• Molecules and Cells
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• v.46 no.10
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• pp.637-653
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• 2023

The physiology of most organisms, including Drosophila, is heavily influenced by their interactions with certain types of commensal bacteria. Acetobacter and Lactobacillus, two of the most representative Drosophila commensal bacteria, have stimulatory effects on host larval development and growth. However, how these effects are related to host immune activity remains largely unknown. Here, we show that the Drosophila development-promoting effects of commensal bacteria are suppressed by host immune activity. Mono-association of germ-free Drosophila larvae with Acetobacter pomorum stimulated larval development, which was accelerated when host immune deficiency (IMD) pathway genes were mutated. This phenomenon was not observed in the case of mono-association with Lactobacillus plantarum. Moreover, the mutation of Toll pathway, which constitutes the other branch of the Drosophila immune pathway, did not accelerate A. pomorum-stimulated larval development. The mechanism of action of the IMD pathway-dependent effects of A. pomorum did not appear to involve previously known host mechanisms and bacterial metabolites such as gut peptidase expression, acetic acid, and thiamine, but appeared to involve larval serum proteins. These findings may shed light on the interaction between the beneficial effects of commensal bacteria and host immune activity.

• BMB Reports
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• v.41 no.4
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• pp.267-277
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• 2008

Insects mount a robust innate immune response against a wide array of microbial pathogens. The hallmark of the Drosophila humoral immune response is the rapid production of anti-microbial peptides in the fat body and their release into the circulation. Two recognition and signaling cascades regulate expression of these antimicrobial peptide genes. The Toll pathway is activated by fungal and many Gram-positive bacterial infections, whereas the immune deficiency (IMD) pathway responds to Gram-negative bacteria. Recent work has shown that the intensity and duration of the Drosophila immune response is tightly regulated. As in mammals, hyperactivated immune responses are detrimental, and the proper down-modulation of immunity is critical for protective immunity and health. In order to keep the immune response properly modulated, the Toll and IMD pathways are controlled at multiple levels by a series of negative regulators. In this review, we focus on recent advances identifying and characterizing the negative regulators of these pathways.

• Proceedings of the Microbiological Society of Korea Conference
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• 2002.10a
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• pp.40-50
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• 2002

Fruit fly, Drosophila melanogaster has developed efficient immune mechanisms to prevent microbial infection, which are consisted of cellular and humoral responses. During the systemic or local infection, two distinct pathways (Toll and Imd) play major roles in antimicrobial peptide synthesis. The Toll pathway is required to defend Gram-positive bacterial and fungal infections, whereas the Imd pathway is important in Gram-negative bacterial infection. We have shown that the infection of the opportunistic Gram-negative bacterium, Pseudomonas aeruginosa strain PA14 (PA14) into fly dorsal thorax can kill the flies within 48 h ($100\%$ mortality) in our optimized infection condition, suggesting that the PA14 strain can cause disease progress in fly model system. We found that flies carrying a constitutively activated mutant form of the Toll receptor $(Tl^{10b})$ showed increased resistance to P. aeruginosa infection and that flies carrying mutations in the Toll signaling pathway as well as in the Imd signaling pathway was more susceptible to PA14 infection. All these results imply that the Toll pathway might be important in the resistance to this pathogenic Gram-negative bacterial infection.

• Molecules and Cells
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• v.28 no.4
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• pp.365-368
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• 2009

Toll-like receptors (TLRs) play an important role in host defense by sensing invading microbial pathogens and initiating innate immune responses. The stimulation of TLRs by microbial components triggers the activation of myeloid differential factor 88 (MyD88)- and toll-interleukin-1 receptor domain-containing adapter inducing interferon-${\beta}$ (TRIF)-dependent downstream signaling pathways. Isoliquiritigenin (ILG), an active ingredient of Licorice, has been used for centuries to treat many chronic diseases. ILG inhibits the MyD88-dependent pathway by inhibiting the activity of inhibitor-${\kappa}B$ kinase. However, it is not known whether ILG inhibits the TRIF-dependent pathway. To evaluate the therapeutic potential of ILG, we examined its effect on signal transduction via the TRIF-dependent pathway of TLRs induced by several agonists. ILG inhibited nuclear factor-${\kappa}B$ and interferon regulatory factor 3 activation induced by lipopolysaccharide or polyinosinic-polycytidylic acid. ILG inhibited the lipopolysaccharide-induced phosphorylation of interferon regulatory factor 3 as well as interferon-inducible genes such as interferon inducible protein-10, and regulated activation of normal T-cell expressed and secreted (RANTES). These results suggest that ILG can modulate TRIF-dependent signaling pathways of TLRs, leading to decreased inflammatory gene expression.

