miRNome Reveals New Insights Into the Molecular Biology of Field Cancerization in Gastric Cancer

Chromatin and noncoding RNA-mediated mechanisms of gastric tumorigenesis

Gastric cancer (GC) is one of the most common and deadly cancers in the world. It is a multifactorial disease highly influenced by environmental factors, which include radiation, smoking, diet, and infectious pathogens. Accumulating evidence suggests that epigenetic regulators are frequently altered in GC, playing critical roles in gastric tumorigenesis. Epigenetic regulation involves DNA methylation, histone modification, and noncoding RNAs. While it is known that environmental factors cause widespread alterations in DNA methylation, promoting carcinogenesis, the chromatin- and noncoding RNA-mediated mechanisms of gastric tumorigenesis are still poorly understood. In this review, we focus on discussing recent discoveries addressing the roles of histone modifiers and noncoding RNAs and the mechanisms of their interactions in gastric tumorigenesis. A better understanding of epigenetic regulation would likely facilitate the development of novel therapeutic approaches targeting specific epigenetic regulators in GC.

Treasures from trash in cancer research

INTRODUCTION

Cancer research has significantly improved in recent years, primarily due to next-generation sequencing (NGS) technology. Consequently, an enormous amount of genomic and transcriptomic data has been generated. In most cases, the data needed for research goals are used, and unwanted reads are discarded. However, these eliminated data contain relevant information. Aiming to test this hypothesis, genomic and transcriptomic data were acquired from public datasets.

MATERIALS AND METHODS

Metagenomic tools were used to explore genomic cancer data; additional annotations were used to explore differentially expressed ncRNAs from miRNA experiments, and variants in adjacent to tumor samples from RNA-seq experiments were also investigated.

RESULTS

In all analyses, new data were obtained: from DNA-seq data, microbiome taxonomies were characterized with a similar performance of dedicated metagenomic research; from miRNA-seq data, additional differentially expressed sncRNAs were found; and in tumor and adjacent to tumor tissue data, somatic variants were found.

CONCLUSIONS

These findings indicate that unexplored data from NGS experiments could help elucidate carcinogenesis and discover putative biomarkers with clinical applications. Further investigations should be considered for experimental design, providing opportunities to optimize data, saving time and resources while granting access to multiple genomic perspectives from the same sample and experimental run.

Atrophic gastritis and gastric cancer tissue miRNome analysis reveals hsa-miR-129-1 and hsa-miR-196a as potential early diagnostic biomarkers

BACKGROUND

Gastric cancer (GC) is one of the most frequently diagnosed tumor globally. In most cases, GC develops in a stepwise manner from chronic gastritis or atrophic gastritis (AG) to cancer. One of the major issues in clinical settings of GC is diagnosis at advanced disease stages resulting in poor prognosis. MicroRNAs (miRNAs) are small noncoding molecules that play an essential role in a variety of fundamental biological processes. However, clinical potential of miRNA profiling in the gastric cancerogenesis, especially in premalignant GC cases, remains unclear.

AIM

To evaluate the AG and GC tissue miRNomes and identify specific miRNAs’ potential for clinical applications (e.g., non-invasive diagnostics).

METHODS

Study included a total of 125 subjects: Controls (CON), AG, and GC patients. All study subjects were recruited at the Departments of Surgery or Gastroenterology, Hospital of Lithuanian University of Health Sciences and divided into the profiling (n = 60) and validation (n = 65) cohorts. Total RNA isolated from tissue samples was used for preparation of small RNA sequencing libraries and profiled using next-generation sequencing (NGS). Based on NGS data, deregulated miRNAs hsa-miR-129-1-3p and hsa-miR-196a-5p were analyzed in plasma samples of independent cohort consisting of CON, AG, and GC patients. Expression level of hsa-miR-129-1-3p and hsa-miR-196a-5p was determined using the quantitative real-time polymerase chain reaction and 2^-ΔΔCt method.

