Biomedical subjects

Hongxing Li

Publications and source records attributed to Hongxing Li.

9 recordsLinked to original sources

PubMed2006

IRF-8/interferon (IFN) consensus sequence-binding protein is involved in Toll-like receptor (TLR) signaling and contributes to the cross-talk between TLR and IFN-gamma signaling pathways.

Toll-like receptor (TLR) and interferon-gamma (IFN-gamma) signaling pathways are important for both innate and adaptive immune responses. However, the cross-talk between these two signaling pathways is incompletely understood. Here we show that IFN-gamma and LPS synergistically induce the expression of proinflammatory factors, including interleukin-1 (IL-1), IL-6, IL-12, NO, and tumor necrosis factor-alpha (TNF-alpha). Comparable synergism was observed between IFN-gamma and peptidoglycan (PGN; a TLR2 ligand) and poly(I:C) (a TLR3 ligand) in the induction of IL-12 promoter activity. IFN-gamma enhanced lipopolysaccharide (LPS)-induced ERK and JNK phosphorylation but had no effect on LPS-induced NF-kappaB activation. Interestingly, we found that IRF-8-/- macrophages were impaired in the activation of LPS-induced ERK and JNK and the production of proinflammatory cytokines induced by LPS or IFN-gamma plus LPS. Retroviral transduction of IRF-8 into IRF-8-/- macrophages rescued ERK and JNK activation. Furthermore, co-immunoprecipitation experiments show that IRF-8 physically interacts with TRAF6 at a binding site between amino acid residues 356 and 305 of IRF-8. Transfection of IRF-8 enhanced TRAF6 ubiquitination, which is consistent with a physical interaction of IRF-8 with TRAF6. Taken together, the results suggest that the interaction of IRF-8 with TRAF6 modulates TLR signaling and may contribute to the cross-talk between IFN-gamma and TLR signal pathways.

Cell Line↗

PubMed2006

Transcytosis of IgE-antigen complexes by CD23a in human intestinal epithelial cells and its role in food allergy.

BACKGROUND & AIMS: Secreted immunoglobulins play an integral role in host defense at mucosal surfaces, and recent evidence shows that IgG can participate in antigen sampling from the intestinal lumen. We examined whether IgE also could facilitate transepithelial antigen sampling. METHODS: Stool samples from food-allergic patients undergoing oral food challenge were analyzed for CD23 and food-specific IgE. CD23 isoform expression on primary human intestinal epithelial cells (IEC) was analyzed by polymerase chain reaction. The role of CD23 isoforms in transcytosis of antigen and IgE-antigen complexes was assessed using polarized human T84 cells retrovirally transfected with CD23a or CD23b. RESULTS: CD23 was expressed constitutively on IECs, and food-allergic patients had increased levels of soluble CD23 and food-specific IgE in the stool after challenge. CD23a, but not CD23b, was expressed by primary human IECs. We show in transcytosis assays that CD23a, but not CD23b, acts as a bidirectional transporter of IgE. In addition, specific IgE facilitated the uptake of antigen from the apical surface of an epithelial monolayer by diverting antigen from delivery to lysosomes. Finally, delivery of antigen-IgE complexes across the epithelial barrier could induce the degranulation of rat basophil leukemia cells transfected with the human high-affinity IgE receptor. CONCLUSIONS: These studies show that CD23a is expressed normally on human IECs, and in the presence of IgE can function as an antigen-sampling mechanism capable of activating subepithelial mast cells. IgE may serve as a secretory immunoglobulin that in concert with CD23 participates in food-induced pathophysiology of the gastrointestinal tract.

Adolescent↗

PubMed2006

Antibody-mediated antigen sampling across intestinal epithelial barriers.

The epithelium of the gastrointestinal tract is the interface between luminal contents and the mucosal immune system. It must function as a selective barrier to limit penetration of antigens yet keep the mucosal immune system "informed" for the purpose of generating oral tolerance responses to food antigens or commensal organisms and host defense responses against pathogens. Alterations in epithelial barrier function have been proposed to play a significant role in gastrointestinal disease. In this review, we will discuss mechanisms of regulation of epithelial barrier function, and we will focus on the emerging understanding of how secreted immunoglobulins play a role in antigen-specific antigen sampling across the gastrointestinal epithelium.

Antibodies↗

PubMed2005

Toll-like receptors on tumor cells facilitate evasion of immune surveillance.

