d by qRT PCR and compared to gene expres sion regulation in MCF 7 cells. The clone SK19 in which GFP ERa behavior was comparable to endogen ous ERa was selected for further investigation. To study the effects of estrogens and antiestrogens, cells were grown for 3 days in medium containing phe nol red free DMEM F 12 supplemented with 5% char coal stripped fetal calf serum, without gentamicin and sodium pyruvate. Cells were subsequently treated or not with 10 nM E2, 1 uM ICI, 1 uM OHT, 1 uM RU39, 1 uM RU58 for the indicated times. To study ERa degradation by the proteasome, cells were pre treated 30 min with 100 uM ALLN, a proteasome inhibitor, or 10 nM LMB, a nuclear export inhibitor. Cell extracts and Western blots MCF 7 cells grown in 6 well plates were treated as indi cated, washed with ice cold PBS and collected by centri fugation.

Total cell lysates were prepared by resuspension of cells in 100 ul lysis buffer. The samples were boiled for 20 min at 95 C and cleared by centrifugation Carfilzomib at 12 000 �� g for 10 min. Protein concentration was determined by an Amido Schwartz assay when the samples contained SDS. Samples were subjected to SDS PAGE and proteins transferred onto nitrocellulose membranes. Western blot analysis was performed as previously described using ERa and GAPDH antibodies and quantified using the TINA PC Base Software from FUJI. qRT PCR experiments Total RNAs were extracted using TRIzol reagent following the manufacturers protocol. 1 5 ug of total RNA was reverse transcribed in a final volume of 20 ul using SuperScript III Reverse Transcriptase.

cDNA was stored at 80 C. All target transcripts were detected using quantitative RT PCR assays on a Mastercycler Realplex device using TBP or RPLP0 genes as endo genous control for normalization of the data. The fol lowing primer pairs were used for amplification, 20 min at 95 C to obtain the insoluble nuclear fraction. The different fractions were stored at 80 C until use. Protein concentrations were determined using the Bio Rad Protein Assay. Immunofluorescence and Fluorescence microscopy For indirect immunofluorescence experiments, SK19 cells were grown for 3 days on coverslips in DMEM without phenol red, containing 5% charcoal stripped fetal serum. After 3 days, cells were treated for 1 h with the following ligands, 10 nM E2, 1 uM ICI, 1 uM OHT, 1 uM RU39, 1 uM RU58.

Cells were then washed twice with PBS, fixed in 4% paraformaldehyde PBS for 10 min at room temperature, subsequently permeabilized with 0. 5% Triton X 100 in PBS for 15 min at room tempera ture, counterstained with DAPI and mounted on microscopy slides. To study co localization of ERa and proteasome by immunofluorescence, SK19 cells were grown for 3 days on coverslips in DMEM without phenol red, containing 5% charcoal stripped fetal serum and next treated for 3 h with drugs as indicated above. To block protea some mediated ERa degradation, the cells were incu bated 30 min with 100 uM ALLN prior to treatment with ICI or RU58.