Abstract

The induction of aryl hydrocarbon hydroxylase was studied in a line of mouse 3T3 fibroblasts (Swiss) grown in continuous cell culture. The level of hydroxylase activity after induction by benz[a]anthracene appeared to be several times higher in this 3T3 line than in other continuously cultured cell lines previously studied. The induction of aryl hydrocarbon hydroxylase was linear for 24 hr after the addition of 13 µM benz[a]-anthracene to the culture medium. Induction of the enzyme by benz[a]anthracene was markedly greater in 3T3 cells grown in the presence than in the absence of serum and was higher in nonconfluent than in confluent cells. Moreover, the addition of 0.01 µM dibutyryl cyclic GMP (a putative signal for increased cell proliferation) to serumless medium containing 6 µM benz[a]anthracene markedly potentiated induction of aryl hydrocarbon hydroxylase by the hydrocarbon. These results suggest that the inducibility of the hydroxylase system by benz[a]anthracene is greater in proliferating than in nonproliferating cells.