere with protein-protein interactions between signalling molecules of the TLR/IL-1R superfamily. Given their central role in innate and adaptive immune responses, it is foreseen that pharmaceutical modulation of TLR/IL-1R signalling pathways by these drugs might yield clinical benefits in the treatment of inflammatory and autoimmune diseases.

Design, synthesis, and in vitro activity of peptidomimetic inhibitors of myeloid differentiation factor 88.

We describe the design and synthesis of a peptidomimetic library derived from the heptapeptide Ac-RDVLPGT-NH 2, belonging to the Toll/IL-1 receptor (TIR) domain of the adaptor protein MyD88 and effective in inhibiting its homodimerization. The ability of the peptidomimetics to inhibit protein-protein interaction was assessed by yeast 2-hybrid assay and further validated in a mammalian cell system by evaluating the inhibition of NF-kappaB activation, a transcription factor downstream of MyD88 signaling pathway that allows production of essential effector molecules for immune and inflammatory responses.

Efficacy of a nanocochleate-encapsulated 3,5-diaryl-s-triazole derivative in a murine model of graft-versus-host disease.

We have previously demonstrated that the compound 3-(2-ethylphenyl)-5-(3-methoxyphenyl)-1H-1,2,4-triazole exerts immunosuppressive effects in several experimental models of autoimmunity. These results were achieved by subcutaneously administering ST1959 after dissolution in an oily vehicle, because of its poor water solubility. To circumvent this problem, we sought to determine whether nanocochleate technology could be successfully exploited to deliver ST1959 and protect mice undergoing lethal acute graft-versus-host disease (GVHD). Orally-administered encochleated ST1959 significantly protected animals from lethality, resulting in survival rates of 57% and 100% at doses of 2 and 10 mg/kg, respectively, whereas oral administration of 2 mg/kg ST1959, mixed with empty nanocochleates, was completely inactive. Increased survival was associated with diminished serum chemokine levels and donor CD8+ T cells in the spleen of ST1959-treated mice. Moreover, ST1959 treatment significantly counteracted GVHD-induced normocitic anemia by increasing hemoglobin, hematocrit, platelet, and red and white blood cell counts. Overall, these data show that orally-administered encochleated ST1959 significantly protects mice from GVHD.

Pivotal Advance: Inhibition of MyD88 dimerization and recruitment of IRAK1 and IRAK4 by a novel peptidomimetic compound.

MyD88 is an adaptor protein, which plays an essential role in the intracellular signaling elicited by IL-1R and several TLRs. Central to its function is the ability of its Toll/IL-1R translation initiation region (TIR) domain to heterodimerize with the receptor and to homodimerize with another MyD88 molecule to favor the recruitment of downstream signaling molecules such as the serine/threonine kinases IL-1R-associated kinase 1 (IRAK1) and IRAK4. Herein, we have synthesized and tested the activity of a synthetic peptido-mimetic compound (ST2825) modeled after the structure of a heptapeptide in the BB-loop of the MyD88-TIR domain, which interferes with MyD88 signaling. ST2825 inhibited MyD88 dimerization in coimmunoprecipitation experiments. This effect was specific for homodimerization of the TIR domains and did not affect homodimerization of the death domains. Moreover, ST2825 interfered with recruitment of IRAK1 and IRAK4 by MyD88, causing inhibition of IL-1beta-mediated activation of NF-kappaB transcriptional activity. After oral administration, ST2825 dose-dependently inhibited IL-1beta-induced production of IL-6 in treated mice. Finally, we observed that ST2825 suppressed B cell proliferation and differentiation into plasma cells in response to CpG-induced activation of TLR9, a receptor that requires MyD88 for intracellular signaling. Our results indicate that ST2825 blocks IL-1R/TLR signaling by interfering with MyD88 homodimerization and suggest that it may have therapeutic potential in treatment of chronic inflammatory diseases.

Dissecting drug and vehicle metabolic effects in rats by a metabonomic approach.

