Jun Activation Domain Binding Protein 1 Expression Is Associated with Low p27 Kip1 Levels in Node-Negative Breast Cancer Francisco J. Esteva, 1,2 Aysegul A. Sahin, 3 George Z. Rassidakis, 3 Linda X. H. Yuan, 1 Terry L. Smith, 4 Ying Yang, 4 Michael Z. Gilcrease, 3 Massimo Cristofanilli, 1 Rita Nahta, 1 Lajos Pusztai, 1 and Franc ¸ois-Xavier Claret 5 Departments of 1 Breast Medical Oncology, 2 Molecular and Cellular Oncology, 3 Pathology, 4 Biostatistics, and 5 Molecular Therapeutics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas ABSTRACT Purpose: The purpose is to evaluate expression levels of Jun activation domain-binding protein 1 (JAB1) in breast cancer tissue and adjacent normal tissue, to determine whether JAB1 expression is associated with p27 Kip1 expres- sion in invasive breast carcinomas, and to evaluate the prog- nostic significance of JAB1 and p27 Kip1 in node-negative breast cancer. Experimental Design: JAB1 levels were measured in 10 matched pairs of invasive breast tumor tissue and adjacent normal tissue using Western blot analysis. We also investi- gated the immunoreactivity of JAB1 and p27 Kip1 levels in paraffin-embedded tissue specimens from 220 patients with node-negative breast cancer who had not received adjuvant systemic therapy. The median follow-up was 15 years. Results: JAB1 was expressed at higher levels in invasive tumors than in adjacent normal tissue (P  0.01). JAB1 overexpression was observed in 57% of invasive breast can- cers. Low levels of p27 Kip1 were noted in 70% of the tumor specimens. We found an inverse correlation between JAB1 and p27 Kip1 expression levels (P  0.01). JAB1 overexpres- sion was associated with patient age of at least 50 years (P  0.03) and tumor size of <2 cm (P  0.01). Elevated levels of p27 Kip1 were associated with low nuclear grade (P  0.01). At 5 years of follow-up, neither JAB1 nor p27 Kip1 expression was related to disease-free survival. Conclusions: These data indicate that JAB1 is com- monly overexpressed in invasive breast carcinomas. JAB1 overexpression is associated with low levels of p27 Kip1 in node-negative breast cancer. In this study, JAB1 and p27 Kip1 were not independent prognostic factors. INTRODUCTION Mammalian cell cycle progression is regulated by the com- bined action of cyclins, CDKs, 6 and CDK inhibitors. Any shift in the balance among these factors can result in abnormal cell proliferation, which may contribute to the development of can- cer (1). The CDK inhibitor p27 Kip1 is a potent inhibitor of the cyclin E-CDK2 and cyclin A-CDK2 complexes, both of which are involved in the regulation of the G 1 -S-phase transition of the cell cycle (1–3). Despite the putative role of p27 Kip1 as a tumor suppressor, mutations in p27 Kip1 are rarely seen in human tu- mors (4). However, in most types of cancer, a decrease in or the absence of p27 Kip1 protein has been associated with tumor aggressiveness and poor patient survival rates (5– 8), suggesting that disruption of p27 Kip1 regulatory mechanisms contributes to neoplasia. The function of p27 Kip1 is regulated by changes in its expression level and localization in the cell. JAB1 is an activator protein-1 coactivator that interacts with and potentiates transactivation by c-Jun and promotes cellular proliferation (9). JAB1 has also been implicated re- cently in promoting cell proliferation by facilitating relocation of p27 Kip1 from the nucleus to the cytoplasm, thereby acceler- ating the degradation of p27 Kip1 by the ubiquitin/proteasome pathway (10). There is a need to identify novel prognostic factors in patients with node-negative breast cancer (11). We hypothesized that JAB1 overexpression plays an important role in the patho- genesis of breast cancer. The purpose of this study was to evaluate the expression levels of JAB1 in invasive breast cancer and adjacent normal tissue and to define patterns of JAB1 expression in human breast cancer. The prognostic significance of JAB1 and p27 Kip1 expression was evaluated in tissue speci- mens from 220 patients with node-negative breast cancer and long-term follow-up. MATERIALS AND METHODS Western Blot Analysis. We performed immunoblot analysis for JAB1 protein in matched pairs of fresh frozen tissue specimens of invasive breast cancer and adjacent normal tissue. Normal tissue was dissected from adjacent cancer at the time of lumpectomy or mastectomy at The University of Texas M. D. Anderson Cancer Center. All tumor and normal samples were Received 4/7/03; revised 8/5/03; accepted 8/6/03. Grant support: NCI Grant K23 CA82119 (to F. J. E.), funds from the Physician Referral Service at The University of Texas M. D. Anderson Cancer Center, and NIH Grant 1R01 CA90853-O1A1 (to F-X. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Requests for reprints: Dr. Francisco J. Esteva, Department of Breast Medical Oncology, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 424, Houston, TX 77030-4009. Phone: (713) 792-2817; Fax: (713) 745-5768; E-mail: festeva@mdanderson.org. 6 The abbreviations used are: CDK, cyclin-dependent kinase; JAB1, Jun activation domain-binding protein 1; ER, estrogen receptor; DFS, dis- ease-free survival. 5652 Vol. 9, 5652–5659, November 15, 2003 Clinical Cancer Research Cancer Research. on December 15, 2021. © 2003 American Association for clincancerres.aacrjournals.org Downloaded from