Fernanda Wisnieski

Epigenetic mechanisms in gastric cancer

Cancer is considered one of the major health issues worldwide, and gastric cancer accounted for 8% of total cases and 10% of total deaths in 2008. Gastric cancer is considered an age-related disease, and the total number of newly diagnosed cases has been increasing as a result of the higher life expectancy. Therefore, the basic mechanisms underlying gastric tumorigenesis is worth investigation. This review provides an overview of the epigenetic mechanisms, such as DNA methylation, histone modifications, chromatin remodeling complex and miRNA, involved in gastric cancer. As the studies in gastric cancer continue, the mapping of an epigenome code is not far for this disease. In conclusion, an epigenetic therapy might appear in the not too distant future.

Reference genes for quantitative RT-PCR data in gastric tissues and cell lines.

AIM To evaluate the suitability of reference genes in gastric tissue samples and cell lines. METHODS The suitability of genes ACTB, B2M, GAPDH, RPL29, and 18S rRNA was assessed in 21 matched pairs of neoplastic and adjacent non-neoplastic gastric tissues from patients with gastric adenocarcinoma, 27 normal gastric tissues from patients without cancer, and 4 cell lines using reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR). The ranking of the best single and combination of reference genes was determined by NormFinder, geNorm™, BestKeeper, and DataAssist™. In addition, GenEx software was used to determine the optimal number of reference genes. To validate the results, the mRNA expression of a target gene, DNMT1, was quantified using the different reference gene combinations suggested by the various software packages for normalization. RESULTS ACTB was the best reference gene for all gastric tissues, cell lines and all gastric tissues plus cell lines. GAPDH + B2M or ACTB + B2M was the best combination of reference genes for all the gastric tissues. On the other hand, ACTB + B2M was the best combination for all the cell lines tested and was also the best combination for analyses involving all the gastric tissues plus cell lines. According to the GenEx software, 2 or 3 genes were the optimal number of references genes for all the gastric tissues. The relative quantification of DNMT1 showed similar patterns when normalized by each combination of reference genes. The level of expression of DNMT1 in neoplastic, adjacent non-neoplastic and normal gastric tissues did not differ when these samples were normalized using GAPDH + B2M (P = 0.32), ACTB + B2M (P = 0.61), or GAPDH + B2M + ACTB (P = 0.44). CONCLUSION GAPDH + B2M or ACTB + B2M is the best combination of reference gene for all the gastric tissues, and ACTB + B2M is the best combination for the cell lines tested.

Role of miRNAs and their potential to be useful as diagnostic and prognostic biomarkers in gastric cancer.

Alterations in epigenetic control of gene expression play an important role in many diseases, including gastric cancer. Many studies have identified a large number of upregulated oncogenic miRNAs and downregulated tumour-suppressor miRNAs in this type of cancer. In this review, we provide an overview of the role of miRNAs, pointing to their potential to be useful as diagnostic and/or prognostic biomarkers in gastric cancer. Moreover, we discuss the influence of polymorphisms and epigenetic modifications on miRNA activity.

Reduced mRNA expression levels of MBD2 and MBD3 in gastric carcinogenesis.

Aberrant methylation has been reported in several neoplasias, including gastric cancer. The methyl-CpG-binding domain (MBD) family proteins have been implicated in the chromatin remodeling process, leading to the modulation of gene expression. To evaluate the role of MBD2 and MBD3 in gastric carcinogenesis and the possible association with clinicopathological characteristics, we assessed the mRNA levels and promoter methylation patterns in gastric tissues. In this study, MBD2 and MBD3 mRNA levels were determined by RT-qPCR in 28 neoplastic and adjacent nonneoplastic and 27 gastritis and non-gastritis samples. The promoter methylation status was determined by bisulfite sequencing, and we found reduced MBD2 and MBD3 levels in the neoplastic samples compared with the other groups. Moreover, a strong correlation between the MBD2 and MBD3 expression levels was observed in each set of paired samples. Our data also showed that the neoplastic tissues exhibited higher MBD2 promoter methylation than the other groups. Interestingly, the non-gastritis group was the only one with positive methylation in the MBD3 promoter region. Furthermore, a weak correlation between gene expression and methylation was observed. Therefore, our data suggest that DNA methylation plays a minor role in the regulation of MBD2 and MBD3 expression, and the presence of methylation at CpGs that interact with transcription factor complexes might also be involved in the modulation of these genes. Moreover, reduced mRNA expression of MBD2 and MBD3 is implicated in gastric carcinogenesis, and thus, further investigations about these genes should be conducted for a better understanding of the role of abnormal methylation involved in this neoplasia.

