Adiponectin and Breast Cancer Figure 9. Inactivation of PTEN was at least partially caused by the augmented Trx1/TrxR1 redox activities in PyVT(+/2)/ADN(+/2) tumor cells. A, activities of PTEN, TrxR1 and Trx were evaluated in the lysates derived from PyVT(+/2)/ADN(+/+) and PyVT(+/2)/ADN(+/2) tumor cells using colorimetric assays. Briefly, cells were treated with vehicle control (CON), 10 mM curcumin (CUR) or 15 mg/ml adiponectin (ADN) for 24 hrs. Immunoprecipitation and phosphatase assay were performed as described in Methods. Results were expressed as fold changes relative to the enzyme activities in PyVT(+/2)/ADN(+/+) tumor cells treated with vehicle control. B, total protein levels of PTEN, TrxR1 and Trx1 in cell lysates from PyVT(+/2)/ADN(+/+) and PyVT(+/2)/ADN(+/2) tumors were analyzed by Western Blotting. C, co-immunoprecipitations were performed with the specific antibodies against PTEN or Trx1 in both PyVT(+/2)/ADN(+/+) and PyVT(+/2)/ADN(+/2) tumor cell lysates. The immune-complexes were analyzed by SDS-PAGE and Western Blotting using antibodies as indicated. D, intrinsic transcriptional activities of TrxR1 promoter (left panel) and the mRNA levels of TrxR1 and Trx1 (right panel) were evaluated in PyVT(+/2)/ADN(+/+) and PyVT(+/2)/ADN(+/2) tumor cells treated without (CON) or with adiponectin (ADN, 15 mg/ml) using TrxR1 reporter assay (left panel) and quantitative RT-PCR respectively (right panel). *, P,0.05 vs PyVT(+/2)/ ADN(+/+) cell control; #, P,0.05 vs PyVT(+/2)/ADN(+/2) cell control (n = 3, from three independent experiments). doi:10.1371/journal.pone.0004968.g009 prognosis. The origin of this subtype tumor is unclear, but suggested to be the basal/myoepithelial cells, derived from epithelial-to-mesenchymal transition as a result of dedifferentia- tion, or from stem cells [43]. It will be interesting to investigate which types of tumor cell transformation could be facilitated by the altered microenvironment associated with adiponectin haploinsufficiency. It has long been noticed that cancer cells exhibit increased glycolysis for ATP production due, in part, to respiration injury (the Warburg effect). The increase in NADH caused by respiratory deficiency inactivates PTEN through a redox modification mechanism, leading to Akt activation. Our group has recently reported that adiponectin deficiency leads to dysregulated mitochondrial functions, which result in decreased activities of the respiratory chain and subsequent accumulation of reactive oxygen species [55]. We have also found that adiponectin can modulate redox-regulated transcription factor Sp1 activities [56]. Interestingly, the expression of both Trx1 and TrxR1 can be regulated by Sp1 [57]. Whether these mechanisms contribute to the dysregulated Trx/TrxR redox system in adiponectin insufficiency-related carcinogenesis are currently under investigation in our laboratory. Nevertheless, these findings might provide a novel mechanistic insight to explain how metabolic alteration in adiponectin haplodeficient tumor may gain a survival advantage. PLoS ONE | www.plosone.org 11 March 2009 | Volume 4 | Issue 3 | e4968