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

Cancer Lett. 2009 Dec 28;286(2):240-9. doi: 10.1016/j.canlet.2009.05.038. Epub 2009 Jul 23.


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.

MeSH terms

  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cells, Cultured
  • Cyclin-Dependent Kinase 2 / genetics
  • Cyclin-Dependent Kinase 2 / metabolism*
  • Cyclin-Dependent Kinase Inhibitor p27 / genetics
  • Cyclin-Dependent Kinase Inhibitor p27 / metabolism*
  • Dose-Response Relationship, Drug
  • Flow Cytometry
  • G1 Phase / drug effects*
  • Humans
  • Immunoblotting
  • Melanoma / genetics
  • Melanoma / metabolism
  • Melanoma / pathology
  • Monoterpenes / pharmacology*
  • Phosphorylation / drug effects
  • Protein Binding / drug effects
  • RNA Interference
  • Retinoblastoma Protein / genetics
  • Retinoblastoma Protein / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • S Phase / drug effects
  • S-Phase Kinase-Associated Proteins / genetics
  • S-Phase Kinase-Associated Proteins / metabolism*
  • Tropolone / analogs & derivatives*
  • Tropolone / pharmacology


  • Monoterpenes
  • Retinoblastoma Protein
  • S-Phase Kinase-Associated Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • Tropolone
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • beta-thujaplicin