Biased signalling is an essential feature of TLR4 in glioma cells.
A distinct feature of the Toll-like receptor 4 (TLR4) is its ability to trigger both MyD88-dependent and MyD88-independent signalling, culminating in activation of pro-inflammatory NF-κB and/or the antiviral IRF3. Although TLR4 agonists (lipopolysaccharides; LPSs) derived from different bacterial species have different endotoxic activity, the impact of LPS chemotype on the downstream signalling is not fully understood. Notably, different TLR4 agonists exhibit anti-tumoural activity in animal models of glioma, but the underlying molecular mechanisms are largely unknown. Thus, we investigated the impact of LPS chemotype on the signalling events in the human glioma cell line U251. We found that LPS of Escherichia coli origin (LPSEC) leads to NF-κB-biased downstream signalling compared to Salmonella minnesota-derived LPS (LPSSM). Exposure of U251 cells to LPSECresulted in faster nuclear translocation of the NF-κB subunit p65, higher NF-κB-activity and expression of its targets genes, and higher amount of secreted IL-6 compared to LPSSM. Using super-resolution microscopy we showed that the biased agonism of TLR4 in glioma cells is neither a result of differential regulation of receptor density nor of formation of higher order oligomers. Consistent with previous reports, LPSEC-mediated NF-κB activation led to significantly increased U251 proliferation, whereas LPSSM-induced IRF3 activity negatively influenced their invasiveness. Finally, treatment with methyl-β-cyclodextrin (MCD) selectively increased LPSSM-induced nuclear translocation of p65 and NF-κB activity without affecting IRF3. Our data may explain how TLR4 agonists differently affect glioma cell proliferation and migration.
Stem Cell Biology and Regenerative Medicine, School of Pharmacy, University of Reading, Reading, United Kingdom.
Marie-Theres
MT
Zeuner
Institute of Physical and Theoretical Chemistry, Goethe-University, Frankfurt, Germany.
Carmen L
CL
Krüger
Department of Cell Biology, University of Bielefeld, Bielefeld, Germany.
Katharina
K
Volk
Institute of Transfusion Medicine and Immunology, Medical Faculty Mannheim, Heidelberg University, Heidelberg, Germany.
Karen
K
Bieback
Cellular and Molecular Neuroscience, School of Pharmacy, University of Reading, Reading, United Kingdom.
Graeme S
GS
Cottrell
Institute of Physical and Theoretical Chemistry, Goethe-University, Frankfurt, Germany.
Mike
M
Heilemann
Stem Cell Biology and Regenerative Medicine, School of Pharmacy, University of Reading, Reading, United Kingdom. Electronic address: d.widera@reading.ac.uk.
Darius
D
Widera
D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D004926:Escherichia coli / Q000737:chemistry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000302:isolation & purification / Q000494:pharmacology*; D021962:Membrane Microdomains / Q000737:chemistry / Q000187:drug effects; D009457:Neuroglia / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D012475:Salmonella / Q000737:chemistry; D015398:Signal Transduction / Q000235:genetics*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D047392:beta-Cyclodextrins / Q000494:pharmacology
C508600:IL6 protein, human; C494232:IRF3 protein, human; D050838:Interferon Regulatory Factor-3; D015850:Interleukin-6; D008070:Lipopolysaccharides; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051996:Transcription Factor RelA; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin
Biased agonism; IRF3; Inflammatory balance; LPS; NF-kappaB; TLR4