Abu Shadat Mohammod Noman

Thalidomide inhibits lipopolysaccharide-induced tumor necrosis factor-α production via down-regulation of MyD88 expression

The effect of thalidomide on lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-α production was studied by using RAW 264.7 murine macrophage-like cells. Thalidomide significantly inhibited LPS-induced TNF-α production. Thalidomide prevented the activation of nuclear factor (NF)-KB by down-regulating phosphorylation of inhibitory KB factor (IKB), and IKB kinase (IKK)-α and IKK-β Moreover, thalidomide inhibited LPS-induced phosphorylation of AKT, p38 and stress-activated protein kinase (SAPK)/JNK. The expression of myeloid differentiation factor 88 (MyD88) protein and mRNA was markedly reduced in thalidomide-treated RAW 264.7 cells but there was no significant alteration in the expression of interleukin-1 receptor-associated kinase (IRAK) 1 and TNF receptor-associated factor (TRAF) 6 in the cells. Thalidomide did not affect the cell surface expression of Toll-like receptor (TLR) 4 and CD14, suggesting the impairment of intracellular LPS signalling in thalidomide-treated RAW 264.7 cells. Thalidomide significantly inhibited the TNF-α production in response to palmitoyl-Cys(RS)-2,3-di(palmitoyloxy) propyl)-Ala-Gly-OH (Pam3Cys) as a MyD88-dependent TLR2 ligand. Therefore, it is suggested that thalidomide might impair LPS signalling via down-regulation of MyD88 protein and mRNA and inhibit LPS-induced TNF-α production. The putative mechanism of thalidomide-induced MyD88 down-regulation is discussed.

Astrocyte elevated gene‐1 (AEG‐1) is induced by lipopolysaccharide as toll‐like receptor 4 (TLR4) ligand and regulates TLR4 signalling

Astrocyte elevated gene‐1 (AEG‐1) is induced by human immunodeficiency virus 1 (HIV‐1) infection and involved in tumour progression, migration and invasion as a nuclear factor‐κB (NF‐κB) ‐dependent gene. The involvement of AEG‐1 on lipopolysaccharide (LPS) ‐induced proinflammatory cytokine production was examined. AEG‐1 was induced via NF‐κB activation in LPS‐stimulated U937 human promonocytic cells. AEG‐1 induced by LPS subsequently regulated NF‐κB activation. The prevention of AEG‐1 expression inhibited LPS‐induced tumour necrosis factor‐α and prostaglandin E2 production. The AEG‐1 activation was not induced by toll‐like receptor ligands other than LPS. Therefore, AEG‐1 was suggested to be a LPS‐responsive gene and involved in LPS‐induced inflammatory response.

B1 cells produce nitric oxide in response to a series of toll-like receptor ligands

The effect of a series of toll-like receptor (TLR) ligands on the production of nitric oxide (NO) in mouse B1 cells was examined by using CD5(+) IgM(+) WEHI 231 cells. The stimulation with a series of TLR ligands, which were Pam3Csk4 for TLR1/2, poly I:C for TLR3, lipopolysaccharide (LPS) for TLR4, imiquimod for TLR7 and CpG DNA for TLR9, resulted in enhanced NO production via augmented expression of an inducible type of NO synthase (iNOS). LPS was most potent for the enhancement of NO production, followed by poly I:C and Pam3Csk4. Imiquimod and CpG DNA led to slight NO production. The LPS-induced NO production was dependent on MyD88-dependent pathway consisting of nuclear factor (NF)-kappaB and a series of mitogen-activated protein kinases (MAPKs). Further, it was also dependent on the MyD88-independent pathway consisting of toll-IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) and interferon regulatory factor (IRF)-3. Physiologic peritoneal B1 cells also produced NO via the iNOS expression in response to LPS. The immunological significance of TLR ligands-induced NO production in B1 cells is discussed.

