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.
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 approximately 22 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.
Department of Biological Chemistry, School of Medicine, University of California, Irvine 92697, USA.
Ahmad
A
Utomo
Xianzhi
X
Jiang
Saori
S
Furuta
Jeanho
J
Yun
David S
DS
Levin
Yi-Chun J
YC
Wang
Kartiki V
KV
Desai
Jeffrey E
JE
Green
Phang-Lang
PL
Chen
Wen-Hwa
WH
Lee
D000595:Amino Acid Sequence; D000818:Animals; D019313:BRCA1 Protein / Q000172:deficiency / Q000235:genetics; D001483:Base Sequence; D001943:Breast Neoplasms; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D017931:DNA Primers; D015118:Eicosapentaenoic Acid / Q000494:pharmacology; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005260:Female; D005979:Glutathione Peroxidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D000080662:Phospholipid Hydroperoxide Glutathione Peroxidase; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017279:Selenocysteine; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D019313:BRCA1 Protein; D002352:Carrier Proteins; D017931:DNA Primers; D005231:Fatty Acids, Unsaturated; C578349:NPGPx protein, mouse; D034741:RNA, Small Interfering; D017279:Selenocysteine; D015118:Eicosapentaenoic Acid; D000080662:Phospholipid Hydroperoxide Glutathione Peroxidase; D005979:Glutathione Peroxidase