From junk to master regulators of invasion: lncRNA functions in migration, EMT and metastasis

The Potential for Circulating Tumor Cells in Pancreatic Cancer Management

Pancreatic cancer is one the most lethal malignancies. Only a small proportion of patients with this disease benefit from surgery. Chemotherapy provides only a transient benefit. Though much effort has gone into finding new ways for early diagnosis and treatment, average patient survival has only been improved in the order of months. Circulating tumor cells (CTCs) are shed from primary tumors, including pre-malignant phases. These cells possess information about the genomic characteristics of their tumor source in situ, and their detection and characterization holds potential in early cancer diagnosis, prognosis, and treatment. Liquid Biopsies present an alternative to tumor biopsy that are hard to sample. Below we summarize current methods of CTC detection, the current literature on CTCs in pancreatic cancer, and future perspectives.

SPRY4-IT1: A novel oncogenic long non-coding RNA in human cancers

Long non-coding RNAs are classified as a kind of RNA, which are longer than 200 nucleotides in length and cannot be translated into proteins. Multiple studies have demonstrated that long non-coding RNAs are involved in various cellular processes, including proliferation, differentiation, cell death, and metastasis. Among numerous long non-coding RNAs, we focus on Sprouty4-Intron 1 (SPRY4-IT1), a well-known long non-coding RNA that is overexpressed in various kinds of tumor tissues and cell lines. Accumulating evidences show that SPRY4-IT1 was dysregulated in various cancers, including melanoma, breast cancer, esophageal squamous cell carcinoma, non-small cell lung cancer, gastric cancer, colon cancer, and hepatocellular carcinoma, and amplification of SPRY4-IT1 was associated with different clinicopathological features of cancer patients. Importantly, SPRY4-IT1 exerts important roles in tumor progression and metastasis. However, detailed molecular mechanisms of SPRY4-IT1 in cancer progression and metastasis were poorly understood. In this review, we have focused on the characteristics of SPRY4-IT1 and illustrated the biological function and mechanism of SPRY4-IT1 in cancer development.

Transposable Elements in Human Cancer: Causes and Consequences of Deregulation

Transposable elements (TEs) comprise nearly half of the human genome and play an essential role in the maintenance of genomic stability, chromosomal architecture, and transcriptional regulation. TEs are repetitive sequences consisting of RNA transposons, DNA transposons, and endogenous retroviruses that can invade the human genome with a substantial contribution in human evolution and genomic diversity. TEs are therefore firmly regulated from early embryonic development and during the entire course of human life by epigenetic mechanisms, in particular DNA methylation and histone modifications. The deregulation of TEs has been reported in some developmental diseases, as well as for different types of human cancers. To date, the role of TEs, the mechanisms underlying TE reactivation, and the interplay with DNA methylation in human cancers remain largely unexplained. We reviewed the loss of epigenetic regulation and subsequent genomic instability, chromosomal aberrations, transcriptional deregulation, oncogenic activation, and aberrations of non-coding RNAs as the potential mechanisms underlying TE deregulation in human cancers.

Absence of Malat1 does not prevent DEN-induced hepatocarcinoma in mice

Long non-coding RNAs (lncRNA) are key regulators of gene expression both at the transcriptional and post-transcriptional levels. The lncRNA metastasis associated lung adenocarcinoma transcript 1 (Malat1) is overexpressed in many types of cancer, including hepatocarcinoma, and induces cell proliferation in several cell lines in vitro. However, the direct causal effects of Malat1 on hepatocyte proliferation and liver carcinogenesis in vivo are not fully understood. To better determine the contribution of Malat1 to hepatocarcinoma oncogenesis, this study was aimed at testing the hypothesis that its absence confers resistance to the development of liver tumors. Male Malat1-/- mice and their wild-type (WT) littermates were studied one year after treatment with the genotoxic agent diethylnitrosamine (DEN), a potent inducer of liver cancer. As expected, in WT mice, Malat1 expression was significantly higher in hepatic tumors than in healthy liver regions. Altered hepatic mRNA levels of Ki67, HDAC3, NFκB and p27 were observed in DEN-treated Malat1-/- mice. Despite this, these mice were characterized by similar liver weight, prevalence of tumors, and histological features compared to those of their WT littermates. In parallel, plasma lipids and glucose homeostasis did not significantly differ between DEN-treated groups. These findings support a role for Malat1 as a marker of liver carcinogenesis, but also suggest that its role in the regulation of hepatocyte hyperproliferation in mice is either minimal or masked by redundant and/or overwhelming mechanisms.

AlncRNA HULC as an effective biomarker for surveillance of the outcome of cancer: A meta-analysis

PURPOSE

High expression of highly upregulated in iver cancer (HULC) has been found associated with increased metastasis and poor prognosis with cancer. This meta-analysis aimed to determine the pooled effect of HULC on metastasis and prognosis of cancers.

METHOD

The studies were accessed using multiple databases. RevMan5.3 and STATA14.0 were used to estimate pooled effects, the heterogeneity among studies, and publication bias for the association of HULC and overall survival (OS).

