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Carcinogenesis Advance Access published online on July 16, 2008
Carcinogenesis, doi:10.1093/carcin/bgn167
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Loss of MKP3 mediated by oxidative stress enhances tumorigenicity and chemoresistance of ovarian cancer cells

David W. Chan1, Vincent W. S. Liu1, George S. W. Tsao2, Kwok-Ming Yao3, Toru Furukawa4, Karen K. L. Chan1 and Hextan Y. S. Ngan1,*

1 Department of Obstetrics and Gynecology, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, P. R. China
2 Department of Anatomy, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, P. R. China
3 Department of Biochemistry, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, P. R. China
4 International Research and Educational Institute for Integrated Medical Sciences, Tokyo Women's Medical University, Japan

* To whom correspondence should be addressed at: Department of Obstetrics and Gynecology, 6/F Professorial Block, Queen Mary Hospital, Pokfulam, Hong Kong. Phone: (852) 2855-4518; Fax: (852) 2855-0947. Email: hysngan{at}hkucc.hku.hk.

The RAS-RAF-MEK-ERK pathway plays a pivotal role in various cellular responses, including cellular growth, differentiation, survival and motility. Constitutive activation of the ERK pathway has been linked to the development and progression of human cancers. Here we reported that MAPK phosphatase 3 (MKP3), a negative regulator of ERK1/2, lost its expression particularly in the protein level, was significantly correlated with high ERK1/2 activity in primary human ovarian cancer cells using quantitative RT-PCR and Western blot analyses. Intriguingly, the loss of MKP3 protein was associated with ubiquitination/proteosome degradation mediated by high intracellular reactive oxygen species (ROS) accumulation such as hydrogen peroxide (H2O2) in ovarian cancer cells. Functionally, short hairpin RNA knockdown of endogenous MKP3 resulted in increased ERK1/2 activity, cell proliferation rate, anchorage-independent growth ability, and resistance to cisplatin in ovarian cancer cells. Conversely, enforced expression of MKP3 in MKP3-deficient ovarian cancer cells significantly reduced ERK1/2 activity and inhibited cell proliferation, anchorage-independent growth ability, and tumor development in nude mice. Furthermore, the enforced expression of MKP3 succeeded to sensitize ovarian cancer cells to cisplatin-induced apoptosis in vitro and in vivo. These results suggest a molecular mechanism by which the accumulation of ROS during ovarian cancer progression may cause the degradation of MKP3, which in turn leads to aberrant ERK1/2 activation and contributes to tumorigenicity and chemoresistance of human ovarian cancer cells.

Key Words: MKP3 • ERK1/2 • ovarian cancer • cisplatin • tumorigenicity

Received May 2, 2008; revised July 7, 2008; accepted July 9, 2008.


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