The signal pathways that trigger tumor cell escape from immune surveillance are incompletely understood. Toll-like receptors (TLRs), which activate innate and adaptive immune responses, are thought to be restricted to immune cells. We show here that TLRs, including TLR4, are expressed on tumor cells from a wide variety of tissues, suggesting that TLR activation may be an important event in tumor cell immune evasion. Activation of TLR4 signaling in tumor cells by lipopolysaccharide induces the synthesis of various soluble factors and proteins including interleukin-6, inducible nitric oxide synthase, interleukin-12, B7-H1, and B7-H2, and results in resistance of tumor cells to CTL attack. In addition, lipopolysaccharide-stimulated tumor cell supernatants inhibit both T cell proliferation and natural killer cell activity. Blockade of the TLR4 pathway by either TLR4 short interfering RNA or a cell-permeable TLR4 inhibitory peptide reverses tumor-mediated suppression of T cell proliferation and natural killer cell activity in vitro, and in vivo, delays tumor growth and thus prolongs the survival of tumor-bearing mice. These findings indicate that TLR signaling results in a cascade leading to tumor evasion from immune surveillance. These novel functions of TLRs in tumor biology suggest a new class of therapeutic targets for cancer therapy.

Amino Acid Sequence↗

PubMed2005

Ubiquitin-dependent degradation of interferon regulatory factor-8 mediated by Cbl down-regulates interleukin-12 expression.

Interferon regulatory factor (IRF)-8/interferon consensus sequence-binding protein is regulated by both transcription and degradation. IRF-8 induced in peritoneal macrophages by interferon-gamma and lipopolysaccharide was degraded rapidly, and degradation of IRF-8 was blocked by MG132, the proteasome inhibitor, but inhibitors of calpain and lysosomal enzymes had no effect. The ubiquitination of IRF-8 was shown by co-immunoprecipitation from RAW264.7 macrophages retrovirally transduced with IRF-8 and hemagglutinin-ubiquitin. The dominant negative ubiquitin mutants K48R and K29R inhibited IRF-8 degradation in 293T cells, confirming the relationship between ubiquitination of IRF-8 and its degradation. IRF-8 carboxyl-terminal truncation mutants were not ubiquitinated and were consequently stable, indicating that the carboxyl-terminal domain of IRF-8 controls ubiquitination. The ubiquitin-protein isopeptide ligase (E3) that ubiquitinated IRF-8 was likely to be Cbl, which formed a complex with IRF-8, demonstrable by both immunoprecipitation and gel filtration. Furthermore, IRF-8 stability was increased by dominant negative Cbl, and IRF-8 ubiquitination was significantly attenuated in Cbl-/- cells. Reflecting increased stability and expression, the IRF-8 carboxyl-terminal deletion mutant induced interleukin (IL)-12 p40 promoter activity much more strongly than IRF-8 did. Furthermore, IRF-8-induced IL-12 p40 synthesis in RAW264.7 cells was enhanced by dominant negative Cbl, and peritoneal macrophages from Cbl-/- mice showed increased IL-12 p40 protein production. Taken together, these results suggest that the proteasomal degradation of IRF-8 mediated by the ubiquitin E3 ligase Cbl down-regulates IL-12 expression.

Animals↗

PubMed2004

Interaction of TRAF6 with MAST205 regulates NF-kappaB activation and MAST205 stability.

The binding of immune complexes to macrophage Fcgamma receptor results in a subsequent inhibition of lipopolysaccharide-stimulated interleukin-12 synthesis without affecting the induction of tumor necrosis factor-alpha. RNA interference targeting MAST205, a 205-kDa serine/threonine kinase, and transfection of dominant negative MAST205 mutants also mimic this type II macrophage phenotype. Our previous epistasis experiments suggested that the position of MAST205 in the TLR4 signal pathway was proximal to the IkappaB kinase complex. We now report that MAST205 forms a complex with TRAF6, resulting in the inhibition of TRAF6 NF-kappaB activation. We have identified a peptide (residues 218-233) from the N terminus of MAST205 that, when coupled to a protein transduction domain, inhibits the lipopolysaccharide-stimulated activation of NF-kappaB, modulates the size of the MAST205.TRAF6 complex, and inhibits ubiquitination of TRAF6. A dominant negative N-terminal MAST205 deletion mutant also inhibits TRAF6 ubiquitination. The domain required for degradation of MAST205 after Fcgamma receptor activation resides within the N-terminal 261 residues, and degradation is triggered by protein kinase C isoform phosphorylation of Ser/Thr residues. These results suggest that MAST205 functions as a scaffolding protein controlling TRAF6 activity and, therefore, plays an important role in regulating inflammatory responses.