RESULTS

Results of tissue analysis revealed 20 differentially expressed miRNAs in AG group compared to CON group, 129 deregulated miRNAs in GC compared to CON, and 99 altered miRNAs comparing GC and AG groups. Only 2 miRNAs (hsa-miR-129-1-3p and hsa-miR-196a-5p) were identified to be step-wise deregulated in healthy-premalignant-malignant sequence. Area under the curve (AUC)-receiver operating characteristic analysis revealed that expression level of hsa-miR-196a-5p is significant for discrimination of CON vs AG, CON vs GC and AG vs GC and resulted in AUCs: 88.0%, 93.1% and 66.3%, respectively. Compar-ing results in tissue and plasma samples, hsa-miR-129-1-3p was significantly down-regulated in GC compared to AG (P = 0.0021 and P = 0.024, tissue and plasma, respectively). Moreover, analysis revealed that hsa-miR-215-3p/5p and hsa-miR-934 were significantly deregulated in GC based on Helicobacter pylori (H. pylori) infection status [log2 fold change (FC) = -4.52, P-adjusted = 0.02; log2FC = -4.00, P-adjusted = 0.02; log2FC = 6.09, P-adjusted = 0.02, respectively].

CONCLUSION

Comprehensive miRNome study provides evidence for gradual deregulation of hsa-miR-196a-5p and hsa-miR-129-1-3p in gastric carcinogenesis and found hsa-miR-215-3p/5p and hsa-miR-934 to be significantly deregulated in H. pylori carrying GC patients.

CircRNAs as Potential Blood Biomarkers and Key Elements in Regulatory Networks in Gastric Cancer

Gastric cancer (GC) is the fifth most common type of cancer and the third leading cause of cancer death in the world. It is a disease that encompasses a variety of molecular alterations, including in non-coding RNAs such as circular RNAs (circRNAs). In the present study, we investigated hsa_circ_0000211, hsa_circ_0000284, hsa_circ_0000524, hsa_circ_0001136 and hsa_circ_0004771 expression profiles using RT-qPCR in 71 gastric tissue samples from GC patients (tumor and tumor-adjacent samples) and volunteers without cancer. In order to investigate the suitability of circRNAs as minimally invasive biomarkers, we also evaluated their expression profile through RT-qPCR in peripheral blood samples from patients with and without GC (n = 41). We also investigated the predicted interactions between circRNA-miRNA-mRNA and circRNA-RBP using the KEGG and Reactome databases. Overall, our results showed that hsa_circ_0000211, hsa_circ_0000284 and hsa_circ_0004771 presented equivalent expression profiles when analyzed by different methods (RNA-Seq and RT-qPCR) and different types of samples (tissue and blood). Further, functional enrichment results identified important signaling pathways related to GC. Thus, our data support the consideration of circRNAs as new, minimally invasive biomarkers capable of aiding in the diagnosis of GC and with great potential to be applied in clinical practice.

MiR-873-5p: A Potential Molecular Marker for Cancer Diagnosis and Prognosis

miR-873 is a microRNA located on chromosome 9p21.1. miR-873-5p and miR-873-3p are the two main members of the miR-873 family. Most studies focus on miR-873-5p, and there are a few studies on miR-873-3p. The expression level of miR-873-5p was down-regulated in 14 cancers and up-regulated in 4 cancers. miR-873-5p has many targeted genes, which have unique molecular functions such as catalytic activity, transcription regulation, and binding. miR-873-5p affects cancer development through the PIK3/AKT/mTOR, Wnt/β-Catenin, NF-κβ, and MEK/ERK signaling pathways. In addition, the target genes of miR-873-5p are closely related to the proliferation, apoptosis, migration, invasion, cell cycle, cell stemness, and glycolysis of cancer cells. The target genes of miR-873-5p are also related to the efficacy of several anti-cancer drugs. Currently, in cancer, the expression of miR-873-5p is regulated by a variety of epigenetic factors. This review summarizes the role and mechanism of miR-873-5p in human tumors shows the potential value of miR-873-5p as a molecular marker for cancer diagnosis and prognosis.

Geospatial Assessments of DNA Adducts in the Human Stomach: A Model of Field Cancerization

BACKGROUND

Field cancerization is a popular concept regarding where cancer cells arise in a plane, such as the opened-up gastrointestinal mucosa. The geospatial distribution of DNA adducts, some of which are believed to initiate mutation, may be a clue to understanding the landscape of the preferred occurrence of gastric cancer in the human stomach, such that the occurrence is much more frequent in the lesser curvature than in the greater curvature.

