ƒx Progestins induce breast cancer cell proliferation through the AP-1 transcription factor

MARIA C.DIAZ FLAQUE; WENDY BEGUELIN; CJ PROIETTI; MARTÍN A. RIVAS; TKACH, MERCEDES; EDUARDO CHARREAU; ROXANA SCHILLACI; ELIZALDE, PATRICIA

San Diego

Congreso; Endocrine Society 92nd Annual Meeting; 2010

The Endocrine Society

Breast cancer is a major health problem that affects a significant number of women around the world. Accumulating evidence has shown the involvement of the progesterone receptor (PR) in breast cancer development. In its classical mechanism of action, PR acts as a ligand-induced nuclear transcription factor. In addition to its direct transcriptional effects, PR activates signal transduction pathways in breast cancer cells through a rapid or nongenomic mechanism, which results in cell proliferation. Interestingly, progestins induce the expression of key regulators of cell cycle progression which do not contain a classical progesterone response element (PRE) in their promoters, such as cyclin D1. We and others have also shown that progestins are able to induce cyclin D1 expression in breast cancer cells. Our present findings demonstrate that the synthetic progestin medroxyprogesterone acetate (MPA) is able to induce an increase in the levels of c-jun and c-fos phosphorylation and AP-1 transcriptional activation. The transcription factor AP-1 consists of two family members Fos and Jun. AP-1 binds to specific DNA sequences called TPA response elements (TRE) in their regulatory regions. Our chromatin immunoprecipitation (ChIP) assays demonstrated that progestin stimulates c-jun, c-fos, and PR recruitment to the TRE site of the cyclin D1 promoter. The simultaneous binding of the three proteins to the cyclin D1 promoter upon progestin stimulation was shown by using sequential ChIP assays. These data identify, for the first time, the interaction between AP-1 and PR regulating cyclin D1 transcription by tethering to DNA-bound at TRE site. Furthermore, we found that the inhibition of c-fos and c-jun activation by the use of dominant negative forms of these proteins (A-Fos and TAM-67 respectively) completely blocked progestin-induced cyclin D1 expression and in vitro breast cancer cell growth. Finally, we addressed the effect of targeting AP-1 in vivo MPA-dependent growth of C4HD progestin-dependent murine mammary tumor. Transfection of C4HD cells with TAM-67 or A-Fos DN expression vectors significantly inhibited these cells¡¦ ability to form tumors in syngeneic mice when compared to empty vector-transfected C4HD cells. This study enhances our current understanding of how progestins induce AP-1 factors function and PR association in breast cancer cells and provide a solid rationale for study selective AP-1 inhibitors for the treatment and prevention of breast cancer.