Silencing of ATP4B of ATPase H+/K+ Transporting Beta Subunit by Intragenic Epigenetic Alteration in Human Gastric Cancer Cells

Harnessing the supremacy of MEG3 LncRNA to defeat gastrointestinal malignancies

Evidence suggests that long non-coding RNAs (lncRNAs) play a pivotal role in the carcinogenesis and progression of various human malignancies including gastrointestinal malignancies. This comprehensive review reports the functions and mechanisms of the lncRNA maternally expressed gene 3 (MEG3) involved in gastrointestinal malignancies. It summarizes its roles in mediating the regulation of cellular proliferation, apoptosis, migration, invasiveness, epithelial-to-mesenchymal transition, and drug resistance in several gastrointestinal cancers such as colorectal cancer, gall bladder cancer, pancreatic cancer, gastric cancer, esophageal cancer, cholangiocarcinoma, gastrointestinal stromal tumors and most importantly, hepatocellular carcinoma. In addition, the authors briefly highlight its implicated mechanistic role and interactions with different non-coding RNAs and oncogenic signaling cascades. This review presents the rationale for developing non coding RNA-based anticancer therapy via harnessing the power of MEG3 in gastrointestinal malignancies.

Differential expression of KCNQ1 and ATP4A genes according to the sex and age in the stomach

We compared the expression of six genes in stomach tissue samples between healthy men and women in different age groups to study sexually dimorphic gene expression. Real-Time RT-PCR was used to compare gene expression between men and women. Our results showed that the expression of KCNQ1 (p = 0.01) was significantly higher in non-menopausal women compared to post-menopausal women. In addition, the expression level of the ATP4A gene in men under 35 years was significantly higher than in men above 50 (p = 0.026). Sexually and age dimorphic gene expression in some genes throughout life may affect gastric function.

Acquired resistance to EGFR-TKIs in NSCLC mediates epigenetic downregulation of MUC17 by facilitating NF-κB activity via UHRF1/DNMT1 complex

Treatment with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) has brought significant benefits to non-small cell lung cancer (NSCLC) patients with EGFR mutations. However, most patients eventually develop acquired resistance after treatment. This study investigated the epigenetic effects of mucin 17 (MUC17) in acquired drug-resistant cells of EGFR-TKIs. We found that GR/OR (gefitinib/osimertinib-resistance) cells enhance genome-wide DNA hypermethylation, mainly in 5-UTR associated with multiple oncogenic pathways, in which GR/OR cells exerted a pro-oncogenic effect by downregulating mucin 17 (MUC17) expression in a dose- and time-dependent manner. Gefitinib/osimertinib acquired resistance mediated down-regulation of MUC17 by promoting DNMT1/UHRF1 complex-dependent promoter methylation, thereby activating NF-κB activity. MUC17 increased the generation of IκB-α and inhibit NF-κB activity by promoting the expression of MZF1. In vivo results also showed that DNMT1 inhibitor (5-Aza) in combination with gefitinib/osimertinib restored sensitivity to OR/GR cells. Acquired drug resistance of gefitinib/osimertinib promoted UHRF1/DNMT1 complex to inhibit the expression of MUC17. MUC17 in GR/OR cells may act as an epigenetic sensor for biomonitoring the resistance to EGFR-TKIs.

ESRRG, ATP4A, and ATP4B as Diagnostic Biomarkers for Gastric Cancer: A Bioinformatic Analysis Based on Machine Learning