RESULTS

A total of 9 studies of 966 cancer patients were included. Risk of lymph node metastasis was increased with high versus low HULC expression (pooled odds ratio [OR] = 4.83, 95% confidence interval [CI] 1.59-14.63) as was distant metastasis (pooled OR = 5.44, 95% CI 2.33-12.74). Furthermore, OS time was shortened with high HULC expression (pooled hazard ratio [HR] = 1.48, 95% CI 1.03-2.12), especially in Chinese patients (pooled HR = 2.04, 95% CI 1.55-2.68), and risk of recurrence was increased (pooled OR = 6.68, 95% CI 2.77-16.13).

CONCLUSION

HULC might be a potential biomarker for therapy and prognosis surveillance in cancers.

Induction of metastasis, cancer stem cell phenotype, and oncogenic metabolism in cancer cells by ionizing radiation

Radiation therapy is one of the major tools of cancer treatment, and is widely used for a variety of malignant tumours. Radiotherapy causes DNA damage directly by ionization or indirectly via the generation of reactive oxygen species (ROS), thereby destroying cancer cells. However, ionizing radiation (IR) paradoxically promotes metastasis and invasion of cancer cells by inducing the epithelial-mesenchymal transition (EMT). Metastasis is a major obstacle to successful cancer therapy, and is closely linked to the rates of morbidity and mortality of many cancers. ROS have been shown to play important roles in mediating the biological effects of IR. ROS have been implicated in IR-induced EMT, via activation of several EMT transcription factors—including Snail, HIF-1, ZEB1, and STAT3—that are activated by signalling pathways, including those of TGF-β, Wnt, Hedgehog, Notch, G-CSF, EGFR/PI3K/Akt, and MAPK. Cancer cells that undergo EMT have been shown to acquire stemness and undergo metabolic changes, although these points are debated. IR is known to induce cancer stem cell (CSC) properties, including dedifferentiation and self-renewal, and to promote oncogenic metabolism by activating these EMT-inducing pathways. Much accumulated evidence has shown that metabolic alterations in cancer cells are closely associated with the EMT and CSC phenotypes; specifically, the IR-induced oncogenic metabolism seems to be required for acquisition of the EMT and CSC phenotypes. IR can also elicit various changes in the tumour microenvironment (TME) that may affect invasion and metastasis. EMT, CSC, and oncogenic metabolism are involved in radioresistance; targeting them may improve the efficacy of radiotherapy, preventing tumour recurrence and metastasis. This study focuses on the molecular mechanisms of IR-induced EMT, CSCs, oncogenic metabolism, and alterations in the TME. We discuss how IR-induced EMT/CSC/oncogenic metabolism may promote resistance to radiotherapy; we also review efforts to develop therapeutic approaches to eliminate these IR-induced adverse effects.

Molecular Mechanisms and Metabolomics of Natural Polyphenols Interfering with Breast Cancer Metastasis

Metastatic cancers are the main cause of cancer-related death. In breast primary cancer, the five-year survival rate is close to 100%; however, for metastatic breast cancer, that rate drops to a mere 25%, due in part to the paucity of effective therapeutic options for treating metastases. Several in vitro and in vivo studies have indicated that consumption of natural polyphenols significantly reduces the risk of cancer metastasis. Therefore, this review summarizes the research findings involving the molecular mechanisms and metabolomics of natural polyphenols and how they may be blocking breast cancer metastasis. Most natural polyphenols are thought to impair breast cancer metastasis through downregulation of MMPs expression, interference with the VEGF signaling pathway, modulation of EMT regulator, inhibition of NF-κB and mTOR expression, and other related mechanisms. Intake of natural polyphenols has been shown to impact endogenous metabolites and complex biological metabolic pathways in vivo. Breast cancer metastasis is a complicated process in which each step is modulated by a complex network of signaling pathways. We hope that by detailing the reported interactions between breast cancer metastasis and natural polyphenols, more attention will be directed to these promising candidates as effective adjunct therapies against metastatic breast cancer in the clinic.

Epigenetic regulation of epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is an essential process for morphogenesis and organ development which reversibly enables polarized epithelial cells to lose their epithelial characteristics and to acquire mesenchymal properties. It is now evident that the aberrant activation of EMT is also a critical mechanism to endow epithelial cancer cells with migratory and invasive capabilities associated with metastatic competence. This dedifferentiation program is mediated by a small cohort of pleiotropic transcription factors which orchestrate a complex array of epigenetic mechanisms for the wide-spread changes in gene expression. Here, we review major epigenetic mechanisms with an emphasis on histone modifications and discuss their implications in EMT and tumor progression. We also highlight mechanisms underlying transcription regulation concerted by various chromatin-modifying proteins and EMT-inducing transcription factors at different molecular layers. Owing to the reversible nature of epigenetic modifications, a thorough understanding of their functions in EMT will not only provide new insights into our knowledge of cancer progression and metastasis, but also facilitate the development of diagnostic and therapeutic strategies for human malignancy.

