Differential effects of 12-O-tetradecanoylphorbol 13-acetate on cytochrome P-450-dependent monooxygenase activities in rat hepatoma cells: induction of P-450I and suppression of P-450II.
We have studied the effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) on cytochrome P-450-dependent monooxygenase activities in several differentiated and dedifferentiated Reuber rat hepatoma cell lines using aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH), ethoxyresorufin O-deethylase (EROD), and aldrin epoxidase (AE) as test systems. The following results were obtained: (1) Exposure of cultures to 400 nM TPA for 18-24 h increased AHH activities in the differentiated lines 2sFou, H41IEC3/G- and Fao as well as in the dedifferentiated line 5L, 1.5-2.5-fold. The phorbol ester did not affect AHH activity in the dedifferentiated line H5. (2) EROD, a marker for P-450I, was induced by the phorbol ester to a similar degree as AHH. (3) A monoclonal antibody directed against P-450I strongly inhibited the AHH activity induced by TPA. (4) The onset of AHH or EROD induction by TPA was much later than that elicited by benz[a]anthracene. (6) In contrast to the induction of AHH and EROD, TPA decreased AE activity, a marker for P-450II, by about 50% in all the cell lines containing this monooxygenase activity. (7) The half-maximum-effect concentration of TPA for inducing or suppressing AHH and AE, respectively, was approximately 20 nM. (8) TPA did not interfere with AHH induction by benz[a]anthracene. However, the phorbol ester moderately decreased AHH induction and markedly suppressed AE induction by dexamethasone. The results indicate that TPA simultaneously induces P-450I and suppresses P-450II forms in rat hepatoma cells. P-450I induction by TPA in these cells did not appear to depend on their status of differentiation. Furthermore, the results suggest that the mechanism of P-450I induction by TPA differs from that elicited by polycyclic aromatic hydrocarbons or glucocorticoids.
Roesch
S F
SF
GSF-Institute of Toxicology, Gesellschaft für Strahlen- und Umweltforschung, Neuherberg, F.R.G.
Wiebel
F J
FJ
D000818:Animals; D000911:Antibodies, Monoclonal; D001551:Benz(a)Anthracenes / Q000494:pharmacology; D001579:Benzopyrene Hydroxylase / Q000096:biosynthesis; D002454:Cell Differentiation; D019363:Cytochrome P-450 CYP1A1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D004347:Drug Interactions; D004790:Enzyme Induction / Q000187:drug effects; D008114:Liver Neoplasms, Experimental / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors; D010088:Oxidoreductases / Q000096:biosynthesis; D010105:Oxygenases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D001551:Benz(a)Anthracenes; D065607:Cytochrome P-450 Enzyme Inhibitors; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; C030935:benz(a)anthracene; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C019647:aldrin epoxidase; D010105:Oxygenases; D001579:Benzopyrene Hydroxylase; D019363:Cytochrome P-450 CYP1A1; D013755:Tetradecanoylphorbol Acetate