CYTOCHROMES P450 (CYP) IN THE POECILIOPSIS-LUCIDA HEPATOCELLULAR-CARCINOMA CELL-LINE (PLHC-1) - DOSE-DEPENDENT AND TIME-DEPENDENT GLUCOCORTICOID POTENTIATION OF CYP1A INDUCTION WITHOUT INDUCTION OF CYP3A

Glucocorticoids are being found to influence expression of cytochrome P450 (CYP) genes in multiple subfamilies in mammals (J. S. Sidhu, and C. J. Omiecinski (1995) Pharmacogenetics 5, 24-36), In the present stu dy we investigated CYP1A and CYP3A expression in the fish Poeciliopsis lucida hepatocellular carcinoma cell line (PLHC-1) after coadministra tion of CYP1A and CYP3A inducers, including glucocorticoids. A putativ e CYP3A protein is expressed in PLHC-1 cells but its content was not a ltered by exposure of cultures to the prototypical mammalian CYP3A ind ucers dexamethasone (DEX), pregnenolone-16 alpha-carbonitrile (PCN), o r rifampicin (RIF). However, when coadministered with 3,3',4,4'-tetrac hlorobiphenyl or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), DM but no t PCN or RIF caused increases in the degree of CYP1A induction by thes e aryl hydrocarbon receptor (AHR) agonists, This increase was seen bot h in CYP1A protein content and rates of ethoxyresorufin-O-deethylase ( EROD) activity, DEX alone caused no induction of CYP1A, indicating tha t the enhancement of CYP1A induction caused by DEX + AHR agonists was not an additive effect but rather a potentiation, The dose of DEX requ ired for maximal potentiation was three orders of magnitude greater at 48 h than the dose required at 24 h, Moreover, the degree of potentia tion of CYP1A induction was much greater at the lower doses than at th e highest doses of TCDD. There was up to 20-fold potentiation of EROD induction in cultures exposed to 0.1 nM TCDD, Two other glucocorticoid receptor (GR) agonists, cortisol and prednisone, also produced a stro ng potentiation of CYP1A induction, but other mammalian CYP3A inducers that are not GR agonists, such as the anti-glucocorticoid PCN, the an ti-mineralocorticoid spironolactone, or the macrolide antibiotics II;I F and troleandomycin, did not potentiate the CYP1A. induction in PLHC- 1 cells, Addition of the mammalian GR antagonists PCN or RU 38486 redu ced the DM-mediated potentiation of CYP1A induction, whereas spironola ctone had no effect on the potentiation, RU 38486 also potentiated the induction of EROD activity by TCDD, which suggests that RU 38486 acts as a partial GR agonist in PLHC-1 cells, These results suggest that p otentiation of CYP1A induction in this nonmammalian cell line proceeds by a classical GR-mediated pathway, independently of the expression o f CYP3A. However, the complex interaction between doses of both GR and AHR agonists and duration of exposure, suggests that additional proce sses influence this potentiation, The unusually strong potentiation at lower doses of TCDD may make PLHC-1 cells particularly suitable in ex ploring further the consequences of this potentiation. (C) 1996 Academ ic Press, Inc.