title: Involvement of TNFα-induced TLR4-NF-κB and TLR4-HIF-1α feed-forward loops in the regulation of inflammatory responses in glioma.
abstract: The precise role of different toll-like receptor (TLR) superfamily members is just beginning to get elucidated in glioblastoma multiforme (GBM). In this study, we observed heightened TLR4 levels in GBM tumor samples as compared to adjacent normal tissue. Since the pro-inflammatory cytokine tumor necrosis factor (TNF)α induces NF-κB activation in GBM, and as several common signaling mediators are involved in TNFα and TLR4-mediated NF-κB activation, we investigated the role of TLR4 in the regulation of NF-κB activation and inflammatory responses in TNFα-treated glioma cells. TNFα elevated TLR4 expression and inhibition of TLR4 signaling by either signaling inhibitor, neutralizing antibody, or small interfering RNA (siRNA)-attenuated TNFα-induced NF-κB activation. TLR4-mediated NF-κB activation was independent of canonical myeloid differentiation factor 88 signaling but involved toll/IL-1R homology domain-containing adaptor protein-inducing interferon-β. Inhibition of TLR4 signaling abrogated TNFα-induced increase in (1) transcription factors interferon (IFN) regulatory factor 3 and STAT-1 and (2) IFNβ and inflammatory cytokines/chemokines expression. Furthermore, TNFα-induced TLR4-dependent increase in AKT activation and HIF-1α transcriptional activation suggested the existence of TLR4-AKT-HIF-1α axis. Importantly, TNFα-induced TLR4 was abrogated in cells transfected with dominant negative IκB and HIF-1α siRNA. Our studies indicate that TNFα triggered TLR4-HIF-1α and NF-κB-TLR4 feed-forward loops act in tandem to sustain inflammatory response in glioma.
authors: National Brain Research Centre, Manesar, Haryana 122 050, India.
authors: Richa
authors: R
authors: Tewari
authors: Saurav Roy
authors: SR
authors: Choudhury
authors: Sadashib
authors: S
authors: Ghosh
authors: Veer Singh
authors: VS
authors: Mehta
authors: Ellora
authors: E
authors: Sen
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D005909:Glioblastoma / Q000378:metabolism / Q000473:pathology; D005910:Glioma / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007249:Inflammation / Q000378:metabolism; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D016899:Interferon-beta / Q000378:metabolism; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D050838:Interferon Regulatory Factor-3; D053594:Myeloid Differentiation Factor 88; D016328:NF-kappa B; D050794:STAT1 Transcription Factor; C470409:TICAM1 protein, human; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D016899:Interferon-beta; D051057:Proto-Oncogene Proteins c-akt