Animals↗

PubMed2004

Microtubule-associated serine/threonine kinase-205 kDa and Fc gamma receptor control IL-12 p40 synthesis and NF-kappa B activation.

Stimulation of murine macrophages with LPS results in the coordinated activation of a set of proinflammatory cytokines and costimulatory molecules, including TNF-alpha, IL-6, IL-1, IL-8, IL-12, and CD80. Macrophage LPS-induced synthesis of IL-12 is inhibited following FcgammaR ligation; TNF-alpha secretion is unchanged. We report that microtubule-associated serine/threonine kinase-205 kDa (MAST205) is required for LPS-induced IL-12 synthesis. RNA interference-mediated suppression of MAST205 results in the inhibition of LPS-stimulated IL-12 promoter activity and IL-12 secretion, from both J774 cells and bone marrow-derived macrophages. Similarly, dominant-negative MAST205 mutants inhibit LPS-stimulated IL-12 synthesis and NF-kappaB activation, but do not affect IL-1 or TNF-alpha signaling. Finally, macrophage FcgammaR ligation regulates MAST205 by inducing the rapid ubiquitination and proteasomal degradation of the protein.

Animals↗

PubMed2004

Efficient learning algorithms for three-layer regular feedforward fuzzy neural networks.

A key step of using gradient descend methods to develop learning algorithms of a regular feedforward fuzzy neural network (FNN) is to differentiate max--min functions, which contain max and min operations. The paper aims at several objectives. First, investigate further the differentiation of max--min functions. Second, employ general fuzzy numbers, which include triangular and trapezoidal fuzzy numbers as special cases to define a three-layer regular FNN. The general fuzzy numbers related can be approximately determined by their corresponding finite level sets. So, we can approximately represent the input-output (I/O) relationship of the regular FNN as functions of the endpoints of all finite level sets. Third, a fuzzy back-propagation algorithm is presented. And to speed up the convergence of the learning algorithm, a fuzzy conjugate gradient algorithm for fuzzy weights and biases is developed, furthermore, the convergence of the algorithm is analyzed, systematically. Finally, some real simulations demonstrate the efficiency of our learning algorithms. The regular FNN is applied to the approximate realization of fuzzy inference rules and fuzzy functions defined on given compact sets.

Algorithms↗

PubMed2002

Complex formation of the interferon (IFN) consensus sequence-binding protein with IRF-1 is essential for murine macrophage IFN-gamma-induced iNOS gene expression.

This study describes the role of the interferon (IFN) consensus sequence-binding protein (ICSBP or IRF-8) in iNOS gene expression by murine macrophages. An ICSBP binding site in the iNOS promoter region (-923 to -913) was identified using an electrophoretic mobility shift assay and chromatin co-immunoprecipitation. Overexpression of ICSBP greatly enhanced IFN-gamma-induced iNOS promoter activation in RAW264.7 cells, and IFN-gamma-induced iNOS promoter activation was abolished in ICSBP-/- macrophages. Furthermore, transduction of retrovirus-ICSBP in ICSBP-/- macrophages rescued IFN-gamma-induced iNOS gene expression. However, transduction of retrovirus-ICSBP in the absence of IFN-gamma activation did not induce iNOS expression in either RAW264.7 cells or ICSBP-/- macrophages. Interestingly, ICSBP alone transduced into ICSBP-/- macrophages did not bind to IFN-stimulated response element site (-923 to -913) of the iNOS promoter region, although following activation with IFN-gamma, a DNA.protein complex was formed that contains ICSBP and IRF-1. Co-transduction of ICSBP with IRF-1 clearly induces nitric oxide production. In addition, interleukin-4 inhibits IFN-gamma-induced iNOS gene expression by attenuating the physical interaction of ICSBP with IRF-1. Complex formation of ICSBP with IRF-1 is essential for iNOS expression, and interleukin-4 attenuates the physical interaction of ICSBP with IRF-1 resulting in the inhibition of INOS gene expression.

Animals↗