Regulation of nuclear receptor and cofactor expression in breast cancer cell lines

The aim of this study was to compare the expression profile of nuclear receptors (NRs) and cofactors in different breast cancer cell lines as well as their regulation by estradiol, insulin and progestin R5020. Expression of NRs and cofactors were determined from MCF-7, T-47D and ZR-75-1 breast cancer cell lines. Multiprobe ribonuclease protection assay and real-time RT-PCR were used to quantitate mRNA levels of steroid receptors, vitamin D receptors (VDR) and retinoic acid receptors (RAR) and cofactors: amplified in breast cancer-1, cyclic AMP response element binding protein (CBP), p300/CBP-associated factor, p300, nuclear receptor corepressor and silencing mediator of repressed transcription. Basal expression levels of NRs and cofactors varied depending on the cell line. Cell line-specific regulation of androgen receptor, estrogen receptor-alpha (ERalpha), RARalpha, RARgamma and VDR expression was observed after estradiol treatment. Likewise, differences in the regulation of ERalpha, RARalpha and VDR expression after R5020 treatment were observed. We did not observe significant regulation of cofactor expression after estradiol, insulin or progestin treatment in any cell line analyzed. The results showed that not only is the expression profile of the NRs and cofactors cell line specific but also the regulation of NR expression. Thus the determinants of the ligand action (receptor and cofactor expression) varied considerably among different cell clones of the breast cancer cells. This suggested a gradient of NR-ligand sensitivities in the hormone-dependent breast cancers, which produces an additional challenge in developing novel ligands for hormone replacement therapy and breast cancer treatment.