Inhibition of arachidonate metabolism in human epidermoid carcinoma A431 cells overexpressing phospholipid hydroperoxide glutathione peroxidase

Phospholipid hydroperoxide glutathione peroxidase (PHGPx), a selenium-dependent glutathione peroxidase, can interact with lipophilic substrates, including phospholipid hydroperoxides, fatty acid hydroperoxides and cholesterol hydroperoxides, and can reduce them to hydroxide compounds. It also seems to be a major regulator of lipid oxygenation in human epidermoid carcinoma A431 cells. In order to study the functional role of PHGPx in the regulation of 12-lipoxygenase and cyclooxygenase, cDNA of PHGPx was inserted into pcDNA3.1/ His, and a plasmid designated as S4 with the His-tag sequence inserted between PHGPx and its T-untranslated region was constructed. A number of stable transfectants of A431 cells that could express the tag-PHGPx were generated using plasmid S4. Using an intact cell assay system, the metabolism of arachidonic acid to prostaglandin E-2 significantly decreased in stable transfectants of overexpressing PHGPx compared to that in a vector control cell line. If the intact cell assay was carried out in the presence of 13-hydroperoxyoctadecadienoic acid as a stimulator of lipid peroxidation, formation of 12-hydroxyeicosatetraenoic acid from arachidonic acid also significantly decreased in stable transfectants of overexpressing PHGPx compared to that in a vector control cell line, indicating that PHGPx could downregulate the 12-lipoxygenase activity in cells. These results support the hypothesis that PHGPx plays a pivotal role in the regulation of arachidonate metabolism in A431 cells.