HSP90 function is required for T2R bitter taste receptor nitric oxide production and innate immune responses in human airway epithelial cells and macrophages

Abstract

Bitter taste receptors (T2Rs) are G protein-coupled receptors (GPCRs) expressed in various cell types including ciliated airway epithelial cells and macrophages. T2Rs in these two airway innate immune cell types are activated by bitter products, including some secreted by Pseudomonas aeruginosa, leading to Ca2+-dependent activation of endothelial nitric oxide (NO) synthase (eNOS). NO enhances mucociliary clearance and has direct antibacterial effects in ciliated epithelial cells and increases phagocytosis by macrophages. Using biochemistry and live cell imaging, we explored the role of heat shock protein 90 (HSP90) in regulating T2R-dependent NO pathways in primary sinonasal epithelial cells, primary monocyte-derived macrophages, and a human bronchiolar cell line (H441). We used immunofluorescence to show that H441 cells express eNOS and certain T2Rs and that the bitterant denatonium benzoate activates NO production in an HSP90-dependent manner in cells grown either as submerged cultures and at air liquid interface. In primary sinonasal epithelial cells, we determined that HSP-90 inhibition reduces T2R-stimulated NO production and ciliary beating which are crucial for pathogen clearance. In primary monocyte-derived macrophages, we found that HSP-90 is integral to T2R-stimulated NO production and phagocytosis of FITC-labeled Escherichia coli and pHrodo-Staphylococcus aureus. Our study demonstrates that HSP90 serves an innate immune role by regulating NO production downstream of T2R signaling by augmenting eNOS activation without impairing upstream calcium signaling. These findings suggest that HSP90 plays an important role in airway antibacterial innate immunity and may be an important target in airway diseases like chronic rhinosinusitis, asthma, or cystic fibrosis.