Metformin inhibits heme oxygenase-1 expression in cancer cells through inactivation of Raf-ERK-Nrf2 signaling and AMPK-independent pathways.

Abstract

Resistance to therapy is the major obstacle to more effective cancer treatment. Heme oxygenase-1 (HO-1) is often highly up-regulated in tumor tissues, and its expression is further increased in response to therapies. It has been suggested that inhibition of HO-1 expression is a potential therapeutic approach to sensitize tumors to chemotherapy and radiotherapy. In this study, we tested the hypothesis that the anti-tumor effects of metformin are mediated by suppression of HO-1 expression in cancer cells. Our results indicate that metformin strongly suppresses HO-1 mRNA and protein expression in human hepatic carcinoma HepG2, cervical cancer HeLa, and non-small-cell lung cancer A549 cells. Metformin also markedly reduced Nrf2 mRNA and protein levels in whole cell lysates and suppressed tert-butylhydroquinone (tBHQ)-induced Nrf2 protein stability and antioxidant response element (ARE)-luciferase activity in HepG2 cells. We also found that metformin regulation of Nrf2 expression is mediated by a Keap1-independent mechanism and that metformin significantly attenuated Raf-ERK signaling to suppress Nrf2 expression in cancer cells. Inhibition of Raf-ERK signaling by PD98059 decreased Nrf2 mRNA expression in HepG2 cells, confirming that the inhibition of Nrf2 expression is mediated by an attenuation of Raf-ERK signaling in cancer cells. The inactivation of AMPK by siRNA, DN-AMPK or the pharmacological AMPK inhibitor compound C, revealed that metformin reduced HO-1 expression in an AMPK-independent manner. These results highlight the Raf-ERK-Nrf2 axis as a new molecular target in anticancer therapy in response to metformin treatment.

• Authors: Minh Truong Do, Hyung Gyun Kim, Tilak Khanal, Jae Ho Choi, Dong Hee Kim, Tae Cheon Jeong, Hye Gwang Jeong
• Journal: Toxicology and applied pharmacology (Toxicol Appl Pharmacol) Vol. 271 Issue 2 Pg. 229-38 (Sep 01 2013) ISSN: 1096-0333 [Electronic] United States
• PMID: 23707609 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2013 Elsevier Inc. All rights reserved.

Chemical References

• Hypoglycemic Agents
• Indicators and Reagents
• NF-E2-Related Factor 2
• NFE2L2 protein, human
• RNA, Small Interfering
• RNA
• Metformin
• Luciferases
• Heme Oxygenase-1
• raf Kinases
• Mitogen-Activated Protein Kinases
• Galactosidases

Topics

• Blotting, Western
• Cell Line, Tumor
• Cell Nucleus (chemistry)
• Cell Survival (drug effects)
• Cytosol (chemistry)
• Galactosidases (metabolism)
• Heme Oxygenase-1 (antagonists & inhibitors)
• Humans
• Hypoglycemic Agents (pharmacology)
• Indicators and Reagents
• Luciferases (metabolism)
• MAP Kinase Signaling System (drug effects)
• Metformin (pharmacology)
• Mitogen-Activated Protein Kinases (drug effects)
• NF-E2-Related Factor 2 (physiology)
• Neoplasms (enzymology)
• Plasmids (genetics)
• RNA (biosynthesis, genetics)
• RNA, Small Interfering
• Real-Time Polymerase Chain Reaction
• Signal Transduction (drug effects)
• Transfection
• raf Kinases (drug effects)