Regulation of mouse P1450 gene expression in monolayer-cultured hepatocytes from responsive and non-responsive strains

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Abstract
Regulation of P1450 gene expression in mouse hepatocytes from responsive (C57BL/6) and non-responsive (DBA/2) strains in primary culture was investigated with respect to aryl hydrocarbon hydroxylase (AHH) activity and P450 transcript levels. Although significant induction of AHH activity in C57BL/6 mouse hepatocytes after exposure to benz[a]anthracene (BA) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was observed 24 h after the beginning of cultivation, the response was more prominent after longer periods. AHH induction in DBA/2 mouse hepatocytes by TCDD was also evident after 24 h treatment, but that by BA was delayed, only becoming significant after 3 days. Limited treatment with cycloheximide (CHI) for the initial 8 h affected AHH activity measured after 24 h; BA-Induced AHH activity was decreased If the treatment started day 1 after seeding of the cells from either strain, whereas If started at day 3 the enzyme activities in hepatocytes from C57BL/6 strain were approximately doubled and those from DBAJ2 increased to 130%. Treatment with dibutyryl cAMP or forskolin, a specific activator for adenyl cyclase, Increased BA-induced AHH activities. 3-Methoxybenzamide, a specific inhibitor of poly(ADP-ribose) polymerase, significantly increased both basal and BA-induced AHH activities of hepatocytes from both strains at days 3 and 5, reduction of P1450 transcripts also being evident in the latter case. The observations indicate qualitatively similar but quantitatively different regulation of Au-h induction In both responsive and non-responsive mouse strains. Furthennore the regulation changed with increasing cultivation period. Previously described regulation mechan isms in cultured cells were observed to operate a few days after seeding, possibly after adaptation of hepatocytes to the culture conditions.

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