Role of BP1 in Estrogen Signalling
Open AccessBP1 is a transcription factor belonging to the family of homeobox genes. BP1 protein (pBP1) appears to play a crucial role in cell survival, aggressiveness and metastasis. It has been shown that pBP1 is expressed in 80% of invasive ductal breast tumors, and that 100% of estrogen receptor (ER) negative tumors. The aim of this study was to determine whether there is a relationship between BP1 and ER-¥á expression due to their significant roles in breast cancer and to determine if BP1 is involved in the genomic and the non-genomic pathways that regulate ER-¥á. Estrogen receptors (ER) are proteins that mediate the cellular response to estrogen. They belong to the nuclear receptor superfamily and act as ligand-dependent transcription factors for genes regulated by estrogen. There are two ER subtypes, ER-¥á and ER- ©¬. ER-¥á expression has long served as a target of antiestrogen therapy in breast cancer patients, and characterization of the molecular actions of ER in breast tissue has become a major focus of studies aimed at elucidating the development of antiestrogen resistance in ER positive cancer cells. In our study, through the Immunostaining and Western blot we showed that the overexpression of pBP1 in MCF-7 cells grown in serum free media leads to the repression of the ER-¥á protein. Further, our qRT-PCR analysis on the genes positively regulated by ER-¥á (Progesterone receptor and pS2) confirm the repression of biologically active ER-¥á protein. In this study we found that, in the presence of serum pBP1 over-expression leads to an increase in the expression of biologically active ER-¥á protein. In our study, through the EMSA and ChIP, we showed that pBP1 binds to the first intron of the ER-¥á gene. However our qRT-PCR data on ER-¥á shows no change in the mRNA expression levels of ER-¥á when the cells over-expressing BP1 were compared with those containing the empty vector. The ER can induce or repress the expression of target genes by genomic and non-genomic pathways. In the genomic pathway, estrogen-bound ER dimerizes, crosses the nuclear membrane, and induces transcription via direct binding to estrogen response elements (EREs) within target genes or by interacting with other transcription factors. In this study, through the ChIP assay we showed ER-¥á binds to the ERE sequence present in the first intron of the BP1 gene. We also showed that the BP1 expression increases after treatment with 10 nM Estradiol (E2). In addition to genomic pathways, ER induces changes in gene expression via several non-genomic pathways, in which it interacts with signaling molecules in the cytoplasm. Most of these pathways necessitate estrogen binding to the ER, although some do not. For example, ER can be phosphorylated by MAPK and Akt; when this occurs, the ER is activated, behaving as a transcription factor in the absence of estrogen. Our studies show that on treatment of cells with E2 and EGF, overexpression of BP1 leads to a decrease in the levels of phospho Akt (Ser473) and phospho ER (Ser167). However on treatment of cells with E2 and EGF, we didn¡¯t observe any change in the levels of Phospho-p44/42 MAPK. Thus our results indicate that BP1 regulates the phosphorylation of ER at Ser167 through the PI3K/AKT pathway. Finally, our findings indicate that BP1 plays a major role in both, genomic and non-genomic signaling.
- All rights reserved
Notice to Authors
If you are the author of this work and you have any questions about the information on this page, please use the Contact form to get in touch with us.