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Pancreatic cancer is one of the most lethal types of cancer, with aggressive properties characterized by metastasis, recurrence and drug resistance. Cancer stem cells are considered to be responsible for these properties. PRDM14, a transcriptional regulator that maintains pluripotency in embryonic stem cells, is overexpressed in some cancers. Here, we assessed PRDM14 expression and the effects of PRDM14 knockdown on cancer stem-like phenotypes in pancreatic cancer. We observed that PRDM14 protein was overexpressed in pancreatic cancer tissues compared with normal pancreatic tissues. Using lentiviral shRNA-transduced pancreatic cancer cells, we found that PRDM14 knockdown decreased sphere formation, number of side population and cell surface marker-positive cells and subcutaneous xenograft tumors and liver metastasis in mice. This was accompanied by upregulation of some microRNAs (miRNAs), including miR-125a-3p. miR-125a-3p, a tumor suppressor that is down-regulated in pancreatic cancer, has been suggested to regulate the expression of the Src-family kinase, Fyn. In PRDM14-knockdown cells, Fyn was expressed at lower levels and downstream proteins were less activated. These changes were considered to cause suppression of the above cancer phenotypes. In addition, we used small interfering RNA (siRNA)-based therapy targeting PRDM14 in a mouse model of liver metastasis induced using MIA-PaCa2 cells, and this treatment significantly decreased metastasis and in vitro migration. Taken together, these results suggest that targeting the overexpression of PRDM14 suppresses cancer stem-like phenotypes, including liver metastasis, via miRNA regulation and siRNA-based therapy targeting it shows promise as a treatment for patients with pancreatic cancer.

Altered expression of microRNA (miRNA) is strongly implicated in cancer, and recent studies have shown that the silencing of some miRNAs is associated with CpG island hypermethylation. To identify epigenetically silenced miRNAs in gastric cancer (GC), we screened for miRNAs induced by treatment with 5-aza-2'-deoxycytidine and 4-phenylbutyrate. We found that miR-34b and miR-34c are epigenetically silenced in GC and that their downregulation is associated with hypermethylation of the neighboring CpG island. Methylation of the miR-34b/c CpG island was frequently observed in GC cell lines (13/13, 100%) but not in normal gastric mucosa from Helicobacter pylori-negative healthy individuals. Transfection of a precursor of miR-34b and miR-34c into GC cells induced growth suppression and dramatically changed the gene expression profile. Methylation of miR-34b/c was found in a majority of primary GC specimens (83/118, 70%). Notably, analysis of non-cancerous gastric mucosae from GC patients (n = 109) and healthy individuals (n = 85) revealed that methylation levels are higher in gastric mucosae from patients with multiple GC than in mucosae from patients with single GC (27.3 versus 20.8%; P < 0.001) or mucosae from H. pylori-positive healthy individuals (27.3 versus 20.7%; P < 0.001). These results suggest that miR-34b and miR-34c are novel tumor suppressors frequently silenced by DNA methylation in GC, that methylation of miR-34b/c is involved in an epigenetic field defect and that the methylation might be a predictive marker of GC risk.

Gastric cancer cells often show altered Ras signaling, though the underlying molecular mechanism is not fully understood. We examined the expression profile of eight ras-association domain family (RASSF) genes plus MST1/2 and found that RASSF2A is the most frequently downregulated in gastric cancer. RASSF2A was completely silenced in 6 of 10 gastric cancer cell lines as a result of promoter methylation, and expression was restored by treating the cells with 5-aza-2'-deoxycytidine. Introduction of RASSF2A into non-expressing cell lines suppressed colony formation and induced apoptosis. These effects were associated with the cytoplasmic localization of RASSF2A and morphological changes to the cells. Complementary DNA microarray analysis revealed that RASSF2A suppresses the expression of inflammatory cytokines, which may in turn suppress angiogenesis and invasion. In primary gastric cancers, aberrant methylation of RASSF2A was detected in 23 of 78 (29.5%) cases, and methylation correlated significantly with an absence of the lymphatic invasion, absence of venous invasion, absence of lymph node metastasis, less advanced stages, Epstein-Barr virus, absence of p53 mutations and the presence of the CpG island methylator phenotype-high. These results suggest that epigenetic inactivation of RASSF2A is required for tumorigenesis in a subset of gastric cancers.

