title: Involvement of down-regulation of Cdk2 activity in hepatocyte growth factor-induced cell cycle arrest at G1 in the human hepatocellular carcinoma cell line HepG2.
abstract: Hepatocyte growth factor (HGF) induces growth stimulation of a variety of cell types, but it also induces growth inhibition of several types of tumor cell lines. We previously investigated the intracellular signaling pathway involved in the antiproliferative effect of HGF on the human hepatocellular carcinoma cell line HepG2. The results suggested that the HGF-induced proliferation inhibition is caused by cell cycle arrest, which results from the retinoblastoma tumor suppressor gene product pRb being maintained in its active hypophosphorylated form via a high-intensity ERK signal. In this study, we examined the molecular mechanism of the HGF-induced cell cycle arrest in HepG2 cells. Cyclin A/Cdk2 complexes phosphorylated serine residues on pRb crucial for the G1 to S phase transition in proliferating HepG2 cells, and HGF treatment inhibited the phosphorylation. The expression of cyclin A was decreased and the expression of a Cdk inhibitor p21(Cip1) was increased in HGF-treated HepG2 cells, and these changes were prevented by pretreatment with a low concentration of a MEK inhibitor. These results suggest that the decrease in cyclin A expression and increase in p21(Cip1) expression through a high-intensity ERK signal by HGF lead to suppression of the phosphorylation of pRb by Cdk2, which contributes to the cell cycle arrest at G1 in HepG2 cells by HGF. Furthermore, the expression of E2F-1, a member of the E2F transcription factor family, was decreased in HGF-treated HepG2 cells, suggesting that the decrease in E2F-1 expression may also contribute to the cell cycle arrest at G1.
authors.affiliation: Department of Biological Sciences, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8501, Japan. nkitamur@bio.titech.ac.jp
authors.forename: Yu-ichi
authors.initials: Y
authors.lastname: Tsukada
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Tanaka
authors.forename: Keiji
authors.initials: K
authors.lastname: Miyazawa
authors.forename: Naomi
authors.initials: N
authors.lastname: Kitamura
mesh_terms: D042846:CDC2-CDC28 Kinases / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019925:Cyclin A / Q000096:biosynthesis / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005419:Flavonoids / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects; D017228:Hepatocyte Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism*; D008934:Mitogens / Q000378:metabolism / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D016196:S Phase / Q000187:drug effects; D014157:Transcription Factors / Q000096:biosynthesis / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology; D053773:Transforming Growth Factor beta1
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D005419:Flavonoids; C066855:HGF protein, human; D008934:Mitogens; C508960:TGFB1 protein, human; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D017228:Hepatocyte Growth Factor; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one