BET bromodomain inhibitor JQ1 modulates microRNA expression in thyroid cancer cells.

Anaplastic thyroid carcinoma (ATC) represents the most lethal thyroid cancer sub-type, currently unresponsive to standard treatments. Recently, bromodomain and extra-terminal (BET) proteins have emerged as attractive therapeutic targets in several diseases, including cancer. In different cancer models, the anti-neoplastic activity of BET inhibitors such as JQ1, I-BET762 and I-BET151 have already been established, due to both direct and indirect effects. miRNAs are 20-22 nucleotide transcriptional regulators which play important roles in proliferation, differentiation and apoptosis. Hitherto, the relationship between JQ1 and miRNAs has not been explored. The goal of this study was to delineate JQ1-associated miRNA regulation in ATC cells. Two ATC-derived cell lines (SW1736 and 8505c) were treated with either 5 µM JQ1 or vehicle for 48 or 72 h. A non-tumorigenic thyroid cell line (Nthy-ori 3-1) was used as a control. miRNome analysis displayed a JQ1-related dysregulation of several miRNAs, 7 of which turned out to be commonly dysregulated in both cell lines at both time-points. Furthermore, miR-4516 turned out to be downregulated in both ATC cell lines, when compared to the non-tumorigenic ones and notably, JQ1 treatment in both ATC cell lines induced its upregulation, restoring, in some way, its basal expression levels. We, therefore, focused on miR-4516 expression and STAT3 levels, since it was previously predicted to be a putative target of this microRNA. Consistently, phospho-STAT3 and its target p21Waf1/Cip1 turned out to be downregulated and upregulated in both JQ1-treated ATC cell lines, respectively. Thus, our data revealed that modulation of miRNA expression is one of the multiple mechanisms of the effect of JQ1 in thyroid cancer cells.

Identification of tumorigenesis-related mRNAs associated with RNA-binding protein HuR in thyroid cancer cells.

RNA binding proteins (RBPs) play a central role in cell physiology and pathology. Among them, HuR is a nuclear RBP, which shuttles to the cytoplasm to allow its RNA targets processing. HuR over-expression and delocalization are often associated to cell transformation. Numerous cancers display increased HuR protein levels and its high cytoplasmic levels has been associated with a worse prognosis.In our study, we first evaluated HuR expression in normal and cancer thyroid tissues and then evaluated its function in thyroid cell lines. HuR is over-expressed in all thyroid tumor tissues; high cytoplasmic levels are detected in all thyroid carcinomas. HuR silencing decreased cell viability and determined apoptotic cell death, in a non-tumorigenic (Nthy-ori-3.1) and a tumorigenic (BCPAP) thyroid cell line. Global transcriptome analysis indicated that HuR silencing, though having similar biological effects, induces distinct gene expression modifications in the two cell lines. By using the RIP-seq approach, the HuR-bound RNA profiles of different thyroid cell lines were evaluated. We show that in distinct cell lines HuR-bound RNA profiles are different. A set of 114 HuR-bound RNAs distinguishing tumorigenic cell lines from the non-tumorigenic one was identified.Altogether, our data indicate that HuR plays a role in thyroid tumorigenesis. Moreover, our findings are a proof of concept that RBP targets differ between cells with the same origin but with distinct biological behavior.

MCM5 as a target of BET inhibitors in thyroid cancer cells.

Anaplastic thyroid carcinoma (ATC) is an extremely aggressive thyroid cancer subtype, refractory to the current medical treatment. Among various epigenetic anticancer drugs, bromodomain and extra-terminal inhibitors (BETis) are considered to be an appealing novel class of compounds. BETi target the bromodomain and extra-terminal of BET proteins that act as regulators of gene transcription, interacting with histone acetyl groups. The goal of this study is to delineate which pathway underlies the biological effects derived from BET inhibition, in order to find new potential therapeutic targets in ATC. We investigated the effects of BET inhibition on two human anaplastic thyroid cancer-derived cell lines (FRO and SW1736). The treatment with two BETis, JQ1 and I-BET762, decreased cell viability, reduced cell cycle S-phase, and determined cell death. In order to find BETi effectors, FRO and SW1736 were subjected to a global transcriptome analysis after JQ1 treatment. A significant portion of deregulated genes belongs to cell cycle regulators. Among them, MCM5 was decreased at both mRNA and protein levels in both tested cell lines. Chromatin immunoprecipitation (ChIP) experiments indicate that MCM5 is directly bound by the BET protein BRD4. MCM5 silencing reduced cell proliferation, thus underlining its involvement in the block of proliferation induced by BETis. Furthermore, MCM5 immunohistochemical evaluation in human thyroid tumor tissues demonstrated its overexpression in several papillary thyroid carcinomas and in all ATCs. MCM5 was also overexpressed in a murine model of ATC, and JQ1 treatment reduced Mcm5 mRNA expression in two murine ATC cell lines. Thus, MCM5 could represent a new target in the therapeutic approach against ATC.