CircFOXK2 Promotes Growth and Metastasis of Pancreatic Ductal Adenocarcinoma by Complexing with RNA-Binding Proteins and Sponging MiR-942.

The detailed biological functions of circular RNA (circRNA) are largely unexplored. Using circRNA sequencing, we identified 169 differentially expressed circRNA in pancreatic ductal adenocarcinoma (PDAC) cells compared with nontumor human pancreatic ductal epithelial cells. Among them, circFOXK2 was validated with significant upregulation in PDAC cells and 63% of primary tumors (53 of 84). circFOXK2 promoted cell growth, migration, and invasion and was involved in cell-cycle progression and apoptosis. circFOXK2 contained multiple miRNA binding sites, functioning as a sponge for miR-942, which in turn promoted expression of ANK1, GDNF, and PAX6. A novel and highly specific circRNA-pulldown followed by mass spectrometry analysis identified 94 circFOXK2-interacting proteins, which were involved in cell adhesion, mRNA splicing, and structural molecule activity. Of these, circFOKX2 interactions with YBX1 and hnRNPK enhanced expression of oncogenes NUF2 and PDXK. Knockdown of circFOXK2 reduced binding of YBX1 and hnRNPK to NUF2 and PDXK, in turn decreasing their expression. Collectively, our findings demonstrate that circFOXK2 in complex with YBX1 and hnRNPK promotes expression of oncogenic proteins that contribute to PDAC progression. SIGNIFICANCE: This study reveals a prominent role for the circRNA circFOXK2 in PDAC progression, suggesting that circFOXK2 might be a novel diagnostic marker for PDAC.

Receptor tyrosine kinase fusions act as a significant alternative driver of the serrated pathway in colorectal cancer development.

Serrated polyps are a clinically and molecularly heterogeneous group of lesions that can contribute to the development of colorectal cancers (CRCs). However, the molecular mechanism underlying the development of serrated lesions is still not well understood. Here, we combined multiple approaches to analyze the genetic alterations in 86 colorectal adenomas (including 35 sessile serrated lesions, 15 traditional adenomas, and 36 conventional adenomatous polyps). We also investigated the in vitro and in vivo oncogenic properties of a novel variant of the NCOA4-RET fusion gene. Molecular profiling revealed that sessile serrated lesions and traditional serrated adenomas have distinct clinicopathological and molecular features. Moreover, we identified receptor tyrosine kinase translocations exclusively in sessile serrated lesions (17%), and the observation was validated in a separate cohort of 34 sessile serrated lesions (15%). The kinase fusions as well as the BRAF and KRAS mutations were mutually exclusive to each other. Ectopic expression of a novel variant of the NCOA4-RET fusion gene promoted cell proliferation in vitro and in vivo, and the proliferation was significantly suppressed by RET kinase inhibitors. All of these underscored the importance of mitogen-activated protein kinase (MAPK) pathway activation in the serrated pathway of colorectal tumorigenesis. In addition, we demonstrated that the kinase fusion may occur early in the precursor lesion and subsequent loss of TP53 may drives the transformation to carcinoma during serrated tumorigenesis. In conclusion, we identified kinase fusions as a significant alternative driver of the serrated pathway in colorectal cancer development, and detecting their presence may serve as a biomarker for the diagnosis of sessile serrated lesions. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

VSTM2A suppresses colorectal cancer and antagonizes Wnt signaling receptor LRP6.

