Long-term 17alpha-ethinyl estradiol treatment decreases cyclin E and cdk2 expression, reduces cdk2 kinase activity and inhibits S phase entry in regenerating rat liver.

Background/aims: The synthetic estrogen 17alpha-ethinyl estradiol (EE), a potent tumor promoter in rat liver, stimulates growth during short-term treatment but inhibits hepatocyte proliferation upon prolonged treatment. To identify the molecular targets of the mitoinhibitory effect of EE, the expression of proteins regulating G(1)- and S-progression were analyzed during the first cell cycle in EE-treated female Wistar rats.

Methods: Long-term (60 days) EE treatment.

Mitoinhibitory effects of the tumor promoter 2-acetylaminofluorene in rat liver: loss of E2F-1 and E2F-3 expression and cdk 2 kinase activity in late G1.

Background/aims: Examine the mitoinhibitory effect of the liver tumor promoter 2-acetylaminofluorene (2-AAF) in vivo, with focus on the proteins regulating G1- and S progression.

Methods: cdk 2 kinase assay to examine histone H1 phosphorylation. cdk 4 kinase assay to examine whether active cdk 4/cyclin D complexes, capable of phosphorylating Rb, are formed.