Differential expression of histone deacetylase and acetyltransferase genes in gastric cancer and their modulation by trichostatin A

Gastric cancer is still the second leading cause of cancer-related death worldwide, even though its incidence and mortality have declined over the recent few decades. Epigenetic control using histone deacetylase inhibitors, such as trichostatin A (TSA), is a promising cancer therapy. This study aimed to assess the messenger RNA (mRNA) levels of three histone deacetylases (HDAC1, HDAC2, and HDAC3), two histone acetyltransferases (GCN5 and PCAF), and two possible targets of these histone modifiers (MYC and CDKN1A) in 50 matched pairs of gastric tumors and corresponding adjacent nontumors samples from patients with gastric adenocarcinoma, as well as their correlations and their possible associations with clinicopathological features. Additionally, we evaluated whether these genes are sensitive to TSA in gastric cancer cell lines. Our results demonstrated downregulation of HDAC1, PCAF, and CDKN1A in gastric tumors compared with adjacent nontumors (P < 0.05). On the other hand, upregulation of HDAC2, GCN5, and MYC was observed in gastric tumors compared with adjacent nontumors (P < 0.05). The mRNA level of MYC was correlated to HDAC3 and GCN5 (P < 0.05), whereas CDKN1A was correlated to HDAC1 and GCN5 (P < 0.05 and P < 0.01, respectively). In addition, the reduced expression of PCAF was associated with intestinal-type gastric cancer (P = 0.03) and TNM stages I/II (P = 0.01). The increased expression of GCN5 was associated with advanced stage gastric cancer (P = 0.02) and tumor invasion (P = 0.03). The gastric cell lines treated with TSA showed different patterns of histone deacetylase and acetyltransferase mRNA expression, downregulation of MYC, and upregulation of CDKN1A. Our findings suggest that alteration of histone modifier genes play an important role in gastric carcinogenesis, contributing to MYC and CDKN1A deregulation. In addition, all genes studied here are modulated by TSA, although this modulation appears to be dependent of the genetic background of the cell line.

Prohibitin Expression Deregulation in Gastric Cancer Is Associated with the 3′ Untranslated Region 1630 C>T Polymorphism and Copy Number Variation

PHB is a reported oncogene and tumor suppressor in gastric cancer. Here, we evaluated whether the PHB copy number and the rs6917 polymorphism affect its expression in gastric cancer. Down-regulation and up-regulation of PHB were observed in the evaluated tumors. Reduced expression was associated with tumor dedifferentiation and cancer initiation. The T allele of the rs6917 polymorphism was associated with reduced PHB mRNA levels. Moreover, the up-regulation of PHB appeared to be regulated by the gain of additional gene copies. Thus, PHB copy number variation and differential expression of the rs6917 polymorphism may play a role in PHB transcriptional regulation.

What gastric cancer proteomic studies show about gastric carcinogenesis

Gastric cancer is a complex, heterogeneous, and multistep disease. Over the past decades, several studies have aimed to determine the molecular factors that lead to gastric cancer development and progression. After completing the human genome sequencing, proteomic technologies have presented rapid progress. Differently from the relative static state of genome, the cell proteome is dynamic and changes in pathologic conditions. Proteomic approaches have been used to determine proteome profiles and identify differentially expressed proteins between groups of samples, such as neoplastic and nonneoplastic samples or between samples of different cancer subtypes or stages. Therefore, proteomic technologies are a useful tool toward improving the knowledge of gastric cancer molecular pathogenesis and the understanding of tumor heterogeneity. This review aimed to summarize the proteins or protein families that are frequently identified by using high-throughput screening methods and which thus may have a key role in gastric carcinogenesis. The increased knowledge of gastric carcinogenesis will clearly help in the development of new anticancer treatments. Although the studies are still in their infancy, the reviewed proteins may be useful for gastric cancer diagnosis, prognosis, and patient management.