Based on multiple bioinformatics methods and machine learning techniques, this study was designed to explore potential hub genes of gastric cancer with a diagnostic value. The novel biomarkers were detected through multiple databases of gastric cancer–related genes. The NCBI Gene Expression Omnibus (GEO) database was used to obtain gene expression files. Three hub genes (ESRRG, ATP4A, and ATP4B) were detected through a combination of weighted gene co-expression network analysis (WGCNA), gene–gene interaction network analysis, and supervised feature selection method. GEPIA2 was used to verify the differences in the expression levels of the hub genes in normal and cancer tissues in the RNA-seq levels of Genotype-Tissue Expression (GTEx) and The Cancer Genome Atlas (TCGA) databases. The objectivity of potential hub genes was also verified by immunohistochemistry in the Human Protein Atlas (HPA) database and transcription factor–hub gene regulatory network. Machine learning (ML) methods including data pre-processing, model selection and cross-validation, and performance evaluation were examined on the hub-gene expression profiles in five Gene Expression Omnibus datasets and verified on a GEO external validation (EV) dataset. Six supervised learning models (support vector machine, random forest, k-nearest neighbors, neural network, decision tree, and eXtreme Gradient Boosting) and one semi-supervised learning model (label spreading) were established to evaluate the diagnostic value of biomarkers. Among the six supervised models, the support vector machine (SVM) algorithm was the most effective one according to calculated performance metrics, including 0.93 and 0.99 area under the curve (AUC) scores on the test and external validation datasets, respectively. Furthermore, the semi-supervised model could also successfully learn and predict sample types, achieving a 0.986 AUC score on the EV dataset, even when 10% samples in the five GEO datasets were labeled. In conclusion, three hub genes (ATP4A, ATP4B, and ESRRG) closely related to gastric cancer were mined, based on which the ML diagnostic model of gastric cancer was conducted.

Construction of miRNA-mRNA-TF Regulatory Network for Diagnosis of Gastric Cancer

Gastric cancer (GC), as an epidemic cancer worldwide, has more than 1 million new cases and an estimated 769,000 deaths worldwide in 2020, ranking fifth and fourth in global morbidity and mortality. In mammals, both miRNAs and transcription factors (TFs) play a partial role in gene expression regulation. The mRNA expression profile and miRNA expression profile of GEO database were screened by GEO2R for differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs). Then, DAVID annotated the functions of DEGs to understand the functions played in biological processes. The prediction of potential target genes of miRNA and key TFs of mRNA was performed by mipathDB V2.0 and CHEA3, respectively, and the gene list comparison was performed to look for overlapping genes coregulated by key TFs and DEMs. Finally, the obtained miRNAs, TF, and overlapping genes were used to construct the miRNA-mRNA-TF regulatory network, which was verified by RT-qPCR. 76 upregulated DEGs, 199 downregulated DEGs, and 3 upregulated miRNAs (miR-199a-3p/miR-199b-3p, miR-125b-5p, and miR-199a-5p) were identified from the expression profiles of mRNA (GSE26899, GSE29998, GSE51575, and GSE13911) and miRNA (GSE93415), respectively. Through database prediction and gene list comparison, it was found that among the 199 downregulated DEGs, 61, 71, and 69 genes were the potential targets of miR-199a-3p/miR-199b-3p, miR-125b-5p, and miR-199a-5p, respectively. 199 downregulated DEGs were used as the gene list for the prediction of key TFs, and the results showed that RFX6 ranked the highest. The potential target overlap genes of miR-199a-3p/miR-199b-3p, miR-125b-5p, and miR-199a-5p were 4 genes (SH3GL2, ATP4B, CTSE, and SORBS2), 7 genes (SLC7A8, RNASE4, ESRRG, PGC, MUC6, Fam3B, and FMO5), and 6 genes (CHGA, PDK4, TMPRSS2, CLIC6, GPX3, and PSCA), respectively. Finally, we constructed a miRNA-mRNA-TF regulatory network based on the above 17 mRNAs, 3 miRNAs, and 1 TF and verified by RT-qPCR and western blot results that the expression of RFX6 was downregulated in GC tissues. These identified miRNAs, mRNAs, and TF have a certain reference value for further exploration of the regulatory mechanism of GC.

Clinical significance of P-class pumps in cancer

P-class pumps are specific ion transporters involved in maintaining intracellular/extracellular ion homeostasis, gene transcription, and cell proliferation and migration in all eukaryotic cells. The present review aimed to evaluate the role of P-type pumps [Na⁺/K⁺ ATPase (NKA), H⁺/K⁺ ATPase (HKA) and Ca2⁺-ATPase] in cancer cells across three fronts, namely structure, function and genetic expression. It has been shown that administration of specific P-class pumps inhibitors can have different effects by: i) Altering pump function; ii) inhibiting cell proliferation; iii) inducing apoptosis; iv) modifying metabolic pathways; and v) induce sensitivity to chemotherapy and lead to antitumor effects. For example, the NKA β2 subunit can be downregulated by gemcitabine, resulting in increased apoptosis of cancer cells. The sarcoendoplasmic reticulum calcium ATPase can be inhibited by thapsigargin resulting in decreased prostate tumor volume, whereas the HKA α subunit can be affected by proton pump inhibitors in gastric cancer cell lines, inducing apoptosis. In conclusion, the present review highlighted the central role of P-class pumps and their possible use and role as anticancer cellular targets for novel therapeutic chemical agents.

Identification of key methylation differentially expressed genes in posterior fossa ependymoma based on epigenomic and transcriptome analysis

Background

Posterior fossa ependymoma (EPN-PF) can be classified into Group A posterior fossa ependymoma (EPN-PFA) and Group B posterior fossa ependymoma (EPN-PFB) according to DNA CpG island methylation profile status and gene expression. EPN-PFA usually occurs in children younger than 5 years and has a poor prognosis.

Methods

Using epigenome and transcriptome microarray data, a multi-component weighted gene co-expression network analysis (WGCNA) was used to systematically identify the hub genes of EPN-PF. We downloaded two microarray datasets (GSE66354 and GSE114523) from the Gene Expression Omnibus (GEO) database. The Limma R package was used to identify differentially expressed genes (DEGs), and ChAMP R was used to analyze the differential methylation genes (DMGs) between EPN-PFA and EPN-PFB. GO and KEGG enrichment analyses were performed using the Metascape database.

Results

GO analysis showed that enriched genes were significantly enriched in the extracellular matrix organization, adaptive immune response, membrane raft, focal adhesion, NF-kappa B pathway, and axon guidance, as suggested by KEGG analysis. Through WGCNA, we found that MEblue had a significant correlation with EPN-PF (R = 0.69, P = 1 × 10^–08) and selected the 180 hub genes in the blue module. By comparing the DEGs, DMGs, and hub genes in the co-expression network, we identified five hypermethylated, lower expressed genes in EPN-PFA (ATP4B, CCDC151, DMKN, SCN4B, and TUBA4B), and three of them were confirmed by IHC.

Conclusion

ssGSEA and GSVA analysis indicated that these five hub genes could lead to poor prognosis by inducing hypoxia, PI3K-Akt-mTOR, and TNFα-NFKB pathways. Further study of these dysmethylated hub genes in EPN-PF and the pathways they participate in may provides new ideas for EPN-PF treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02834-1.

Tumor suppressor ATP4B serve as a promising biomarker for worsening of gastric atrophy and poor differentiation

BACKGROUND

Hydrogen/potassium ATPase β (ATP4B) is a proton pump acting an essential role in gastric acid secretion. This study aimed to investigate the diagnostic performance of ATP4B and its biological role in tumor progression in gastric cancer.

METHODS

The correlations between ATP4B expression level and clinicopathologic parameters, as well as the relevance of ATP4B expression with overall survival were assessed. The functional roles of ATP4B in gastric cancer were verified by gain- and loss-of-function cell models and tumor xenograft models. The possible downstream effects of ATP4B were analyzed by iTRAQ-based quantitative proteomics analysis.

RESULTS

A dramatic decrease in ATP4B was associated with malignant transformation in gastric mucosa lesions and correlated with poor differentiation. Restoration of ATP4B expression in gastric cancer cells significantly suppressed cell proliferation, cell viability, migration, invasion, tumorigenicity and induced apoptosis, whereas ATP4B silencing exerted the opposite effects. Mechanistically, we found a quality control on mitochondrial metabolism and functions in ATP4B-overexpression GC cells.

CONCLUSIONS

Our data suggest that decreasing ATP4B is an indicator for gastric mucosa malignant transformation and GC aggressive phenotype and it plays an inhibitory role in gastric cancer as a tumor suppressor via regulating mitochondrial metabolism and apoptosis pathway.

Gastric H+/K+-ATPase Expression in Normal Laryngeal Tissue and Laryngeal Carcinoma

Background

Several studies have suggested that laryngopharyngeal reflux disease (LPRD) or gastroesophageal reflux disease (GERD) is an independent risk factor for laryngeal carcinoma. However, it remains unclear whether either condition affects the level of H⁺/K⁺-ATPase expression in laryngeal carcinoma.

Materials and Methods

Immunohistochemistry, real-time RT-PCR, and Western blotting were used to explore the distributions of proton pump (H⁺/K⁺-ATPase) α- and β-subunits in normal laryngeal tissue and laryngeal carcinoma.

Results

Messenger RNAs encoding both the α- and β-subunits were found in the normal epiglottic, ventricular fold, vocal fold, and arytenoid mucosae, as well as epiglottic cartilage. The distributions and expression levels of H+/K+-ATPase α-subunits in various laryngeal subregions did not significantly differ in IHC, RT-PCR, or Western blotting. However, Western blotting revealed a significant difference between the expression level of the β-subunit protein in the epiglottic cartilage and the levels in other sites. The expression levels of both subunits were significantly higher in carcinomatous than in paracarcinomatous tissue and normal laryngeal tissue. The mean follow-up duration was 66.2 months (range, 17–162 months). In all, 4 patients died during follow-up, 4 were lost to follow-up, and 22 were alive and free of disease at the end of follow-up. Two patients developed lung metastases and six developed disease recurrences (at 2, 8, 14, 16, 36, and 41 months). The 3- and 5-year overall survival (OS) rates were 93.0% and 77.0%, respectively. Univariate analyses showed that the 5-year OSs were significantly associated with the T, N, and clinical stages but not with age, alcohol use, pathological differentiation, or the expression levels of the α- or β-subunits (as revealed by IHC, RT-PCR, or Western blotting). However, in multivariate regression analyses, the 5-year OSs were not significantly associated with any clinicopathological factor or the expression levels of either subunit.

Conclusion

H⁺/K⁺-ATPase is expressed in the normal larynx, including in the epiglottic cartilage and the mucosae of the epiglottis, ventricular fold, and arytenoid vocal fold. The expression levels of the H⁺/K⁺-ATPase α- and β-subunits in laryngeal carcinomas were higher than in normal laryngeal tissues.

Transcriptomic investigation reveals toxic damage due to tilmicosin and potential resistance against tilmicosin in primary chicken myocardial cells

Tilmicosin is widely used to treat respiratory infections in animals and has been reported to induce cardiac damage and even sudden death. However, its exact mechanisms, especially in chickens, remain unclear. This study confirmed the dose-dependent damaging effect of tilmicosin on primary chicken myocardial cells. Primary chicken myocardial cells treated with tilmicosin (0.5 μg/mL) for 0 h, 12 h, and 48 h were subjected to RNA sequencing and bioinformatics analysis. Transcriptomic analysis revealed that cytokine-cytokine receptor interactions, calcium signaling pathway, peroxisomes, phagosomes, mitogen-activated protein kinase (MAPK) signaling pathway, and oxidative phosphorylation were significantly and differentially affected after 12 h or 48 h of tilmicosin treatment. Further evidence demonstrated consistently increased proinflammatory factors, peroxidation, and ferroptosis, and intracellular ion imbalance was caused by tilmicosin for 12 h, but this imbalance had recovered at 48 h. Meanwhile, intracellular resistance to tilmicosin-induced toxicity involved the active regulation of cyclooxygenase-1 and ATPase H⁺/K⁺-transporting beta subunit at 48 h, sustained activation of MAPK12, and downregulation of dual specificity phosphatase 10 at 12 h. In summary, this study suggests that tilmicosin exerts its cardiotoxicity in primary chicken myocardial cells through multiple mechanisms and finds several intracellular molecular targets to resist the toxicity.

Identification of potential key genes in gastric cancer using bioinformatics analysis

Gastric cancer (GC) is one of the most common types of cancer worldwide. Patients must be identified at an early stage of tumor progression for treatment to be effective. The aim of the present study was to identify potential biomarkers with diagnostic value in patients with GC. To examine potential therapeutic targets for GC, four Gene Expression Omnibus (GEO) datasets were downloaded and screened for differentially expressed genes (DEGs). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were subsequently performed to study the function and pathway enrichment of the identified DEGs. A protein-protein interaction (PPI) network was constructed. The CytoHubba plugin of Cytoscape was used to calculate the degree of connectivity of proteins in the PPI network, and the two genes with the highest degree of connectivity were selected for further analysis. Additionally, the two DEGs with the largest and smallest log Fold Change values were selected. These six key genes were further examined using Oncomine and the Kaplan-Meier plotter platform. A total of 99 upregulated and 172 downregulated genes common to all four GEO datasets were screened. The DEGs were primarily enriched in the Biological Process terms: ‘extracellular matrix organization’, ‘collagen catabolic process’ and ‘cell adhesion’. These three KEGG pathways were significantly enriched in the categories: ‘ECM-receptor interaction’, ‘protein digestion and absorption’, and ‘focal adhesion’. Based on Oncomine, expression of ATP4A and ATP4B were downregulated in GC, whereas expression of the other genes were all upregulated. The Kaplan-Meier plotter platform confirmed that upregulated expression of the identified key genes was significantly associated with worse overall survival of patients with GC. The results of the present study suggest that FN1, COL1A1, INHBA and CST1 may be potential biomarkers and therapeutic targets for GC. Additional studies are required to explore the potential value of ATP4A and ATP4B in the treatment of GC.

Reactivation of Atp4a concomitant with intragenic DNA demethylation for cancer inhibition in a gastric cancer model

Accumulating evidence suggests that aberrant DNA methylation and gene silencing of tumor suppressors are pervasive in gastric malignancies, supporting reactivation of tumor suppressors through DNA demethylation as a potential therapeutic opportunity. Atp4a is an important tumor suppressor gene, encoding H⁺, K⁺-ATPase, and mediating gastric acid secretion in the stomach. Using transgenic gastric cancer model K19-Wnt1/C2mE (Gan) mice, by combining the transcriptome and MeDIP (methylated DNA immunoprecipitation) sequencing, together with qRT-PCR, we showed that Atp4a was expressed at low levels in tumor tissues and multiple GC cells, while both 5-aza-CdR and 18β-glycyrrhetinic acid (GRA) pharmacological treatment triggered Atp4a activation with downregulation of DNMT1. In addition, CpG island (CGI) search showed that the CpG rich region is absent in the promoter region but present in exons 9-14 of Atp4a. Methylation specific PCR (MSP) indicated that Atp4a was fully or partly methylated in multiple GC cells. Further MassArray suggested that the demethylation in the CpG site 75, 183, 196, 262-268 might be responsible for the reactivation of Atp4a. Our research identified that GRA, a bioactive component found in abundance in Radix Glycyrrhiza, reactivated Atp4a expression and inhibited gastric tumorigenesis as a potential demethylation agent.

Hypermethylated long noncoding RNA MEG3 promotes the progression of gastric cancer

This study aims to explore the expression and degree of methylation of lncRNA MEG3 in gastric cancer tissues and to analyze its effect on the migration and proliferation of gastric cancer patients and the mechanism by which this occurs. The targeting relationship between MEG3, miR-181a-5p and ATP4B was detected through molecular biology experiments. Wound healing, transwell, colony formation and flow cytometry assays were used to analyze the effects of lncRNA MEG3 and methylation on tumor cell migration, invasion, proliferation and apoptosis. In addition, a tumor xenotransplantation model was established to study the influence of MEG3 on tumor growth in vivo. Bioinformatics analysis showed that lncRNA MEG3 and ATP4B were downregulated in gastric cancer tissues compared with normal tissues. Bioinformatics predicted that ATP4B might be regulated by targeting miR-181a-5p. The overexpression of MEG3 and the application of 5-Aza treatment inhibited the migration, invasion and proliferation of MGC-803 cells and promoted apoptosis. In gastric cancer tissues, MEG3 is hypermethylated to decrease expression. Once the expression of MEG3 is restored or methylation is inhibited, tumor growth can be inhibited both in vivo and in vitro. This finding could be utilized as a clinical reference for gastric cancer treatment in the future.

Epigenetic downregulation of MUC17 by H. pylori infection facilitates NF-κB-mediated expression of CEACAM1-3S in human gastric cancer

BACKGROUND AND AIMS

Helicobacter pylori invades the mucosal barrier and infects the mucins of gastric epithelial cells. However, whether gastric carcinogenesis caused by H. pylori infection involves the membrane-bound mucins is unclear. This study explored the role of mucin 17 (MUC17) in gastric cancer (GC) associated with H. pylori infection.

METHODS

The expression of MUC17 and carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) was examined in human GC cells and tissues with H. pylori infection. Gain- and loss-of-function assays were performed to assess the role of MUC17 in regulating CEACAM1 in H. pylori-infected GC cells.

RESULTS

MUC17 was downregulated in H. pylori-infected GC cells and tissues in association with poor survival of GC patients. Downregulation of MUC17 was attributable to MUC17 promoter methylation mediated by DNA methyltransferase 1 (DNMT1) H. pylori-enhanced GC cell proliferation and colony formation associated with MUC17 downregulation. Gain- and loss-of-function assays showed that MUC17 inhibited the H. pylori-enhanced GC cell growth by preventing the translocation of H. pylori CagA into GC cells. Moreover, MUC17 downregulated the expression of CEACAM1 variant 3S (CEACAM1-3S) in GC cells and tissues with H. pylori infection. Additionally, MUC17 downregulated CEACAM1 promoter activity via attenuation of NF-κB activation in GC cells.

CONCLUSIONS

MUC17 was epigenetically downregulated in GC with H. pylori infection. MUC17 inhibited H. pylori CagA translocation via attenuation of NF-κB-mediated expression of CEACAM1-3S in GC cells. Thus, MUC17 may serve as a valuable prognostic biomarker for H. pylori-associated GC.

PON1 hypermethylation is associated with progression of renal cell carcinoma

In this study, our aim was to exploring the influences of DNA methylation of PON1 on cell proliferation, migration and apoptosis of renal cancer cells. The genome‐wide methylation array of renal cell carcinoma samples and adjacent tissues were obtained from the cancer genome atlas (TCGA) database. By analysing the DNA methylation and conducting the CpG islands array, methylation status expressed in renal tumour samples and normal renal tissue samples were detected. Methylation‐specific PCR (MS‐PCR) and qRT‐PCR were employed to detect the methylation level and mRNA expression of PON1. Wound‐healing assay, transwell assay and MTT assay were utilized to detecting the migration, invasion and proliferation abilities, respectively. The cell apoptosis was testified by Tunnel assay. In addition, the effect of PON1 on renal cancer cells was verified by experiments in vivo. The methylation status of different genes in renal cell carcinoma samples was obtained by CpG islands arrays and hypermethylated PON1 was selected for further study. PON1 was down‐regulated in renal cell carcinoma tissues detected by qRT‐PCR and Western blot. Both in vitro and vivo experiments indicated that the sunitinib‐resistant in renal cancer cells could be suppressed by treat with 5‐Aza‐dC or TSA, and the effect came out more obvious after 5‐Aza‐dC and TSA co‐treatment. In detail, the demethylation of PON1 inhibited the migration, invasion and proliferation of renal cancer cells and also arrested more cells in G0/G1 phase. The vivo experiment indicated that demethylated PON1 suppressed the growth of tumour. Hypermethylated PON1 promoted migration, invasion and proliferation of sunitinib‐resistance renal cancer cells and arrested more cells in G0/G1 phase.

