• BMB Reports
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• v.32 no.5
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• pp.419-428
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• 1999

Tumor necrosis factor (TNF) receptor members have unique structures composed of 2-4 cysteine - rich pseudorepeats in the extracellular domain. On ligation by trimeric ligand molecules, oligomerization of three receptor molecules occurs, which in turn activates the receptor and recruits intracellular signaling molecules to the cytoplasmic tail to initiate biological events. Recently, the numbers of tumor necrosis factor receptor and ligand family members have been rapidly expanding. Functional characterization of the new members has indicated redundant roles with other known members as well as provided insights into novel functions. In particular, identification of soluble decoy receptors which have the ability to bind multiple ligands highlights a complex control mechanism of immune responses by these molecules. Studies of the new members have also revealed that the TNF receptor and ligand family members play an important role in other than the immune system.

• Journal of Microbiology and Biotechnology
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• v.10 no.5
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• pp.707-713
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• 2000

Myasthenia gravis (MG) is caused mainly by autoantibodies directed against acetylcholine receptors located in the postsynaptic muscle cell membrane. Using in vitro selection techniques, we isolated an RNA containing 2'-fluoro pyrimidines that can specifically and avidly ($K_d$ ~25 nM) bind rat monoclonal antibody called mAb198, which recognizes the main immunogenic region on the acetylcholine receptors. This RNA can act as a very effective decoy and block mAb198 binding to the receptors in vitro. Furthermore, this RNA decoy can prevent the antigenic modulation of the acetylcholine receptor caused by mAb198 in human muscle cell cultures with and $IC_{50} $of approximately $2.4{\mu}M$. These results indicate that the RNA selected in this study is a more potent decly inhibitor of myashthenic antibodies than the previously identified RNA with 2'-amino pyrimidines [11]. Moreover, this RNA cross-reacts with autoantibodies from patients with MG and can protect human cells from the effects of these antibodies. These observations have important implications for developing an antigen-specific treatment of autoimmune diseases including MG, which is based on decoy RNAs selected in vitro.

• BMB Reports
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• v.56 no.4
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• pp.240-245
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• 2023

Glial cells play important roles during neurogenesis and in maintaining complex functions of the nervous system. Here, we report the characterization of a gene, Sdr, which contains a putative insulin-like growth factor receptor domain and is required to maintain critical nervous system functions in Drosophila. Sdr is expressed in glial cells during embryonic and larval stages of development, but its role in adult flies is poorly understood. As insulin signaling is important throughout the lifespan in human, we investigated the Sdr's role in adult flies. Our results demonstrate that Sdr is expressed on surface glial cells that surround the nervous system. Mutation of Sdr did not affect development but caused defects in locomotion and lifespan. Sdr mutants also showed increasingly severe defects in the blood-brain- and blood-retina-barriers as they aged. Therefore, we suggest a novel role of Sdr in maintaining the integrity of the blood-brain- and blood-retina-barriers in adult flies.

• IMMUNE NETWORK
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• v.24 no.3
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• pp.21.1-21.16
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• 2024

IL-1, a pleiotropic cytokine with profound effects on various cell types, particularly immune cells, plays a pivotal role in immune responses. The proinflammatory nature of IL-1 necessitates stringent control mechanisms of IL-1-mediated signaling at multiple levels, encompassing transcriptional and translational regulation, precursor processing, as well as the involvement of a receptor accessory protein, a decoy receptor, and a receptor antagonist. In T-cell immunity, IL-1 signaling is crucial during both the priming and effector phases of immune reactions. The fine-tuning of IL-1 signaling hinges upon two distinct receptor types; the functional IL-1 receptor (IL-1R) 1 and the decoy IL-1R2, accompanied by ancillary molecules such as the IL-1R accessory protein (IL-1R3) and IL-1R antagonist. IL-1R1 signaling by IL-1β is critical for the differentiation, expansion, and survival of Th17 cells, essential for defense against extracellular bacteria or fungi, yet implicated in autoimmune disease pathogenesis. Recent investigations emphasize the physiological importance of IL-1R2 expression, particularly in its capacity to modulate IL-1-dependent responses within Tregs. The precise regulation of IL-1R signaling is indispensable for orchestrating appropriate immune responses, as unchecked IL-1 signaling has been implicated in inflammatory disorders, including Th17-mediated autoimmunity. This review provides a thorough exploration of the IL-1R signaling complex and its pivotal roles in immune regulation. Additionally, it highlights recent advancements elucidating the mechanisms governing the expression of IL-1R1 and IL-1R2, underscoring their contributions to fine-tuning IL-1 signaling. Finally, the review briefly touches upon therapeutic strategies targeting IL-1R signaling, with potential clinical applications.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2001.04a
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• pp.103-112
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• 2001

