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

✍ Scribed by Yi-Fan Hsu; Tong-Sheng Lee; Shyr-Yi Lin; Sung-Po Hsu; Shu-Hui Juan; Yuan-Hsun Hsu; Wen-Bin Zhong; Wen-Sen Lee

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 327 KB
• Volume: 46
• Category: Article
• ISSN: 0899-1987
• DOI: 10.1002/mc.20274

✦ Synopsis

Abstract

Previously, we showed that magnolol induces cell‐cycle arrest in cultured colon and liver cancer cells through an upregulation of the p21 protein [1]. 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. © 2007 Wiley‐Liss, Inc.