ENaC alpha-subunit variants are expressed in lung epithelial cells and are suppressed by oxidative stress.
Amiloride-sensitive epithelial sodium channel (ENaC) is a major sodium channel in the lung facilitating fluid absorption. ENaC is composed of alpha-, beta-, and gamma-subunits, and the alpha-subunit is indispensable for ENaC function in the lung. In human lungs, the alpha-subunit is expressed as various splice variants. Among them, alpha(1)- and alpha(2)-subunits are two major variants with different upstream regulatory sequences that possess similar channel characteristics when tested in Xenopus oocytes. Despite the importance of alpha-ENaC, little was known about the relative abundance of its variants in lung epithelial cells. Furthermore, lung infection and inflammation are often accompanied by reduced alpha-ENaC expression, oxidative stress, and pulmonary edema. However, it was not clear how oxidative stress affects expression of alpha-ENaC variants. In this study, we examined relative expression levels of alpha-subunit variants in four human lung epithelial cell lines. We also tested the hypothesis that oxidative stress inhibits alpha-ENaC expression. Our results show that both alpha(1)- and alpha(2)-ENaC variants are expressed in the cells we tested, but relative abundance varies. In the two monolayer-forming cell lines, H441 and Calu-3, alpha(2)-ENaC is the predominant variant. We also show that H(2)O(2) specifically suppresses alpha(1)- and alpha(2)-ENaC variant expression in H441 and Calu-3 cells in a dose-dependent fashion. This suppression is achieved by inhibition of their promoters and is attenuated by dexamethasone. These data demonstrate the importance of the alpha(2)-subunit variant and suggest that glucocorticoids and antioxidants may be useful in correcting infection/inflammation-induced lung fluid imbalance.
Xu
Haishan
H
McGuire Veterans Affairs Medical Center, Richmond, VA 23249, USA.
Chu
Shijian
S
D045744:Cell Line, Tumor; D003907:Dexamethasone / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008168:Lung / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects; D011401:Promoter Regions, Genetic; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D012333:RNA, Messenger; D003907:Dexamethasone; D006861:Hydrogen Peroxide