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.

Abstract

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.

• Authors: Shicheng Liu, Hitoshi Yamauchi
• Journal: Cancer letters (Cancer Lett) Vol. 286 Issue 2 Pg. 240-9 (Dec 28 2009) ISSN: 1872-7980 [Electronic] Ireland
• PMID: 19631451 (Publication Type: Journal Article)

Chemical References

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

Topics

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