Signal Transduction and Gene Expression

Acrolein Causes ER Stress and Apoptosis in A549 Lung Carcinoma Cells Diana A. Averill-Bates1, Pragathi Pallepati1, Ahmed Bettaieb1, André Tanel1, and Patrick Morin1 1Université du Québec à Montréal, Canada Acrolein is a -unsaturated aldehyde. It is a ubiquitous environmental pollutant found in smoke and is a by-product of lipid peroxidation. Acrolein has been implicated in multiple respiratory diseases and in the pathogenesis of other human diseases that are associated with oxidative stress such as Alzheimer's and Parkinson diseases, atherosclerosis and cardiovascular diseases, and diabetes. Acrolein causes protein modifications that could lead to protein misfolding and aggregation. an accumulation of aberrantly-folded proteins in the endoplasmic reticulum (ER) triggers a defined set of transducers to correct the defects or commit the cells to apoptosis if the rescue effort is exhausted. This study determines whether acrolein can disrupt ER homeostasis in human A549 adenocarcinoma lung cells. Exposure of cells to low doses of acrolein activated several signature ER stress markers: (a) survival/rescue molecules such as phosphorylated forms of protein kinase like ER resident kinase (p-PERK), eukaryotic initiation factor- - and inositol-requiring enzyme-1 (IRE- activating transcription factor 6 (ATF6); and the chaperone glucose-regulated protein (GRP)-78/BiP. Higher doses of acrolein caused ER-mediated apoptosis whereby expression of CAAT/enhancer binding protein homologous protein (CHOP) increased, and there was activation of proteases such as caspases-4, -7 and -3, and calpain. These findings indicate that the ER stress response plays a role in mediating the toxic effect of acrolein in lung cells. Financial support: Natural Sciences and Engineering Research Council of Canada (NSERC)

Reactive Electrophiles in Cigarette Smoke Decrease Airway Epithelial Barrier Integrity and Promote EMT through Activation of Src Robert a Bauer1, Page Spiess1, Milena Hristova1, Aida Habibovic1, and Albert van der Vliet1 1University of Vermont, United States Many of the adverse effects of cigarette smoke can be attributed to reactive electrophiles such as the -unsaturated aldehyde acrolein, which forms Michael adducts with protein cysteine, histidine and lysine residues. to examine the effects of acrolein inhalation in vivo, mice were exposed to aerosolized acrolein (5 ppm) either acutely (4 hrs/day) or more chronically (4 hrs/day, 4 days/week for 2 weeks). Exposure to acrolein led to a decrease in airway epithelial integrity, as indicated by increased epithelial permeability to dextran-FITC or by appearance of epithelial shedding into bronchial alveolar lavage (BAL) fluids. Furthermore, acrolein exposure also promoted allergic sensitization to inhaled ovalbumin, and fibrotic responses (as indicated by Masson

Trichrome staining), events associated with loss of epithelial integrity. in vitro studies using mouse tracheal epithelial cells or the human epithelial cell line H292 indicate that acrolein exposure decreased trans-epithelial electrical resistance (TER) and loss of E-cadherin at the cell surface, suggesting a possible role in the initiation of epithelial to mesenchymal transition (EMT). Because various recent studies have indicated that development of EMT (e.g. in response to cigarette smoke) may be associated with activation of the redox-sensitive tyrosine kinase Src, we explored the potential importance of Src in acrolein-mediated epithelial changes. Acrolein exposure of mice in vivo, and H292 cells in vitro, resulted in activation of Src, detected by the phosphorylation of Y416. Using affinity chromatography it was also shown that acrolein formed direct adducts to Src, which could be a factor in its activation. Studies using the Src inhibitor PP2, or siRNA-mediated Src silencing, indicated that acrolein-induced loss of e-cadherin localization at cell-cell junctions, as well as induction of heme oxygenase-1 (HO-1), as an adaptive response, depend on Src activation. Collectively these studies show that epithelial responses to acrolein are at least partially dependent on Src activation through direct modification.

Impairment of NOX/PKC/MAPK/COX-2/PGE2 Signaling in G6PD-Knockdown A549 Cells and Subsequent Effect on TNF- Mediated Anti-Viral Response Hsin-Ru Lin1, Yi-Hsuan Wu2, Chuen-Mao Yang1, and Daniel Tsun-Yee Chiu2 1Graduate Institute of Biomedical Science, Taiwan, 2Department of Medical Biotechnology and Laboratory Science, Chang Gung University, Taiwan Glucose-6-phosphate dehydrogenase (G6PD) plays a key role in regenerating NADPH thus maintaining the cellular redox homeostasis. Previously, G6PD-deficient cells have been found to be more susceptible to viral infection than normal counterparts. However, how G6PD deficiency affects inflammatory signaling thus influences antiviral response has not been fully explored. by comparing the level of TNF- mediated inflammatory response, decreased expression pattern of Cox-2, PGE2 and accompany increased susceptibility to Coronavirus 229E infection were observed in G6PD-knockdown A549 cells. Further evidence proved that these phenomena were due to decreased phosphorylation level of MAPK and NF- B. the impairment of TNF- -mediated inflammatory response was observed via the NOX/PKC signaling. in conclusion, these findings suggest that altered cellular inflammatory responses and decreased TNF- -mediated anti-viral response in G6PD-knockdown A549 cells as a consequence of G6PD deficiency is through dysregulated NOX/PKC/MAPK/Cox-2 /PGE2 signaling.

doi: 10.1016/j.freeradbiomed.2013.10.787

doi: 10.1016/j.freeradbiomed.2013.10.788

doi: 10.1016/j.freeradbiomed.2013.10.789