Cigarette Smoke Induces Canonical Stress Granule Formation in Human Bronchial Epithelial Cells in Reactive Oxygen Species- and PERK-Dependent Manners

Cigarette smoke (CS) is the primary risk factor for the development of chronic obstructive pulmonary disease (COPD). Investigating the impact of CS on human airway epithelium is important for understanding COPD development and combating its effects. While some studies show that long exposure to CS activates inflammasome formation in airway epithelium, leading to cytokines' maturation and release, its acute effect on inflammation regulation requires further elucidation. Due to the importance of acute cellular responses in modulating cell survival and controlling inflammatory outcomes, we examined the effect of acute cigarette smoke extract exposure on human bronchial epithelial cells. Due to the high reactive oxygen species content in CS, we hypothesize that acute CS exposure activates the integrated stress response (ISR) pathway leading to stress granules (SG) formation to facilitate oxidative stress resolution and promote cell survival. Immunostaining, fluorescence confocal imaging, quantitative analyses, and immunoblotting were performed to test our hypothesis. We report here that acute exposure to CS extract triggers canonical SG formation by activating the ISR pathway via the PERK/eIF2α arm in a reactive oxygen species-dependent manner. SG formation is abolished upon inhibiting PERK or eIF2α function, or by scavenging oxidants prior to smoke exposure. Characterizing SG formation in terms of measuring SG size and abundance and the sequestration of the SG marker G3BP1 reveals that SG formation is maximal at 15% CS extract exposure for 2 h and undergoes gradual disassembly at longer exposure times. This is closely dependent on cytoplasmic p-eIF2α levels. These results demonstrate that acute exposure to CS activates the protective ISR pathway to potentially reduce the detrimental effects of CS and promote stress resolution and cell survival.