Involvement of Ras/Raf-1/ERK actions in the magnolol-induced upregulation of p21 and cell-cycle arrest in colon cancer cells

Mol Carcinog. 2007 Apr;46(4):275-83. doi: 10.1002/mc.20274.


Previously, we showed that magnolol induces cell-cycle arrest in cultured colon and liver cancer cells through an upregulation of the p21 protein. The aim of this study was to delineate the molecular mechanism underlying this magnolol-induced increase of p21 protein. Thus our RT-PCR analysis demonstrated that the mRNA levels of p21 were increased at 1 h after magnolol treatment and sustained for at least 24 h. The p21 promoter activity was also increased by magnolol treatment. Western blot analysis demonstrated that treatment of COLO-205 cells with magnolol increased the levels of phosphorylation of extracellular signal-regulated kinase (ERK). Pretreatment of the cells with PD98059 abolished the magnolol-induced upregulation of p21 protein, suggesting the involvement of an ERK pathway in the magnolol-induced upregulation of p21 in COLO-205 cells. Ras inhibitor peptide abolished the magnolol-induced increase of phosphorylated ERK protein levels, increase of p21 protein, and decrease of thymidine incorporation. Moreover, treatment of COLO-205 with magnolol increased the phosphorylated Raf-1 protein (the Ras target molecule). Pretreatment of the cells with Raf-1 inhibitor reversed the magnolol-induced decrease in thymidine incorporation. Treatment of the cells with CaM kinase inhibitor, but not protein kinase A (PKA) inhibitor or phosphatidylinosital 3-kinase (PI3K) inhibitor, abolished the magnolol-induced activation of ERK and decrease of thymidine incorporation. Taken together, our results suggest that magnolol activates ERK phosphorylation through a Ras/Raf-1-mediated pathway. Subsequently, p21 expression is increased, and finally thymidine incorporation is decreased.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biphenyl Compounds / pharmacology*
  • Cell Cycle / drug effects*
  • Cell Line, Tumor
  • Colonic Neoplasms / metabolism*
  • Colonic Neoplasms / pathology
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Humans
  • Lignans / pharmacology*
  • Nitric Oxide Synthase / antagonists & inhibitors
  • Phosphorylation / drug effects
  • Proto-Oncogene Proteins c-raf / metabolism*
  • Proto-Oncogene Proteins p21(ras) / metabolism*
  • Signal Transduction / drug effects
  • Up-Regulation / drug effects


  • Biphenyl Compounds
  • Lignans
  • magnolol
  • Nitric Oxide Synthase
  • Proto-Oncogene Proteins c-raf
  • Extracellular Signal-Regulated MAP Kinases
  • Proto-Oncogene Proteins p21(ras)