title: Colocalization of MnSOD expression in response to oxidative stress.
abstract: The loss of manganese superoxide dismutase function has been associated with increased incidence of Barrett's esophagus and esophageal adenocarcinoma. In previous studies, we have demonstrated that loss of MnSOD resulted in severe esophageal damage by both endogenous and exogenous bile. However, the alterative manner of MnSOD in esophageal epithelium is largely unknown. In this study, we investigated the expression and localization of MnSOD in response to the exposure to bile salts in an esophageal epithelial cell line. Het-1A cells were seeded at 5 x 10(5) and 10(7) and incubated with taurocholate, cholate, glycocholate, deoxycholate, and the mixture of these bile salts. Mitochondria and cytoplasma were separated, and the expression and localization of MnSOD was determined by Western blot and immunocytochemical assay. Proliferation rates were strongly inhibited in the groups with taurocholate and bile salts mixture at 4 h, with 0.367 +/- 0.042 and 0.396 +/- 0.046, respectively, compared to 0.684 +/- 0.054 in untreated groups (P < 0.05). An increased apoptotic rate compared to untreated group (3.65 +/- 0.59) were significantly increased in taurocholate group and in bile salts mixture group were 33.62 +/- 10.25 and 31.52 +/- 8.97 at 4 h, respectively (P < 0.05). The protein level of MnSOD in mitochondria was increased at 4 h, but with a decreased enzymatic activity after bile salts treatment. Cytoplasmic MnSOD was detected in the cells with bile salts treatment. Immunocytochemical staining demonstrated that esophageal epithelial cell underwent morphological alteration and MnSOD relocalization after bile salts treatment. This is the first study to demonstrate cellular cytosolic MnSOD expression and that this relocalization to the cytosol is a cause for decreased MnSOD enzymatic activity. This suggests that bile salts may contribute to the dysfunction of mitochondria, by enzymatically inhibiting of MnSOD localization and thus activation in the mitochondria.
authors.affiliation: University of Louisville School of Medicine, Kentucky 40202, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Nathaniel P
authors.initials: NP
authors.lastname: Reuter
authors.forename: Xuanshe
authors.initials: X
authors.lastname: Li
authors.forename: Qiaohong
authors.initials: Q
authors.lastname: Liu
authors.forename: Jingwen
authors.initials: J
authors.lastname: Zhang
authors.forename: Robert C G
authors.initials: RC
authors.lastname: Martin
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001647:Bile Acids and Salts / Q000494:pharmacology*; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D004947:Esophagus / Q000166:cytology; D006801:Humans; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology; D018384:Oxidative Stress; D013482:Superoxide Dismutase / Q000378:metabolism*; D013656:Taurocholic Acid / Q000494:pharmacology
chemical_list: D001647:Bile Acids and Salts; D013656:Taurocholic Acid; D013482:Superoxide Dismutase