title: Effects of E2F1-cyclin E1-E2 circuit down regulation in hepatocellular carcinoma cells.
abstract: BACKGROUND
  No effective therapy is available for hepatocellular carcinoma. To identify novel therapeutic strategies, we explored the effects of the depletion of E2F1, cyclin E1-E2 whose inter-relationships in hepatocellular carcinoma cell proliferation have never been defined.
  
  
  METHODS
  siRNA-mediated depletion of the targets was studied in the hepatocellular carcinoma cells HepG2, HuH7 and JHH6 characterized by high, medium and low hepatocyte differentiation grade, respectively; a model of normal human hepatocytes was also considered.
  
  
  RESULTS
  The depletion of each target mRNA reduced the levels of the other two mRNAs, thus demonstrating a close regulatory control, also confirmed by over-expression experiments. At the protein level, an exception to this trend was observed for cyclinE1 whose amount increased upon cyclin E2 (HepG2, HuH7, JHH6) and E2F1 (HepG2) depletion. In HepG2, reduced cyclinE1 proteolysis accounted for this observation. Additionally, cyclin E1-E2-E2F1 targeting decreased the levels of cyclin A2 mRNA and of the hyper-phosphorylated form of pRb thus leading to an S-phase cell decrease; migration was impaired as well. Finally, the model of human hepatocytes used was clearly less affected by target mRNAs depletion than hepatocellular carcinoma cells.
  
  
  CONCLUSIONS
  Our data provide novel mutual relationships amongst cyclin E1-E2-E2F1 and indicate their role in sustaining hepatocellular carcinoma cell proliferation/migration, validating the concept of an anti-cyclin E1-E2-E2F1 therapeutic approach for hepatocellular carcinoma.
authors.affiliation: Department of Medical, Technological and Translational Sciences, University Hospital of Cattinara, Trieste, Italy.
authors.forename: Rossella
authors.initials: R
authors.lastname: Farra
authors.forename: Barbara
authors.initials: B
authors.lastname: Dapas
authors.forename: Gabriele
authors.initials: G
authors.lastname: Pozzato
authors.forename: Bruna
authors.initials: B
authors.lastname: Scaggiante
authors.forename: Francesco
authors.initials: F
authors.lastname: Agostini
authors.forename: Cristina
authors.initials: C
authors.lastname: Zennaro
authors.forename: Mario
authors.initials: M
authors.lastname: Grassi
authors.forename: Natalia
authors.initials: N
authors.lastname: Rosso
authors.forename: Carlo
authors.initials: C
authors.lastname: Giansante
authors.forename: Nicola
authors.initials: N
authors.lastname: Fiotti
authors.forename: Gabriele
authors.initials: G
authors.lastname: Grassi
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002465:Cell Movement; D049109:Cell Proliferation; D002470:Cell Survival; D056751:Cyclin A2 / Q000235:genetics / Q000378:metabolism; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism*; D034741:RNA, Small Interfering; D059807:S Phase Cell Cycle Checkpoints
chemical_list: C475820:CCNE1 protein, human; C503688:CCNE2 protein, human; D056751:Cyclin A2; D019927:Cyclin E; D016213:Cyclins; D050687:E2F1 Transcription Factor; D015513:Oncogene Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering