p27-Associated G1 arrest induced by hinokitiol in human malignant melanoma cells is mediated via down-regulation of pRb, Skp2 ubiquitin ligase, and impairment of Cdk2 function.
Increasing evidence has confirmed that hinokitiol (beta-thujaplicin), a tropolone-related compound, exhibits anticancer activity in a variety of cancers through inhibition of cell proliferation. The present study indicates that hinokitiol selectively inhibits cell growth and DNA synthesis in FEM human melanoma cells. Hinokitiol-induced growth inhibition was associated with strong G1 cell cycle arrest. Consistent with blocking the G1-S-phase transition, hinokitiol markedly increased p27 protein levels, but caused only a moderate increase in p21, in addition to a decrease in Cdk2, cyclin E, and phosphorylated Rb. In addition, hinokitiol increased the stability of the p27 protein by inhibiting p27 phosphorylation at Thr(187) and by down-regulating Skp2 expression. siRNA knockdown of p27 abrogated hinokitiol-mediated growth inhibition, while knockdown of Skp2 exacerbated the G1 arrest. In addition to increasing Cdk inhibitor levels and decreasing cyclin A expression, hinokitiol also impaired Cdk2 function by inhibiting Cdk2 kinase activity, impeding cyclin E or A/Cdk2 binding, and inducing translocation of the Cdk2 protein complex. Taken together, our data demonstrate that the novel anticancer mechanism of hinokitiol involves accumulation of p27, down-regulation of Skp2, and impairment of Cdk2 function in FEM human melanoma cells. The therapeutic potential of hinokitiol may lead to novel cell-cycle-based anticancer strategies for malignant melanoma.
Liu
Shicheng
S
Research and Development Department, Nipro Patch Co., Ltd., Kasukabe, Saitama 344-0057, Japan. liu@nipro-patch.co.jp
Yamauchi
Hitoshi
H
D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects*; D006801:Humans; D015151:Immunoblotting; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D039821:Monoterpenes / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D034622:RNA Interference; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase / Q000187:drug effects; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D014334:Tropolone / Q000031:analogs & derivatives* / Q000494:pharmacology
D039821:Monoterpenes; D016160:Retinoblastoma Protein; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D014334:Tropolone; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C009479:beta-thujaplicin