Journal of the National Cancer Institute Advance Access originally published online on May 26, 2009
JNCI Journal of the National Cancer Institute 2009 101(11):793-805; doi:10.1093/jnci/djp103
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© The Author 2009. Published by Oxford University Press.
ARTICLES |
MYC-Dependent Regulation and Prognostic Role of CIP2A in Gastric Cancer
Affiliations of authors: Institute of Medical Technology, University of Tampere and Tampere University Hospital, Tampere, Finland (AK, JW); Tampere Graduate School in Biomedicine and Biotechnology, University of Tampere, Tampere, Finland (AK); Genome-Scale Biology Research Program, Biomedicum Helsinki (CB, AH, SJ, AR), Department of Pathology, HUSLAB and Haartman Institute (CB, AH, AR), Department of Surgery (CB, J-PW, ML, CH), Biomedicum Biochip Center and Institute of Biomedicine/Medical Biochemistry and Developmental Biology (SJ), University of Helsinki, Helsinki, Finland; Department of Pathology, University of California at San Francisco, San Francisco, CA (MRJ, DJM, GIE); The Enrique Cepero, PhD, Fellow of the Damon Runyon Cancer Research Foundation (MRJ); Centre for Biotechnology, University of Turku and Åbo Akademi University, Turku, Finland (JW); Department of Pathology, Institute of Diagnostics, University of Oulu and Oulu University Hospital, Oulu, Finland (AR)
Correspondence to: Ari Ristimäki, MD, PhD, Genome-Scale Biology Research Program, Biomedicum Helsinki, University of Helsinki, PO Box 63 (Haartmaninkatu 8), FIN-00014 Helsinki, Finland (e-mail: ari.ristimaki{at}helsinki.fi).
Background: Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently identified human oncoprotein that stabilizes the c-Myc (MYC) protein. However, the clinical relevance of CIP2A to human cancers had not been demonstrated, but the mechanism of its regulation and its clinical role in cancer were completely unknown.
Methods: Tissue microarrays consisting of 223 gastric adenocarcinoma specimens were evaluated for the presence of CIP2A using immunohistochemistry, and the association of CIP2A expression with survival was assessed using Kaplan–Meier analysis. The effects of MYC and CIP2A on each other's expression and on cell proliferation were investigated in several gastric cancer cell lines using small interfering RNAs to CIP2A and MYC and immunoblotting. To further evaluate the role of MYC in CIP2A regulation, an inhibitor of MYC dimerization, 10058-F4, and an inducible MycER model were used.
Results: Expression of CIP2A protein was associated with reduced overall survival for gastric cancer patients with tumors 5 cm or smaller, with a 10-year overall survival in the CIP2A-immunopositive group of 8.1% as compared with 37.6% in the CIP2A-negative group (difference = 29.5%, 95% confidence interval = 12.5% to 46.5%, P = .001). In gastric cancer cell lines, CIP2A depletion led to decreased proliferation and anchorage-independent growth of the cells, as well as to reduced stability and expression of MYC protein. Interestingly, MYC depletion led to reduced expression of CIP2A mRNA and protein. Moreover, experiments with an MYC inhibitor and activator suggested that MYC directly promotes CIP2A gene expression. Finally, CIP2A and MYC immunopositivities were associated in gastric cancer specimens (P = .021).
Conclusions: CIP2A immunopositivity is a predictor of survival for some subgroups of gastric cancer patients. CIP2A and MYC appear to be regulated in a positive feedback loop, wherein they promote each other's expression and gastric cancer cell proliferation.
| CONTEXT AND CAVEATS Prior knowledge Cancerous inhibitor of protein phosphatase 2A (CIP2A) was recently reported by the authors to interact with and prevent degradation of the MYC oncoprotein by inhibiting PP2A-mediated dephosphorylation of MYC phosphoserine 62. CIP2A was reported to be overexpressed in head and neck and colon cancers, but the mechanism of its regulation and its clinical role in cancer were unclear. Study design CIP2A expression in gastric tumor specimens was compared with patient survival data. Experiments were performed that used short interfering RNAs, a MYC inhibitor, or an inducible MYC construct in several gastric cancer cell lines to clarify the roles of MYC and CIP2A in each other's expression and in cell proliferation. Contribution CIP2A immunopositivity was associated with substantially decreased 10-year overall survival among gastric cancer patients, and presence of CIP2A was associated with increased proliferation, anchorage-independent growth, and MYC protein stability in gastric cancer cells. In addition, MYC appeared to promote CIP2A mRNA and protein expression. Implications MYC and CIP2A appear to reinforce each other's expression (or inhibition) in a positive feedback loop that would appear to be an attractive target for cancer therapeutics. Limitations Additional experiments will be necessary to definitively demonstrate a functional role for CIP2A in human tumorigenesis. Also, a direct effect of MYC on CIP2A transcription has not yet been shown, probably because MYC responsive elements lie outside the proximal CIP2A promoter. From the Editors
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A. Khanna and C. Böckelman and the senior authors A. Ristimäki and J. Westermarck contributed equally to this work.
The study sponsors had no role in the design of the study; the collection, analysis, and interpretation of the data; the writing of the manuscript; or the decision to submit the manuscript for publication.
MKN and TMK cell lines were a kind gift from Hiroshi Yokozaki, Kobe University Graduate School of Medicine, Kobe, Japan. Phospho-specific S62-Myc antibody was a kind gift of Prof Hideo Shinagawa, BioAcademia, Inc., Osaka, Japan. Jumonji primers were a kind gift from Prof Tapio Visakorpi, University of Tampere.
We thank Päivi Peltokangas, Tuire Koski, Paula Kosonen, Merja Lehtinen, Alfonso Urbanucci, and Kati Porkka for their excellent technical assistance.
Manuscript received June 3, 2008; revised March 13, 2009; accepted April 1, 2009.
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J Natl Cancer Inst 2009 101: 769.