Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype. We explored the role of androgen receptor (AR) in TNBC focusing on its association with ERß in ligand-independent AR activation.
We performed in vitro experiments in breast cancer cell lines BT-20 and MDA-MB 453, which express high and low levels of AR, respectively. We have also studied PI3K/AKT pathway molecules mTOR, PTEN and AKT with immunoblot analysis and RT-PCR. Immunoblot analysis of BT-20 and MDA-MB 453 cells for ERß following transfection with increasing amounts of ERß was also performed. In order to test if a physical association (ERß-AR) occurs, immunoprecipitation (IP) was performed. &Tgr;reatment with agonists and antagonists of AR and ERß was also applied.
We have verified the endogenous expression of ERß in TNBC cell lines. We have demonstrated that the cellular model that expresses only ERß (BT-20) holds a different molecular profile compared to that expressing only AR (MDA-MB 453). The presence of ERß led to PTEN increase; subsequently, expression levels of phosphorylated (p) molecules of PI3K/AKT pathway (p-mTOR, p-Akt) were reduced. Contrarily, AR (+) cellular model showed high expression levels of the same molecules, indicating the strong proliferative effect of AR in TNBC. The cellular model which expresses both AR and ERß showed that ERß modulates AR proliferative activity by increasing PTEN and reducing activation of downstream molecules of PI3K/AKT pathway. Agonists of both receptors (testosterone and 17ß-estradiol for AR and ERß, respectively) enhanced receptors expression, affecting the expression levels of the PI3K/AKT signaling pathway molecules. Treatment with the AR antagonist bicalutamide did not have significant impact. Using IP, a specific interaction between ERß and AR was revealed.
There is strong evidence that ERß is involved in TNBC progression. Our data provide a strong anti-proliferative effect of ERß in TNBC cells via the PI3K/AKT signaling pathway and may represent a significant therapeutic target. More detailed studies are ongoing to this concept, which may have considerable impact for the treatment of TNBC patients.
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Department of Biological Chemistry, Medical School, National and Kapodistrian University of Athens, Athens, Greece
All authors have declared no conflicts of interest.