Expression of cytochromes P-450 in rat hepatoma cells. Analysis by monoclonal antibodies specific for cytochromes P-450 from rat liver induced by 3-methylcholanthrene or phenobarbital

Abstract

We have studied the expression of aldrin epoxidase (AE), 7‐ethoxycoumarin‐O‐deethylase (ECDE), and aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) in nine differentiated or dedifferentiated cell lines derived from H4IIEC3 rat hepatoma cells. The nature of the cytochromes P‐450 mediating AE, ECDE and AHH activities was analysed using monoclonal antibodies (MAb) made to the major 3‐methylcholanthrene‐induced cytochrome P‐450 (MAb‐MC) or phenobarbital‐induced cytochrome P‐450 (MAb‐PB) from rat liver. The cells were treated with 5 μM dexamethasone for 30 h to increase the levels of the monooxygenase activities. (a) The six differentiated cell lines examined (Faza967, Fao, HF1‐4, 2sFou, C2Rev7, and H4IIEC3/G⁻) contained MAb‐PB‐sensitive AE comprising 30–75% of the total AE activity. In most of these cell lines MAb‐PB also markedly inhibited ECDE; however, the antibody had a considerably weaker effect on AHH. (b) MAb‐PB‐sensitive AHH, ECDE and AE activities were also observed in untreated and phenobarbital‐treated cells. (c) MAb‐MC inhibited AHH and ECDE in the two dedifferentiated lines HF1 and H5 by 50–80%. The antibody also inhibited AHH activities in the poorly differentiated line H4IIEC3/T and in the majority of the differentiated lines by 40–65%. MAb‐MC‐sensitive AHH was found in Fao cells after treatment with benz[a]anthracene but not with dexamethasone. C2Rev7 cells did not contain detectable MAb‐MC‐sensitive AHH. (d) Benz[a]anthracene induced AHH in H4IIEC3/T, H4IIEC3/G⁻, and 2sFou cells 20–30‐fold and in Faza 967 and Fao cells 3–5‐fold. Benz[a]anthracene remained without effect on AHH activity in C2Rev7 cells. The results show that the hepatoma cells examined express to various degrees phenobarbital‐inducible cytochrome P‐450 and/or 3‐methylcholanthrene‐inducible cytochrome P‐450. These cell lines are versatile tools for studying the regulation of monooxygenase activities and analysing their role in the activation and inactivation of xenobiotics such as carcinogens, drugs and pesticides.