Spatially coordinated extracellular signal-regulated kinase (ERK) signaling events (SPREADs) transmit radially from a central point to adjacent cells via secreted ligands for EGFR (epidermal growth factor receptor) and other receptors. SPREADs maintain homeostasis in nonpulmonary epithelia, but it is unknown whether they play a role in the airway epithelium or are dysregulated in inflammatory disease. To address these questions, we measured SPREAD activity with live-cell ERK biosensors in human bronchial epithelial cell lines (HBE1 and 16HBE) and primary human bronchial epithelial cells, in both submerged and biphasic air-liquid interface culture conditions (i.e., differentiated cells). Airway epithelial cells were exposed to proinflammatory cytokines relevant to asthma and chronic obstructive pulmonary disease. Type 1 proinflammatory cytokines significantly increased the frequency of SPREADs, which coincided with epithelial barrier breakdown in differentiated primary human bronchial epithelial cells. Furthermore, SPREADs correlated with IL-6 peptide secretion and the appearance of localized clusters of phospho-STAT3 immunofluorescence. To probe the mechanism of SPREADs, cells were cotreated with pharmacological treatments (gefitinib, tocilizumab, hydrocortisone) or metabolic modulators (insulin, 2-deoxyglucose). Hydrocortisone, inhibitors of receptor signaling, and suppression of metabolic function decreased SPREAD occurrence, implying that proinflammatory cytokines and glucose metabolism modulate SPREADs in human airway epithelial cells via secreted EGFR and IL6R ligands. We conclude that spatiotemporal ERK signaling plays a role in barrier homeostasis and dysfunction during inflammation of the airway epithelium. This novel signaling mechanism could be exploited clinically to supplement corticosteroid treatment for asthma and chronic obstructive pulmonary disease.
Keywords: Forster resonance energy transfer; epidermal growth factor receptor; interleukin; mitogen activated protein kinase.