Min-Jung Kang

Flagellin promotes the proliferation of gastric cancer cells via the Toll-like receptor 5

Signaling of the Toll-like receptor (TLR) is closely associated with tumor development and progression processes including cell proliferation, angiogenesis, metastasis, and immunosuppression. In this study, we examined the expression of TLR5 in gastric cancer cells and its function in cell proliferation. RT-PCR revealed that the TLR5 gene was expressed in all gastric cancer cell lines examined, SNU638, SNU601, SNU216, and AGS. The TLR5 agonist, flagellin, induced IL-8 production and NF-κB activation in the gastric cancer cell lines. In addition, flagellin enhanced the proliferation of all gastric cancer cells examined, whereas LPS did not affect that of SNU638 cells. Blockade of TLR5 using an antibody, restored the proliferation of SNU638 cells enhanced by flagellin, indicating that TLR5 is essential for cell proliferation by flagellin. Flagellin also led to phosphorylation of ERK in SNU638 cells. The ERK inhibitor, PD98059, restored the proliferation ability of SNU638 cells enhanced by flagellin, suggesting that ERK may play an important role in the proliferation of gastric cancer cells. These findings suggest that TLR5 may play an important role in tumor progression of gastric cancer via the regulation of cell proliferation.

Diverse Toll-Like Receptors Mediate Cytokine Production by Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans in Macrophages

ABSTRACT Toll-like receptors (TLRs) orchestrate a repertoire of immune responses in macrophages against various pathogens. Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans are two important periodontal pathogens. In the present study, we investigated TLR signaling regulating cytokine production of macrophages in response to F. nucleatum and A. actinomycetemcomitans. TLR2 and TLR4 are redundant in the production of cytokines (interleukin-6 [IL-6] and tumor necrosis factor alpha [TNF-α]) in F. nucleatum- and A. actinomycetemcomitans-infected macrophages. The production of cytokines by macrophages in response to F. nucleatum and A. actinomycetemcomitans infection was impaired in MyD88-deficient macrophages. Moreover, cytokine concentrations were lower in MyD88-deficient macrophages than in TLR2/TLR4 (TLR2/4) double-deficient cells. An endosomal TLR inhibitor, chloroquine, reduced cytokine production in TLR2/4-deficient macrophages in response to F. nucleatum and A. actinomycetemcomitans, and DNA from F. nucleatum or A. actinomycetemcomitans induced IL-6 production in bone marrow-derived macrophages (BMDMs), which was abolished by chloroquine. Western blot analysis revealed that TLR2/4 and MyD88 were required for optimal activation of NF-κB and mitogen-activated protein kinases (MAPKs) in macrophages in response to F. nucleatum and A. actinomycetemcomitans, with different kinetics. An inhibitor assay showed that NF-κB and all MAPKs (p38, extracellular signal-regulated kinase [ERK], and Jun N-terminal protein kinase [JNK]) mediate F. nucleatum-induced production of cytokines in macrophages, whereas NF-κB and p38, but not ERK and JNK, are involved in A. actinomycetemcomitans-mediated cytokine production. These findings suggest that multiple TLRs may participate in the cytokine production of macrophages against periodontal bacteria.

Nod2 and Rip2 contribute to innate immune responses in mouse neutrophils

Nod‐like receptors are a family of innate immune receptors that link cytosolic sensing of microbial and danger stimuli to the activation of immune responses. Two Nod‐like receptor family members, Nod1 and Nod2, recognize bacterial peptidoglycan and activate immune responses via nuclear factor‐κB (NF‐κB) and mitogen‐activated protein kinase (MAPK). The function of Nod1 and Nod2 has been largely studied in macrophages, but the role of these receptors in other innate immune cells remains unclear. In this study, we examined the function of Nod1 and Nod2 in innate immune responses of neutrophils. Mice were injected intraperitoneally with thioglycollate, and then peritoneal neutrophils were isolated 4 hr after injection. Tri‐DAP and muramyl‐dipeptide (MDP) were used as Nod1 and Nod2 agonists, respectively. The level of cytokines [interleukin‐6 (IL‐6) and tumour necrosis factor‐α (TNF‐α)] and chemokines (CXCL1 and CCL2) was increased by MDP, but not Tri‐DAP in wild‐type (WT) neutrophils. Increased production of cytokines and chemokines with MDP was abolished in Nod2‐ and Rip2‐deficient neutrophils. MDP also induced the activation of NF‐κB and MAPK in WT neutrophils, but not in Nod2‐ and Rip2‐deficient cells. Flow cytometry analysis showed that L‐selectin shedding was induced by MDP in WT neutrophils, but not in Nod2‐ and Rip2‐deficient cells. MDP and Toll‐like receptor (TLR) agonists (Pam3CSK4 and lipopolysaccharide) exerted synergistic effects on the production of IL‐6 and CXCL1 in neutrophils. Moreover, Nod2 and TLR4 cooperated to produce IL‐6, TNF‐α, CXCL1 and CCL2 in neutrophils in response to Gram‐negative bacteria. Our findings suggest that the Nod2–Rip2 axis may contribute to the innate immune response of neutrophils against bacterial infection.