Bone homeostasis is maintained by a balance between activities of osteoblasts(bone forming cells) and osteoclasts (bone resorbing cells). The activities of these cells are closely regulated by multiple factors including hormones and cytokines. The cessation of estrogen at menopause disrupts the balanced regulation and is the main cause of osteoporosis in postmenopausal women. Recent molecular biological studies led to a discovery of tumor necrosis factor(TNF) and TNF receptor families genes that play critical roles in the regulation of osteoclast formation and function. RANKL (receptor activator of nuclear factor kappa B ligand; also called ODF, TRANCE, and OPGL) expressed on cells supporting osteoclast is essential for osteoclast differentiation, activation, and survival. RANK, the counter-receptor for RANKL, is expressed on progenitor and mature osteoclasts. The interaction between RANKL and RANK is requlated by a soluble decoy receptor OPG (osteoprotegerin). Gene knock out studies of these molecules showed profound effects on bone. These results prompted development of new strategies for treatment of bone diseases. Inhibition of osteoclast activity by blocking the RANKL-RANK interaction using OPG is being attempted. Research on the signaling pathways of RANK is also actively carried out. Screening natural products that inhibit the RANKL-RANK interaction or the activity of obteoclasts would be another effective means to a new drug target for bone resorbing diseases.

• Molecules and Cells
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• v.25 no.3
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• pp.352-357
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• 2008

Osteoprotegerin (OPG) is a soluble decoy receptor that inhibits osteoclastogenesis and is closely associated with bone resorption processes. We have designed and determined the solution structures of potent OPG analogue peptides, derived from sequences of the cysteine-rich domain of OPG. The inhibitory effects of the peptides on osteoclastogenesis are dose-dependent ($10^{-6}M-10^{-4}M$), and the activity of the linear peptide at $10^{-4}M$ is ten-fold higher than that of the cyclic OPG peptide. Both linear and cyclic peptides have a ${\beta}$-turn-like conformation and the cyclic peptide has a rigid conformation, suggesting that structural flexibility is an important factor for receptor binding. Based on structural and biochemical information about RANKL and the OPG peptides, we suggest that complex formation between the peptide and RANKL is mediated by both hydrophobic and hydrogen bonding interactions. These results provide structural insights that should aid in the design of peptidyl-mimetic inhibitors for treating metabolic bone diseases caused by abnormal osteoclast recruitment.

• International Journal of Oral Biology
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• v.30 no.3
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• pp.105-110
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• 2005

Periodontitis is a chronic infectious disease that leads to the destruction, one of the major cause of tooth loss in human. Osteoclast Differentiation Factor(ODF), also called as Receptor activator of NF-${\kappa}B$ ligand(RANKL), a surface-associated ligand on bone marrow stromal cells and osteoblasts, activates its cognate receptor RANK on osteoclast progenitor cells, which leads to differentiation of these mononucleated precursor cells. Osteoprotegerin(OPG), a decoy receptor, is released from stromal cells and osteoblasts to inhibit the interaction between RANKL and RANK. The experiment for the effect of pregnancy on gingival health showed greater gingival inflammation and edema during pregnancy, despite similar plaque index. There should be many factors affecting the periodontal health in pregnancy. In this experiment, we examined the direct effects of sex hormones(estrogen and progesterone) on the ODF/OPG expression in human gingival fibroblasts and periodontal ligament cells at the serum concentration of pregnancy. The ratio was high in the 1st trimester of pregnancy by estrogen and in the late 2nd trimester by progesterone. Therefore, the local periodontal destruction might be accelerated by these hormonal effect on the periodontal cells.

