Comparison of the continuous rat hepatoma cell line 2sFou with primary rat hepatocyte cultures for the induction of DNA repair synthesis by nitrosamines, benzo[a]pyrene and hydroxyurea

Relative importance of oxidation and Ca(2+) in DNA strand breakage by H(2)O(2) in the 2sFou cell line

The rat hepatoma cell line (2sFou) was used to assess the mechanism of DNA strand breakage using the model oxidant H(2)O(2). Exposure of the cells to H(2)O(2) (100 mum) at 37 degrees C significantly reduced the amount of double-stranded DNA remaining after alkaline unwinding at 15 degrees C (control = 75.0 +/- 7.3%, n = 9, 100 mum H(2)O(2) = 46.5 +/- 8.0, n = 8, P < 0.02). The catalase inhibitor 3-amino-1,2,4-triazole halved the concentration of H(2)O(2) needed to give a significant level of strand breakage (control = 58.6 +/- 3.9%, n = 8, 50 mum H(2)O(2) = 36.5 +/- 2.1, n = 3, P < 0.02). The calcium chelator Quin-2 and the endonuclease inhibitor aurintricarboxylic acid both inhibited DNA strand breakage following treatment with 100 mum H(2)O(2) by 92% and 94%, respectively, whereas the lipid peroxidation inhibitor N, N-diphenyl-1,2,4-phenylene-diamine had no effect on H(2)O(2)-induced strand breakage. Analysis of the 2sFou cellular DNA for the 8-oxodG adduct following H(2)O(2) exposure provided no evidence for direct attack of the DNA mediated by hydroxyl radicals. Ca(2+) appears to be the major mediator of H(2)O(2)-induced DNA strand breakage.

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.