Adiponectin and Breast Cancer Figure 5. Mammary tumor cells derived from adiponectin haplodeficient mice were more aggressive. Primary mammary tumor cells were isolated from FVB/N PyVT mice with normal [PyVT(+/2)/ADN(+/+)] or reduced [PyVT(+/2)/ADN(+/2)] adiponectin expressions, and implanted into nude mice for assessing their tumor development in vivo (A and B), or subjected to culture and [3H]-thymidine incorporation assays for evaluating their proliferations in vitro (C and D). The comparison between PyVT(+/2)/ADN(+/+) and PyVT(+/2)/ADN(+/2) groups were performed for tumor cells derived from both female (A and C) and male (B and D) mice. Tumor growth was presented as the fold changes of tumor volume against the first measurement at day 4 (A and B). DNA synthesis was monitored in 0.5% and 10% FBS culture conditions at 24 and 48 hrs after seeding (C and D). CPM, counts per minute. *, P,0.05 and **, P,0.01 vs corresponding groups (n = 13–18). doi:10.1371/journal.pone.0004968.g005 these results suggested that in tumor cells derived from adiponectin haplodeficient mice, the increased TrxR1/Trx1 redox activities might be involved in inactivation of PTEN and hyperactivation of PI3K/Akt signalling pathways. Discussion Although the anti-tumor activities of adiponectin have been suggested by numerous clinical and experimental evidences, the underlying mechanisms remain to be established. Here, we have evaluated the impacts of reduced adiponectin expression on mammary tumor development in MMTV-PyVT mice. Our results demonstrate that in both FVB/N and C57BL/6J genetic backgrounds, adiponectin inadequacy is associated with earlier tumor onset and accelerated tumor growth (Figure 2, Figure 3 and Table 1). The aggressive phenotypes of tumor cells derived from PyVT(+/2)/ADN(+/2) mice are retained during serial trans-implantations in nude mice as well as multiple passages in culture (Figure 5), suggesting that insufficient adiponectin production from adipose tissue might result in an abnormal microenvironment that leads to distinct but permanent genetic and phenotypic modifications of mammary epithelial cells. Indeed, both histological and gene expression analyses suggest a distinct basal-like subtype of tumors in PyVT(+/2)/ADN(+/2) mice (Figure 4). Tumor cells derived from adiponectin haplodefi- cient mice show enhanced beta-catenin nuclear activities and protein stabilities, which might be partly attributed to the hyperactivated PI3K/Akt signaling (Figure 7). While adiponectin treatment restores most of the changes downstream of PI3K, including Akt and GSK3beta and beta-catenin, it has little effects on p110alpha (Figure 8). On the other hand, adiponectin deficiency causes inactivation of PTEN and results in the hyper-activated PI3K/Akt signaling in PyVT(+/2)/ADN(+/2) tumors (Figure 9). PLoS ONE | www.plosone.org 7 March 2009 | Volume 4 | Issue 3 | e4968