Adiponectin and Breast Cancer Table 2. Total net weights (g) of tumor and lung tissues collected from nude mice implanted with primary tumor cells isolated from female and male PyVT(+/2)/ADN(+/+) and PyVT(+/2)/ADN(+/2) mice. Nude mice Female (18 days after implantation) Tumor Lungs ADN (+/+) (n = 17) 0.50360.262 0.16060.063 ADN (+/2) (n = 13) 0.87560.693* 0.17460.014 *p,0.05 vs the corresponding PyVT(+/2)/ADN(+/+) mice group. doi:10.1371/journal.pone.0004968.t002 PTEN/PI3K/Akt constitutes an important pathway regulating the signaling of multiple biological processes such as apoptosis, metabolism and cell proliferation [46]. PTEN activity is lost by mutations, deletions, promoter methylation silencing, or protein modifications at high frequency in many primary and metastatic human cancers [47]. Hyperactivation of the PI3K/Akt signaling pathway triggered by PTEN inactivation has been found to correlate with increased breast cancer risks, poor prognosis and resistance to hormone therapy [44]. In adiponectin haplodeficient PyVT tumors, while the total protein levels of PTEN are not altered, its activities are significantly decreased (Figure 9). PTEN is well-known to be regulated by the redox state of the active site cysteine residues [48]. Oxidation of PTEN resulted from thiol modification leads to reversible inhibition of its phosphatase activity. The thioredoxin system, composed of TrxR, Trx, and NADPH, represents one of the main thiol-dependent electron Male (24 days after implantation) ADN (+/+) (n = 13) 0.44960.366 0.18760.0407 ADN (+/2) (n = 18) 0.83160.425* 0.24860.0928* donor systems and plays critical roles in the regulation of the cellular redox environment [49]. Although the reduction of oxidized PTEN appears to be dominantly mediated by Trx, it has been reported that Trx1 inhibits its phosphatase activity by binding in a redox dependent manner to PTEN through disulfide bond formation [45]. Moreover, knocking out of thioredoxin- interacting protein, an inhibitor of Trx NADPH-dependent reduction of PTEN, causes accumulation of oxidized PTEN and elevated Akt phosphorylation [50]. We find that there is a significantly augmented formation of Trx1-PTEN complexes in tumor cells derived from adiponectin haplodeficient PyVT mice, possibly due to elevated TrxR1 and Trx1 activities (Figure 9A). Adiponectin treatment decreases TrxR1 promoter-mediated transcription and its mRNA levels, which are highly upregulated in adiponectin haplodeficient tumors (Figure 9D). These results suggest that adiponectin might regulate PTEN activities through Figure 6. Tumor cells derived from male PyVT(+/2)/ADN(+/2) mice show increased metastatic capacities in nude mice comparing with those of PyVT(+/2)/ADN(+/+) mice. Both hematoxylin and eosin staining (upper panel) and the morphological evaluations (bottom panel) were performed to evaluate metastasis of the lung tissues. doi:10.1371/journal.pone.0004968.g006 PLoS ONE | www.plosone.org 8 March 2009 | Volume 4 | Issue 3 | e4968