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.
Mesh Terms:
Cell Line, Tumor, Cell Proliferation, Cells, Cultured, Cyclin-Dependent Kinase 2, Cyclin-Dependent Kinase Inhibitor p27, Dose-Response Relationship, Drug, Flow Cytometry, G1 Phase, Humans, Immunoblotting, Melanoma, Monoterpenes, Phosphorylation, Protein Binding, RNA Interference, Retinoblastoma Protein, Reverse Transcriptase Polymerase Chain Reaction, S Phase, S-Phase Kinase-Associated Proteins, Tropolone
Cell Line, Tumor, Cell Proliferation, Cells, Cultured, Cyclin-Dependent Kinase 2, Cyclin-Dependent Kinase Inhibitor p27, Dose-Response Relationship, Drug, Flow Cytometry, G1 Phase, Humans, Immunoblotting, Melanoma, Monoterpenes, Phosphorylation, Protein Binding, RNA Interference, Retinoblastoma Protein, Reverse Transcriptase Polymerase Chain Reaction, S Phase, S-Phase Kinase-Associated Proteins, Tropolone
Cancer Lett.
Date: Dec. 28, 2009
PubMed ID: 19631451
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