The critical role of the ZNF217 oncogene in promoting breast cancer metastasis to the bone

Bone metastasis affects >70% of patients with advanced breast cancer. However, the molecular mechanisms underlying this process remain unclear. On the basis of analysis of clinical datasets, and in vitro and in vivo experiments, we report that the ZNF217 oncogene is a crucial mediator and indicator of bone metastasis. Patients with high ZNF217 mRNA expression levels in primary breast tumours had a higher risk of developing bone metastases. MDA-MB-231 breast cancer cells stably transfected with ZNF217 (MDA-MB-231-ZNF217) showed the dysregulated expression of a set of genes with bone-homing and metastasis characteristics, which overlapped with two previously described 'osteolytic bone metastasis' gene signatures, while also highlighting the bone morphogenetic protein (BMP) pathway. The latter was activated in MDA-MB-231-ZNF217 cells, and its silencing by inhibitors (Noggin and LDN-193189) was sufficient to rescue ZNF217-dependent cell migration, invasion or chemotaxis towards the bone environment. Finally, by using non-invasive multimodal in vivo imaging, we found that ZNF217 increases the metastatic growth rate in the bone and accelerates the development of severe osteolytic lesions. Altogether, the findings of this study highlight ZNF217 as an indicator of the emergence of breast cancer bone metastasis; future therapies targeting ZNF217 and/or the BMP signalling pathway may be beneficial by preventing the development of bone metastases. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

MicroRNA-125b upregulation confers aromatase inhibitor resistance and is a novel marker of poor prognosis in breast cancer

Introduction

Increasing evidence indicates that microRNAs (miRNAs) are important players in oncogenesis. Considering the widespread use of aromatase inhibitors (AIs) in endocrine therapy as a first-line treatment for postmenopausal estrogen receptor α–positive breast cancer patients, identifying deregulated expression levels of miRNAs in association with AI resistance is of utmost importance.

Methods

To gain further insight into the molecular mechanisms underlying the AI resistance, we performed miRNA microarray experiments using a new model of acquired resistance to letrozole (Res-Let cells), obtained by long-term exposure of aromatase-overexpressing MCF-7 cells (MCF-7aro cells) to letrozole, and a model of acquired anastrozole resistance (Res-Ana cells). Three miRNAs (miR-125b, miR-205 and miR-424) similarly deregulated in both AI-resistant cell lines were then investigated in terms of their functional role in AI resistance development and breast cancer cell aggressiveness and their clinical relevance using a cohort of 65 primary breast tumor samples.

Results

We identified the deregulated expression of 33 miRNAs in Res-Let cells and of 18 miRNAs in Res-Ana cells compared with the sensitive MCF-7aro cell line. The top-ranked Kyoto Encyclopedia of Genes and Genomes pathways delineated by both miRNA signatures converged on the AKT/mTOR pathway, which was found to be constitutively activated in both AI-resistant cell lines. We report for the first time, to our knowledge, that ectopic overexpression of either miR-125b or miR-205, or the silencing of miR-424 expression, in the sensitive MCF-7aro cell line was sufficient to confer resistance to letrozole and anastrozole, to target and activate the AKT/mTOR pathway and to increase the formation capacity of stem-like and tumor-initiating cells possessing self-renewing properties. Increasing miR-125b expression levels was also sufficient to confer estrogen-independent growth properties to the sensitive MCF-7aro cell line. We also found that elevated miR-125b expression levels were a novel marker for poor prognosis in breast cancer and that targeting miR-125b in Res-Let cells overcame letrozole resistance.

Conclusion

This study highlights that acquisition of specific deregulated miRNAs is a newly discovered alternative mechanism developed by AI-resistant breast cancer cells to achieve constitutive activation of the AKT/mTOR pathway and to develop AI resistance. It also highlights that miR-125b is a new biomarker of poor prognosis and a candidate therapeutic target in AI-resistant breast cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0515-1) contains supplementary material, which is available to authorized users.

ZNF217 confers resistance to the pro-apoptotic signals of paclitaxel and aberrant expression of Aurora-A in breast cancer cells

BACKGROUND

ZNF217 is a candidate oncogene located at 20q13, a chromosomal region frequently amplified in breast cancers. The precise mechanisms involved in ZNF217 pro-survival function are currently unknown, and utmost importance is given to deciphering the role of ZNF217 in cancer therapy response.

RESULTS

We provide evidence that stable overexpression of ZNF217 in MDA-MB-231 breast cancer cells conferred resistance to paclitaxel, stimulated cell proliferation in vitro associated with aberrant expression of several cyclins, and increased tumor growth in mouse xenograft models. Conversely, siRNA-mediated silencing of ZNF217 expression in MCF7 breast cancer cells, which possess high endogenous levels of ZNF217, led to decreased cell proliferation and increased sensitivity to paclitaxel. The paclitaxel resistance developed by ZNF217-overexpressing MDA-MB-231 cells was not mediated by the ABCB1/PgP transporter. However, ZNF217 was able to counteract the apoptotic signals mediated by paclitaxel as a consequence of alterations in the intrinsic apoptotic pathway through constitutive deregulation of the balance of Bcl-2 family proteins. Interestingly, ZNF217 expression levels were correlated with the oncogenic kinase Aurora-A expression levels, as ZNF217 overexpression led to increased expression of the Aurora-A protein, whereas ZNF217 silencing was associated with low Aurora-A expression levels. We showed that a potent Aurora-A kinase inhibitor was able to reverse paclitaxel resistance in the ZNF217-overexpressing cells.

CONCLUSION

Altogether, these data suggest that ZNF217 might play an important role in breast neoplastic progression and chemoresistance, and that Aurora-A might be involved in ZNF217-mediated effects.