Rumi Hino

Activation of DNA Methyltransferase 1 by EBV Latent Membrane Protein 2A Leads to Promoter Hypermethylation of PTEN Gene in Gastric Carcinoma

CpG island promoter methylation of tumor suppressor genes is one of the most characteristic abnormalities in EBV-associated gastric carcinoma (GC). Aberrant promoter methylation and expression loss of PTEN were evaluated in cancer tissues of GC by methylation-specific PCR and immunohistochemistry, respectively, showing that both abnormalities occurred concurrently in EBV-associated GC. PTEN abnormalities were reiterated in GC cell lines MKN-1 and MKN-7 infected with recombinant EBV, and DNA methyltransferase 1 (DNMT1) was commonly overexpressed in both cell lines. Stable and transient transfection systems in MKN-1 similarly showed that viral latent membrane protein 2A (LMP2A) up-regulated DNMT1, leading to an increase in methylation of the PTEN promoter. Importantly, the level of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) increased in the nuclei of LMP2A-expressing GC cells, and knockdown of STAT3 counteracted LMP2A-mediated DNMT1 overexpression. Immunohistochemistry for both pSTAT3 and DNMT1 showed diffuse labeling in the nuclei of the cancer cells in GC tissues, especially in EBV-associated GC. Taken together, LMP2A induces the phosphorylation of STAT3, which activates DNMT1 transcription and causes PTEN expression loss through CpG island methylation of the PTEN promoter in EBV-associated GC. LMP2A plays an essential role in the epigenetic abnormalities in host stomach cells and in the development and maintenance of EBV-associated cancer.

CpG island methylation status in gastric carcinoma with and without infection of Epstein-Barr virus

Purpose: EBV-associated gastric carcinoma shows global CpG island methylation of the promoter region of various cancer-related genes. To further clarify the significance of CpG island methylator phenotype (CIMP) status in gastric carcinoma, we investigated methylation profile and clinicopathologic features including overall survival in four subgroups defined by EBV infection and CIMP status: EBV-associated gastric carcinoma and EBV-negative/CIMP-high (H), EBV-intermediate (I), and EBV-negative (N) gastric carcinoma. Experimental Design: Methylation-specific PCR was applied to 106 gastric carcinoma cases. CIMP-N, CIMP-I, and CIMP-H status was determined by the number (0, 1-3, and 4-5, respectively) of methylated marker genes (LOX, HRASLS, FLNc, HAND1, and TM), that were newly identified as highly methylated in gastric cancer cell lines. The methylation status of 10 other cancer-related genes (p14, p15, p16, p73, TIMP-3, E-cadherin, DAPK, GSTP1, hMLH1, and MGMT) was also evaluated. Results: Nearly all (14 of 15) of EBV-associated gastric carcinoma exhibited CIMP-H, constituting a homogenous group (14%). EBV-negative gastric carcinoma consisted of CIMP-H (24%), CIMP-I (38%), and CIMP-N (24%). EBV-associated gastric carcinoma showed significantly higher frequencies of methylation of cancer-related genes (mean number ± SD = 6.9 ± 1.5) even if compared with EBV-negative/CIMP-H gastric carcinoma (3.5 ± 1.8). Among EBV-negative gastric carcinoma subgroups, CIMP-H gastric carcinoma showed comparatively higher frequency of methylation than CIMP-I or CIMP-N, especially of p16 and hMLH1. CIMP-N gastric carcinoma predominantly consisted of advanced carcinoma with significantly higher frequency of lymph node metastasis. The prognosis of the patients of CIMP-N was significantly worse compared with other groups overall by univariate analysis (P = 0.0313). Conclusion: The methylation profile of five representative genes is useful to stratify gastric carcinomas into biologically different subgroups. EBV-associated gastric carcinoma showed global CpG island methylation, comprising a pathogenetically distinct subgroup in CIMP-H gastric carcinoma.

Classification of Epstein–Barr Virus–Positive Gastric Cancers by Definition of DNA Methylation Epigenotypes

Epstein-Barr virus (EBV) is associated with Burkitt lymphoma, nasopharyngeal carcinoma, opportunistic lymphomas in immunocompromised hosts, and a fraction of gastric cancers. Aberrant promoter methylation accompanies human gastric carcinogenesis, though the contribution of EBV to such somatic methylation changes has not been fully clarified. We analyzed promoter methylation in gastric cancer cases with Illuminas Infinium BeadArray and used hierarchical clustering analysis to classify gastric cancers into 3 subgroups: EBV(-)/low methylation, EBV(-)/high methylation, and EBV(+)/high methylation. The 3 epigenotypes were characterized by 3 groups of genes: genes methylated specifically in the EBV(+) tumors (e.g., CXXC4, TIMP2, and PLXND1), genes methylated both in EBV(+) and EBV(-)/high tumors (e.g., COL9A2, EYA1, and ZNF365), and genes methylated in all of the gastric cancers (e.g., AMPH, SORCS3, and AJAP1). Polycomb repressive complex (PRC) target genes in embryonic stem cells were significantly enriched among EBV(-)/high-methylation genes and commonly methylated gastric cancer genes (P = 2 × 10(-15) and 2 × 10(-34), respectively), but not among EBV(+) tumor-specific methylation genes (P = 0.2), suggesting a different cause for EBV(+)-associated de novo methylation. When recombinant EBV was introduced into the EBV(-)/low-methylation epigenotype gastric cancer cell, MKN7, 3 independently established subclones displayed increases in DNA methylation. The promoters targeted by methylation were mostly shared among the 3 subclones, and the new methylation changes caused gene repression. In summary, DNA methylation profiling classified gastric cancer into 3 epigenotypes, and EBV(+) gastric cancers showed distinct methylation patterns likely attributable to EBV infection.

Epstein-Barr virus and gastric carcinoma : virus-host interactions leading to carcinoma

Epstein–Barr virus (EBV)‐associated gastric carcinoma (GC) is a distinct subgroup of GC, comprising 10% of all cases of GC. EBV‐associated carcinoma is the monoclonal growth of EBV‐infected epithelial cells, and it represents a model of virus–host interactions leading to carcinoma. EBV‐infected cells express several latent proteins (latency I program of viral latent gene expression) in EBV‐associated GC. However, latent membrane protein 2A (LMP2A) up‐regulates the cellular survivin gene through the NFkB pathway, conferring resistance to apoptotic stimuli on the neoplastic cells. EBV‐associated GC also shows characteristic abnormality, that is, global and non‐random CpG island methylation of the promoter region of many cancer‐related genes. Since the viral genes are also regulated by promoter methylation in the infected cells, the DNA methylation mechanism specific to EBV‐associated GC may be an exaggeration of the cellular mechanism, which is primarily for defense against foreign DNA. Production of several immunomodulator molecules, inducing tumor‐infiltrating lymphocyte and macrophages, serves to form the characteristic histologic pattern in EBV‐associated GC. The proposed sequence of events within the mucosa is as follows: EBV infection of certain gastric stem cells; expression of viral latent genes; abnormality of signal pathways caused by viral gene products; DNA methylation‐mediated repression of tumor suppressor genes; and monoclonal growth of EBV–infected cells through interaction with other etiologic factors. Potentially useful therapeutic approaches to EBV‐associated GC are those that utilize the virus–host interactions, such as bortezomib‐induced and viral enzyme‐targeted radiotherapy. (Cancer Sci 2008; 99: 1726–1733)

Downregulation of MicroRNA-200 in EBV-Associated Gastric Carcinoma

EBV-associated gastric carcinoma is a distinct gastric carcinoma subtype with characteristic morphologic features similar to those of cells that undergo epithelial-to-mesenchymal transition. The effect of microRNA abnormalities in carcinogenesis was investigated by measuring the expression of the epithelial-to-mesenchymal transition-related microRNAs, miR-200a and miR-200b, in 36 surgically resected gastric carcinomas using quantitative reverse transcription-PCR analysis. MiR-200 family expression was decreased in EBV-associated gastric carcinoma, as compared with that in EBV-negative carcinoma. Downregulation of the miR-200 family was found in gastric carcinoma cell lines infected with recombinant EBV (MKN74-EBV, MKN7-EBV, and NUGC3-EBV), accompanied by the loss of cell adhesion, reduction of E-cadherin expression, and upregulation of ZEB1 and ZEB2. E-cadherin expression was partially restored by transfection of EBV-infected cells with miR-200 family precursors. Reverse transcription-PCR analysis of primary precursors of miR-200 (pri-miR-200) revealed that the transcription of pri-miR-200 was decreased in EBV-infected cells. Transfection of MKN74 cells with BARF0, EBNA1, and LMP2A resulted in a decrease of pri-miR-200, whereas transfection with EBV-encoded small RNA (EBER) did not. These four latent genes contributed to the downregulation of the mature miR-200 family and the subsequent upregulation of ZEB1/ZEB2, resulting in the reduction of E-cadherin expression. These findings indicate that all the latency type I genes have a synergetic effect on the downregulation of the miR-200 family that leads to reduced E-cadherin expression, which is a crucial step in the carcinogenesis of EBV-associated gastric carcinoma.

