Hypermethylation of the TSLC1 gene promoter in primary gastric cancers and gastric cancer cell lines.

The TSLC1 (tumor suppressor in lung cancer-1) gene is a novel tumor suppressor gene on chromosomal region 11q23.2, and is frequently inactivated by concordant promoter hypermethylation and loss of heterozygosity (LOH) in non-small cell lung cancer (NSCLC). Because LOH on 11q has also been observed frequently in other human neoplasms including gastric cancer, we investigated the promoter methylation status of TSLC1 in 10 gastric cancer cell lines and 97 primary gastric cancers, as well as the corresponding non-cancerous gastric tissues, by bisulfite-SSCP analysis followed by direct sequencing. Allelic status of the TSLC1 gene was also investigated in these cell lines and primary gastric cancers. The TSLC1 promoter was methylated in two gastric cancer cell lines, KATO-III and ECC10, and in 15 out of 97 (16%) primary gastric cancers. It was not methylated in non-cancerous gastric tissues, suggesting that this hypermethylation is a cancer-specific alteration. KATO-III and ECC10 cells retained two alleles of TSLC1, both of which showed hypermethylation, associated with complete loss of gene expression. Most of the primary gastric cancers with promoter methylation also retained heterozygosity at the TSLC1 locus on 11q23.2. These data indicate that bi-allelic hypermethylation of the TSLC1 promoter and resulting gene silencing occur in a subset of primary gastric cancers.     

Epigenetic inactivation of TSLC1 gene in nasopharyngeal carcinoma

Deletion of 11q23 is a common genetic aberration in nasopharyngeal carcinoma (NPC). Multiple candidate tumor suppressor genes (TSG) were mapped to this region but few of them were investigated in NPC. TSLC1 (tumor suppressor in lung cancer) is recently reported to be a putative TSG on 11q23. This gene was found to be inactivated by promoter hypermethylation in non-small cell lung carcinoma (NSCLC), liver cancer, and breast cancer. To study the role of TSLC1 gene in NPC tumorigenesis, we screened for mutations and aberrant methylation of TSLC1 gene in 5 NPC cell lines, 3 NPC xenografts, and 38 primary NPC cases. No somatic mutations of TSLC1 were detected in the NPC samples, but a 9-bp (CCACCACCA) deletion in exon 8 was found in a primary NPC and its corresponding blood sample. Bisulfite sequencing revealed aberrant methylation of TSLC1 promoter in four NPC cell lines. Loss of TSLC1 gene expression was found in two cell lines (HK-1 and CNE-2) with dense methylation. Expression of this gene was restored in these cell lines after treatment with demethylating agent 5-aza-2'-deoxycytidine. Our results showed that silencing of TSLC1 gene expression in NPC was associated with promoter hypermethylation. Promoter hypermethylation of TSLC1 gene was further illustrated in 34.2% (13/38) of primary NPCs. No aberrant promoter methylation was found in any of the four investigated normal nasopharyngeal epithelia. Frequent epigenetic inactivation of TSLC1 gene in NPC suggested that this gene is one of the target tumor suppressor genes of this endemic cancer.     

Promoter methylation of the TSLC1 gene in advanced lung tumors and various cancer cell lines

We previously identified TSLC1, a tumor suppressor gene in human nonsmall cell lung cancer (NSCLC). TSLC1 belongs to immunoglobulin superfamily molecules and is involved in cell adhesion. Loss of TSLC1 expression was strongly correlated with the promoter hypermethylation in several NSCLC cell lines. Here, we examined the methylation status of the TSLC1 gene promoter in 48 primary NSCLC tumors by bisulfite SSCP in combination with bisulfite sequencing. Six CpG sites around the promoter regions were significantly methylated in 21 of 48 primary NSCLC tumors (44%). Promoter methylation was more likely to be observed in relatively advanced tumors with TNM classification of pT2, pT3 or pT4 (19 of 33, 58%) than in those with pT1 (2 of 15, 13%), suggesting that alteration of TSLC1 would be involved in the progression of human NSCLC. Loss of TSLC1 expression was also observed in 20 of 46 (43%) human cancer cell lines, including those from esophageal (3 of 3), gastric (8 of 9), ovarian (2 of 5), endometrial (2 of 2), breast (1 of 3), colorectal (2 of 8) and small cell lung cancers (2 of 10). Combined analysis of promoter methylation and the allelic state in these cell lines indicated that the TSLC1 gene was often silenced not only by mono-allelic methylation associated with loss of the other allele but also through bi-allelic methylation. These results suggest that alteration of TSLC1 would be involved in advanced NSCLC as well as in many other human cancers.     

Expression of TSLC1, a candidate tumor suppressor gene mapped to chromosome 11q23, is downregulated in unfavorable neuroblastoma without promoter hypermethylation

Although it has been well documented that loss of human chromosome 11q is frequently observed in primary neuroblastomas, the smallest region of overlap (SRO) has not yet been precisely identified. Previously, we performed array-comparative genomic hybridization (array-CGH) analysis for 236 primary neuroblastomas to search for genomic aberrations with high-resolution. In our study, we have identified the SRO of deletion (10-Mb or less) at 11q23. Within this region, there exists a TSLC1/IGSF4/CADM1 gene (Tumor suppressor in lung cancer 1/Immunoglobulin superfamily 4/Cell adhesion molecule 1), which has been identified as a putative tumor suppressor gene for lung and some other cancers. Consistent with previous observations, we have found that 35% of primary neuroblastomas harbor loss of heterozygosity (LOH) on TSLC1 locus. In contrast to other cancers, we could not detect the hypermethylation in its promoter region in primary neuroblastomas as well as neuroblastoma-derived cell lines. The clinicopathological analysis demonstrated that TSLC1 expression levels significantly correlate with stage, Shimada's pathological classification, MYCN amplification status, TrkA expression levels and DNA index in primary neuroblastomas. The immunohistochemical analysis showed that TSLC1 is remarkably reduced in unfavorable neuroblastomas. Furthermore, decreased expression levels of TSLC1 were significantly associated with a poor prognosis in 108 patients with neuroblastoma. Additionally, TSLC1 reduced cell proliferation in human neuroblastoma SH-SY5Y cells. Collectively, our present findings suggest that TSLC1 acts as a candidate tumor suppressor gene for neuroblastoma.     

Biallelic inactivation of the RIZ1 gene in human gastric cancer

The distal short arm of chromosome 1 is commonly deleted in a variety of human neoplasms including gastrointestinal cancer. Genetic alterations of the retinoblastoma protein-interacting zing-finger gene (RIZ)1 including loss of heterozygosity (LOH) at 1p36, frameshift mutations, and promoter hypermethylation were reported previously in several cancers. In this study, we evaluated RIZ1 in 30 primary gastric cancers and found frameshift mutations in two cases (6.7%). Moreover, using real-time quantitative methylation-specific PCR, methylation of the RIZ1 promoter was detected in 11 (37%) cases. In all 11 cases with methylation, inactivation of the second allele occurred through frameshift mutation, LOH or promoter methylation. Our results suggest that RIZ1 is a specific target of inactivation in human gastric cancer.     

Less frequent promoter hypermethylation of DLC-1 gene in primary breast cancers

Absence or low expression of DLC-1, a tumor suppressor gene, in breast cancers has been shown recently. LOH of 8p12-p22, on which DLC-1 is located, is frequent in breast cancers, but the correlation between low expression of DLC-1 and LOH has not been confirmed. To determine the implication of aberrant methylation, one of the most frequent mechanisms of silencing the tumor suppressor or cancer-related genes, we examined the methylation status of DLC-1 promoter region in breast cancer cell lines and primary breast tumors. The hypermethylation status was examined by MSP and 25% of cell lines harbored a methylated allele. The gene silencing by methylation was also confirmed by the re-expression of DLC-1 by the 5-aza-2'-deoxycytidine treatment in DLC-1 hypermethylated cell line. But the methylation of DLC-1 gene was less frequently shown in primary breast cancers (10%). These data suggest that hypermethylation is responsible for silencing of DLC-1 gene in a limited portion of breast cancers.     

Promoter Methylation of TSLC1 and Tumor Suppression by Its Gene Product in Human Prostate Cancer

We recently identified TSLC1 , a tumor suppressor gene in human lung cancer. Gene silencing by promoter methylation has been observed frequently in adenocarcinoma of the lung, liver, and pancreas. Here, we demonstrate that TSLC1 expression is also absent or markedly reduced in 3 of 4 prostate cancer cell lines. Promoter sequences of TSLC1 were heavily methylated in PPC-1 cells that lacked TSLC1 expression, supporting the idea that promoter methylation is strongly correlated with complete loss of gene expression. Promoter sequences of TSLC1 were also methylated significantly in 7 of 22 (32%) primary prostate cancers. Hypermethylation of the promoter occurred not only in advanced tumors, but also in relatively early-stage tumors. Restoration of TSLC1 expression substantially suppressed tumor formation of PPC-1 cells in nude mice. These findings indicate that alteration of TSLC1 is involved in prostate cancer.     

Promoter methylation of TSLC1 and tumor suppression by its gene product in human prostate cancer.

