Identification of a Novel Putative Non-selenocysteine Containing Phospholipid Hydroperoxide Glutathione Peroxidase (NPGPx) Essential for Alleviating Oxidative Stress Generated from Polyunsaturated Fatty Acids in Breast Cancer Cells

Abstract

A dramatic reduction in the expression of a novel phospholipid hydroperoxide glutathione peroxidase (PHGPx), which incorporates cysteine instead of selenocysteine in the conserved catalytic motif was observed in a microarray analysis using cDNAs amplified from mRNA of Brca1-null mouse embryonic fibroblasts. This non-selenocysteine PHGPx named NPGPx is a cytoplasmic protein with molecular mass of ϳ22 kDa and has little detectable glutathione peroxidase activity in vitro. Ectopic expression of NPGPx in Brca1-null cells that were sensitive to oxidative stress induced by hydrogen peroxide conferred a similar resistance level to that of the wild-type cells, suggesting the importance of this protein in reducing oxidative stress. Expression of NPGPx was found in many tissues, including developing mammary gland. However, the majority of breast cancer cell lines studied (11 of 12) expressed very low or undetectable levels of NPGPx irrespective of BRCA1 status. Re-expression of NPGPx in breast cancer lines, MCF-7 and HCC1937, which have very little or no endogenous NPGPx, induced resistance to eicosapentaenoic acid (an omega-3 type of polyunsaturated fatty acid)-mediated cell death. Conversely, inhibition of the expression of NPGPx by the specific small interfering RNA in HS578T breast cancer cells that originally express substantial amounts of endogenous NPGPx increased their sensitivity to eicosapentaenoic acid-mediated cell death. Thus, NPGPx plays an essential role in breast cancer cells in alleviating oxidative stress generated from polyunsaturated fatty acid metabolism.

Redox Balance Mechanisms in Schistosoma mansoni Rely on Peroxiredoxins and Albumin and Implicate Peroxiredoxins as Novel Drug Targets

“…Analysis of the GPx2-predicted peptide identified a 19-amino acid leader sequence with a likely cleavage site between amino acids 18 and 19 (34). The first in-frame UGA codon of the open reading frame is likely to encode a selenocysteine (Sec ϭ U), as was also found in GPx1 (7,8,35) and in 5 of 7 classes of mammalian GPx proteins (36). The second in-frame UGA is the actual stop codon.…”

Comparison of the seleno-transcriptome expression between human non-cancerous mammary epithelial cells and two human breast cancer cell lines

“…In detail, GPX4 has been demonstrated to have a reduced expression in a number of cell lines, including breast cancer MCF-7, colon cancer HT29 and ovarian cancer A2780 cell lines (36), while the absence of non-Sec phospholipid hydroperoxide glutathione peroxidase complex with GPX6 expression has been identified in the majority of breast cancer cell lines (37). The potential role in alleviating oxidative stress induced by dietary consumption of fatty acids has been suggested for GPX7 in breast cancer cells (38). By contrast, in the present study, GPX2 and GPX3 were upregulated in ER-positive MCF-7 and ER-negative MDA-MB231 cells.…”

Molecular biology of glutathione peroxidase 4: from genomic structure to developmental expression and neural function

“…Molecular biology and bioinformatics have recently revealed at least 25 selenoproteins, five of which are glutathione peroxidases (GPxs) (Kryukov et al, 2003;Utomo et al, 2004). All selenoproteins with known enzymatic activity bear a selenocysteine at their active center that is essential for catalytic activity and cannot simply be replaced by a cysteine residue.…”