• IMMUNE NETWORK
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• v.11 no.4
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• pp.223-226
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• 2011

Although exercise-induced growth factors such as Insulin-like growth factor-I (IGF-I) are known to affect various aspects of physiology in skeletal muscle cells, the molecular mechanism by which IGF-I modulates anti-inflammatory effects in these cells is presently unknown. Here, we showed that IGF-I stimulation suppresses the expression of toll-like receptor 4 (TLR4), a key innate immune receptor. A pharmacological inhibitor study further showed that PI3K/Akt signaling pathway is required for IGF-I-mediated negative regulation of TLR4 expression. Furthermore, IGF-I treatment reduced the expression of various NF-${\kappa}B$-target genes such as TNF-${\alpha}$ and IL-6. Taken together, these findings indicate that the anti-inflammatory effect of exercise may be due, at least in part, to IGF-I-induced suppression of TLR4 and subsequent downregulation of the TLR4-dependent inflammatory signaling pathway.

• Molecular & Cellular Toxicology
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• v.5 no.3
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• pp.187-192
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• 2009

Toll-like receptors (TLRs) play an important role in host defense by sensing invading microbial pathogens. The stimulation of TLRs by microbial components triggers the activation of the myeloid differential factor 88 (MyD88)- and toll-interleukin-1 receptor domain-containing adapter inducing interferon-$\beta$ (TRIF)-dependent downstream signaling pathways. TLR/MyD88 signaling pathway induces the activation of nuclear factor-kappa B (NF-${\kappa}B$) and the expression of inflammatory cytokine genes, including tumor necrosis factor-alpha, interleukin (IL)-6, IL-12, and IL-$1{\beta}$. On the other hand, TLR/TRIF signaling pathway induces the delayed-activation of NF-${\kappa}B$ and interferon regulatory factor 3 (IRF3), and the expression of type I interferons (IFNs) and IFN-inducible genes. The divalent heavy metal cadmium (Cd) is clearly toxic to most mammalian organ systems, especially the immune system. Yet, the underlying toxic mechanism(s) remain unclear. Cd inhibits the MyD88-dependent pathway by ceasing the activity of inhibitor-${\kappa}B$ kinase. However, it is not known whether Cd inhibits the TRIF-dependent pathway. Presently, Cd inhibited NF-${\kappa}B$ and IRF3 activation induced by lipopolysaccharide (LPS) and polyinosinic-polycytidylic acid. Cd inhibited LPS-induced IRF3 phosphorylation and IFN-inducible genes such as interferon inducible protein-10 and regulated on activation normal T-cell expressed and secreted (RANTES). These results suggest that Cd can modulate TRIF-dependent signaling pathways of TLRs.

• BMB Reports
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• v.49 no.6
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• pp.305-310
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• 2016

Toll-like receptors (TLRs) play a critical role in the innate immune response against pathogens. Each TLR recognizes specific pathogen-associated molecular patterns, after which they activate the adaptor protein MyD88 or TRIF-assembled signaling complex to produce immune mediators, including inflammatory cytokines and type I IFNs. Although the activation of TLR is important for host defense, its uncontrolled activation can damage the host. During the past decade, numerous studies have demonstrated that GSK3β is a key regulator of inflammatory cytokine production in MyD88-mediated TLR signaling via TLR2 and TLR4. Recently, GSK3β has also been implicated in the TRIF-dependent signaling pathway via TLR3. In this review, we describe current advances on the regulatory role of GSK3β in immune responses associated with various TLRs. A better understanding of the role of GSK3β in TLR signaling might lead to more effective anti-inflammatory interventions.

