The oncogenic role of circPVT1 in head and neck squamous cell carcinoma is mediated through the mutant p53/YAP/TEAD transcription-competent complex

Background: Circular RNAs are a class of endogenous RNAs with various functions in eukaryotic cells. Worthy of note, circular RNAs play a critical role in cancer. Currently, nothing is known about their role in head and neck squamous cell carcinoma (HNSCC). The identification of circular RNAs in HNSCC might become useful for diagnostic and therapeutic strategies in HNSCC. Results: Using samples from 115 HNSCC patients, we find that circPVT1 is over-expressed in tumors compared to matched non-tumoral tissues, with particular enrichment in patients with TP53 mutations. circPVT1 up-and down-regulation determine, respectively, an increase and a reduction of the malignant phenotype in HNSCC cell lines. We show that circPVT1 expression is transcriptionally enhanced by the mut-p53/YAP/TEAD complex. circPVT1 acts as an oncogene modulating the expression of miR-497-5p and genes involved in the control of cell proliferation. Conclusions: This study shows the oncogenic role of circPVT1 in HNSCC, extending current knowledge about the role of circular RNAs in cancer

Argonaute 2 drives miR-145-5p-dependent gene expression program in breast cancer cells

To perform their regulatory functions, microRNAs (miRNAs) must assemble with any of the four mammalian Argonaute (Ago) family of proteins, Ago1–4, into an effector complex known as the RNA-induced silencing complex (RISC). While the mature miRNA guides the RISC complex to its target mRNA, the Ago protein represses mRNA translation. The specific roles of the various Ago members in mediating miRNAs activity, however, haven’t been clearly established. In this study, we investigated the contribution of Ago2, the only human Ago protein endowed with nuclease activity, to the function of tumor-suppressor miR-145-5p in breast cancer (BC). We show that miR-145-5p and Ago2 protein are concomitantly downregulated in BC tissues and that restoration of miR-145-5p expression in BC cells leads to Ago2 protein induction through the loosening of Ago2 mRNA translational repression. Functionally, miR-145-5p exerts its inhibitory activity on cell migration only in presence of Ago2, while, upon Ago2 depletion, we observed increased miR-145/Ago1 complex and enhanced cell motility. Profiling by microarray of miR-145-5p target mRNAs, in BC cells depleted or not of Ago2, revealed that miR-145-5p drives Ago2-dependent and -independent activities. Our results highlight that the Ago2 protein in cancer cells strictly dictates miR-145-5p tumor suppressor activity

Contribution of miR-145-5p/Ago2 complex to the regulation of epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is essential for cell fate determination during development but it is involved in pathological processes like cancer as well, being one of the first steps in the mechanisms leading to metastasis. miR-145-5p is one of the most widely recognized tumor-suppressor miRNAs, able to regulate cell migration and EMT through the contribution of the RISC complex in which Argonaute (Ago) proteins are required for target recognition and gene silencing [1]. Ago2 is an important member of the Ago family and its overexpression correlates with a transformed phenotype in breast cancer cells [2]. With the aim to unravel miR-145-5p/Ago2 contribution to the suppression of cancer progression in epithelial tumors, here we show that: i) miR-145-5p and Ago2 are down-regulated in breast tumor vs normal tissues; ii) the restored expression of miR-145-5p in breast cancer cell lines results in the reduction of tumor phenotype; iii) Ago2 expression is positively and specifically regulated by miR-145-5p; iv) miR-145-5p-dependent Ago2 induction is necessary for the inhibition of cell migration; v) when Ago2 is depleted, the formation of an alternative miR-145-5p/Ago1 active complex redirects miR-145-5p tumor suppressor function and correlates with a more invasive phenotype in breast cancer cells. These results open to the identification of miR-145-5p/Ago2-dependent molecular networks involved in the maintenance and progression of cancer phenotype

The mutant p53-ID4 complex controls VEGFA isoforms by recruiting lncRNA MALAT1

The abundant, nuclear-retained, metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been associated with a poorly differentiated and aggressive phenotype of mammary carcinomas. This long non-coding RNA (lncRNA) localizes to nuclear speckles, where it interacts with a subset of splicing factors and modulates their activity. In this study, we demonstrate that oncogenic splicing factor SRSF1 bridges MALAT1 to mutant p53 and ID4 proteins in breast cancer cells. Mutant p53 and ID4 delocalize MALAT1 from nuclear speckles and favor its association with chromatin. This enables aberrant recruitment of MALAT1 on VEGFA pre-mRNA and modulation of VEGFA isoforms expression. Interestingly, VEGFA-dependent expression signatures associate with ID4 expression specifically in basal-like breast cancers carrying TP53 mutations. Our results highlight the key role for MALAT1 in control of VEGFA isoforms expression in breast cancer cells expressing gain-of-function mutant p53 and ID4 proteins

MicroRNA expression profiling of thymic epithelial tumors

Background: Thymic epithelial tumors (TET) are the most frequent human primary mediastinal tumors in adults. A deep biological characterization of the processes at the basis of the transformed phenotype could strongly improve our understanding of the morphological and clinical heterogeneity of these diseases. MicroRNAs (miRNAs) are non-coding RNAs involved in post-transcriptional regulation and their altered expression accounts for the pathogenesis of several tumors. Objectives: The aim of this study was to identify the miRNAs that are differentially expressed in tumor vs normal thymic tissues or among the different tumor histotypes and that could impact on the biology of TET. Materials and methods: microRNAs expression profiling was performed by microarray analysis of formalin-fixed paraffin embedded (FFPE) tissue from 54 thymic tumor samples and 12 normal counterparts, derived from two patient cohorts. Results and conclusion: We identified groups of miRNAs differentially expressed between: (i) TET and normal thymic tissues, (ii) thymomas and thymic carcinomas, (iii) histotype groups. Moreover, we identified putative molecular pathways targeted by these differentially expressed miRNAs that could be involved in thymic carcinogenesis and in the maintenance and spreading of this tumor. © 2014 Elsevier Ireland Ltd