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

MARÍA C. DÍAZ FLAQUÉ, WENDY BÉGUELIN, ROCIO VICARIO, CECILIA PROIETTI, MARTÍN RIVAS, MERCEDES TKACH, FRANCO IZZO, EDUARDO CHARREAU, ROXANA SCHILLACI, PATRICIA ELIZALDE

Orlando, Florida, USA.

Congreso; 102nd Annual Meeting of the American Association for Cancer Research; 2011

We have previously demonstrated that progestin induces the rapid activation of AP-1 transcription factor and its nuclear interaction with the progesterone receptor (PR) by tethering in C4HD cells an experimental model of hormonal carcinogenesis in which the synthetic progestin medroxyprogesterone acetate (MPA) induced mammary adenocarcinomas in female Balb/c mice and in the human breast cancer line T47D. In this work, we demonstrated that MPA induces AP-1 transcriptional activation through the activation of MAPKs signaling pathways. Our 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 siteS 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 blockage of any of the members of the complex prevents its assembly and inhibits the MPA-induced cyclin D1 up-regulation and cell proliferation.