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

M. CELESTE DÍAZ FLAQUÉ, WENDY BÉGUELIN, VICTORIA SUNDBLAD, CINTHIA ROSEMBLIT, CECILIA J. PROIETTI, MARTÍN A. RIVAS, MERCEDES TKACH, EDUARDO H. CHARREAU, ROXANA SCHILLACI, PATRICIA V. ELIZALDE

9-13 de junio 2009, Washington DC, USA

Congreso; 91st Annual Meeting of the Endocrine Society of America; 2009

The Endocrine Society of America

Accumulating evidence indicates that progestins induce proliferation of breast cancer cellsthrough up regulation of key regulatory molecules that do not contain a classicalprogesterone response element (PRE) in the promoter region, such as Cyclin D1. We haverecently demonstrated that the synthetic progestin medroxyprogesterone acetate (MPA)induces Cyclin D1 expression in the murine breast cancer cell line LM3 transientlytransfected with the B isoform of the human progesterone receptor (LM3-hPR-B cells). Wepropose that MPA regulation of Cyclin D1 may occur through a transcriptional mechanism(tethering), that involves progesterone-bound PR interaction with AP-1 factors (composedof jun and fos family members), at specific AP-1 binding sites (TRE) in the Cyclin D1promoter. In the present work, we found that MPA regulates c-Jun and c-Fos proteinexpression and activation in LM3-hPR-B cells. Considering that the activation of AP-1 byERK 1/2 has been previously reported, we then explore the involvement of ERK 1/2 in theactivation of the AP-1 by MPA. LM3-hPR-B cells were incubated with U0126, apharmacological inhibitor of ERK 1/2, before MPA stimulation. We found that addition ofU0126 inhibited MPA induced c-Jun and c-Fos activation. To further investigate theinteraction between AP-1 factors and PR at the Cyclin D1 promoter, we used the humanbreast cancer cell line T47D, which endogenously expresses PR. We performed ChromatinImmunoprecipitation (ChIP) assays and observed that MPA was able to induce a c-Jun andPR occupancy at the TRE site of the Cyclin D1 promoter. We then assessed whether c-Junand PR simultaneously bind to the Cyclin D1 gene promoter, using sequential ChIP assayin T47D cells. Interestingly, we found that, c-Jun and PR co-occupy the Cyclin D1promoter at the TRE site in cells stimulated with MPA. Our findings show for the firsttime that progestins induce AP-1 transcription factor activation and the c-Jun and PRoccupancy at the TRE site of the Cyclin D1 promoter.