Nuclear and cytoplasmic interaction of pRb2/p130 and ER-β in MCF-7 breast cancer cells

Estrogens exhibit important biological functions and influence several pathological processes of hormone-dependent diseases. The biological actions of estrogens require their interaction with two estrogen receptors (ER-α and ER-β), which are ligand-dependent transcription factors. ER-α and ER-β exhibit distinct tissue expression patterns as well as show different patterns of gene regulation. In addition, it has been suggested that ER-β works as a counter partner of ER-α through inhibition of the transactivating functions of ER-α. For instance, ER-β seems to play a different role in breast tumorigenesis than ER-α, as ER-β decreased expression in breast cancer has been correlated with bad prognosis. Biological activities of ER-α and ER-β could be controlled by a number of interacting proteins such as activators/inhibitors, ligand binding and kinases. We have previously reported that pRb2/p130, retinoblastoma related protein, could be involved in the silencing of ER-α gene during breast tumorigenesis. Here, we report that ER-β and pRb2/p130 proteins co-immunoprecipitate in both nucleus and cytoplasm of MCF-7 breast cancer cells. Our hypothesis is that the interaction of pRb2/130 with ER-β may have a functional significance in regulating ER-β activity.