Characterization of an 8-lipoxygenase activity induced by the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate in mouse skin in vivo

An enzymatic activity has been found in cytosolic preparations from mouse epidermis which catalyzes the formation of 8-hydroperoxyeicosatetraenoic acid/8-hydroxyeicosatetraenoic acid (8-HPETE/8-HETE) from arachidonate. In contrast to 12-lipoxygenase this enzyme activity was not detectable in normal (untreated) mouse skin but only after in vivo treatment with the phorbol ester tumor promoter TPA (12-O-tetradecanoylphorbol-13-acetate). The induction showed a maximum at 24 h after TPA treatment strictly depended on the age of the mice and the TPA dose and was prevented by cycloheximide. The primary product formed from arachidonic acid was 8-HPETE, and the enzyme seems not to possess a significant peroxidase activity. This result as well as studies with specific inhibitors and its cytosolic localization indicates this enzyme to be a member of the lipoxygenase family. Most of the 8-lipoxygenase activity is located in cells of the suprabasal compartment of the epidermis. In spite of being a cytosolic enzyme 8-lipoxygenase appeared to be lipophilic to some extent and was activated by lecithin. The enzyme did not require calcium ions or ATP and showed a pH optimum at 7.5-8.0. 8-HPETE/8-HETE levels in mouse epidermis in vivo were determined by gas chromatography-mass spectrometry and found to be strongly increased after phorbol ester treatment, in agreement with the induction of 8-lipoxygenase observed.     

Functional role of extracellular signal-regulated kinase activation and c-Jun induction in phorbol ester-induced promoter activation of human 12(S)-lipoxygenase gene

The functional role of mitogen-activated protein kinase (MAPK) signaling and c-Jun induction in phorbol 12-myristate 13-acetate (PMA)-induced human 12(S)-lipoxygenase gene expression was studied in human epidermoid carcinoma A431 cells. Among the family of MAPK, PMA only increased the activity of extracellular signal-regulated kinase (ERK). Treatment of cells with PD98059, which is an inhibitor of mitogen-activated protein kinase kinase (MEK), decreased the PMA-induced expression of 12(S)-lipoxygenase. Transfection of cells with Ras, Raf and ERK2 dominant negative mutants inhibited the PMA-induced promoter activation of the 12(S)-lipoxygenase gene in all cases. PMA-induced expression of c-Jun was inhibited by pretreatment with PD98059. Following treatment with PMA, the interaction between c-Jun and simian virus 40 promoter factor 1 (Sp1) in cells increased with time. Enhancement of binding between the c-Jun-Sp1 complex and the Sp1 oligonucleotide was observed in cells treated with PMA, suggesting the possible interaction of c-Jun-Sp1 with GC-rich binding sites in the gene promoter. These results indicate that PMA treatment induced ERK activation mainly through the Raf-MEK-ERK signaling pathway following induction of c-Jun expression, and the formation of the c-Jun-Sp1 complex. Finally, PMA activated the promoter activity of the 12(S)-lipoxygenase gene in cells overexpressing protein kinase C (PKC)delta but not PKCalpha, indicating that PKCdelta played the functional role in mediating the gene activation of 12(S)-lipoxygenase induced by PMA.     

Wortmannin inhibits activation of nuclear transcription factors NF-kappaB and activated protein-1 induced by lipopolysaccharide and phorbol ester

The effect of the expression of murine Bax protein on growth and vitality was examined in Saccharomyces cerevisiae and compared with the effect of Bax in mutant cells lacking functional mitochondria. The cytotoxic effect of Bax on yeast does not require functional oxidative phosphorylation, respiration, or mitochondrial proteins (ADP/ATP carriers) implicated in the formation of the permeability transition pore in mammalian mitochondria. In the wild type S. cerevisiae the expression of Bax does not result in a severe effect on mitochondrial membrane potential and respiration. On the basis of Bax induced differences in the fluorescence of green fluorescent protein fused to mitochondrial proteins, it is proposed that Bax may interfere with one essential cellular process in yeast: the mitochondrial protein import pathway that is specific for the proteins of the mitochondrial carrier family.