Toll Like Receptor 4 is not targeted to the lysosome in Cystic Fibrosis airway epithelial cells.

1Keele University.
AJP Lung Cellular and Molecular Physiology (Impact Factor: 4.08). 01/2013; 304(5). DOI: 10.1152/ajplung.00372.2011
Source: PubMed


The innate immune response to bacterial infection is mediated through Toll-Like-Receptors, which trigger tightly regulated signaling cascades through transcription factors including Nuclear Factor-kappa B (NF-κB). LPS activation of TLR4 triggers internalisation of the receptor-ligand complex which is directed towards lysosomal degradation or endocytic recycling. Cystic Fibrosis (CF) patients display a robust and uncontrolled inflammatory response to bacterial infection, suggesting a defect in regulation. This study examined the intracellular trafficking of TLR4 in CF and non-CF airway epithelial cells following stimulation with LPS. We employed cells lines (16HBE14o-, CFBE41o- (CF) and CFTR-complemented CFBE41o-) and confirmed selected experiments in primary nasal epithelial cells from non-CF controls and CF patients (F508del homozygous). In control cells TLR4 expression (surface / cytoplasmic) was reduced after LPS, but remained unchanged in CF cells, and was accompanied by a heightened inflammatory response 24h after stimulation. All cells expressed markers of the early (EEA1) and late (Rab7b) endosomes at basal levels. Only CF cells displayed persistent expression of Rab7b following stimulation. Rab7 variants may directly internalize bacteria to the Golgi (recycling) or the lysosome (degradation). TLR4 co-localised with the lysosomal marker LAMP1 in 16HBE14o-, suggesting that TLR4 is targeted for lysosomal degradation in these cells. This co-localisation was not observed in CFBE41o- where persistent expression of Rab7 and release of pro-inflammatory cytokines was detected. Consistent with the apparent inability of CF cells to target TLR4 towards the lysosome, we observed persistent surface and cytoplasmic TLR4 expression in CFBE41o-. This defect may account for the prolonged inflammation associated with CF.

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Available from: Catriona Kelly, Feb 01, 2016
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