• Molecular & Cellular Toxicology
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• v.4 no.4
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• pp.267-277
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• 2008

Benzene and ethylbenzene (BE), the volatile organic compounds (VOCs) are common constituents of cleaning and degreasing agents, paints, pesticides, personal care products, gasoline and solvents. VOCs are evaporated at room temperature and most of them exhibit acute and chronic toxicity to human. Chronic exposure of benzene is responsible for myeloid leukemia and also ethylbenzene is also recognized as a possible carcinogen. To evaluate the BE effect on human, whole human genome 35 K oligonucleotide microarray were screened for the identification of the differential expression profiling. We identified 280 up-regulated and 201 down-regulated genes changed by more than 1.5 fold by BE exposure. Functional analysis was carried out by using DAVID bioinformatics software. Clustering of these differentially expressed genes were associated with immune response, cytokine-cytokine receptor interaction, toll-like signaling pathway, small cell lung cancer, immune response, apoptosis, p53 signaling pathway and MAPKKK cascade possibly constituting alternative or subordinate pathways of hematotoxicity and immune toxicity. Gene ontology analysis methods including biological process, cellular components, molecular function and KEGG pathway thus provide a fundamental basis of the molecular pathways through BEs exposure in human lymphoma cells. This may provides a valuable information to do further analysis to explore the mechanism of BE induced hematotoxicity.

• Parasites, Hosts and Diseases
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• v.54 no.5
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• pp.679-684
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• 2016

Clonorchiasis, caused by direct contact with Clonorchis sinensis worms and their excretory-secretory products (ESPs), is associated with chronic inflammation, malignant changes in bile ducts, and even cholangiocarcinogenesis. Our previous report revealed that intracellular free radicals enzymatically generated by C. sinensis ESPs cause NF-${\kappa}B$-mediated inflammation in human cholangiocarcinoma cells (HuCCT1). Therefore, the present study was conducted to examine the role of upstream Toll-like receptors (TLRs) on the initial host innate immune responses to infection. We found that treatment of HuCCT1 cells with native ESPs induced changes in TLR mRNA levels in a time-dependent manner, concomitant with the generation of free radicals. ESP-mediated free radical generation was markedly attenuated by preincubation of the cells with TLR1-4-neutralizing antibodies, indicating that at least TLR1 through 4 participate in stimulation of the host innate immune responses. These findings indicate that free radicals triggered by ESPs are critically involved in TLR signal transduction. Continuous signaling by this pathway may function in initiating C. sinensis infection-associated inflammation cascades, a detrimental event leading to progression to more severe hepatobiliary diseases.

• Korean Journal of Food Science and Technology
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• v.39 no.5
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• pp.481-487
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• 2007

Toll-like receptors (TLRs) induce innate immune responses that are essential for host defenses against invading microbial pathogens, thus leading to the activation of adaptive immune responses. In general, TLRs have two major downstream signaling pathways: the MyD88- and TRIF-dependent pathways, which lead to the activation of $NF-{\kappa}B$ and IRF3. Numerous studies have demonstrated that certain phytochemicals possessing anti-inflammatory effects inhibit $NF-{\kappa}B$ activation induced by pro-inflammatory stimuli, including lipopolysaccharides and $TNF{\alpha}$. However, the direct molecular targets for such anti-inflammatory phytochemicals have not been fully identified. Identifying the direct targets of phytochemicals within the TLR pathways is important because the activation of TLRs by pro-inflammatory stimuli can induce inflammatory responses that are the key etiological conditions in the development of many chronic inflammatory diseases. In this paper we discuss the molecular targets of resveratrol, (-)-epigallocatechin-3-gallate (EGCG), and curcumin in the TLR signaling pathways. Resveratrol specifically inhibited the TRIF pathway in TLR3 and TLR4 signaling, by targetting TBK1 and RIP1 in the TRIF complex. Furthermore, EGCG suppressed the activation of IRF3 by targetting TBK1 in the TRIF-dependent signaling pathways. In contrast, the molecular target of curcumin within the TLR signaling pathways is the receptor itself, in addition to $IKK{\beta}$. Together, certain dietary phytochemicals can modulate TLR-derived signaling and inflammatory target gene expression, and in turn, alter susceptibility to microbial infection and chronic inflammatory diseases.