Hyperactivation of Wnt/ß-catenin signaling pathway is a critical step in colorectal tumorigenesis. In this study, we identified that V-set and transmembrane domain containing 2A (VSTM2A) was a top-downregulated secreted protein that negatively regulated Wnt singling pathways in colorectal cancer (CRC). We investigated the functional mechanisms and clinical implication of VSTM2A in CRC. Methods: Function of VSTM2A was investigated in vitro and in vivo. VSTM2A binding partner was identified by mass spectrometry, immunoprecipitation and Western blot. The clinical impact of VSTM2A was assessed in 355 CRC patients and TCGA cohort. Results: VSTM2A protein was prominently silenced in CRC tumor tissues and cell lines mediated by its promoter hypermethylation. VSTM2A DNA promoter hypermethylation and VSTM2A protein downregulation was associated with poor survival of CRC patients. Ectopic expression of VSTM2A inhibited colon cancer cell lines and organoid growth, induced CRC cells apoptosis, inhibited cell migration and invasion, and suppressed growth of xenograft tumors in nude mice. VSTM2A was released from CRC cells through a canonical secretion pathway. Secreted VSTM2A significantly suppressed Wnt signaling pathway in colon cancer cells. Wnt signaling co-receptor LDL receptor related protein 6 (LRP6) was identified as a cell membrane binding partner of VSTM2A. Using deletion/mutation and immunoprecipitation, we demonstrated that VSTM2A bound to LRP6 E1-4 domain with its IgV domain. VSTM2A suppressed LRP6 phosphorylation in a time and dose dependent manner, and induced LRP6 endocytosis and lysosome-mediated degradation, which collectively contributing to the inactivation of Wnt signaling. Conclusions: VSTM2A is a novel antagonist of canonical Wnt signaling by directly binding to LRP6 and induces LRP6 endocytosis and degradation. VSTM2A is a potential prognostic biomarker for the outcome of CRC patients.

EBV-encoded miRNAs target ATM-mediated response in nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC) is a highly invasive epithelial malignancy that is prevalent in southern China and Southeast Asia. It is consistently associated with latent Epstein-Barr virus (EBV) infection. In NPC, miR-BARTs, the EBV-encoded miRNAs derived from BamH1-A rightward transcripts, are abundantly expressed and contribute to cancer development by targeting various cellular and viral genes. In this study, we establish a comprehensive transcriptional profile of EBV-encoded miRNAs in a panel of NPC patient-derived xenografts and an EBV-positive NPC cell line by small RNA sequencing. Among the 40 miR-BARTs, predominant expression of 22 miRNAs was consistently detected in these tumors. Among the abundantly expressed EBV-miRNAs, BART5-5p, BART7-3p, BART9-3p, and BART14-3p could negatively regulate the expression of a key DNA double-strand break (DSB) repair gene, ataxia telangiectasia mutated (ATM), by binding to multiple sites on its 3'-UTR. Notably, the expression of these four miR-BARTs represented more than 10% of all EBV-encoded miRNAs in tumor cells, while downregulation of ATM expression was commonly detected in all of our tested sequenced samples. In addition, downregulation of ATM was also observed in primary NPC tissues in both qRT-PCR (16 NP and 45 NPC cases) and immunohistochemical staining (35 NP and 46 NPC cases) analysis. Modulation of ATM expression by BART5-5p, BART7-3p, BART9-3p, and BART14-3p was demonstrated in the transient transfection assays. These findings suggest that EBV uses miRNA machinery as a key mechanism to control the ATM signaling pathway in NPC cells. By suppressing these endogenous miR-BARTs in EBV-positive NPC cells, we further demonstrated the novel function of miR-BARTs in inhibiting Zta-induced lytic reactivation. These findings imply that the four viral miRNAs work co-operatively to modulate ATM activity in response to DNA damage and to maintain viral latency, contributing to the tumorigenesis of NPC. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Helicobacter pylori-induced STAT3 activation and signalling network in gastric cancer.

BACKGROUND: Helicobacter pylori (H. pylori) is the most important gastric carcinogen. However, the mechanisms of H. pylori induced gastric carcinogenesis through STAT3 activation are largely unknown. We evaluated the effects of H. pylori infection on STAT3 activation and dissected the signalling network of STAT3 in H. pylori- infected gastric carcinogenesis. METHODS: The expression of phospho-STAT3 (pSTAT3) was evaluated by immunohistochemistry and western blot. Gene expression array and chromatin immunoprecipitation were used to dissect the STAT3 signalling network on H. pylori co-cultured AGS. RESULTS: pSTAT3 was significantly higher in H. pylori -positive gastritis than in H. pylori -negative gastritis ( P = 0.003). In addition, 98% of H. pylori positive intestinal metaplasia specimens showed STAT3 activation, whereas pSTAT3 was significantly decreased in all 43 specimens one year after H. pylori eradication ( P < 0.001). Moreover, pSTAT3 was only detected in the H. pylori -infected gastric tissues of mice but not in control mice. We further identified 6 candidates ( BRUNOL4, FGFR1, SHOX2, JAK3, MAPK8, and PDPN ) were directly up-regulated by H. pylori induced STAT3 activation. CONCLUSION: H. pylori infection triggers the activation of STAT3 and de-regulates multitude of tumorigenic genes which may contribute to the initiation and progression of gastric cancer.

TOP2A overexpression in hepatocellular carcinoma correlates with early age onset, shorter patients survival and chemoresistance.

Genomic gain represents an important mechanism in the activation of proto-oncogenes. In many instances, induced oncogenes hold clinical implications both as prognostic markers and targets for therapeutic design. In hepatocellular carcinoma (HCC), although chromosomal gains are common, information on underlying oncogenes induced remains minimal. Here, we examined 7 causal sites of HCC for overexpressed genes by array-based transcriptional mapping. In 22 HCC cell lines and early passages of cultures studied, clusters of up-regulated genes were indicated, where TOP2A expression ranked the highest. Distinct TOP2A transcriptions were confirmed in an independent series of HCC tumors relative to adjacent non-tumoral liver (p=0.0018). By tissue microarray analysis of 172 HCC, we found TOP2A expressions correlated with advance histological grading (p<0.001), microvascular invasion (p=0.004) and an early age onset of the malignancy (

Correlative Analysis of DNA Methyltransferase Expression and Promoter Hypermethylation of Tumor Suppressor Genes in Hepatocellular Carcinoma.

BACKGROUND: Promoter hypermethylation of tumor suppressor genes (TSGs) is a common phenomenon in liver carcinogenesis, although the controlling mechanism remains unclear. MATERIALS AND METHODS: The mRNA expression of DNA methyltransferases (DNMT1, 2, 3a, 3b and splice variants 3b3 and 3b4) and methyl-CpG binding protein (MBD2) were quantitated in 51 liver specimens (41 hepatocellular carcinoma (HCC), 1 cholangiocarcinoma, 1 macroregenerative nodule and 8 HCC cell lines) and the expression levels were correlated with the promoter methylation status of 14 TSG, including APC, RASSF1A, SOCS-1, GSTP1, E-cadherin, p14, p15, p16, DAP-kinase, HIC1, MGMT, TIMP-3, hMLH1 and HLTF. RESULTS: Up-regulations of DNMT1, DNMT2, DNMT3a, DNMT3b4 and MBD2 were suggested in more than 40% of the cases. In particular, the overexpression of DNMT3b and the splice variant DNMT3b3 were identified in as many as 91% and 97.8% of cases, respectively. Using methylation-specific PCR, the most frequently methylated TSGs were APC (90.2%), RASSF1A (86.3%), SOC-1 (74.5%), GSTP1 (72.5%), E-cadherin (64.7%) and p16 (58%). Statistical correlations did not suggest the DNMTs and MBD2 expressions in association with cumulative methylated index in individual cases, but increased expression levels of DNMT2 and DNMT3a showed significant association with the hypermethylation of GSTP1 (p=0.014) and DAP-kinase (p=0.006), respectively. Furthermore, the analysis with clinicopathological data indicated aberrant DAP-kinase methylation was significantly associated with advanced stage T3/T4 HCC tumors (p=0.032) and that p16 hypermethylation was distinct more prevalent in tumors arising from a cirrhotic background (p=0.005). CONCLUSION: Our study indicated that DNMT deregulations are common in liver cancers and the existence of a relationship between DNMT2 and DNMT3a overexpression and promoter hypermethylation of candidate tumor suppressor genes in HCC.