METHODS

Seven DNA adducts, C5-methyl-2'-deoxycytidine, 2'-deoxyinosine, C5-hydroxymethyl-2'-deoxycytidine, N6-methyl-2'-deoxyadenosine, 1,N6-etheno-2'-deoxyadenosine, N6-hydroxymethyl-2'-deoxyadenosine, and C8-oxo-2'-deoxyguanosine, from different points and zones of the human stomach were semi quantitatively measured by liquid chromatography/tandem mass spectrometry. The differences in the quantity of these DNA adducts from the lesser and greater curvature, the upper, middle and lower third zones, the anterior and posterior wall of the stomach, and the mucosae distant from and near the tumor were compared to determine whether the location preference of cancer in the stomach could be explained by the distribution of these DNA adducts. Comparisons were conducted considering the tumor locations and operation methods.

CONCLUSIONS

Regarding the DNA adducts investigated, significant differences in quantities and locations in the whole stomach were not noted; thus, these DNA adducts do not explain the preferential occurrence of cancer in particular locations of the human stomach.

Altered microRNA Transcriptome in Cultured Human Liver Cells upon Infection with Ebola Virus

Ebola virus (EBOV) is a virulent pathogen, notorious for inducing life-threatening hemorrhagic fever, that has been responsible for several outbreaks in Africa and remains a public health threat. Yet, its pathogenesis is still not completely understood. Although there have been numerous studies on host transcriptional response to EBOV, with an emphasis on the clinical features, the impact of EBOV infection on post-transcriptional regulatory elements, such as microRNAs (miRNAs), remains largely unexplored. MiRNAs are involved in inflammation and immunity and are believed to be important modulators of the host response to viral infection. Here, we have used small RNA sequencing (sRNA-Seq), qPCR and functional analyses to obtain the first comparative miRNA transcriptome (miRNome) of a human liver cell line (Huh7) infected with one of the following three EBOV strains: Mayinga (responsible for the first Zaire outbreak in 1976), Makona (responsible for the West Africa outbreak in 2013–2016) and the epizootic Reston (presumably innocuous to humans). Our results highlight specific miRNA-based immunity pathways and substantial differences between the strains beyond their clinical manifestation and pathogenicity. These analyses shed new light into the molecular signature of liver cells upon EBOV infection and reveal new insights into miRNA-based virus attack and host defense strategy.

Gastric Cancer Microbiome

Identifying a microbiome pattern in gastric cancer (GC) is hugely debatable due to the variation resulting from the diversity of the studied populations, clinical scenarios, and metagenomic approach. H. pylori remains the main microorganism impacting gastric carcinogenesis and seems necessary for the initial steps of the process. Nevertheless, an additional non-H. pylori microbiome pattern is also described, mainly at the final steps of the carcinogenesis. Unfortunately, most of the presented results are not reproducible, and there are no consensual candidates to share the H. pylori protagonists. Limitations to reach a consistent interpretation of metagenomic data include contamination along every step of the process, which might cause relevant misinterpretations. In addition, the functional consequences of an altered microbiome might be addressed. Aiming to minimize methodological bias and limitations due to small sample size and the lack of standardization of bioinformatics assessment and interpretation, we carried out a comprehensive analysis of the publicly available metagenomic data from various conditions relevant to gastric carcinogenesis. Mainly, instead of just analyzing the results of each available publication, a new approach was launched, allowing the comprehensive analysis of the total sample amount, aiming to produce a reliable interpretation due to using a significant number of samples, from different origins, in a standard protocol. Among the main results, Helicobacter and Prevotella figured in the "top 6" genera of every group. Helicobacter was the first one in chronic gastritis (CG), gastric cancer (GC), and adjacent (ADJ) groups, while Prevotella was the leader among healthy control (HC) samples. Groups of bacteria are differently abundant in each clinical situation, and bacterial metabolic pathways also diverge along the carcinogenesis cascade. This information may support future microbiome interventions aiming to face the carcinogenesis process and/or reduce GC risk.