Essential role of toll-like receptor 4 in Acinetobacter baumannii-induced immune responses in immune cells

TLR4 is a membrane sensor for lipopolysaccharide (LPS), a major cell wall component of gram-negative bacteria. In this study, we investigated the role of TLR4 on innate immune responses in immune cells against Acinetobacter baumannii. Bone marrow-derived macrophages (BMDMs) and dendritic cells (BMDCs) were isolated from WT and TLR4-deficient mice and infected with A. baumannii ATCC 15150. ELISA assay revealed that the production of IL-6 and TNF-α by A. baumannii was impaired in TLR4-deficient macrophages. However, absence of TLR2 did not affect A. baumannii-induced cytokines production in BMDMs. In addition, TLR4 was required for the optimal production of IL-6, TNF-α, and IL-12 in BMDCs in response to A. baumannii. Western blot analysis showed that A. baumannii leads to the activation of NF-κB and MAPKs (p38, ERK, and JNK) in macrophages via TLR4-dependent pathway. mRNA expression of iNOS and NO production was elicited in WT BMDMs in response to A. baumannii, which was abolished in TLR4-deficienct cells. Bacterial killing ability against A. baumannii was impaired in TLR4-deficient BMDMs. In addition, A. baumannii induced apoptosis in BMDMs via TLR4-independent pathway. Our results demonstrate that TLR4 is essential for initiating innate immune response of macrophages against A. baumannii infection.

NLRP3 inflammasome mediates IL‐1β production in immune cells in response to Acinetobacter baumannii and contributes to pulmonary inflammation in mice

Acinetobacter baumannii is a multi‐drug resistant, Gram‐negative bacteria and infection with this organism is one of the major causes of mortality in intensive care units. Inflammasomes are multiprotein oligomers that include caspase‐1, and their activation is required for maturation of interleukin‐1β (IL‐1β). Inflammasome signalling is involved in host defences against various microbial infections, but the precise mechanism by which A. baumannii activates inflammasomes and the roles of relevant signals in host defence against pulmonary A. baumannii infection are unknown. Our results showed that NLRP3, ASC and caspase‐1, but not NLRC4, are required for A. baumannii‐induced production of IL‐1β in macrophages. An inhibitor assay revealed that various pathways, including P2X7R, K+ efflux, reactive oxygen species production and release of cathepsins, are involved in IL‐1β production in macrophages in response to A. baumannii. Interleukin‐1β production in bronchoalveolar lavage (BAL) fluid was impaired in NLRP3‐deficient and caspase‐1/11‐deficient mice infected with A. baumannii, compared with that in wild‐type (WT) mice. However, the bacterial loads in BAL fluid and lungs were comparable between WT and NLRP3‐deficient or caspase‐1/11‐deficient mice. The severity of lung pathology was reduced in NLRP3‐ deficient, caspase‐1/11‐ deficient and IL‐1‐receptor‐deficient mice, although the recruitment of immune cells and production of inflammatory cytokines and chemokines were not altered in these mice. These findings indicate that A. baumannii leads to the activation of NLRP3 inflammasome, which mediates IL‐1β production and lung pathology.

Withaferin A Inhibits Helicobacter pylori-induced Production of IL-1β in Dendritic Cells by Regulating NF-κB and NLRP3 Inflammasome Activation

Helicobacter pylori infection is associated with chronic gastritis, peptic ulcer, and gastric cancer. There is evidence that IL-1β is associated with the development of gastric cancer. Therefore, downregulation of H. pylori-mediated IL-1β production may be a way to prevent gastric cancer. Withaferin A (WA), a withanolide purified from Withania somnifera, is known to exert anti-inflammatory and anti-tumor effects. In the present study, we explored the inhibitory activity of WA on H. pylori-induced production of IL-1β in murine bone marrow-derived dendritic cells (BMDCs) and the underlying cellular mechanism. Co-treatment with WA decreased IL-1β production by H. pylori in BMDCs in a dose-dependent manner. H. pylori-induced gene expression of IL-1β and NLRP3 (NOD-like receptor family, pyrin domain containing 3) were also suppressed by WA treatment. Moreover, IκB-α phosphorylation by H. pylori infection was suppressed by WA in BMDCs. Western blot analysis revealed that H. pylori induced cleavage of caspase-1 and IL-1β, as well as increased procaspase-1 and pro IL-1β protein levels, and that both were suppressed by co-treatment with WA. Finally, we determined whether WA can directly inhibit ac tivation of the NLRP3 inflammasome. NLRP3 activators induced IL-1β secretion in LPS-primed macrophages, which was inhibited by WA in a dose-dependent manner, whereas IL-6 production was not affected by WA. Moreover, cleavage of IL-1β and caspase-1 by NLRP3 activators was also dose-dependently inhibited by WA. These findings suggest that WA can inhibit IL-1β production by H. pylori in dendritic cells and can be used as a new preventive and therapeutic agent for gastric cancer.