Interleukin (IL)-10 attenuates lipopolysaccharide-induced IL-6 production via inhibition of IκB-ζ activity by Bcl-3

The inhibitory effect of interleukin-10 (IL-10), an anti-inflammatory cytokine, on lipopolysaccharide (LPS)-induced IL-6 production was characterized by simultaneous stimulation of RAW 264.7 cells with LPS and IL-10. The presence of IL-10 significantly inhibited LPS-induced IL-6 production at a transcriptional level. The expression of IκB-ζ, which promotes IL-6 production, was induced in response to LPS and it was definitely suppressed in the presence of IL-10. Further, IL-10 inhibited LPS-induced NF-κB activation. A pharmacological inhibitor of NF-κB prevented LPS-induced IκB-ζ expression, suggesting that IL-10 might inhibit LPS-induced IκB-ζ expression via the inactivation of NF-κB. In LPS- and IL-10-stimulated cells, the expression of Bcl-3 that inhibits NF-κB activation was significantly augmented. Introduction of Bcl-3 siRNA abolished IL-10-mediated IκB-ζ inhibition. In the presence of Bcl-3, siRNA IL-10 failed to inhibit LPS-induced IL-6 production. Therefore, it was suggested that Bcl-3 induced by IL-10 might reduce LPS-induced IκB-ζ activity via inactivation of NF-κB and that reduced IκB-ζ activity failed to promote LPS-induced IL-6 production.

Tumor necrosis factor‐α augments lipopolysaccharide‐induced suppressor of cytokine signalling 3 (SOCS‐3) protein expression by preventing the degradation

The regulatory role of tumour necrosis factor‐α (TNF‐α) on the expression of suppressor of cytokine signalling 3 (SOCS‐3) in response to lipopolysaccharide (LPS) was examined using peritoneal macrophages from TNF‐α‐deficient mice. The LPS‐induced SOCS‐3 expression was markedly augmented in macrophages from wild‐type mice whereas such augmentation was not seen in the cells from TNF‐α‐deficient mice. However, there was no significant difference in the level of SOCS‐3 messenger RNA expression between macrophages from wild‐type mice and those from TNF‐α‐deficient mice. The addition of exogenous TNF‐α augmented the LPS‐induced SOCS‐3 expression in macrophages from TNF‐α‐deficient mice. The pulse chase analysis suggested augmented degradation of LPS‐induced SOCS‐3 protein in macrophages from TNF‐α‐deficient mice. Moreover, MG 132, a 26S proteasome inhibitor, sustained the LPS‐induced SOCS‐3 expression in those cells. The tyrosine phosphorylation of SOCS‐3 was definitely induced in LPS‐stimulated macrophages from TNF‐α‐deficient mice but not wild‐type mice. A tyrosine phosphatase inhibitor enhanced the tyrosine phosphorylation of SOCS‐3 in wild‐type mice and accelerated the degradation. Therefore, it was suggested that TNF‐α prevented the degradation of SOCS‐3 protein via inhibition of the tyrosine phosphorylation in LPS‐stimulated macrophages.

Retinoblastoma protein-interacting zinc finger 1 (RIZ1) participates in RANKL-induced osteoclast formation via regulation of NFATc1 expression.

The role of retinoblastoma protein-interacting zinc finger 1 (RIZ1) in receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast formation was examined in mouse RAW 264.7 macrophage-like cells. The expression of RIZ1 was significantly augmented by RANKL-treated cells. Silencing of RIZ1 with the siRNA significantly reduced the appearance of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells as osteoclasts in RANKL-treated cells. The expression of nuclear factor of activated T cell 1 (NFATc1) as the terminal transcription factor of osteoclast formation was prevented by RIZ1 siRNA. It was suggested that that RIZ1 might participate in RANKL-induced osteoclast formation through the regulation of NFATc1 expression.

Thalidomide inhibits lipopolysaccharide-induced nitric oxide production and prevents lipopolysaccharide-mediated lethality in mice

The effect of thalidomide on lipopolysaccharide-induced nitric oxide (NO) production was studied using RAW 264.7 macrophage-like cells. Thalidomide significantly inhibited lipopolysaccharide-induced NO production via reduced expression of an inducible NO synthase. Thalidomide reduced the phosphorylation of the p65 nuclear factor-kappaB subunit, inhibitory kappaB (IkappaB) and IkappaB kinase in lipopolysaccharide-stimulated cells. However, thalidomide did not affect the expression of interferon-beta (IFN-beta) and interferon regulatory factor-1 in response to lipopolysaccharide. Further, thalidomide inhibited the MyD88 augmentation in lipopolysaccharide-stimulated cells, whereas it did not alter the expression of TIR domain-containing adaptor-inducing IFN-beta in the MyD88-independent pathway. Thalidomide significantly inhibited the NO production in response to Pam(3)Cys, CpG DNA and imiquimod as MyD88-dependent Toll-like receptor (TLR) ligands, but not polyI:C as a MyD88-independent TLR ligand. Therefore, thalidomide was suggested to inhibit lipopolysaccharide-induced NO production via downregulation of the MyD88-dependent signal pathway. The anti-inflammatory action of thalidomide might be involved in the prevention of lipopolysaccharide-mediated lethality in mice.