p73 gene promoter methylation in Epstein‐Barr virus‐associated gastric carcinoma

To clarify the significance of p73 in Epstein‐Barr virus (EBV)‐associated gastric carcinoma (GC), the immunohistochemical expression and CpG‐island methylation of p73 were evaluated in cancer tissues and adjacent nonneoplastic tissues of GC with and without EBV infection. Loss of p73 expression by immunohistochemistry was specific to EBV‐associated GC (11/13) compared to EBV‐negative GC (3/38), which was independent of abnormal p53 expression. With methylation‐specific polymerase chain reaction (MSP), the aberrant methylation of p73 exon 1 was similarly specific to EBV‐associated GC (12/13), and also rare in EBV‐negative GC (2/38). Bisulfite sequencing for p73 exon 1 and its 5′ region confirmed the MSP results, showing uniform and high‐density methylation in EBV‐associated GC. Comparative MSP analysis of p14, p16 and p73 methylation, using 20 cases each of formalin‐fixed and paraffin‐embedded tissues of early GC with and without EBV infection, confirmed 2 types of methylation: global methylation with increased rates (p14 and p16) and specific methylation of p73 in EBV‐associated GC. In nonneoplastic mucosa, p14, p16 and p73 methylation occurred in both EBV‐associated (8/33, 6/34 and 3/38, respectively) and EBV‐negative GC (6/23, 4/35, and 1/35). p73 methylation was observed in the mucosa without H. pylori infection in all 4 samples. Loss of p73 expression through aberrant methylation of the p73 promoter occurs specifically in EBV‐associated GC, together with the global methylation of p14 and p16. A specific type of gastritis, prone to a higher grade of atrophy and p73 methylation, may facilitate the development of EBV‐associated GC.

Survival Advantage of EBV-Associated Gastric Carcinoma : Survivin Up-regulation by Viral Latent Membrane Protein 2A

EBV-associated gastric carcinoma is a distinct subset of gastric carcinoma infected with EBV, which shows latency I type expression of EBV latent genes (EBNA1, EBER, BARF0, and LMP2A). To clarify the role of EBV in this type of gastric carcinoma, the cell biological characteristics (growth, apoptosis, and migration) were evaluated in gastric carcinoma cell lines (MKN-1, TMK1, MKN-74 and MKN-7) with and without infection of recombinant EBV harboring the neomycin resistance gene. The infection reiterated the latency I type infection, and the only difference observed in EBV-infected gastric carcinoma cell lines was the resistance to serum deprivation-induced apoptosis. Comparative analyses of transcripts of apoptosis-associated genes in MKN-1 and EBV-MKN-1 and subsequent quantitative reverse transcription-PCR analysis showed up-regulation of the cellular survivin gene in EBV-infected gastric carcinoma cell lines. Small interfering RNA-mediated knockdown of survivin increased apoptosis in EBV-MKN-1 to the level of the original MKN-1 cells. Transfection of EBV-latent genes into MKN-1 showed that LMP2A, but not EBNA1, EBER, or BARF0, up-regulated survivin gene expression. LMP2A-mediated survivin up-regulation in gastric carcinoma cells was inhibited with a nuclear factor-kappaB (NF-kappaB) inhibitor, Bay 11-7082. In parallel with these findings in vitro, survivin expression was frequent in carcinoma tissues of gastric carcinoma by immunohistochemistry, and significantly more in EBV-associated gastric carcinoma (12 of 13) than in EBV-negative gastric carcinoma in the advanced stage (P = 0.0307). Thus, EBV uses its latent protein, LMP2A, to activate the NF-kappaB-survivin pathway to rescue EBV-infected epithelial cells from serum deprivation, and up-regulation of survivin may play a role in the progression of this specific type of gastric carcinoma infected with EBV.

SOX9 expression and its methylation status in gastric cancer.

