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

EE causes a cell cycle block before S-phase. The reduction of the cdk2 kinase activity, essential for G1/S-transition, might be involved in the cell cycle block. Also, EE treatment results in p53 activation and upregulation of the cdk inhibitor p21 that might contribute to the G1 arrest.