Nucleotide-binding oligomerization domain 2 (Nod2) is dispensable for the innate immune responses of macrophages against Yersinia enterocolitica

Nucleotide-binding oligomerization domain 2 (Nod2) is a cytosolic sensor for muramyl dipeptide, a component of bacterial peptidoglycan. In this study, we have examined whether Nod2 mediates the immune response of macrophages against Yersinia enterocolitica. Bone-marrow-derived macrophages (BMDMs) were isolated from WT and Nod2-deficient mice and were infected with various strains of Y. enterocolitica. ELISA showed that the production of IL-6 and TNF-α in BMDMs infected with Y. enterocolitica was not affected by the Nod2 deficiency. iNOS mRNA expression was induced in both WT and Nod2-deficienct BMDMs in response to Y. enterocolitica, beginning 2 h after infection. Nitric oxide (NO) production by Y. enterocolitica did not differ between WT and Nod2-deficient BMDMs. Western blot analysis revealed that Y. enterocolitica induces activation of NF-κB, p38, and ERK MAPK through a Nod2-independent pathway. Neither LDH release by Y. enterocolitica nor the phagocytic activity of the macrophages was altered by Nod2 deficiency. An in vivo experiment showed that bacterial clearance ability and production of IL-6 and KC in serum were comparable in WT and Nod2-deficient mice infected with Y. enterocolitica. These findings suggest that Nod2 may not be critical for initiating the innate immune response of macrophages against Yersinia infection.

Inhibitory effect of withaferin A on Helicobacter pylori‑induced IL‑8 production and NF‑κB activation in gastric epithelial cells

Withaferin A (WA), a withanolide purified from Withania somnifera, has been known to exert anti-inflammatory effects. The present study sought to determine the effects of WA on Helicobacter (H.) pylori-mediated inflammation in the AGS gastric epithelial cell line. Cellular production of interleukin (IL)-8 and vascular endothelial growth factor (VEGF) was measured by ELISA. Western blot analysis was performed to determine the activation of nuclear factor (NF)-κB and mitogen-activated protein kinases (MAPKs) as well as hypoxia-inducible factor 1α stabilization. Bacterial growth was also examined by measuring the optical density. Pre-treatment or co-treatment with WA efficiently reduced IL-8 production by AGS cells in response to H. pylori infection. H. pylori-induced activation of NF-κB, but not MAPKs, was also inhibited by pre-treatment of WA in the cells. However, WA did not affect VEGF production and HIF-1α stabilization induced by H. pylori in AGS cells. In addition, WA did not influence the growth of H. pylori, suggesting that the anti-inflammatory effect of WA was not due to any bactericidal effect. These findings indicate that WA is a potential preventive or therapeutic agent for H. pylori-mediated gastric inflammation.

Toll‑like receptor 2 promotes bacterial clearance during the initial stage of pulmonary infection with Acinetobacter baumannii

Toll‑like receptor 2 (TLR2) has been identified as a sensor for bacterial lipoprotein. To determine the role of TLR2 in host defense against Acinetobacter baumannii infection, wild‑type (WT) and TLR2‑deficient mice were infected intranasally with A. baumannii. Body weight, cytokine and chemokine levels in bronchoalveolar (BAL) fluid and lung histopathology were examined. Body weight changes in TLR2‑deficient mice were comparable to those of WT mice throughout the experimental period. However, TLR2‑deficient mice exhibited an increased bacterial load in the lungs and increased levels of interleukin‑6 and chemokine (C‑X‑C motif) ligand 2 in BAL fluids compared with WT mice 1 day after infection. Histopathological features of lung tissue in WT and TLR2‑deficient mice were comparable between WT and TLR2‑deficient mice. Results of the present study demonstrate that TLR2 may have a minimal role in the host defense against A. baumannii at the early stages of infection.

TLR7 expression is decreased during tumour progression in transgenic adenocarcinoma of mouse prostate mice and its activation inhibits growth of prostate cancer cells.

Although various Toll‐like receptors (TLRs) have been associated with immune response and tumorigenesis in the prostate cells, little is known about the role of TLR7. Accordingly, we examined the expression of TLR7 during tumour progression of TRMAP (transgenic mouse model for prostate cancer) mice and its role on cell growth.