Involvement of Ras/Raf-1/ERK actions in the magnolol-induced upregulation of p21 and cell-cycle arrest in colon cancer cells.
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.
Hsu
Yi-Fan
YF
Graduate Institute of Cell and Molecular Biology, Medical College, Taipei Medical University, Taipei, Taiwan.
Lee
Tong-Sheng
TS
Lin
Shyr-Yi
SY
Hsu
Sung-Po
SP
Juan
Shu-Hui
SH
Hsu
Yuan-Hsun
YH
Zhong
Wen-Bin
WB
Lee
Wen-Sen
WS
D001713:Biphenyl Compounds / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D017705:Lignans / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
D001713:Biphenyl Compounds; D017705:Lignans; C005498:magnolol; D019001:Nitric Oxide Synthase; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; D016283:Proto-Oncogene Proteins p21(ras)