Magnolol elicits activation of the extracellular signal-regulated kinase pathway by inducing p27KIP1-mediated G2/M-phase cell cycle arrest in human urinary bladder cancer 5637 cells

• Published in: Biochemical pharmacology 2008-06, Vol.75 (12), p.2289-2300
• Main Authors: Lee, Se-Jung, Cho, Young-Hwa, Park, Keerang, Kim, Eun-Jung, Jung, Kyung-Hwan, Park, Sung-Soo, Kim, Wun-Jae, Moon, Sung-Kwon
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents, Phytogenic - pharmacology; Apoptosis - drug effects; Biological and medical sciences; Biphenyl Compounds - pharmacology; Bladder cancer 5637 cells; Cell Cycle - drug effects; Cell Division - drug effects; Cell Line, Tumor; Cell Proliferation - drug effects; Cell Survival - drug effects; Cyclin-Dependent Kinase Inhibitor p27 - biosynthesis; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Extracellular Signal-Regulated MAP Kinases - metabolism; G2 Phase - drug effects; G2/M-phase cell cycle arrest; Humans; Lignans - pharmacology; Magnolol; Medical sciences; Nephrology. Urinary tract diseases; p27KIP1; Pharmacology. Drug treatments; Phosphorylation; Signal Transduction - drug effects; Tumors of the urinary system; Urinary Bladder Neoplasms - enzymology; Urinary Bladder Neoplasms - pathology; Urinary system involvement in other diseases. Miscellaneous; Urinary tract. Prostate gland
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/j.bcp.2008.03.022

Magnolol has been reported to play a role in antitumor activity. However, the relevant pathway integrating cell cycle regulation and signaling pathways involved in growth inhibition in cancer cells remains to be identified. In the present study, magnolol treatment of these cells resulted in significant dose-dependent growth inhibition together with apoptosis, G1- and G2/M-phase cell cycle arrest at a 60 μM (IC 50) dose in 5637 bladder cancer cells. In addition, magnolol treatment strongly induced p27KIP1 expression, and down-regulated expression of cyclin-dependent kinases (CDKs) and cyclins. Moreover, treatment with magnolol-induced phosphorylation of ERK, p38 MAP kinase, and JNK. Among the pathway inhibitors examined, only PD98059, an ERK-specific inhibitor, blocked magnolol-dependent p27KIP1 expression. Blockade of ERK function consistently reversed magnolol-mediated inhibition of cell proliferation and decreased G2/M cell cycle proteins, but not G1 cell cycle proteins. Furthermore, magnolol treatment increased both Ras and Raf activation. Transfection of cells with dominant negative Ras (RasN17) and Raf (RafS621A) mutant genes suppressed magnolol-induced ERK activity and p27KIP1 expression. Finally, the magnolol-induced reduction in cell proliferation and G2/M cell cycle proteins was also abolished in the presence of RasN17 and RafS621A mutant genes. These data demonstrate that the Ras/Raf/ERK pathway participates in p27KIP1 induction, leading to a decrease in the levels of cyclin B1/Cdc2 complexes and magnolol-dependent inhibition of cell growth. Overall, these novel findings concerning the molecular mechanisms of magnolol in 5637 bladder cancer cells provide a theoretical basis for therapeutic treatment of malignancies.