Exosome-mediated delivery of miR-9 induces cancer-associated fibroblast-like properties in human breast fibroblasts.

S Baroni,I Plantamura,M V Iorio,A Rossini,E D’Ippolito,A Cataldo,S Romero-Cordoba,G Cosentino,M Dugo,M G Daidone,V Angeloni

doi:10.1038/cddis.2016.224

Abstract

It is established that the interaction between microenvironment and cancer cells has a critical role in tumor development, given the dependence of neoplastic cells on stromal support. However, how this communication promotes the activation of normal (NFs) into cancer-associated fibroblasts (CAFs) is still not well understood. Most microRNA (miRNA) studies focused on tumor cell, but there is increasing evidence of their involvement in reprogramming NFs into CAFs. Here we show that miR-9, upregulated in various breast cancer cell lines and identified as pro-metastatic miRNA, affects the properties of human breast fibroblasts, enhancing the switch to CAF phenotype, thus contributing to tumor growth. Expressed at higher levels in primary triple-negative breast CAFs versus NFs isolated from patients, miR-9 improves indeed migration and invasion capabilities when transfected in immortalized NFs; viceversa, these properties are strongly impaired in CAFs upon miR-9 inhibition. We also demonstrate that tumor-secreted miR-9 can be transferred via exosomes to recipient NFs and this uptake results in enhanced cell motility. Moreover, we observed that this miRNA is also secreted by fibroblasts and in turn able to alter tumor cell behavior, by modulating its direct target E-cadherin, and NFs themselves. Consistently with the biological effects observed, gene expression profiles of NFs upon transient transfection with miR-9 show the modulation of genes mainly involved in cell motility and extracellular matrix remodeling pathways. Finally, we were able to confirm the capability of NFs transiently transfected with miR-9 to promote in vivo tumor growth. Taken together, these data provide new insights into the role of miR-9 as an important player in the cross-talk between cancer cells and stroma.

Highlights

Tumorigenesis is not considered anymore a tumor cellautonomous mechanism triggered by accumulation of somatic aberrations, but fostered by a two-way interaction between cancer cells and the surrounding microenvironment
To investigate whether a different expression of miR-9 could play a role in the acquisition of normal fibroblasts to a cancer-associated fibroblast phenotype, the level of mature miR-9 was first evaluated in couples of primary NFs/cancer-associated fibroblasts (CAFs) isolated from patients with different breast cancer subtypes
MiRNA microarrays of CAFs and NFs in breast cancer identified a small group of differentially expressed miRNAs,[13] including miR-200 s, which have been recently demonstrated to be direct mediators of NFs reprogramming into CAFs and extracellular matrix (ECM) remodeling.[15]

Summary

Introduction

Tumorigenesis is not considered anymore a tumor cellautonomous mechanism triggered by accumulation of somatic aberrations, but fostered by a two-way interaction between cancer cells and the surrounding microenvironment. Cancer cells are integrated in a biologically complex stroma, composed of different cell types (such as immune system components, endothelial cells, fibroblasts and adipocytes) as well as extracellular matrix (ECM), which originates the heterogeneity of the tumor microenvironment (TME).[1] It is known that a permissive TME has a key role in tumorigenesis. Breast cancer is the leading cause of cancer-related deaths in women.[6] Clinically, this heterogeneous disease is categorized into four major molecular subtypes: luminal-A, luminal-B, human epidermal growth factor receptor 2 (HER2). Triple-negative breast cancer (TNBC) constitutes approximately 15–20% of all breast cancer cases, with the worst outcome of all subtypes.[7]

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Conclusion