Role of miRNAs in Sigmoid Colon Cancer: A Search for Potential Biomarkers

The aberrant expression of microRNAs in known to play a crucial role in carcinogenesis. Here, we evaluated the miRNA expression profile of sigmoid colon cancer (SCC) compared to adjacent-to-tumor (ADJ) and sigmoid colon healthy (SCH) tissues obtained from colon biopsy extracted from Brazilian patients. Comparisons were performed between each group separately, considering as significant p-values < 0.05 and |Log2(Fold-Change)| > 2. We found 20 differentially expressed miRNAs (DEmiRNAs) in all comparisons, two of which were shared between SCC vs. ADJ and SCC vs. SCH. We used miRTarBase, and miRTargetLink to identify target-genes of the differentially expressed miRNAs, and DAVID and REACTOME databases for gene enrichment analysis. We also used TCGA and GTEx databases to build miRNA-gene regulatory networks and check for the reproducibility in our results. As findings, in addition to previously known miRNAs associated with colorectal cancer, we identified three potential novel biomarkers. We showed that the three types of colon tissue could be clearly distinguished using a panel composed by the 20 DEmiRNAs. Additionally, we found enriched pathways related to the carcinogenic process in which miRNA could be involved, indicating that adjacent-to-tumor tissues may be already altered and cannot be considered as healthy tissues. Overall, we expect that these findings may help in the search for biomarkers to prevent cancer progression or, at least, allow its early detection, however, more studies are needed to confirm our results.

Vidal A, Pinto P, Ribeiro-dos-Santos AM, Cruz RLS, Fonseca Cabral G, Anaissi AKM, Lopes KDP, Ribeiro-dos-Santos A, Demachki S, de Assumpção PP, Ribeiro-dos-Santos Â, Santos S. Global Analyses of Expressed Piwi-Interacting RNAs in Gastric Cancer

Gastric cancer (GC) represents a notable amount of morbidity and mortality worldwide. Understanding the molecular basis of CG will offer insight into its pathogenesis in an attempt to identify new molecular biomarkers to early diagnose this disease. Therefore, studies involving small non-coding RNAs have been widely explored. Among these, PIWI-interacting RNAs (piRNAs) are an emergent class that can play important roles in carcinogenesis. In this study, small-RNA sequencing was used to identify the global piRNAs expression profile (piRNome) of gastric cancer patients. We found 698 piRNAs in gastric tissues, 14 of which were differentially expressed (DE) between gastric cancer (GC), adjacent to gastric cancer (ADJ), and non-cancer tissues (NC). Moreover, three of these DE piRNAs (piR-48966*, piR-49145, piR-31335*) were differently expressed in both GC and ADJ samples in comparison to NC samples, indicating that the tumor-adjacent tissue was molecularly altered and should not be considered as a normal control. These three piRNAs are potential risk biomarkers for GC, especially piR-48966* and piR-31335*. Furthermore, an in-silico search for mRNAs targeted by the differentially expressed piRNAs revealed that these piRNAs may regulate genes that participate in cancer-related pathways, suggesting that these small non-coding RNAs may be directly and indirectly involved in gastric carcinogenesis.

MicroRNA-936/ERBB4/Akt axis exhibits anticancer properties of gastric cancer through inhibition of cell proliferation, migration, and invasion

Gastric cancer is one of the most common cancers globally and has a poor prognosis. MiR-936 has been reported to regulate cell activity and tumor progression in non-small cell lung cancer, glioma, and epithelial ovarian cancer. However, the specific role and mechanism of miR-936 in gastric cancer have not been explored. In present study, gastric cancer cells were transfected with miR-936 mimic, and cell proliferation, cell cycle distribution, cell apoptosis, migration and invasion were assessed via cell-counting kit-8, flow cytometry, wound healing, and transwell assay, respectively. Dual luciferase reporter assay was used to check miR-936 binding to its downstream target. It was shown that miR-936 was downregulated in gastric cancer tissues and cells. Erb-B2 Receptor Tyrosine Kinase 4 (ERBB4) was confirmed as a direct target of miR-936 and negatively regulated its expression by miR-936. Overexpression of miR-936 suppressed cell proliferation, cell cycle progression, cell migration and invasion, and enhanced cell apoptosis in gastric cancer cells, which could be reversed by further ERBB4 overexpression. Western blot results showed that miR-936/ERBB4 axis regulated Akt-related pathways to control gastric cancer cell activities. Therefore, our data suggest that miR-936 overexpression inhibits cell proliferation and invasion and promotes cell apoptosis through Akt-related pathways by targeting ERBB4, which provides novel insight to target miR-936 or miR-936/ERBB4 axis for the treatment of gastric cancer.

The Biological Role of Sponge Circular RNAs in Gastric Cancer: Main Players or Coadjuvants?

Circular RNAs (circRNAs) are a new class of long noncoding RNAs able to perform multiple functions, including sponging microRNAs (miRNAs) and RNA-Binding Proteins (RBPs). They play an important role in gastric carcinogenesis, but its involvement during gastric cancer (GC) development and progression are not well understood. We gathered miRNA and/or RBPs sponge circRNAs present in GC, and accessed their biological roles through functional enrichment of their target genes or ligand RBPs. We identified 54 sponge circRNAs in GC that are able to sponge 51 miRNAs and 103 RBPs. Then, we evaluated their host gene expression using The Cancer Genome Atlas (TCGA) database and observed that COL1A2 is the most overexpressed gene, which may be due to circHIPK3/miR-29b-c/COL1A2 axis dysregulation. We identified 27 GC-related pathways that may be affected mainly by circPVT1, circHIPK3 and circNF1. Our results indicate that circHIPK3/miR-107/BDNF/LIN28 axis may mediate chemoresistance in GC, and that circPVT1, circHIPK3, circNF1, ciRS-7 and circ_0000096 appear to be involved in gastrointestinal cancer development. Lastly, circHIPK3, circNRIP1 and circSMARCA5 were identified in different ethnic populations and may be ubiquitous modulators of gastric carcinogenesis. Overall, the studied sponge circRNAs are part of a complex RBP-circRNA-miRNA-mRNA interaction network, and are involved in the establishment, chemoresistance and progression of GC.

Inhibition of Splicing Factor 3b Subunit 1 (SF3B1) Reduced Cell Proliferation, Induced Apoptosis and Resulted in Cell Cycle Arrest by Regulating Homeobox A10 (HOXA10) Splicing in AGS and MKN28 Human Gastric Cancer Cells

Background

Small nuclear ribonucleoproteins (snRNPs) complexes of protein and noncoding RNA accumulate in the cell nucleus and catalyze pre-mRNA splicing to form the spliceosome. This study aimed to investigate the role of the spliceosome, splicing factor 3b subunit 1 (SF3B1), in AGS and MKN28 human gastric cancer cells in vitro, including gene knockdown with small interfering RNA (siRNA), and the use of the selective mRNA splicing inhibitor of SF3B1, pladienolide B.

Material/Methods

In AGS and MKN28 human gastric cancer cells, SF3B1expression was inhibited with siRNA and pladienolide B. Following SF3B1 inhibition, the Cell Counting Kit-8 (CCK-8) assay measured cell proliferation, and flow cytometry was used to investigate cell apoptosis and cell cycle arrest. The downstream HOXA10 and AKT pathways were studied by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. The presence of alternative splicing, or differential splicing, of single-gene coding for multiple proteins, was analyzed using The Cancer Genome Atlas (TCGA) SpliceSeq.

Results

Inhibition of SF3B1 reduced the proliferation rate of AGS and MKN28 human gastric cancer cells by inducing apoptosis and G2/M phase arrest. SF3B1 knockdown resulted in reduced homeobox A10 (HOXA10) mRNA expression and expression of long noncoding RNA (lncRNA) isoforms of HOXA10 (exons 1 and 3) and HOXA10 (exons 2 and 3). SF3B1 inhibition increased PTEN levels and reduced AKT protein phosphorylation.

Conclusions

In AGS and MKN28 human gastric cancer cells in vitro, inhibition of SF3B1 reduced cell proliferation, induced apoptosis, and resulted in cell cycle arrest by regulating HOXA10 splicing.