Expression of TRAF6 and pro-inflammatory cytokines through activation of TLR2, TLR4, NOD1, and NOD2 in human periodontal ligament fibroblasts

OBJECTIVE

Human periodontal ligament fibroblasts (HPDLFs) play a crucial role in protecting against oral bacteria in periapical tissue. Toll-like receptors (TLRs) and nucleotide-binding oligomerization domain (NOD) are two major forms of innate immune sensors that recognize microbial pathogens and initiate pro-inflammatory signalling. Tumour necrosis factor receptor-associated factor 6 (TRAF6) is an adapter protein for TLR-mediated nuclear factor-κB (NF-κB) signalling pathway activation that induces the production of pro-inflammatory cytokines. The aim of this study was to investigate the expression of TLR2, TLR4, NOD1, and NOD2 in HPDLFs. We also investigated the expression of TRAF6 and pro-inflammatory cytokines induced by the activation of TLRs and NODs.

METHODS

The expression of TLR2, TLR4, NOD1, and NOD2 was measured by reverse transcription-polymerase chain reaction (RT-PCR), flow cytometry, and immunostaining. HPDLFs were stimulated with TLR and NOD agonists. Then, the expression of TRAF6 was measured by real-time PCR and western blot. Concentrations of IL-1β, IL-6, and IL-8 in the culture supernatants were determined by enzyme-linked immunosorbent assay (ELISA). Finally, by using small interfering RNA (siRNA) for TRAF6, we analysed the production of IL-1β, IL-6, and IL-8 in HPDLFs upon stimulation with TLRs and NODs agonists.

RESULTS

We found clear mRNA and protein expression of TLR2, TLR4, NOD1, and NOD2 in HPDLFs. The expression levels of TRAF6 and pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) were markedly up-regulated upon the activation of TLRs and NODs. Furthermore, the co-activation of TLRs and NODs had synergistic effect on the production of TRAF6 and pro-inflammatory cytokines. We also found TRAF6 suppression resulted in reduced IL-1β, IL-6, and IL-8 expression upon TLR and NOD agonists challenge.

CONCLUSION

These findings indicated that TLR2, TLR4, NOD1, and NOD2 are functional receptors in HPDLFs during innate immune responses to invading bacteria, and a combination of signalling through TLRs and NODs leads to the synergistic enhancement of inflammatory reactions in HPDLFs. In addition, TLR and NOD signalling involving TRAF6 contribute to inflammatory responses in HPDLFs.

Glucosamine and its N-acetyl-phenylalanine derivative prevent TNF-alpha-induced transcriptional activation in human chondrocytes

OBJECTIVES

Glucosamine (GlcN) is used in the treatment of osteoarthritis as symptomatic slow-acting drug, but its mode of action is not completely known. We analyzed the influence of GlcN and its N-acetyl-phenylalanine derivative (NAPA) on mRNA transcription level of TNF-alpha-stimulated genes in cell culture.

METHODS

Human immortalized chondrocyte cell line lbpva55 was stimulated with TNF-alpha and treated with GlcN and NAPA. mRNA transcription level of several genes, identified by complementary DNA microarray (cDNA microarray), was validated by Quantitative Real-Time Polymerase Chain Reaction (Q-RT-PCR).

RESULTS

Several genes, whose mRNA level was increased by TNF-alpha treatment and significantly reduced by GlcN and NAPA in lbpva55 cells, were identified. These include cytokine receptors TNF-R1 and TNF-R2, their associated factor TRAF-6, signaling intermediates IGFB-6 and Rnd1, as well as cell cycle regulating proteins CUL-2 and G1S protein 1. Down- regulation of mRNA expression level of some of these genes is in accordance with inactivation of NF-kB transcription factor. Moreover, we found down-regulation of c-jun mRNA level, a component of AP-1 transcription factor.

CONCLUSIONS

Our study suggests that GlcN and NAPA interfere with activation of NF-kB and AP-1 transcription factors, which are responsible for the expression of genes involved in diverse biological processes, such as cell growth and death, inflammatory and stress responses, accounting for the beneficial effects of GlcN in osteoarthritis.

Tumor necrosis factor receptor superfamily member TROY is a novel melanoma biomarker and potential therapeutic target

Incidence of melanoma continues to rise, and a better understanding of its genetics will be critical to improve diagnosis and develop new treatments. Here, we search for novel melanoma-specific genes that may serve as biomarkers and therapeutic targets by using an in vitro genetic screen. One identified cDNA encoded TROY, a member of the tumor necrosis factor receptor superfamily (TNFRSF). TROY is widely expressed during embryogenesis, but in adults expression is restricted to hair follicles and brain. However, TROY had never been associated with melanoma, and it was selected for further study. First we show that expression in melanoma is specific by semiquantitative RT-PCR analysis of a large panel of established tumor cell lines. Next, specificity of expression was evaluated by immunohistochemistry analysis of primary cell cultures and patient tissues. TROY is expressed in 2/2 primary melanoma cells and 45/45 melanoma tissue samples (p < 0.0001). With the exception of sebaceous glands, TROY is not expressed in normal skin biopsies (p < 0.0001) or primary skin cell cultures that contain keratinocytes and epidermal melanocytes, nor is it expressed in other skin tumor cells (p < 0.0001). Finally, we show that TROY regulates melanoma growth, because replication of melanoma cells with reduced TROY levels through treatment with short-interfering RNA was significantly decreased relative to control cells (p < 0.004). In summary, TROY is the first TNFRSF member that is a biomarker for melanoma. TROY also presents a potentially novel cell surface signaling target for inhibitors, cell and/or antibody-based immunotherapies.

Mammalian cell entry protein of Mycobacterium tuberculosis induces the proinflammatory response in RAW 264.7 murine macrophage-like cells

Mammalian cell entry (Mce1A) protein of Mycobacterium tuberculosis (Mtb) is involved in bacterial entry and survival in macrophages, which has been shown to induce production of tumor necrosis factor alpha (TNF-alpha). It remains unclear whether and how Mce1A functions upon the type I interleukin-1 receptor-associated protein kinase (IRAK-1) and TNF receptor-associated factor 6 (TRAF-6) of important proinflammatory cytokines. In this study, His-tagged Mce1A was expressed and purified. Also, two pieces of small interfering RNA (siRNA) were designed and synthesized by in vitro transcription, which exhibit specific and efficient silencing effect on mce1a expression. Furthermore, RAW 264.7 murine macrophage-like cells were exposed to His-tagged Mce1A or co-transfected with the Mce1A-expressing plasmid and efficient siRNA, and levels of IRAK-1 and TRAF-6 were then determined by Western blot. We show here that Mce1A induces up-regulations of IRAK-1 and TRAF-6 in macrophages in a dose-dependent manner. The level of Caspase-3 closely related with apoptosis was also determined, whereas no changes were observed. These results indicate that Mtb Mce1A protein induces a proinflammatory response in macrophages.