Induction of cyclooxygenase-2 by tumor promoters in transformed and cytochrome P450 2E1-expressing hepatocytes.
The induction of cyclooxygenase (COX)-2 expression has been implicated as a mechanism for the formation of non-hepatic tumors. Recent investigations have demonstrated COX-2 expression in human hepatocellular carcinomas, but little is known about the regulation of hepatocyte COX-2 expression. Employing the adult, rat hepatocyte line RALA255-10G, the effects of cellular transformation or expression of the alcohol-inducible cytochrome P450 2E1 (CYP2E1) on COX-2 expression were examined. Transformed and non-transformed hepatocytes did not express COX-2 by western and northern blot analysis. The tumor promoters phorbol 12-myristate 13-acetate (PMA) and chenodeoxycholic acid (CD) induced COX-2 protein expression in transformed, but not non-transformed cells. CYP2E1-expressing cells lacked constitutive COX-2 expression, and PMA but not CD induced COX-2 in these cells. PMA-treated transformed and CYP2E1-expressing cells expressed functional COX-2 as demonstrated by marked inductions in prostaglandin E(2) synthesis. PMA-induced COX-2 expression in both transformed and CYP2E1-expressing cells resulted from an induction in COX-2 mRNA, and was dependent on extracellular signal-regulated kinase, p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase. The differential induction of COX-2 by PMA in transformed and non-transformed cells could not be explained by differences in NF-kappaB or C/EBPalpha activation. PMA did not induce COX-2 transcriptional activity as determined by transient transfections with a luciferase reporter gene driven by the COX-2 promoter. The data demonstrate that cellular transformation and CYP2E1 expression fail to lead to the induction of COX-2 expression in hepatocytes. However, these conditions do render hepatocytes susceptible to COX-2 induction from tumor promoters by post-transcriptional mechanisms.
de Lédinghen
Victor
V
Department of Medicine, Strang Cancer Prevention Center, Weill Medical College of Cornell University, New York, NY 10021, USA.
Liu
Hailing
H
Zhang
Fan
F
Lo
Chau R
CR
Subbaramaiah
Kotha
K
Dannenberg
Andrew J
AJ
Czaja
Mark J
MJ
D000818:Animals; D015153:Blotting, Western; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D002273:Carcinogens / Q000494:pharmacology*; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000378:metabolism* / Q000473:pathology; D002635:Chenodeoxycholic Acid / Q000494:pharmacology; D051546:Cyclooxygenase 2; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D004790:Enzyme Induction / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology* / Q000473:pathology; D007249:Inflammation / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D022762:CCAAT-Enhancer-Binding Proteins; D002273:Carcinogens; D007527:Isoenzymes; D016328:NF-kappa B; D012333:RNA, Messenger; D002635:Chenodeoxycholic Acid; D019392:Cytochrome P-450 CYP2E1; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate