Epigenetic silencing of E-cadherin gene induced by lncRNA MALAT-1 in acute myeloid leukaemia

Long non-coding RNA MALAT1 in hematological malignancies and its clinical applications

ABSTRACT

Metastasis-associated lung adenocarcinoma transcript 1 ( MALAT1 ) is a well-established oncogenic long non-coding RNA, the higher expression of which is strongly correlated with cancer events such as tumorigenesis, progression, metastasis, drug resistance, and treatment outcome in solid cancers. Recently, a series of studies has highlighted its potential role in hematological malignancies in terms of these events. Similar to solid cancers, MALAT1 can regulate various target genes via sponging and epigenetic mechanisms, but the miRNAs sponged by MALAT1 differ from those identified in solid cancers. In this review, we systematically describe the role and underlying mechanisms of MALAT1 in multiple types of hematological malignancies, including regulation of cell proliferation, metastasis, stress response, and glycolysis. Clinically, MALAT1 expression is related to poor treatment outcome and drug resistance, therefore exhibiting potential prognostic value in multiple myeloma, lymphoma, and leukemia. Finally, we discuss the evaluation of MALAT1 as a novel therapeutic target against cancer in preclinical studies.

Epithelial-Mesenchymal Transition in Acute Leukemias

Epithelial-mesenchymal transition (EMT) is a metabolic process that confers phenotypic flexibility to cells and the ability to adapt to new functions. This transition is critical during embryogenesis and is required for the differentiation of many tissues and organs. EMT can also be induced in advanced-stage cancers, leading to further malignant behavior and chemotherapy resistance, resulting in an unfavorable prognosis for patients. Although EMT was long considered and studied only in solid tumors, it has been shown to be involved in the pathogenesis of hematological malignancies, including acute leukemias. Indeed, there is increasing evidence that EMT promotes the progression of acute leukemias, leading to the emergence of a more aggressive phenotype of the disease, and also causes chemotherapy resistance. The current literature suggests that the levels and activities of EMT inducers and markers can be used to predict prognosis, and that targeting EMT in addition to conventional therapies may increase treatment success in acute leukemias.

Targeting integrins in drug-resistant acute myeloid leukaemia

Acute myeloid leukaemia (AML) continues to have a poor prognosis, warranting new therapeutic strategies. The bone marrow (BM) microenvironment consists of niches that interact with not only normal haematopoietic stem cells (HSC) but also leukaemia cells like AML. There are many adhesion molecules in the BM microenvironment; therein, integrins have been of central interest. AML cells express integrins that bind to ligands in the microenvironment, enabling adhesion of leukaemia cells in the microenvironment, thereby initiating intracellular signalling pathways that are associated with cell migration, cell proliferation, survival, and drug resistance that has been described to mediate cell adhesion-mediated drug resistance (CAM-DR). Identifying and targeting integrins in AML to interrupt interactions with the microenvironment have been pursued as a strategy to overcome CAM-DR. Here, we focus on the BM microenvironment and review the role of integrins in CAM-DR of AML and discuss integrin-targeting strategies. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

Leaf Extract from European Olive (Olea europaea L.) Post-Transcriptionally Suppresses the Epithelial-Mesenchymal Transition and Sensitizes Gastric Cancer Cells to Chemotherapy