BMP8B is a Tumor Suppressor Gene Regulated by Histone Acetylation in Gastric Cancer

Different from genetic alterations, the reversible nature of epigenetic modifications provides an interesting opportunity for the development of clinically relevant therapeutics in different tumors. In this study, we aimed to screen and validate candidate genes regulated by the epigenetic marker associated with transcriptional activation, histone acetylation, in gastric cancer (GC). We first compared gene expression profile of trichostatin A‐treated and control GC cell lines using microarray assay. Among the 55 differentially expressed genes identified in this analysis, we chose the up‐regulated genes BMP8B and BAMBI for further analyses, that included mRNA and histone acetylation quantification in paired GC and nontumor tissue samples. BMP8B expression was reduced in GC compared to nontumor samples (P < 0.01). In addition, reduced BMP8B expression was associated with poorly differentiated GC (P = 0.02). No differences or histopathological associations were identified concerning BAMBI expression. Furthermore, acetylated H3K9 and H4K16 levels at BMP8B were increased in GC compared to nontumors (P < 0.05). However, reduced levels of acetylated H3K9 and H4K16 were associated with poorly differentiated GC (P < 0.05). Reduced levels of acetylated H3K9 was also associated with diffuse‐type histological GC (P < 0.05). Notably, reduced BMP8B mRNA and acetylated H4K16 levels were positively correlated in poorly differentiated GC (P < 0.05). Our study demonstrated that BMP8B seems to be a tumor suppressor gene regulated by H4K16 acetylation in poorly differentiated GC. Therefore, BMP8B may be a potential target for TSA‐based therapies in this GC sample subset. J. Cell. Biochem. 118: 869–877, 2017.

Genetic variants in gastric cancer: Risks and clinical implications

Cancer is a multifactorial disease that involves many molecular alterations. Gastric cancer (GC) is the third leading cause of cancer death worldwide. GC is a highly heterogeneous disease with different molecular and genetics features. Therefore, this review focuses on an overview of the genetic aspects of gastric cancer by highlighting the important impact and role of deletions and/or duplications of chromosomal segments, genomic variants, H. pylori infection and interleukin variants, as found in gene expression and newly proposed molecular classification studies. The challenge is to better understand the mechanisms and different pathways that lead to the development and progression of GC.

Identification of IL11RA and MELK amplification in gastric cancer by comprehensive genomic profiling of gastric cancer cell lines

AIM To identify common copy number alterations on gastric cancer cell lines. METHODS Four gastric cancer cell lines (ACP02, ACP03, AGP01 and PG100) underwent chromosomal comparative genome hybridization and array comparative genome hybridization. We also confirmed the results by fluorescence in situ hybridization analysis using the bacterial artificial chromosome clone and quantitative real time PCR analysis. RESULTS The amplification of 9p13.3 was detected in all cell lines by both methodologies. An increase in the copy number of 9p13.3 was also confirmed by fluorescence in situ hybridization analysis. Moreover, the interleukin 11 receptor alpha (IL11RA) and maternal embryonic leucine zipper kinase (MELK) genes, which are present in the 9p13.3 amplicon, revealed gains of the MELK gene in all the cell lines studied. Additionally, a gain in the copy number of IL11RA and MELK was observed in 19.1% (13/68) and 55.9% (38/68) of primary gastric adenocarcinoma samples, respectively. CONCLUSION The characterization of a small gain region at 9p13.3 in gastric cancer cell lines and primary gastric adenocarcinoma samples has revealed MELK as a candidate target gene that is possibly related to the development of gastric cancer.