• Archives of Pharmacal Research
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• v.27 no.12
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• pp.1258-1262
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• 2004

Phosphodiesterase (PDE) 4 is an enzyme that degrades intracellular cAMP. In the present study, the effect of rolipram, a specific phosphodiesterase (PDE) 4 inhibitor, on osteoclast formation was investigated. Rolipram induced osteoclast formation in cocultures of mouse bone marrow cells and calvarial osteoblasts. This activity was not observed in the absence of calvarial osteoblasts, suggesting that calvarial osteoblasts are likely target cells of rolipram. Osteoclast formation by rolipram was completely blocked by the addition of osteoprotegerin (OPG), a soluble decoy receptor for the osteoclast differentiation factor, TNF-related activation-induced cytokine (TRANCE, identical to RANKL, ODF, and OPGL). Northern blot analysis revealed the effect of rolipram to be associated with the increased expression of TRANCE mRNA in mouse calvarial osteoblasts. Collectively, these data indicate that PDE4 inhibitor up-regulates the TRANCE mRNA expression in osteoblasts, which in turn controls osteoclast formation.

• YAKHAK HOEJI
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• v.48 no.3
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• pp.197-201
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• 2004

Phosphodiesterases (PDEs) are enzymes that degrade intracellular cAMP. In the present study, pentoxifylline, a PDE inhibitor, induced osteoclast formation in co-cultures of mouse bone marrow cells and calvarial osteoblasts. To address the involvement of the osteoclast differentiation factor TNF-related activation-induced cytokine (TRANCE, identical to RANKL, ODF, and OPGL), mouse bone marrow cells and calvarial osteoblasts were co-cultured with pentoxifylline in the presence of OPG, a decoy receptor for TRANCE. The osteoclastogenic effect of pentoxifylline was completely blocked by addition of OPG, suggesting that TRANCE is involved in the osteoclast formation induced by pentoxifylline, Northern blot analysis revealed that pentoxifylline significantly induced TRANCE mRNA expression in calvarial osteoblasts. These results suggests that pentoxifylline regulates TRANCE expression in osteoblasts, which in turn controls osteoclast formation.

• Molecules and Cells
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• v.28 no.3
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• pp.201-207
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• 2009

Silibinin is a polyphenolic flavonoid compound isolated from milk thistle (Silybum marianum), with known hepatoprotective, anticarcinogenic, and antioxidant effects. Herein, we show that silibinin inhibits receptor activator of $NF-{\kappa}B$ ligand (RANKL)-induced osteoclastogenesis from RAW264.7 cells as well as from bone marrow-derived monocyte/macrophage cells in a dose-dependent manner. Silibinin has no effect on the expression of RANKL or the soluble RANKL decoy receptor osteoprotegerin (OPG) in osteoblasts. However, we demonstrate that silibinin can block the activation of $NF-{\kappa}B$, c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein (MAP) kinase, and extracellular signal-regulated kinase (ERK) in osteoclast precursors in response to RANKL. Furthermore, silibinin attenuates the induction of nuclear factor of activated T cells (NFAT) c1 and osteoclast-associated receptor (OSCAR) expression during RANKL-induced osteoclastogenesis. We demonstrate that silibinin can inhibit $TNF-{\alpha}$-induced osteoclastogenesis as well as the expression of NFATc1 and OSCAR. Taken together, our results indicate that silibinin has the potential to inhibit osteoclast formation by attenuating the downstream signaling cascades associated with RANKL and $TNF-{\alpha}$.