Anterograde trafficking of Toll-like receptors requires the cargo sorting adaptors TMED-2 and 7

Toll-Like Receptors (TLRs) play a pivotal role in immunity by recognising conserved structural features of pathogens and initiating the innate immune response. TLR signalling is subject to complex regulation that remains poorly understood. Here we show that two small type I transmembrane receptors, TMED2 and 7, that function as cargo sorting adaptors in the early secretory pathway are required for transport of TLRs from the ER to Golgi. Protein interaction studies reveal that TMED7 interacts with TLR2, TLR4 and TLR5 but not with TLR3 and TLR9. On the other hand, TMED2 interacts with TLR2, TLR4 and TLR3. Dominant negative forms of TMED7 suppress the export of cell surface TLRs from the ER to the Golgi. By contrast TMED2 is required for the ER-export of both plasma membrane and endosomal TLRs. Together, these findings suggest that association of TMED2 and TMED7 with TLRs facilitates anterograde transport from the ER to the Golgi.     

Dual character of Toll-like receptor signaling: Pro-tumorigenic effects and anti-tumor functions

As a major class of pattern-recognition receptors, Toll-like receptors (TLRs) play a critical role in defense against invading pathogens. Increasing evidence demonstrates that, in addition to infection, TLRs are involved in other important pathological processes, such as tumorigenesis. Activation of TLRs results in opposing outcomes, pro-tumorigenic effects and anti-tumor functions. TLR signaling can inhibit apoptosis and promote chronic inflammation-induced tumorigenesis. TLR activation in tumor cells and immune cells can induce production of cytokines, increase tumor cell proliferation and apoptosis resistance, promote invasion and metastasis, and inhibit immune cell activity resulting in tumor immune escape. In contrast, the engagement of other TLRs directly induces growth inhibition and apoptosis of tumor cells and triggers activation of immune cells enhancing anti-tumor immune responses. Thus, the interpretation of the precise function of each TLR in tumors is very important for targeting TLRs and using TLR agonists in tumor therapy. We review the role of TLR signaling in tumors and discuss the factors that affect outcomes of TLR activation.     

唾液酸酶Neu1及其相关信号通路研究进展

唾液酸广泛存在于生物体内,常存在于糖复合物的糖链末端,对组织器官特别是脑神经的发育至关重要,并且与多种疾病的发生和发展过程密切相关.唾液酸被唾液酸酶水解后,可改变糖复合物的构象从而调控相关因子的生物学功能.在目前发现的4种唾液酸酶中,对Neu1的研究较为深入.研究表明,Neu1的剪切底物具有多样性,其与细胞表面受体的结构和功能调节密切相关.随着研究的深入,Neu1逐渐被认为是唾液酸介导的调控疾病发生过程中的重要因子,Neu1在人类疾病中的作用比预想的还要深远.本篇综述了在已有总结的唾液酸酶性质和生理病理学功能的基础上,概述了近年来Neu1的研究进展,并对其作用及与不同细胞表面受体的相互作用机制做了总结.     

Potential roles and targeted therapy of the CXCLs/CXCR2 axis in cancer and inflammatory diseases

The chemokine receptor CXCR2 and its ligands are implicated in the progression of tumours and various inflammatory diseases. Activation of the CXCLs/CXCR2 axis activates multiple signalling pathways, including the PI3K, p38/ERK, and JAK pathways, and regulates cell survival and migration. The CXCLs/CXCR2 axis plays a vital role in the tumour microenvironment and in recruiting neutrophils to inflammatory sites. Extensive infiltration of neutrophils during chronic inflammation is one of the most important pathogenic factors in various inflammatory diseases. Chronic inflammation is considered to be closely correlated with initiation of cancer. In addition, immunosuppressive effects of myeloid-derived suppressor cells (MDSCs) against T cells attenuate the anti-tumour effects of T cells and promote tumour invasion and metastasis. Over the last several decades, many therapeutic strategies targeting CXCR2 have shown promising results and entered clinical trials. In this review, we focus on the features and functions of the CXCLs/CXCR2 axis and highlight its role in cancer and inflammatory diseases. We also discuss its potential use in targeted therapies.     

