Hepatic nuclear protein kinases in young rats pretreated with 3-methylcholanthrene.

The activities of rat liver nucleolar and nucleoplasmic protein kinases were investigated after administration of a single intraperitoneal (i.p.) dose of 100 mg/kg body weight 3-methylcholanthrene (3-MC). A significant increase was observed in the activities of both the nucleolar and nucleoplasmic protein kinases in the hepatic cells from young rats. The maximum stimulation was evident 24 h after pretreatment with 3-MC. The extent of the maximum activation was distinctly greater in the nucleolar (186%) than in the nucleoplasmic fraction (133% compared with the controls). A second activation of the extranucleolar protein kinase fractions was demonstrated 96 h after 3-MC pretreatment. It is suggested that both kinds of enzymes are involved in the mechanism of the cytochrome P-448-inducing action of 3-MC via stimulating nuclear RNA polymerases.