SOX9 is a member of the SOX [Sry-related high-mobility group (HMG) box] family and is required for the development and differentiation of multiple cell lineages. To clarify the significance of SOX9 in gastric carcinoma (GC), immunohistochemical expression of SOX9 and the CpG island methylation status of SOX9 were evaluated and compared with clinicopathological factors including overall survival. SOX9 expression was immunohistochemically evaluated in 382 GC tumors and the methylation status was examined in 121 GC tumors. SOX9 expression and its methylation status in six GC cell lines, their Epstein–Barr virus (EBV)-infected cell lines, and two EBV-associated GC cell lines was also examined. The SOX9 expression increased from non-neoplastic mucosa to early cancer. High expression of SOX9 was seen in 212 cases (56%). SOX9 expression was inversely related to advanced tumor stage, vessel infiltration, nodal metastasis, and EBV infection. Fifty-eight (48%) of 121 GC tumors had a methylated promoter in GC and the methylated status was related to low expression. The expression and methylation status were not related to prognosis. Three of six cell lines had increased methylation through EBV infection and decreased SOX9 expression. Upregulation of SOX9 is related to GC development. Downregulation by promoter methylation is related to GC progression and EBV infection. SOX9 is closely related to GC carcinogenesis and EBV-associated GC carcinogenesis.

Platelet-derived growth factor-A and vascular endothelial growth factor-C contribute to the development of pulmonary tumor thrombotic microangiopathy in gastric cancer

Pulmonary tumor thrombotic microangiopathy is a rare but lethal complication in cancer-bearing patients, particularly those with gastric cancer. It is characterized by cancer cell emboli with marked intimal proliferation. In the present study, we tried to elucidate the pathogenesis of pulmonary tumor thrombotic microangiopathy, notably angiogenic factors specific for cancer cells lodged in pulmonary arteries. An autopsy series of gastric cancer (51 cases) was reviewed for pulmonary tumor thrombotic microangiopathy and pulmonary tumor cell emboli without intimal proliferation. Pathological and immunohistochemical characteristics were compared between two groups. In eight cases in muscular pulmonary arteries, tumor thrombotic microangiopathy was noted, and in three cases pulmonary tumor emboli without intimal proliferation was noted. Histological features of pulmonary tumor thrombotic microangiopathy included small nests or single cancer cells accompanied by intimal proliferation, whereas in pulmonary tumor emboli large cell nests prevailed. By immunohistochemistry, in pulmonary tumor thrombotic microangiopathy, cancer cells expressed platelet-derived growth factor-A (7/8 cases) and vascular endothelial growth factor-C (8/8) more frequently than in pulmonary tumor emboli (0/3 and 1/3; P = 0.02 and P = 0.055, respectively). Expression of tissue factor, vascular endothelial growth factor-A and -D, osteopontin, fibroblast growth factor-2, and platelet-derived growth factor-B was similar in both groups. Platelet-derived growth factor-A and vascular endothelial growth factor-C might induce intimal proliferation in pulmonary arteries and contribute to the development of pulmonary tumor thrombotic microangiopathy.

Epstein-Barr Virus-associated Gastric Carcinoma: A Distinct Carcinoma of Gastric Phenotype by Claudin Expression Profiling

Epstein-Barr virus (EBV)-associated gastric carcinoma (GC) is a distinct subtype with characteristic clinicopathological features. To better characterize its cellular characteristics, 43 cases of EBV-associated GC, 68 cases of EBV-negative GC, and non-neoplastic gastric mucosa in adults and fetuses were examined immunohistochemically. We quantified the expression of the major tight-junction protein claudin (CLDN) -1, -3, -4, -7, and -18 together with gastric mucins (MUC5AC and MUC6), intestinal mucin (MUC2), and CD10. EBV-associated GC showed a high frequency of CLDN18 expression (84%) and a low frequency of CLDN3 expression (5%). This expression profile corresponded to that of normal gastric epithelium in adults and fetuses. Almost half of the EBV-associated GC cases demonstrated gastric mucin expression, whereas the other half lacked mucin or CD10 expression. In contrast, as demonstrated by the expression profiles of CLDN3 and CLDN18, EBV-negative GC comprised a heterogeneous group of four different CLDN phenotypes: gastric, intestinal, mixed, and an undifferentiated type with variable expression patterns of mucins. These results indicate that EBV-associated GC is considerably homogenous with regard to cellular differentiation and that it preserves well the nature of the cells of origin. EBV-associated GC may undergo distinct carcinogenic processes, which differ from those of EBV-negative GC.