Nod1-mediated lipolysis promotes diacylglycerol accumulation and successive inflammation via PKCδ-IRAK axis in adipocytes

Chronic inflammation contributes to obesity mediated metabolic disturbances, including insulin resistance. Obesity is associated with altered microbial load in metabolic tissues that can contribute to metabolic inflammation. Different bacterial components such as, LPS, peptidoglycans have been shown to underpin metabolic disturbances through interaction with host innate immune receptors. Activation of Nucleotide-binding oligomerization domain-containing protein 1 (Nod1) with specific peptidoglycan moieties promotes insulin resistance, inflammation and lipolysis in adipocytes. However, it was not clear how Nod1-mediated lipolysis and inflammation is linked. Here, we tested if Nod1-mediated lipolysis caused accumulation of lipid intermediates and promoted cell autonomous inflammation in adipocytes. We showed that Nod1-mediated lipolysis caused accumulation of diacylglycerol (DAG) and activation of PKCδ in 3T3-L1 adipocytes, which was prevented with a Nod1 inhibitor. Nod1-activated PKCδ caused downstream stimulation of IRAK1/4 and was associated with increased expression of proinflammatory cytokines such as, IL-1β, IL-18, IL-6, TNFα and MCP-1. Pharmacological inhibition or siRNA mediated knockdown of IRAK1/4 attenuated Nod1-mediated activation of NF-κB, JNK, and the expression of proinflammatory cytokines. These results reveal that Nod1-mediated lipolysis promoted accumulation of DAG, which engaged PKCδ and IRAK1/4 to augment inflammation in 3T3-L1 adipocytes.     

Escherichia coli ghosts promote innate immune responses in human keratinocytes

Bacterial ghosts (BGs) as non-living bacterial envelopes devoid of cytoplasmic content with preserved and intact inner and outer membrane structures of their living counterparts have been used to study the ability of their surface components for the induction of antimicrobial peptides and pro-inflammatory cytokines in human primary keratinocytes (KCs). Quantitative real-time PCR analysis revealed that incubation of KCs with BGs generated from wild-type Escherichia coli induced the mRNA expression of antimicrobial psoriasin (S100A7c) in a BGs particle concentration-dependent manner. Using immunoblot analysis we showed that BGs generated from the flagellin-deficient (ΔFliC) E. coli strain NK9375 were as effective as its isogenic wild-type (wt) E. coli strain NK9373 to induce psoriasin expression when normalized to BG particles being taken up by KCs. However, results obtained from endocytic activity of KCs reflect that internalization of BGs is greatly dependent on the presence of flagellin on the surface of BGs. Moreover, BGs derived from wt E. coli NK9373 strongly induced the release of the pro-inflammatory cytokines IL-6 and IL-8, compared to ΔFliC E. coli NK9375 BGs. Taken together, obtained data demonstrate that non-living BGs possessing all bacterial bio-adhesive surface properties in their original state while not posing any infectious threat have the capacity to induce the expression of innate immune modulators and that these responses are partially dependent on the presence of flagellin.     

In vitro response to Candida albicans in cultures of whole human blood from young and aged donors

Invasive infections with opportunistic fungi, such as Candida albicans, have become an increasing problem in aged adults in recent years. This work investigates the influence of human ageing on C. albicans recognition by toll-like receptors (TLRs), essential components of the innate immune system, using a cohort of 96 young (15-42 years) and aged (>70 years) human volunteers. No significant differences between aged and young donors were observed on (1) cell surface TLR2, TLR6 and TLR4 expression on lymphocytes, monocytes and granulocytes, (2) production of cytokines [IL-8, IL-1beta, IL-6, IL-10, tumour necrosis factor (TNF)-alpha and IL-12p70] and prostaglandin E(2) (PGE(2)) by whole human blood in response to C. albicans and (3) fungicidal activity of whole blood. A statistically significant higher titre of natural anti-C. albicans antibodies was found in plasma of volunteers between 80 and 95 years old when compared with other age groups, probably as a consequence of the increased levels of serum Ig that has been described in elderly subjects. Therefore, the results indicate that the increased susceptibility to C. albicans infections in the elderly is not a consequence of defects in TLRs expression or signalling, nor of an impaired fungicidal activity of blood.     

Triggering of TLR3 by polyI:C in human corneal epithelial cells to induce inflammatory cytokines

Epithelial cells of the ocular surface are key in the first-line defense as a part of the mucosal immune system against pathogens. We investigated whether polyI:C induces the production by human corneal epithelial cells (HCEC) of pro-inflammatory cytokines and IFN-beta, and whether Toll-like receptor (TLR)-3 expression is amplified by polyI:C. TLR3 was expressed on the surface of HCEC. Stimulation with polyI:C elicited the elevated production and mRNA expression of IL-6 and IL-8 in HCEC. While polyI:C induced IFN-beta, far stronger than human fibroblasts, and TLR3 gene expression in HCEC, LPS stimulation did not. Similarly, polyI:C, but not LPS, induced the gene expression of IkappaBalpha and MAIL, members of the IkappaB family, in HCEC. The innate immune response of HCEC is distinct from that of immune-competent cells, and we suggest that this is indicative of the symbiotic relationship between corneal epithelium and microbes inhabiting the ocular surface.