title: Testosterone regulation of cyclin E kinase: A key factor in determining gender differences in hepatocarcinogenesis.
abstract: OBJECTIVE
  While gender differences in hepatocellular carcinoma (HCC) are profound, the mechanism is unclear. Using castration and hormone replacement strategies, we tested whether these gender differences are attributable to testosterone or estradiol/progesterone effects on cell cycle regulators and p53.
  
  
  METHODS
  We studied dysplastic liver and HCCs in intact and castrated diethylnitrosamine-injected C57BL/6J male and female mice, with or without hormonal replacement. Effects of sex steroids on proliferation and survival of primary hepatocytes and primary HCC cells were also characterized.
  
  
  RESULTS
  Diethylnitrosamine-injected female mice displayed fewer dysplastic foci and slower onset of HCC than male mice, with smaller/more differentiated tumors and fewer metastases. Castration of diethylnitrosamine-injected male mice reduced cyclin E kinase and augmented hepatocyte apoptosis compared with intact male mice; estradiol/progesterone enhanced these effects. In intact female mice, cyclin E kinase activity was less than in males; testosterone administered to ovariectomized female mice upregulated cyclin E, increased cyclin E kinase, and accelerated hepatocarcinogenesis. In vitro, testosterone increased expression of cell cycle regulators (cyclin D1, cyclin E, and cyclin-dependent kinase 2) and reduced p53 and p21, which enhanced hepatocyte viability. In contrast, estradiol both suppressed hepatocyte cell cycle markers, upregulated p53 and reduced viability of hepatocytes and HCC cells.
  
  
  CONCLUSIONS
  Testosterone is the positive regulator of hepatocyte cell cycle via cyclin E, while estradiol plays a negative role by effects of p53 and p21. Together, both sex hormones determine the male predominance of gender differences in hepatocarcinogenesis.
authors.affiliation: Liver Research Group, Australian National University Medical School, Canberra Hospital.
authors.forename: Sharon
authors.identifier: http://orcid.org/0000-0003-2117-2285
authors.initials: S
authors.lastname: Pok
authors.affiliation: Liver Research Group, Australian National University Medical School, Canberra Hospital.
authors.forename: Vanessa A
authors.initials: VA
authors.lastname: Barn
authors.affiliation: Liver Research Group, Australian National University Medical School, Canberra Hospital.
authors.forename: Heng Jian
authors.initials: HJ
authors.lastname: Wong
authors.affiliation: Molecular Genetics Group, John Curtin School of Medical Research, Canberra, Australian Capital Territory, Australia.
authors.forename: Anneke C
authors.initials: AC
authors.lastname: Blackburn
authors.affiliation: Molecular Genetics Group, John Curtin School of Medical Research, Canberra, Australian Capital Territory, Australia.
authors.forename: Philip
authors.initials: P
authors.lastname: Board
authors.affiliation: Liver Research Group, Australian National University Medical School, Canberra Hospital.
authors.forename: Geoffrey C
authors.initials: GC
authors.lastname: Farrell
authors.affiliation: Liver Research Group, Australian National University Medical School, Canberra Hospital.
authors.forename: Narci C
authors.initials: NC
authors.lastname: Teoh
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology; D002369:Castration; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced* / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004052:Diethylnitrosamine; D004958:Estradiol / Q000633:toxicity; D015914:Estrogen Replacement Therapy / Q000009:adverse effects; D005260:Female; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D020249:Hormone Replacement Therapy / Q000009:adverse effects*; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology; D008297:Male; D008810:Mice, Inbred C57BL; D061251:Primary Cell Culture; D012737:Sex Factors; D013739:Testosterone / Q000494:pharmacology* / Q000633:toxicity*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C493957:Cdkn1a protein, mouse; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016159:Tumor Suppressor Protein p53; D004052:Diethylnitrosamine; D013739:Testosterone; D004958:Estradiol; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2
keywords: apoptosis; estradiol; p21; p53; progesterone; testosterone