title: Rapid downregulation of cyclin D1 induced by geranylgeranoic acid in human hepatoma cells.
abstract: Geranylgeranoic acid (GGA) and its derivatives are currently under development as chemopreventive agents against second primary hepatoma in Japan. We aimed to evaluate chemoprevention targets of GGA and a surrogate marker of chemopreventive response to clarify the molecular mechanism of hepatoma chemoprevention with GGA. Human hepatoma-derived cell lines such as HuH-7, PLC/PRF/5, and HepG-2, were treated with GGA and its derivatives. Cellular dynamics of several cell-cycle-related proteins were assessed by either immunoblotting or immunofluorescence method. The cellular expression of cyclin D1 protein was suppressed immediately after GGA treatment. This reduction was partially blocked by pretreatment with 26S proteasome inhibitor MG-132, indicating that proteasomal degradation was involved in GGA-induced disappearance of cyclin D1. A phosphorylation of retinoblastoma protein (RB) at serine 780, a target site of cyclin D1-dependent kinase 4, was rapidly decreased in GGA-treated HuH-7 cells. Furthermore, subcellular fractionation, Western blotting, and immunofluorescence revealed GGA-induced nuclear accumulation of RB. These results strongly suggest that cyclin D1 may be a target of chemopreventive GGA in human hepatoma cells. GGA-induced rapid repression of cyclin D1, and a consequent dephosphorylation and nuclear translocation of RB, may influence cell cycle progression and may be relevant to GGA-induced cell death mechanisms.
authors.affiliation: Molecular and Cellular Biology, Graduate School of Human Health Science, University of Nagasaki, Nagasaki, Japan.
authors.forename: Shohei
authors.initials: S
authors.lastname: Shimonishi
authors.forename: Takashi
authors.initials: T
authors.lastname: Muraguchi
authors.forename: Maiko
authors.initials: M
authors.lastname: Mitake
authors.forename: Chiharu
authors.initials: C
authors.lastname: Sakane
authors.forename: Kyoko
authors.initials: K
authors.lastname: Okamoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Shidoji
mesh_terms: D002453:Cell Cycle; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D004224:Diterpenes / Q000633:toxicity*; D015536:Down-Regulation; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D056945:Hep G2 Cells; D006801:Humans; D007976:Leupeptins / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C530104:CCND1 protein, human; D004224:Diterpenes; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D007976:Leupeptins; D016160:Retinoblastoma Protein; D019938:Cyclin D1; C040155:geranylgeranic acid; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde