Adiponectin Haploinsufficiency Promotes Mammary Tumor Development in MMTV-PyVT Mice by Modulation of Phosphatase and Tensin Homolog Activities Janice B. B. Lam1,2,3,7., Kim H. M. Chow1,2,3., Aimin Xu1,2,3, Karen S. L. Lam2,3, Jing Liu1,2,3, Nai-Sum Wong 4 , Randall T. Moon 6 , Peter R. Shepherd8, Garth J. S. Cooper8, Yu Wang1,3,5* 1 Department of Pharmacology and Pharmacy, University of Hong Kong, Hong Kong, China, 2 Department of Medicine, University of Hong Kong, Hong Kong, China, 3 Research Center of Heart, Brain, Hormone, and Healthy Aging, University of Hong Kong, Hong Kong, China, 4 Department of Biochemistry, University of Hong Kong, Hong Kong, China, 5 Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug Discovery and Synthesis, University of Hong Kong, Hong Kong, China, 6 Howard Hughes Medical Institute, University of Washington School of Medicine, Seattle, Washington, United States of America, 7 School of Biological Sciences, University of Auckland, Auckland, New Zealand, 8 Maurice Wilkins Centre for Molecular Biodiscovery, University of Auckland, Auckland, New Zealand Abstract Background: Adiponectin is an adipokine possessing beneficial effects on obesity-related medical complications. A negative association of adiponectin levels with breast cancer development has been demonstrated. However, the precise role of adiponectin deficiency in mammary carcinogenesis remains elusive. Methodology/Principal Findings: In the present study, MMTV-polyomavirus middle T antigen (MMTV-PyVT) transgenic mice with reduced adiponectin expressions were established and the stromal effects of adiponectin haploinsufficiency on mammary tumor development evaluated. In mice from both FVB/N and C57BL/6J backgrounds, insufficient adiponectin production promoted mammary tumor onset and development. A distinctive basal-like subtype of tumors, with a more aggressive phenotype, was derived from adiponectin haplodeficient MMTV-PyVT mice. Comparing with those from control MMTV-PyVT mice, the isolated mammary tumor cells showed enhanced tumor progression in re-implanted nude mice, accelerated proliferation in primary cultures, and hyperactivated phosphatidylinositol-3-kinase (PI3K)/Akt/beta-catenin signaling, which at least partly attributed to the decreased phosphatase and tensin homolog (PTEN) activities. Further analysis revealed that PTEN was inactivated by a redox-regulated mechanism. Increased association of PTEN-thioredoxin complexes was detected in tumors derived from mice with reduced adiponectin levels. The activities of thioredoxin (Trx1) and thioredoxin reductase (TrxR1) were significantly elevated, whereas treatment with either curcumin, an irreversible inhibitor of TrxR1, or adiponectin largely attenuated their activities and resulted in the re-activation of PTEN in these tumor cells. Moreover, adiponectin could inhibit TrxR1 promoter-mediated transcription and restore the mRNA expressions of TrxR1. Conclusion: Adiponectin haploinsufficiency facilitated mammary tumorigenesis by down-regulation of PTEN activity and activation of PI3K/Akt signalling pathway through a mechanism involving Trx1/TrxR1 redox regulations. Citation: Lam JBB, Chow KHM, Xu A, Lam KSL, Liu J, et al. (2009) Adiponectin Haploinsufficiency Promotes Mammary Tumor Development in MMTV-PyVT Mice by Modulation of Phosphatase and Tensin Homolog Activities. PLoS ONE 4(3): e4968. doi:10.1371/journal.pone.0004968 Editor: Nils Cordes, Dresden University of Technology, Germany Received November 19, 2008; Accepted February 20, 2009; Published March 25, 2009 Copyright: 2009 Lam et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the grants from Seeding Funds for Basic Research of the University of Hong Kong (Y. Wang), Hong Kong Research Grant Council grants HKU 777908M (Y. Wang) and HKU 779707M (A. Xu), and the Area of Excellent Scheme (AoE/P-10-01) established under the University Grants Committee, HKSAR. Adiponectin knockout mice were kindly provided by Dr. Lawrence Chan at Baylor College of Medicine, who generated these mice with the support of the US National Institutes of Health grant HL-51586. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: yuwanghk@hku.hk . These authors contributed equally to this work. Introduction The prevalence of obesity and obesity-related cancers has risen alarmingly for the past several decades [1,2,3]. Unfortunately, the mechanisms underlying the association between obesity and cancer are not well understood. Recent evidences suggest that adipokines, referring to a group of secreted factors from adipose tissue, could be the key players in regulating obesity-related carcinogenesis [4,5,6,7]. Adiponectin is an abundant adipocyte- derived hormone that can elicit pleiotropic beneficial functions against obesity-related medical conditions, such as diabetes, chronic inflammation, atherosclerosis and tumorigenesis [8,9]. Decreased circulating concentrations of adiponectin are associated with many obesity-related cancer diseases, including breast cancer, endometrial cancer, gastric cancer, colorectal cancer, renal cell carcinoma and prostate cancer [10,11,12,13,14,15,16]. Breast cancer represents the second leading cause of death among women. An inverse correlation of circulating adiponectin levels PLoS ONE | www.plosone.org 1 March 2009 | Volume 4 | Issue 3 | e4968