DNA mismatch repair (MMR) deficiency results in a strong mutator phenotype and high-frequency microsatellite instability (MSI-H), which are the hallmarks of tumors arising within Lynch syndrome. MSI-H is characterized by length alterations within simple repeated sequences, microsatellites. Lynch syndrome is primarily due to germline mutations in one of the DNA MMR genes; mainly hMLH1 or hMSH2 and less frequently hMSH6 and rarely hPMS2. Germline hemiallelic methylation of MLH1, termed epimutation, has been reported to be a new cause of Lynch syndrome. MSI-H is also observed in approximately 15% of colorectal, gastric and endometrial cancers and in lower frequencies in a minority of other tumors, where it is associated with the hypermethylation of the promoter region of hMLH1. MSI-H underlies a distinctive tumorigenic pathway because cancers with MSI-H exhibit many differences in genotype and phenotype relative to cancers without MSI-H, irrespective of their hereditary or sporadic origins. Genetic, epigenetic and transcriptomic differences exist between cancers with and those without the MSI-H. The BRAF V600E mutation is associated with sporadic MSI-H colorectal cancers (CRCs) harboring hMLH1 methylation but not Lynch syndrome-related CRCs. The differences in genotype and phenotype between cancers with and those without MSI-H are likely to be causally linked to their differences in biological and clinical features. Therefore, the diagnosis of MSI-H in cancers is thus considered to be of increasing relevance, because MSI-H is a useful screening marker for identifying patients with Lynch syndrome, a better prognostic factor and could affect the efficacy of chemotherapy. This review addresses recent advances in the field of microsatellite instability research.

Activation of Wnt signaling has been implicated in tumorigenesis, and epigenetic silencing of Wnt antagonist genes has been detected in various cancers. In the present study, we examined the expression and methylation of DICKKOPF (DKK) family genes in gastrointestinal cancer cell lines. We found that all known DKK genes were frequently silenced in colorectal cancer (CRC) cells (DKK1, 3/9, 33%; DKK2, 8/9, 89%; DKK3, 5/9, 56% and DKK4, 5/9, 56%), but not in normal colon mucosa. DKK1, -2 and -3 have 5' CpG islands, and show an inverse relation between expression and methylation. DKK methylation also was frequently observed in gastric cancer (GC) cell lines (DKK1, 6/16, 38%; DKK2, 15/16, 94% and DKK3, 10/16, 63%), but was seen less frequently in hepatocellular carcinoma and pancreatic cancer cell lines. DKKs also were frequently methylated in primary CRCs (DKK1, 7/58, 12%; DKK2, 45/58, 78% and DKK3, 12/58, 21%) and GCs (DKK1, 15/31, 48%; DKK2, 26/31, 84% and DKK3, 12/31, 39%). Against a background of CTNNB1 or APC mutations, Dickkopfs (Dkks) were less effective inhibitors of Wnt signaling than secreted frizzled-related proteins, though over-expression of Dkks suppressed colony formation of CRC cells with such mutations. Our results demonstrate that DKKs are frequent targets of epigenetic silencing in gastrointestinal tumors, and that loss of DKKs may facilitate tumorigenesis through beta-catenin/T-cell factor-independent mechanisms.