A combined application of high resolution (1)H NMR spectroscopy and multivariate statistical techniques focused on establishing a consistent statistical approach to metabonomic studies was tested. The data reduction, which is preliminary to the application of multivariate analysis to NMR spectra, was carried out by means of two complementary methods: pure Pattern Recognition (PR) and Assigned Signal Analysis (ASA). The simultaneous use of both approaches allowed us to obtain additional information in the analysis of metabonomic data, compared to the use of PR alone. This additional information consists in the possibility of a biochemical interpretation of the effects induced by treatment with xenobiotics, such as drugs or drug vehicles, on the metabolic networks of the systems under investigation. This approach allowed us to ascertain that a single-dose treatment with ST1959 vehicled by Sesame oil affects the production of hepatic glucose associated to an increment of the amino acid ketogenic process.

Effect of a novel immunosuppressant, ST1959, on the immune system and renal allograft survival in rats.

BACKGROUND: ST1959 is a 3,5-diaryl-s-triazole belonging to a novel class of contragestional agents with immunosuppressant activity. The aim of the present study was to investigate the effects of this drug on allogeneic immune response and on renal allograft survival in rats. METHODS: One group of naive and one group of allosensitized Lewis rats received ST1959 (0.5 mg/kg/day for 6 days administered subcutaneously). The respective control groups received vehicle alone. At the end of treatment, all rats were killed and thymus, spleen, lymph nodes, bone marrow, and blood were harvested. Cell number, leukocyte subpopulations, and lymphocyte alloreactivity were evaluated. Three additional groups of Lewis rats received an allogeneic (Brown Norway [BN]) kidney transplant: two groups received ST1959 (0.5 mg/kg daily until death or for 6 days and then twice weekly), and the last one received vehicle. RESULTS: In naive rats, ST1959 reduced the percentage of CD4CD8 (74.2+/-2.7%; vehicle, 89.1+/-1.1%; P<0.05) and increased the percentage of CD4CD8 thymocytes (5.7+/-0.8% vs. 2.8+/-0.4%; P<0.05). Infusion of allogeneic (BN) splenocytes caused a twofold increase of activated CD4 T cells (CD4CD25) that was prevented by ST1959 treatment. Consistently, the alloreactivity of lymphocytes from naive and allosensitized animals treated with ST1959 was significantly lower than that of control rats. ST1959 (in both tested regimens) significantly prolonged renal allograft survival in comparison with vehicle (12.4+/-0.5 vs. 7.7+/-0.5 days; P<0.001). CONCLUSIONS: ST1959 possesses immunomodulatory effects and significantly prolongs survival of renal allografts in rats.

In vivo and in vitro cytokine modulatory activity of newly synthesised 2-aminotetraline derivatives.

In the present study, the protective effect of newly synthesised 2-aminotetralines was investigated in murine models of toxic shock. A few derivatives protected mice against lethality induced by lipopolysaccharide from different bacterial strains and shock induced by staphylococcal enterotoxin B in mice sensitized by D-Galactosamine (D-Galn). Notably, one derivative, S(-)-2-amino-6-fluoro-7-methoxy-1,2,3,4 tetrahydronaphthalene hydrochloride (ST1214), was also effective when administered orally (30 mg kg-1) in a therapeutic regimen. ST1214 markedly inhibited the production of the proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha), Interleukin-1beta (IL-1beta), Interleukin-12 (IL-12), interferon-gamma (IFN-gamma), as well as the inflammatory mediator nitric oxide (NO), and concurrently enhanced the production of the anti-inflammatory cytokine IL-10. Moreover, ST1214 dose-dependently reduced TNF-alpha production by human peripheral blood mononuclear cells and promonocytic THP-1 cells in vitro. In the latter, ST1214 was found to inhibit lipopolysaccharide-induced TNF-alpha secretion but not cytokine mRNA accumulation. These results suggest that the mechanism of action of ST1214 involves blockade of posttranscriptional events of TNF-alpha production, apparently independent of p38 and ERK kinase activity. These results show beneficial effects of 2-aminotetralines in murine shock models and indicate a distinct counter-regulatory activity in down-regulating proinflammatory cytokine response, and upregulating IL-10. One derivative, i.e., ST1214, can be regarded as a lead compound in the development of novel drugs effective in anti-inflammatory strategies.

