title: 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.
abstract: OBJECTIVE
  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. Immunohistochemical staining for proliferation cell nuclear antigen (PCNA) to detect cells in S phase and quantification of mitosis. Western blot to monitor protein expression. Cdk2 kinase assay to examine histone H1 phosphorylation.
  
  
  RESULTS
  EE reduced the number of cells in S phase and mitosis by about 70%. Cyclin D1 and D3 were unaffected, while cdk4 was moderately decreased. Cyclin E and cdk2 were markedly decreased with concomitant marked reduction of cdk2 kinase activity. EE also decreased cyclin A and increased G1 levels of p53 and p21.
  
  
  CONCLUSIONS
  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.
authors: Department of Natural Science, Södertörns Högskola (University College), Box 4101, S-141 89 Huddinge, Sweden. koroxenidou@yahoo.se
authors: Lena
authors: L
authors: Koroxenidou
authors: Lena C E
authors: LC
authors: Ohlson
authors: Inger
authors: I
authors: Porsch Hällström
mesh_terms: D000818:Animals; D042846:CDC2-CDC28 Kinases / Q000235:genetics* / Q000378:metabolism; D019938:Cyclin D1 / Q000235:genetics; D056743:Cyclin D3; D019927:Cyclin E / Q000235:genetics*; D051357:Cyclin-Dependent Kinase 2; D016213:Cyclins / Q000235:genetics; D004261:DNA Replication; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D008099:Liver / Q000187:drug effects / Q000502:physiology*; D008115:Liver Regeneration / Q000187:drug effects / Q000502:physiology*; D008938:Mitosis / Q000187:drug effects; D009641:Norethynodrel / Q000031:analogs & derivatives* / Q000627:therapeutic use; D051381:Rats; D017208:Rats, Wistar; D016196:S Phase / Q000187:drug effects / Q000502:physiology*
chemical_list: C534698:Ccnd3 protein, rat; D056743:Cyclin D3; D019927:Cyclin E; D016213:Cyclins; D019938:Cyclin D1; C002029:17alpha-ethynylestr-5(10)-ene-3alpha,17beta-diol; D009641:Norethynodrel; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2