Morphologically, early colorectal tumors are divided into two groups, protruded-type tumors and flat-type tumors. Although some studies have shown genetic alterations in protruded-type tumors, little is known about genetic and epigenetic alterations in flat-type tumors, as well as pT1 (early invasive) colorectal cancers (CRCs). In the current study, we compared the frequencies of genetic and epigenetic alterations of the RAS-RAF and Wnt signaling pathways in flat-type and protruded-type tumors. In addition, we investigated the relationship between those alterations and invasive potential of pT1 CRCs. Methylations of RASSF2, O-6-methylguanine-DNA methyltransferase (MGMT), Wnt inhibitory factor-1 (WIF-1), EPHB2, CDKN2A and MLH1 were detected in 44.3, 30.3, 81.4, 7.5, 43.6 and 13.4% of the 307 early colorectal tumors, respectively. Mutations of KRAS, BRAF, catalytic subunit alpha of phosphatidylinositol 3'-kinase (PIK3CA) and beta-catenin were detected in 25.4, 4.6, 1.6 and 9.4% of those tumors, respectively. Methylations of MGMT, WIF-1 and CDKN2A were detected in significantly higher percentages of protruded-type tumors than in flat-type tumors. Mutation of at least one gene was detected in a significantly higher percentage of flat-type tumors than in protruded-type tumors. RASSF2 methylation was correlated significantly with KRAS, BRAF or PIK3CA mutation. Multiple logistic analysis showed that lymphatic invasion and RASSF2 methylation with KRAS, BRAF or PIK3CA mutation were independent risk factors for venous invasion in pT1 CRCs. In conclusion, since genetic alterations of these pathways have frequently occurred in flat-type tumors, flat-type tumors seem to have a distinct genetic profile different from that of protruded-type tumors. RASSF2 methylation with oncogenic activation is a promising biomarker for predicting invasive potential of pT1 CRCs.

A subset of colorectal cancers (CRCs) show simultaneous methylation of multiple genes; these tumors have the CpG island methylator phenotype (CIMP). CRCs with CIMP show a specific pattern of genetic alterations, including a high frequency of BRAF mutations and a low frequency of p53 mutations. We therefore hypothesized that genes inactivated by DNA methylation are involved in the BRAF- and p53-signaling pathways. Among those, we examined the epigenetic inactivation of insulin-like growth factor-binding protein 7 (IGFBP7) expression in CRCs. We found that in CRC cell lines, the silencing of IGFBP7 expression was correlated with high levels of DNA methylation and low levels of histone H3K4 methylation. Luciferase and chromatin immunoprecipitation assays in unmethylated cells revealed that p53 induces expression of IGFBP7 upon binding to a p53 response element within intron 1 of the gene. Treating methylated CRC cell lines with 5-aza-2'-deoxycytidine restored p53-induced IGFBP7 expression. Levels of IGFBP7 methylation were also significantly higher in primary CRC specimens than in normal colonic tissue (P < 0.001). Methylation of IGFBP7 was correlated with BRAF mutations, an absence of p53 mutations and the presence of CIMP. Thus, epigenetic inactivation of IGFBP7 appears to play a key role in tumorigenesis of CRCs with CIMP by enabling escape from p53-induced senescence.

Insulin-like growth factor-I receptor (IGF-IR) signaling is required for carcinogenicity and proliferation of gastrointestinal (GI) cancers. We have previously shown significant therapeutic activity for recombinant adenoviruses expressing dominant-negative insulin-like growth factor-I receptor (IGF-IR/dn), including suppression of tumor invasion. In this study, we sought to evaluate the mechanism of inhibition of invasion and the relationship between IGF-IR and matrix metalloproteinase (MMP) activity in GI carcinomas. We analyzed the role of IGF-IR on invasion in three GI cancer cell lines, colorectal adenocarcinoma, HT29; pancreatic adenocarcinoma, BxPC3 and gastric adenocarcinoma, MKN45, using a modified Boyden chamber method and subcutaneous xenografts in nude mice. The impact of IGF-IR signaling on the expression of MMPs and the effects of blockade of matrilysin or IGF-IR on invasiveness were assessed using recombinant adenoviruses, a tyrosine kinase inhibitor NVP-AEW541 and antisense matrilysin. Invasive subcutaneous tumors expressed several MMPs. IGF-IR/dn reduced the expression of these MMPs but especially matrilysin (MMP-7). Insulin-like growth factor (IGF) stimulated secretion of matrilysin and IGF-IR/dn blocked IGF-mediated matrilysin induction in three GI cancers. Both IGF-IR/ dn and inhibition of matrilysin reduced in vitro invasion to the same degree. NVP-AEW541 also reduced cancer cell invasion both in vitro and in murine xenograft tumors via suppression of matrilysin. Thus, blockade of IGF-IR is involved in the suppression of cancer cell invasion through downregulation of matrilysin. Strategies of targeting IGF-IR may have significant therapeutic utility to prevent invasion and progression of human GI carcinomas.

