Progesterone receptor, AP-1 and Stat3 cooperative transcriptional complex in breast cancer

MARÍA C. DÍAZ FLAQUÉ; WENDY BEGUELIN; ROCIO VICARIO; CECILIA J. PROIETTI; MARTÍN A. RIVAS; TKACH, MERCEDES; EDUARDO CHARREAU; R SCHILLACI; ELIZALDE, PATRICIA

Congreso; AACR Annual Meeting; 2011

We have previously demonstrated that progestin induces the rapid activation of AP-1 transcription factor and its nuclear colocalization with Progesterone Receptor (PR) in human T47D breast cancer cells and C4HD cells, from a murine progestin-dependent mammary tumor. In this work we demonstrate that MPA induces AP-1 transcriptional activation through the activation of MAPKs signaling pathways. Recent findings have demonstrated that MPA induces the recruitment of Stat3 and PR to the GAS site in the cyclin D1 promoter. Here, we identified a novel PR/AP-1/Stat3 transcriptional complex in breast cancer cells. Cyclin D1 is a cancer-related protein whose promoter contains AP-1 binding sites (TRE sites) and Stat3 binding sites (GAS sites) in a very close proximity and lacks progesterone response elements (PRE sites). By using quantitative chromatin immunoprecipitation (ChIP) and sequential ChIP, we demonstrated that progestin induces the recruitment of c-jun, c-fos and PR to the TRE site and this recruitment is abolished when we pretreat the cells with the MAPKs inhibitor U0126. When cells were transfected with c-jun and c-fos Dominant Negatives Forms (TAM-67 and A-Fos respectively) none of these proteins are able to activate cyclin D1 promoter or are recruited to the TRE site and there is not MPA-induced Stat3 recruitment to the GAS site. In the same way when we pre-treat the cells with siRNAs against Stat3 neither c-jun, c-fos, PR or Stat3 are recruited to the AP-1 or GAS site in the cyclin D1 promoter. Inhibition of MPA-induced AP-1 transcriptional activation by transfection of breast cancer cells with TAM-67 and A-Fos resulted in complete abrogation of progestin-induced in vitro and in vivo breast cancer growth. Our findings reveal a novel MPA-induced PR/AP-1/Stat3 cooperative transcriptional complex in breast cancer cells. Interestingly the blokeage of any of the members of the complex inhibit the MPA-induced cyclin D1 up-regulation and cell proliferation