Thymic Epithelial Tumors phenotype relies on miR-145-5p epigenetic regulation

Teresa Bellissimo,Silvia Masciarelli,Claudio Pulito,Claudia Tito,Francesco Fazi,Francesco Facciolo,Felice Giangaspero,Giovanni Blandino,Edoardo Pescarmona,Vincenzo Petrozza,Daniele Diso,Marco Anile,Luciana De Angelis,Enzo Gallo,Andrea Sacconi,Federico Venuta,Federica Ganci,Mirella Marino

doi:10.1186/s12943-017-0655-2

Teresa Bellissimo, Silvia Masciarelli + Show 16 more

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https://doi.org/10.1186/s12943-017-0655-2

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Abstract

BackgroundThymoma and thymic carcinoma are the most frequent subtypes of thymic epithelial tumors (TETs). A relevant advance in TET management could derive from a deeper molecular characterization of these neoplasms. We previously identified a set of microRNA (miRNAs) differentially expressed in TETs and normal thymic tissues and among the most significantly deregulated we described the down-regulation of miR-145-5p in TET. Here we describe the mRNAs diversely regulated in TETs and analyze the correlation between these and the miRNAs previously identified, focusing in particular on miR-145-5p. Then, we examine the functional role of miR-145-5p in TETs and its epigenetic transcriptional regulation.MethodsmRNAs expression profiling of a cohort of fresh frozen TETs and normal tissues was performed by microarray analysis. MiR-145-5p role in TETs was evaluated in vitro, modulating its expression in a Thymic Carcinoma (TC1889) cell line. Epigenetic transcriptional regulation of miR-145-5p was examined by treating the TC1889 cell line with the HDAC inhibitor Valproic Acid (VPA).ResultsStarting from the identification of a 69-gene signature of miR-145-5p putative target mRNAs, whose expression was inversely correlated to that of miR-145-5p, we followed the expression of some of them in vitro upon overexpression of miR-145-5p; we observed that this resulted in the down-regulation of the target genes, impacting on TETs cancerous phenotype. We also found that VPA treatment of TC1889 cells led to miR-145-5p up-regulation and concomitant down-regulation of miR-145-5p target genes and exhibited antitumor effects, as indicated by the induction of cell cycle arrest and by the reduction of cell viability, colony forming ability and migration capability. The importance of miR-145-5p up-regulation mediated by VPA is evidenced by the fact that hampering miR-145-5p activity by a LNA inhibitor reduced the impact of VPA treatment on cell viability and colony forming ability of TET cells. Finally, we observed that VPA was also able to enhance the response of TET cells to cisplatin and erlotinib.ConclusionsAltogether our results suggest that the epigenetic regulation of miR-145-5p expression, as well as the modulation of its functional targets, could be relevant players in tumor progression and treatment response in TETs.

Highlights

Thymoma and thymic carcinoma are the most frequent subtypes of thymic epithelial tumors (TETs)
epidermal growth factor receptor (EGFR) mutations are rare in TETs, the receptor has been shown frequently overexpressed in thymomas and thymic carcinomas [17, 18]
Differential mRNA expression between thymic epithelial tumors and normal thymic tissues Starting from a selection of frozen tissue samples showing high RNA quality, we performed a gene expression profiling using 6 TET specimens and 3 normal counterparts (Fig. 1a)

Summary

Introduction

Thymoma and thymic carcinoma are the most frequent subtypes of thymic epithelial tumors (TETs). The oncogenic potential of these rare neoplasms is still largely undefined and a deeper molecular characterization could result in a relevant advance in their management greatly improving diagnosis, prognosis and treatment choice [15, 16] In this direction, different studies investigated the epidermal growth factor receptor (EGFR) as a potential therapeutic target in TETs. EGFR mutations are rare in TETs, the receptor has been shown frequently overexpressed in thymomas and thymic carcinomas [17, 18]. Single-case reports suggest that EGFR-tyrosine kinase inhibitors (Erlotinib or Gefitinib) or anti-EGFR mAb (Cetuximab) may be effective in some patients, two clinical phase II studies (44 patients in total) using Erlotinib and Gefitinib reported no complete remissions and only two partial responses [12, 15, 23] These considerations suggest that studies addressing novel therapeutic strategies and the molecular basis of TETs are greatly needed. In this direction a recent work evidenced that Valproic Acid (VPA), a histone deacetilase (HDAC) inhibitor, might markedly increase the sensitivity of tyrosine kinase inhibitor (TKI)-

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