CYP2E1 overexpression up-regulates both non-specific delta-aminolevulinate synthase and heme oxygenase-1 in the human hepatoma cell line HLE/2E1.
Cytochrome P450 (CYP) is known to turn over rapidly both in vivo in the liver, and in vitro in cultured hepatoma cells expressing CYP. We examined changes in heme metabolism by analyzing gene expression of the non-specific delta-aminolevulinate synthase (ALAS-N), and heme oxygenase-1 (HO-1), the rate limiting enzyme in heme synthesis and catabolism, respectively, in the human hepatoma cell line HLE/2E1, in which CYP2E1 was overexpressed by transfection of its expression vector. Both ALAS-N mRNA and HO-1 mRNA levels were found to be markedly up-regulated in HLE/2E1 cells as compared with those in non-transfected cells (HLE), or in mock-transfected cells (HLE/MOCK). Treatment of HLE/2E1 cells with succinylacetone (SA), a potent inhibitor of delta-aminolevulinate dehydratase and thereby heme synthesis, resulted in a further increase in ALAS-N mRNA but a decrease in HO-1 mRNA levels. In contrast, treatment of cells with heme, as heme arginate, to SA-pretreated HLE/2E1 cells restored both mRNA levels to the untreated control level. These findings suggest that the overexpression of CYP2E1 results in the up-regulation of ALAS-N in order to meet with an increased demand for heme synthesis for CYP2E1 formation, while it also results in the up-regulation of HO-1 presumably by enzyme induction by free heme released from CYP2E1, which then results in the elimination of toxic excess free heme and ultimately restores the physiologic milieu.
Takahashi
Shuji
S
Department of Anesthesiology and Resuscitology, Okayama University Medical School, Okayama 700-8558, Japan.
Takahashi
Toru
T
Mizobuchi
Satoshi
S
Matsumi
Masaki
M
Yokoyama
Masataka
M
Morita
Kiyoshi
K
Miyazaki
Masahiro
M
Namba
Masayoshi
M
Akagi
Reiko
R
Sassa
Shigeru
S
D000624:5-Aminolevulinate Synthetase / Q000037:antagonists & inhibitors / Q000235:genetics*; D006528:Carcinoma, Hepatocellular; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics*; D051547:Heme Oxygenase-1; D006537:Heptanoates / Q000494:pharmacology; D006801:Humans; D008113:Liver Neoplasms; D008565:Membrane Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D006537:Heptanoates; D008565:Membrane Proteins; D011994:Recombinant Proteins; C020804:succinylacetone; D019392:Cytochrome P-450 CYP2E1; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D000624:5-Aminolevulinate Synthetase