Long non-coding RNA FOXP4-AS1 is an unfavourable prognostic factor and regulates proliferation and apoptosis in colorectal cancer

OBJECTIVES

Despite improvements in diagnosis and treatment, colorectal cancer (CRC) remains the third most common malignancy, and fourth-leading cause of cancer-related death worldwide, and has a particularly high incidence in Western countries. Recent studies have suggested that long non-coding RNAs (lncRNAs) compose a novel class of regulators of cancer biological processes, such as proliferation, apoptosis and metastasis. Here, we report that lncRNA FOXP4-AS1 acts as a functional oncogene in CRC pathogenesis. Moreover, we have attempted to investigate the effects of FOXP4-AS1 on tumour progression, both in vitro and in vivo.

MATERIALS AND METHODS

In this study, bioinformatic analyses and qPCR were performed to investigate FOXP4-AS1 expression in CRC tissue samples and CRC cell lines. We inhibited FOXP4-AS1 expression via FOXP4-AS1-specific siRNA transfection. Cell proliferation was assessed using cell viability and colony formation assays, as well as by flow cytometry and ethynyl deoxyuridine (Edu) analyses. Apoptosis was assessed using flow cytometry. Animal tumour xenografts were generated, and immunohistochemistry (IHC) was performed to evaluate effects of FOXP4-AS1 on CRC tumour growth in vivo.

RESULTS

We found that FOXP4-AS1 was up-regulated in CRC tissues and cell lines and that its overexpression positively correlated with advanced pathological stages and larger tumour size. Additionally, we found that FOXP4-AS1 knockdown inhibited cell proliferation and induced apoptosis. Furthermore, FOXP4-AS1 knockdown induced marked increase in number of cells in G0/G1 phase and reduction in number of cells in S phase, in DLD-1, HT-29 and HCT116 cell lines. Consistent with these findings, FOXP4-AS1 silencing inhibited tumour growth in vivo.

CONCLUSION

These findings suggest that FOXP4-AS1 plays a crucial role in CRC progression and may be a new biomarker in patients with CRC.

The emerging role of long noncoding RNAs in oral cancer

Although less than 3% of the genome encodes proteins, at least 75% of the genome is transcribed into RNAs with no protein-coding potential (noncoding RNAs [ncRNAs]). On the basis of their size and the arbitrary 200 nucleotides cutoff, ncRNAs are classified into long ncRNAs (lncRNAs) or small ncRNAs (including microRNAs). Over the last few years, the role of microRNAs in oral squamous cells carcinoma (OSCC) has been extensively addressed, but the possible role of lncRNAs in OSCC remains unclear. We aimed to explore and discuss the potential role of lncRNAs in OSCC. The detection of lncRNAs in saliva holds promise not only as a noninvasive diagnostic tool in OSCC but also in the early detection of oral cancer recurrence. lncRNAs are promising future therapeutic targets in the OSCC scenario, and research in this field may expand greatly in the next decade.

Long non-coding RNA TUG1 contributes to tumorigenesis of human osteosarcoma by sponging miR-9-5p and regulating POU2F1 expression

Recent studies have shown that long non-coding RNAs (lncRNAs) have critical roles in tumorigenesis, including osteosarcoma. The lncRNA taurine-upregulated gene 1 (TUG1) was reported to be involved in the progression of osteosarcoma. Here, we investigated the role of TUG1 in osteosarcoma cells and the underlying mechanism. TUG1 expression was measured in osteosarcoma cell lines and human normal osteoblast cells by quantitative real-time PCR (qRT-PCR). The effects of TUG1 on osteosarcoma cells were studied by RNA interference in vitro and in vivo. The mechanism of competing endogenous RNA (ceRNA) was determined using bioinformatic analysis and luciferase assays. Our data showed that TUG1 knockdown inhibited cell proliferation and colony formation, and induced G0/G1 cell cycle arrest and apoptosis in vitro, and suppressed tumor growth in vivo. Besides, we found that TUG1 acted as an endogenous sponge to directly bind to miR-9-5p and downregulated miR-9-5p expression. Moreover, TUG1 overturned the effect of miR-9-5p on the proliferation, colony formation, cell cycle arrest, and apoptosis in osteosarcoma cells, which involved the derepression of POU class 2 homeobox 1 (POU2F1) expression. In conclusion, our study elucidated a novel TUG1/miR-9-5p/POU2F1 pathway, in which TUG1 acted as a ceRNA by sponging miR-9-5p, leading to downregulation of POU2F1 and facilitating the tumorigenesis of osteosarcoma. These findings may contribute to the lncRNA-targeted therapy for human osteosarcoma.

Gastric cancer pathogenesis

Gastric cancer (GC) results from a multistep process that is influenced by Helicobacter pylori infection, genetic susceptibility of the host, as well as of other environmental factors. GC results from the accumulation of numerous genetic and epigenetic alterations in oncogenes and tumor suppressor genes, leading to dysregulation of multiple signaling pathways, which disrupt the cell cycle and the balance between cell proliferation and cell death. For this special issue, we have selected to review last year's advances related to three main topics: the cell of origin that initiates malignant growth in GC, the mechanisms of direct genotoxicity induced by H. pylori infection, and the role of aberrantly expressed long noncoding RNAs in GC transformation. The understanding of the molecular basis of GC development is of utmost importance for the identification of novel targets for GC prevention and treatment.