Induction of Glutathione Peroxidase 4 Expression during Enterocytic Cell Differentiation

Abstract

Glutathione peroxidase 4 (GPx4), an abundant selenoenzyme, is ubiquitously expressed in a tissue-, cell-and differentiationdependent manner, and it is localized in cytoplasmic, mitochondrial, and nuclear cellular compartments. Here, we report cytoplasmic and nuclear localization of GPx4 in Caco-2 intestinal epithelial cells. Enterocytic differentiation of Caco-2 cells triggers an increase in GPx4 mRNA and protein levels, mediated by enhanced promoter activity. We identified a combined cAMP response element (CREB) and CCAAT/enhancer binding protein (C/EBP) site as critical for the differentiation-triggered GPx4 promoter activity. Induction of GPx4 correlated with C/EBP␣ transcript levels during differentiation, suggesting a role of C/EBP␣ as regulator of enterocytic GPx4 expression. Consistent with the in vitro results, GPx4 protein was detected in cytoplasmic and nuclear compartments of enterocytes in human intestinal epithelia. GPx4 is uniformly expressed in colonic crypts and is differentially expressed along the cryptto-villus axis in the small intestine with a more pronounced expression of GPx4 in the upper villi, which contain fully differentiated enterocytes. These data suggest that intestinal GPx4 expression is modulated by the enterocytic differentiation program, and the results support a direct role of nuclear GPx4 in the (selenium-dependent) prevention of oxidative damage in the gastrointestinal tract.The essential trace element selenium is of fundamental importance to human health, acting through low molecular weight selenium compounds as well as selenocysteine-containing selenoproteins (1). Adequate selenium intake, maintaining optimized expression and/or activity of selenoproteins, has been proposed to be beneficial with respect to prevention of several oxidative stress-related neurodegenerative and cardiovascular diseases and, most notably, cancer (1, 2). Secondary end point analyses of the Nutritional Prevention of Cancer study provided compelling evidence that dietary supplementation with 200 g selenium/day in form of high selenium yeast lowered the incidence of lung, prostate, and colorectal cancer as well as cancer mortality (3). Since the publication of this landmark trial, the anticarcinogenic capacity of selenium compounds has been further substantiated, particularly with regard to the gastrointestinal tract (4 -7). Mice with genetically impaired biosynthesis of selenoproteins due to a mutant selenocysteine transfer RNA gene have been shown to be more susceptible to colon cancer than wild-type mice, thus suggesting a key role for selenoproteins as mediators of the cancer-protective effects of selenium in the colon (5). Selenoproteins that are abundantly expressed in the healthy gastrointestinal tract and putatively relevant in malignant transformation comprise thioredoxin reductases, selenoprotein P, and glutathione peroxidases (GPx) 3 (8 -11). To date, five selenium-dependent GPx isoenzymes have been identified in humans: GPx1 and GPx2 are highly expressed in the intestinal epithelium, havi...

Toward Understanding Success and Failures in the Use of Selenium for Cancer Prevention

“…Expression of SBP1 is frequently downregulated in colorectal carcinoma tissue, and low SBP1 expression levels are correlated with poorer patient survival rates, as shown in two independent studies (43,51). Similar to the selenoproteins SeP and GPx4 (82,81), SBP1 levels increase during enterocytic cellular differentiation. Maximal SBP1 expression is observed in terminally differentiated cells of the intestinal epithelium (51).…”

“…GPx4 is localized in the cytoplasm and nuclei of epithelial cells of the small and large intestine (81). GPx4 might be particularly interesting in regard to Se-dependent chemoprevention, given its nuclear localization and its broad and unique substrate spectrum, including lipid and thymine hydroperoxides.…”

Glutathione peroxidase 4 has a major role in protecting mitochondria from oxidative damage and maintaining oxidative phosphorylation complexes in gut epithelial cells

“…We conclude that in undifferentiated Caco-2 gut epithelial cells changes in GPx4 activity lead to altered AIF expression, which then leads to changes in both the mitochondrial oxidative phosphorylation system and apoptotic signaling. Interestingly, it has recently been observed that GPX4 expression is increased during Caco-2 cell differentiation and that there is higher expression in upper villus enterocytes that are fully differentiated [42]. This suggests that the AIF-related protective role of GPx4 may be particularly important in differentiated enterocytes.…”

Redox biology of the intestine

“…Gpx3, an extracellular Gpx isoform secreted by intestinal cells into the lumen, reportedly participates in protecting the intestinal mucosa against oxidant injury [91]. Gpx4, the only Se-Gpx protein known to reduce phospholipid hydroperoxides, is present in the cytoplasmic and nuclear compartments of human small intestine and colon [92]; interestingly, Se deficiency has no effect on Gpx4 message level or its stability [90]. Pprotein expression and enzymatic activity of Gpx4 are notably increased in differentiated colonocytes in association with enhanced antioxidant protection, especially in the nuclear compartment [92].…”