The overall survival of patients with the advanced and recurrent gastric cancer (GC) remains unfavorable. In particular, this is due to cancer spreading and resistance to chemotherapy associated with the epithelial-mesenchymal transition (EMT) of tumor cells. EMT can be identified by the transcriptome profiling of GC for EMT markers. Indeed, analysis of the TCGA and GTEx databases (n = 408) and a cohort of GC patients (n = 43) revealed that expression of the CDH2 gene was significantly decreased in the tumors vs. non-tumor tissues and correlated with the overall survival of GC patients. Expression of the EMT-promoting transcription factors SNAIL and ZEB1 was significantly increased in GC. These data suggest that targeting the EMT might be an attractive therapeutic approach for patients with GC. Previously, we demonstrated a potent anti-cancer activity of the olive leaf extract (OLE). However, its effect on the EMT regulation in GC remained unknown. Here, we showed that OLE efficiently potentiated the inhibitory effect of the chemotherapeutic agents 5-fluorouracil (5-FU) and cisplatin (Cis) on the EMT and their pro-apoptotic activity, as was demonstrated by changes in the expression of the EMT markers (E- and N-cadherins, vimentin, claudin-1) in GC cells treated with the aforementioned chemotherapeutic agents in the presence of OLE. Thus, culturing GC cells with 5-FU + OLE or Cis + OLE attenuated the invasive properties of cancer cells. Importantly, upregulation of expression of the apoptotic markers (PARP cleaved form) and increase in the number of cells undergoing apoptosis (annexin V-positive) were observed for GC cells treated with a combination of OLE and 5-FU or Cis. Collectively, our data illustrate that OLE efficiently interferes with the EMT in GC cells and potentiates the pro-apoptotic activity of certain chemotherapeutic agents used for GC therapy.

The interactions between DNA methylation machinery and long non-coding RNAs in tumor progression and drug resistance

DNA methylation is one of the main epigenetic mechanisms in cancer development and progression. Aberrant DNA methylation of CpG islands within promoter regions contributes to the dysregulation of various tumor suppressors and oncogenes; this leads to the appearance of malignant features, including rapid proliferation, metastasis, stemness, and drug resistance. The discovery of two important protein families, DNA methyltransferases (DNMTs) and Ten-eleven translocation (TET) dioxygenases, respectively, which are responsible for deregulated transcription of genes that play pivotal roles in tumorigenesis, led to further understanding of DNA methylation-related pathways. But how these enzymes can target specific genes in different malignancies; recent studies have highlighted the considerable role of Long Non-coding RNAs (LncRNAs). LncRNAs recruit these enzymes to promoter regions of genes and mediate their functions, showing great potential as therapeutic agents targeting the epigenetic regulation of various genes. Considering the importance of combining the current treatment methods, especially chemotherapies, with DNA methylation inhibitors in improving patients' outcomes, this review aimed to summarize the recent findings about the interaction between DNA methylation machinery and LncRNAs in regulating genes involved in tumorigenesis and drug resistance. So, these studies could provide insights toward developing novel strategies for cancer-targeted therapy.

Selective Concurrence of the Long Non-Coding RNA MALAT1 and the Polycomb Repressive Complex 2 to Promoter Regions of Active Genes in MCF7 Breast Cancer Cells

In cancer cells, the long non-coding RNA (lncRNA) MALAT1 has arisen as a key partner for the Polycomb Repressive Complex 2 (PRC2), an epigenetic modifier. However, it is unknown whether this partnership occurs genome-wide at the chromatin level, as most of the studies focus on single genes that are usually repressed. Due to the genomic binding properties of both macromolecules, we wondered whether there are binding sites shared by PRC2 and MALAT1. Using public genome-binding datasets for PRC2 and MALAT1 derived from independent ChIP- and CHART-seq experiments performed with the breast cancer cell line MCF7, we searched for regions containing PRC2 and MALAT1 overlapping peaks. Peak calls for each molecule were performed using MACS2 and then overlapping peaks were identified by bedtools intersect. Using this approach, we identified 1293 genomic sites where PRC2 and MALAT1 concur. Interestingly, 54.75% of those sites are within gene promoter regions (<3000 bases from the TSS). These analyses were also linked with the transcription profiles of MCF7 cells, obtained from public RNA-seq data. Hence, it is suggested that MALAT1 and PRC2 can concomitantly bind to promoters of actively-transcribed genes in MCF7 cells. Gene ontology analyses revealed an enrichment of genes related to categories including cancer malignancy and epigenetic regulation. Thus, by re-visiting occupancy and transcriptomic data, we identified a key gene subset controlled by the collaboration of MALAT1 and PRC2.