A Regulatory “miRcircuitry” Involving miR221&222 and ERα Determines ERα Status of Breast Cancer Cells

Estrogen Receptor α (ERα) is the most important diagnostic and prognostic factor in breast cancer. Several lines of evidence have suggested that ERα-negative breast tumors, highly aggressive and non-responsive to hormonal therapy, arise from ERα-positive precursors through different molecular pathways. microRNAs (miRs) are small non-coding RNAs that regulate gene expression at post-transcriptional level and are aberrantly expressed in breast cancer. We hypothesized that microRNAs may have a pivotal role in ERα suppression and ERα-negative tumors formation. MicroRNAs microarray, quantitative real-time PCR, immunohistochemistry and in-situ hybridization analyses of breast cancer cell lines and primary tumors with different ERα-status indicated that miR221&222 are exclusively expressed in ERα-negative breast tumors. Overexpression of both microRNAs in ERα- positive cell lines strongly reduces the levels of ERα protein and, using luciferase reporter assays, we clearly demonstrated that ERα is a bona fide target of miR221&222. Gene expression profiles were analyzed after miR221 or miR222 over-expression in ERα-positive cells: up-regulation of anti-apoptotic genes, growth factors and down modulation of adhesion molecules indicated that miR221&222 may not only increase the ability to suppress apoptosis and accelerate tumor formation but also promote remodeling of the tumor microenvironment and escape of tumor cells through the basement membrane, all characteristics of ERα-negative cells. To gain more insights into the inverse correlation between miR221&222 and ERα in breast cancer, by computational analyses and reporter assay, we characterized the transcriptional unit of miR221&222. We identified several estrogen-responsive elements (ERE) at the genomic locus of miR221&222 and, by using different approaches, we demonstrated that ERα suppresses miR221&222 expression. Overexpression of exogenous or endogenous ERα protein in ERα-negative cells markedly repressed miR221&222; conversely, knockdown of ERα in ERα-positive cells increased their expression. Finally, chromatin immunoprecipitation (ChIP) on ERα-positive cells showed that ligand-bound ERα and its co-repressor proteins, NcoR and SMRT, were highly enriched at miR221&222 genomic locus. Notably, ChIP experiments after estradiol (E2) stimulation or ERα-knockdown revealed that ERα recruitment is essential for the corepressor enrichment and miR221&222 repression. These findings suggest that the negative regulatory loop involving miR221&222 and ERα may confer proliferative advantage and migratory activity to breast cancer cells and promote the transition from ERα-positive to ERα-negative tumors. Therefore, the elucidation of this pathway could be an important step in the development of the next generation of breast cancer therapeutics agents that may prevent hormone-resistance that frequently occurs during treatment

Reflections on the Role of the Panel

Over the past thirty years, the World Bank and the Inspection Panel have had a supportive relationship regarding the principle of accountability, particularly as applied to the field of development finance operations and the role and responsibility of the Bank as a multilateral public sector financial institution. This relationship has been apparent in at least three key aspects: i) following the Bank’s lead, many development institutions around the globe have taken steps to improve their own accountability and developed independent accountability mechanisms (IAMs) modeled on the Inspection Panel; ii) the Bank and other development institutions have been supporting the development of stronger and more comprehensive environmental and social policies for which they hold themselves to account; and iii) there has been steady growth in the availability and breadth of grievance services and mechanisms, at the management and project level, to help implement policy requirements and resolve issues for affected peopl

Oncosuppressive role of p53-induced miR-205 in triple negative breast cancer.

An increasing body of evidence highlights an intriguing interaction between microRNAs and transcriptional factors involved in determining cell fate, including the well known "genome guardian" p53. Here we show that miR-205, oncosuppressive microRNA lost in breast cancer, is directly transactivated by oncosuppressor p53. Moreover, evaluating miR-205 expression in a panel of cell lines belonging to the highly aggressive triple negative breast cancer (TNBC) subtype, which still lacks an effective targeted therapy and characterized by an extremely undifferentiated and mesenchymal phenotype, we demonstrated that this microRNA is critically down-expressed compared to a normal-like cell line. Re-expression of miR-205 where absent strongly reduces cell proliferation, cell cycle progression and clonogenic potential in vitro, and inhibits tumor growth in vivo, and this tumor suppressor activity is at least partially exerted through targeting of E2F1, master regulator of cell cycle progression, and LAMC1, component of extracellular matrix involved in cell adhesion, proliferation and migration