Ameliorating effects of the immunomodulator 3-(2-ethylphenyl)-5-(3-methoxyphenyl)-1H-1,2,4-triazole in an experimental model of colitis in the rat.

The therapeutic efficacy of the immunomodulator 3-(2-ethylphenyl)-5-(3-methoxyphenyl)-1H-1,2,4-triazole (ST1959) in colonic inflammation was assessed in rats. One hour following colonic instillation of ethanolic 2,4,6-trinitrobenzene sulphonic acid (TNBS), intracolonic administration of 0.4 mg/kg ST1959 was started and continued once daily for 1 or 2 weeks. Daily administration of ST1959 for 1 week significantly reduced macroscopic and histological damage, myeloperoxidase activity, and colonic tissue levels of tumour necrosis factor-alpha and interferon-gamma. ST1959 did not affect interleukin-12 levels but significantly enhanced the production of interleukin-10 (sixfold increase). Two weeks of ST1959 treatment reduced the thickness of the colonic wall and myeloperoxidase activity to the same extent, and the histologic appearance of the mucosa was largely restored. The ameliorating effects seem to be ascribable to an impairment of both neutrophil infiltration/activation and tumour necrosis factor-alpha and interferon-gamma production, possibly consequent to the observed increase in the colonic tissue levels of the potent anti-inflammatory cytokine interleukin-10. Similar results were observed with the reference drug 5-aminosalycilic acid.

Targeting the Toll-like receptor/interleukin 1 receptor pathway in human diseases: rational design of MyD88 inhibitors.

Toll-like receptor (TLR)/interleukin (IL) 1 receptor (IL-1R) play a fundamental role in the immune response. These receptors are distributed in various cellular compartments and recognize different components of pathogens. All TLR/IL-1Rs, with the exception of TLR3, interact with MyD88, an intracellular adapter protein that triggers a signaling cascade that culminates in the expression of inflammatory genes. Because aberrant activation of TLR/IL-1Rs can promote the onset of inflammatory or autoimmune diseases and malignancies, this pathway has attracted considerable interest as a potential therapeutic target. Given the central role of MyD88 in TLR/IL-1R signaling, we set out different strategies to develop drugs that can block its function. Structural and functional analysis of the MyD88 domains allowed us to identify crucial residues required for MyD88 homodimerization. Moreover, we developed small cell-permeable peptides and peptidomimetic agents that inhibit MyD88 homodimerization and function. Our results pave the way for the development of new therapeutic drugs for the inhibition of MyD88-dependent signaling.

Peptide-mediated interference of TIR domain dimerization in MyD88 inhibits interleukin-1-dependent activation of NF-{kappa}B.

Myeloid differentiation factor 88 (MyD88) plays a crucial role in the signaling pathways triggered by interleukin (IL)-1 and Toll-like receptors in several steps of innate host defense. A crucial event in this signaling pathway is represented by dimerization of MyD88, which allows the recruitment of downstream kinases like IRAK-1 and IRAK-4. Herein, we have investigated the function of the Toll/IL-1 receptor (TIR) domain in MyD88 homodimerization in cell-free and in vitro experimental settings by using epta-peptides that mimic the BB-loop region of the conserved TIR domain of different proteins. By using a pull-down assay with purified glutathione S-transferase-MyD88 TIR or co-immunoprecipitation experiments, we found that epta-peptides derived from the TIR domain of MyD88 and IL-18R are the most effective in inhibiting homodimerization with either the isolated TIR or full-length MyD88. Moreover, we demonstrated that a cell permeable analog of MyD88 epta-peptide inhibits homodimerization of MyD88 TIR domains in an in vitro cell system and significantly reduces IL-1 signaling, as assayed by activation of the downstream transcription factor NF-kappaB. Our results indicate that the BB-loop in TIR domain of MyD88 is a good target for specific inhibition of MyD88-mediated signaling in vivo.