Insulin-like growth factor (IGF)-I receptor (IGF-Ir) signaling is required for tumorigenicity and progression of many tumors but this pathway has not been well studied as a prognostic factor or potential therapeutic target in esophageal squamous cell carcinoma (ESCC). In this paper, the association between the expression of IGF-Ir and IGF-II ligand and prognosis was investigated immunohistochemically in 100 surgically resected ESCC. We then assessed the therapeutic effect of blocking IGF receptor signaling using dominant negative IGF-Ir (IGF-Ir/dn) in ESCC in vitro. Expression of IGF-Ir and IGF-II were detected in 60 and 50% of tumors, respectively, and were associated with invasion depth, metastasis, advanced tumor stage and recurrence. Patients with tumors expressing both IGF-Ir and IGF-II had a significantly shorter survival than those expressing either alone or neither in both single and multivariate analysis. IGF-Ir/dn suppressed proliferation and motility as well as upregulating chemotherapy-induced apoptosis through blocking ligand-induced Akt activation. We propose that detection of IGF-Ir/IGF-II in ESCC may be useful for the prediction of recurrence and poor prognosis and for selecting patients for IGF-Ir-targeted therapy. Therapeutic blockade of IGF-Ir may be a useful anticancer therapeutic for ESCC.

It is now becoming clear that matrix metalloproteinases (MMPs) play a key role in tumor development and growth. MMPs are overexpressed in a variety of premalignant tumor tissues, including colorectal adenoma. Little is known about the mechanisms underlying the overexpression of MMPs in adenoma tissues. E1AF, an Ets family transcriptional factor, has been shown to play an important role in the expression of MMPs and cyclooxygenase-2 (COX-2) in advanced colorectal cancers. The aim of this study was to examine the E1AF expression and determine whether it is correlated with the expression of MMPs, COX-2 and inducible nitric oxide synthase (iNOS) in human colorectal adenoma and submucosal cancer (pT1). Using the semi-quantitative RT-PCR, 90 colorectal tumors, including 63 adenomas and 27 cancers (pT1), were analyzed for the expression of E1AF, MMPs, COX-2 and iNOS. Immunohistochemical analysis and in vitro transfection assays were also performed. E1AF mRNA was detected in 43 (47.8%) of the 90 colorectal tumors. E1AF overexpression was significantly correlated with histopathology. E1AF expression was correlated significantly with the expression of MMP-1 and MMP-7. Overexpression of COX-2 and iNOS mRNA expression was observed in 42.2% and 66.7% of the 90 colorectal tumors, respectively. COX-2 was correlated significantly with size, gender, histopathology and E1AF. iNOS was correlated significantly with size, histopathology, E1AF and COX-2. The correlation of E1AF expression with COX-2 and iNOS expression was also demonstrated by immunohistochemistry. Northern blot analysis of transfectants showed the effect of E1AF on COX-2 expression as well as iNOS on E1AF/COX-2 expression in colon cancer cell lines. The results suggest that E1AF, in conjunction with the expression of MMP-1, MMP-7, COX-2 and iNOS, plays an important role in the early stage of colorectal carcinogenesis.

