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.

Characterization of squamous esophageal cells resistant to bile acids at acidic pH: implication for Barrett's esophagus pathogenesis

“…The loss of MnSOD function was previously shown to be associated with increased incidence of BE (37). Furthermore, a recent study by Li et al (35) suggests that exposure to hydrophobic bile acids decreases MnSOD activity. Our data demonstrate that MnSOD activity can be significantly decreased by chronic treatment with bile acids at low pH.…”

The Resistance of Esophageal Adenocarcinoma to Bile Salt Insult is Associated with Manganese Superoxide Dismutase Expression

“…In our previous studies, we determined that SOD enzymatic activity was decreased in rat esophageal tissue after esophagoduodenal anastomosis (EDA) and external bile acid perfusion16–22. Supplementation with MnTBAP, an MnSOD mimetic, can protect rat esophageal epithelium from oxidative injury induced from increased bile acid exposure20.…”

“…The three types of SOD are cytosolic copper/zinc-dependent SOD (CuZnSOD), iron-dependent extracellular SOD (EC-SOD), and manganese-dependent mitochondria SOD (MnSOD). Deficiency of MnSOD has been associated with carcinogenesis because MnSOD acts a tumor suppressor by inhibiting ROS and preventing cellular damage16.…”

“…MnSOD contributes to this loss of enzymatic activity16–22. Supplementation with MnSOD mimetic Mn(III)tetrakis (4-benzoic acid) porphyrin (MnTBAP) can protect rat esophageal epithelium from oxidative injury induced from increased bile acid exposure20.…”

Apoptosis, Free Radicals and Antioxidant Defense in Antitumor Therapy

“…Tumor cells nearly always show a decrease in SOD1 and SOD2 expression. Glutathione peroxidase activities have been found to be changeable, while catalase activity is generally lower in tumor cells than in healthy tissue [133][134][135].…”