Nystatin-induced nitric oxide production in mouse macrophage-like cell line RAW264.7

Nystatin is known to deplete lipid rafts from mammalian cell membranes. Lipid rafts have been reported to be necessary for lipopolysaccharide signaling. In this study, it was unexpectedly found that lipopolysaccharide‐induced nitric oxide production was not inhibited, but rather increased in the presence of a non‐cytotoxic concentration of nystatin. Surprisingly, treatment with nystatin induced only NO production and iNOS expression in RAW264.7 cells. At the concentration used, no changes in the expression of GM1 ganglioside, a lipid raft marker on RAW264.7 cells, was seen. From studies using several kinds of inhibitors for signaling molecules, nystatin‐induced NO production seems to occur via the iκB/NF‐κB and the PI3 K/Akt pathway. Furthermore, because nystatin is known to activate the Na‐K pump, we examined whether the Na‐K pump inhibitor amiloride suppresses nystatin‐induced NO production. It was found that amiloride significantly inhibited nystatin‐induced NO production. The results suggest that a moderate concentration of nystatin induces NO production by Na‐pump activation through the PI3 kinase/Akt/NF‐κB pathway without affecting the condition of lipid rafts.

Flavopiridol inhibits lipopolysaccharide-induced TNF-α production through inactivation of nuclear factor-κB and mitogen-activated protein kinases in the MyD88-dependent pathway

Flavopiridol is a cyclin‐dependent kinase inhibitor and inhibits the growth of various cancer cells. The effect of flavopiridol on lipopolysaccharide (LPS)‐induced proinflammatory mediator production was examined in RAW 264.7 macrophage‐like cells. Flavopiridol significantly reduced the production of tumor necrosis factor‐α and, to a lesser extent, nitric oxide in LPS‐stimulated cells. Flavopiridol inhibited the activation of nuclear factor‐κB and IκB kinase in response to LPS. Flavopiridol also inhibited the activation of a series of mitogen‐activated protein kinases, such as p38, stress‐activated protein kinase/ c‐Jun N‐terminal kinase and extracellular signal‐regulated kinase 1/2 in response to LPS. However, flavopiridol did not alter the expression of tumor necrosis factor receptor‐associated factor 6, myeloid differentiation factor 88 (MyD88) or CD14/toll‐like receptor (TLR) 4. Flavopiridol inhibited nitric oxide production induced by a MyD88‐dependent TLR2 ligand, but not a MyD88‐independent TLR3 ligand. Further, flavopiridol did not alter the phosphorylation of interferon regulatory factor 3 in the MyD88‐independent pathway. Therefore, it was suggested that flavopiridol exclusively inhibited the activation of nuclear factor‐κB and mitogen‐activated protein kinases in the MyD88‐dependent pathway. Flavopiridol might be useful for the prevention of LPS‐induced inflammatory response.

Retinoblastoma protein-interacting zinc finger 1, a tumor suppressor, augments lipopolysaccharide-induced proinflammatory cytokine production via enhancing nuclear factor-κB activation

The involvement of retinoblastoma protein-interacting zinc finger 1 (RIZ1), a tumor suppressor, in lipopolysaccharide (LPS)-induced inflammatory responses was investigated by using RAW 264.7 macrophage-like cells. LPS significantly augmented the expression of RIZ1 and the augmentation was mediated by the activation of nuclear factor (NF)-kappaB and Akt. The silencing of RIZ1 with the siRNA led to the inactivation of NF-kappaB in response to LPS. Moreover, the RIZ1 silencing caused the down-regulation of p53 activation and a p53 pharmacological inhibitor attenuated the RIZ1 expression. LPS-induced tumor necrosis factor-alpha and interleukin-6 production was prevented by RIZ1 siRNA or a p53 pharmacological inhibitor. Therefore, RIZ1 was suggested to augment LPS-induced NF-kappaB activation in collaboration with p53 and enhance the production of proinflammatory cytokines in response to LPS.