Expression of matrilysin-2, matrix metalloproteinase (MMP)-26, has been implicated in the progression of several types of human cancer. Matrilysin-2 has been reported to be a physiological and pathological activator of pro-MMP-9. The aim of this study was to examine matrilysin-2 expression and determine whether it is correlated with progression of human esophageal squamous cell carcinoma (ESCC). Semi-quantitative reverse transcriptase-polymerase chain reaction, immunohistochemical analysis, zymography and an in vitro invasion assay were performed. Matrilysin-2 mRNA expression was undetectable or only faintly detected in non-tumor tissues, but its overexpression was detected in 24 of the 50 ESCC tissues. Matrilysin-2 overexpression was significantly correlated with depth of invasion, lymph node metastasis and an advance in pathological tumor node metastasis (pTNM) stage. Sections with immunostaining signals in >10% of carcinoma cells at the invasive front, which were observed in 46 of 100 cases, were judged to be positive for matrilysin-2 expression. Matrilysin-2 expression was significantly correlated with depth of invasion, lymph node and distant metastasis, advance in pTNM stage and recurrence. Expression of matrilysin-2 was significantly correlated with nuclear beta-catenin expression and MMP-9 expression. Patients with matrilysin-2-positive cancer had significantly shorter overall and disease-free survival periods than did those with matrilysin-2-negative cancer. Matrilysin-2 expression retained its significant predictive value for overall and disease-free survival in multivariate analysis. Moreover, patients with concomitant expression of matrilysin-2 and MMP-9 had the worst prognosis. Zymography revealed that matrilysin-2 expression was significantly correlated with expression of active MMP-9 in ESCC tissues. Matrilysin-2-transfected TE-1 ESCC cells showed active MMP-9 activity and were more invasive in vitro compared with mock-transfected TE-1 cells. The results of this study suggest that matrilysin-2, the expression of which is closely correlated with nuclear beta-catenin expression and active MMP-9 activity, plays a key role in the progression of ESCC.

Expression of E1AF/PEA3 (ETV4), an ets family transcriptional factor, has been implicated in tumor progression through induction of matrix metalloproteinase (MMP) expression. The aim of this study was to examine E1AF mRNA expression and to determine whether it is correlated with progression of, and/or MMP expression in, human gastric cancer. Using the semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), we analyzed 100 gastric cancer tissues for E1AF mRNA expression. Expression of ER81 (ETV1) and ERM (ETV5), the other two members of the PEA3 subfamily, and Ets-1 and Ets-2 was also analyzed. The results were correlated with clinicopathological characteristics and MMP expression. Immunohistochemical analysis and an in vitro invasion assay were also performed. E1AF mRNA expression was detected in 64% of the 100 gastric cancer tissues, but was undetectable or only faintly detected in adjacent non-tumor tissues. E1AF expression was significantly correlated with depth of invasion, lymphatic and venous invasion, lymph node and distant metastasis, advance in pathological tumor-node-metastasis stage and recurrence. Patients with E1AF-positive tumors had significantly shorter overall and disease-free survival periods than did those with E1AF-negative tumors (P < 0.0001 and P < 0.0001, respectively). E1AF expression retained its significant predictive value for overall and disease-free survival in multivariate analysis that included conventional clinicopathological factors (P = 0.0082 and P = 0.0096, respectively). Among the MMPs analyzed, expression of matrilysin (MMP-7) was significantly correlated with E1AF expression. Immunohistochemical expression of E1AF was predominantly observed at the invasive front, where the expression of matrilysin was often co-localized. Antisense E1AF-transfected MKN45 gastric cancer cells expressed reduced levels of matrilysin and were less invasive in vitro than mock-transfected MKN45 cells. The results of this study suggest that E1AF, the expression of which is closely correlated with the expression of matrilysin, plays a key role in the progression of gastric cancer.

The matrix metalloproteinase matrilysin has been implicated in the progression of gastrointestinal and other cancers. The aim of this study was to examine matrilysin mRNA expression and determine whether it is correlated with K-ras mutations and/or progression of pancreatic carcinoma. Using the semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), we analyzed 11 pancreatic cancer cell lines and 70 pancreatic adenocarcinoma tissues for matrilysin mRNA expression. The results were correlated with clinicopathological characteristics and K-ras mutations. Significant amounts of matrilysin mRNA were detected in six of the eight cell lines with K-ras mutations but not in the three cell lines with wild-type K-ras. Matrilysin mRNA was detected in 57 (81.4% ) of the 70 tumor tissues and in all of the eight liver metastases, but not in any of the adjacent non-tumorous tissues. Matrilysin expression was significantly correlated with the size of tumor, tumor spreading, lymph node metastasis, advanced pathologic tumor-node- metastasis stage and K-ras mutations. The relative amounts of matrilysin mRNA in tumor tissues increased with increase in tumor stage and were highest in liver metastatic tumor tissues. Our results suggest that matrilysin, the expression of which is correlated with K-ras mutations, plays a key role in tumor growth and progression of pancreatic carcinoma.