DNA methyltransferases and gastric cancer: insight into targeted therapy

Gastric cancer is a major health problem worldwide occupying most frequent causes of cancer-related mortality. In addition to genetic modifications, epigenetic alterations catalyzed by DNA methyltransferases (DNMTs) are a well-characterized epigenetic hallmark in gastric cancer. The reversible nature of epigenetic alterations and central role of DNA methylation in diverse biological processes provides an opportunity for using DNMT inhibitors to enhance the efficacy of chemotherapeutics. In this review, we discussed key factors or mechanisms such as SNPs, infections and genetic modifications that trigger DNMTs level modification in gastric cancer, and their potential roles in cancer progression. Finally, we focused on how inhibitors of the DNMTs can most effectively be used for the treatment of gastric cancer with multidrug resistance.

Epigenetic silencing of PRSS3 provides growth and metastasis advantage for human hepatocellular carcinoma

Protease, serine, 3 (PRSS3), a member of the trypsin family of serine proteases, has been shown to be aberrantly expressed in several cancer types and to play important roles in tumor progression and metastasis. However, the expression and function of PRSS3 gene in hepatocellular carcinoma (HCC) remain unclear. Here we found that PRSS3 expression was decreased in human HCC cell lines and HCC surgical specimens. This was associated with intragenic methylation of PRSS3 gene. Treatment with DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine and/or histone deacetylase inhibitor trichostatin A restored PRSS3 expression in HCC cell lines. Ectopic overexpression of PRSS3 gene in HCC cell lines significantly suppressed cell proliferation and colony formation and arrested cell cycle at G1/S phase, accompanied with downregulation of cyclin D1 (CCND1)/CDK4 and cyclin E1 (CCNE1)/CDK2 complexes. Moreover, PRSS3 overexpression in HCC cells inhibited HCC cell migration and invasion with downregulation of matrix metallopeptidase 2 (MMP2). Further study showed that PRSS3 overexpression diminished the phosphorylation of mitogen-activated protein kinase/extracellular-signal-regulated kinase signaling protein, mitogen-activated protein kinase kinase 1 (MEK1)/mitogen-activated protein kinase kinase 2 (MEK2) and extracellular-signal related kinase 1 (ERK1)/extracellular-signal related kinase 2 (ERK2), in HCC cells. In contrast, knockdown of PRSS3 by small interfering RNA resulted in opposite effects on an HCC cell line SNU-387 which constitutively expresses PRSS3. These results demonstrate that downregulation of PRSS3 by intragenic hypermethylation provides growth and metastasis advantage to HCC cells. The clinical relevance of PRSS3 to human HCC was shown by the intragenic methylation of PRSS3 in HCC specimens and its association with poor tumor differentiation in patients with HCC. Thus, PRSS3 is a potential prognostic biomarker and an epigenetic target for intervention of human HCC.

KEY MESSAGES

• PRSS3 is downregulated by intragenic hypermethylation in HCC. • Epigenetic silencing of PRSS3 facilitates growth, migration, and invasion of HCC. • PRSS3 intragenic methylation has implication in diagnosis of HCC.