Progestins Induce Activation of the AP-1 Transcription Factor through ERK1/2 in Breast Cancer Cells.

DIAZ FALQUE MC; BEGUELIN W; SUNDBALD V; ROSEMBLIT C; PROIETTI CJ; RIVAS MA; TKACH M; CHARREAU EH; SCHILLACI R; ELIZALDE PV

Washingtong, DC

Congreso; 100 th Annual Meeting of the Endocrine Society of America (ENDO); 2009

Endocrine Society of America (ENDO)

Progestins induce activation of the AP-1 transcription factor through ERK 1/2 in breast cancer cells.   MC Díaz Flaqué, W Beguelin ,V Sundblad, C Rosemblit , CJ Proietti, MA Rivas, M Tkach, EH Charreau, R Schillaci, PV Elizalde.   Accumulating evidence indicates that progestins induce proliferation of breast cancer cells through up regulation of key regulatory molecules that do not contain a classical progesterone response element (PRE) in the promoter region, such as Cyclin D1. We have recently demonstrated that the synthetic progestin medroxyprogesterone acetate (MPA) induces Cyclin D1 expression in the murine breast cancer cell line LM3 transiently transfected with the B isoform of the human progesterone receptor (LM3-hPR-B cells). We propose that MPA regulation of Cyclin D1 may occur through a transcriptional mechanism (tethering), that involves progesterone-bound PR interaction with AP-1 factors (composed of jun and fos family members), at specific AP-1 binding sites (TRE) in the Cyclin D1 promoter. In the present work, we found that MPA regulates c-Jun and c-Fos protein expression and activation in LM3-hPR-B cells. Considering that the activation of AP-1 by ERK 1/2 has been previously reported, we then explore the involvement of ERK 1/2 in the activation of the AP-1 by MPA. LM3-hPR-B cells were incubated with U0126, a pharmacological inhibitor of ERK 1/2, before MPA stimulation. We found that addition of U0126 inhibited MPA induced c-Jun and c-Fos activation. To further investigate the interaction between AP-1 factors and PR at the Cyclin D1 promoter, we used the human breast cancer cell line T47D, which endogenously expresses PR. We performed Chromatin Immunoprecipitation (ChIP) assays and observed that MPA was able to induce a c-Jun and PR occupancy at the TRE site of the Cyclin D1 promoter. We then assessed whether c-Jun and PR simultaneously bind to the Cyclin D1 gene promoter, using sequential ChIP assay in T47D cells. Interestingly, we found that, c-Jun and PR co-occupy the Cyclin D1 promoter  at the TRE site in cells stimulated with MPA. Our findings show for the first time that progestins induce AP-1 transcription factor activation and the c-Jun and PR occupancy at the TRE site of the Cyclin D1 promoter.