We recently identified TSLC1, a tumor suppressor gene in human lung cancer. Gene silencing by promoter methylation has been observed frequently in adenocarcinoma of the lung, liver, and pancreas. Here, we demonstrate that TSLC1 expression is also absent or markedly reduced in 3 of 4 prostate cancer cell lines. Promoter sequences of TSLC1 were heavily methylated in PPC-1 cells that lacked TSLC1 expression, supporting the idea that promoter methylation is strongly correlated with complete loss of gene expression. Promoter sequences of TSLC1 were also methylated significantly in 7 of 22 (32%) primary prostate cancers. Hypermethylation of the promoter occurred not only in advanced tumors, but also in relatively early-stage tumors. Restoration of TSLC1 expression substantially suppressed tumor formation of PPC-1 cells in nude mice. These findings indicate that alteration of TSLC1 is involved in prostate cancer.     

Hypermethylation and Clinicopathological Significance of RASAL1 Gene in Gastric Cancer

Background: Recent studies have suggested that expression of the RAS protein activator like-1 gene (RASAL1)is decreased in gastric carcinoma tissues and cell lines, indicated a role in tumorigenesis and development ofgastric cancer. Reduced expression of RASAL1 could result in aberrant increase of activity of RAS signalingpathways in cancer cells. However, the exact mechanism which induces down-regulation of the RASAL1 generemains unclear. This study aimed to determine the methylation status and regulation of RASAL1 in gastric cancer.Materials and Methods: Using the methylation-specific polymerase chain reaction (MSP), the methylation statusof CpG islands in the RASAL1 promoter in gastric cancers and paired adjacent non-cancerous tissues from 40patients was assessed and its clinicopathological significance was analyzed. The methylation status of RASAL1 ingastric cancer lines MKN-28, SGC-790l, BGC-823, as well as in normal gastric epithelial cell line GES-l was alsodetermined after treatment with a DNA methyltransferase inhibitor, 5-aza-2’-doexycytidine (5-Aza-CdR). RASactivity (GAS-GTP) was assessed through a pull-down method, while protein levels of ERK1/2, a downstreammolecule of RAS signaling pathways, were determined by Western blotting. Results: The frequencies of RASAL1promoter methylation in gastric cancer and paired adjacent non-cancerous tissues were 70% (28/40) and 30%(12/40) respectively (P<0.05). There were significantly correlations between RASAL1 promoter methylation withtumor differentiation, tumor size, invasive depth and lymph node metastasis in patients with gastric cancer(all P<0.05), but no correlation was found for age or gender. Promoter hypermethylation of the RASAL1 genewas detected in MKN-28, SGC-790l and BGC-823 cancer cells, but not in the normal gastric epithelial cell lineGES-1. Elevated expression of the RASAL1 protein, a decreased RAS-GTP and p-ERK1/2 protein were detectedin three gastric cancer cell lines after treatment with 5-Aza-CdR. Conclusions: Aberrant hypermethylation ofthe RASAL1 gene promoter frequently occurs in gastric cancer tissues and cells. In addition, the demethylatingagent 5-Aza-CdR can reverse the hypermethylation of RASAL1 gene and up-regulate the expression of RASAL1significantly in gastric cancer cells in vivo. Our study suggests that RASAL1 promoter methylation may have acertain relationship with the reduced RASAL1 expression in gastric cancer.     

Aberrant methylation of the 5' CpG island of TSLC1 is common in pancreatic ductal adenocarcinoma and is first manifest in high-grade PanlNs

The recently identified tumor-suppressor gene TSLC1 on chromosome 11q23.2 is frequently inactivated in human non-small cell lung adenocarcinoma by DNA methylation-associated silencing. The aim of this study was to determine if TSLC1 is inactivated in adenocarcinoma of the pancreas. We analyzed 17 pancreatic cancer cell lines, 91 primary pancreatic adenocarcinoma, 46 pancreatic intraepithelial (PanIN) precursor lesions and 15 microscopically normal pancreata for methylation of the 5' CpG island of the TSLC1 gene through methylation-specific PCR. We observed 5' CpG methylation of TSLC1 in 4 of 17 cell lines (24%). In each cell line the aberrant methylation was associated with loss of TSLC1 expression by RT-PCR that was reversible after treatment with the DNA methyl-transferase inhibitor 5-aza-2'- deoxycytidine. Furthermore, we observed that TSLC1 was methylated in 25 of 91 primary pancreatic adenocarcinomas (27%), and in 2 of 7 highgrade PanIN-3 lesions (29%), but not in low-grade PanIN (0 of 9 PanlN-2 and 0 of 30 PanIN-1) lesions or in normal pancreata (n=15). We conclude that epigenetic silencing of TSLC1 expression through 5' CpG island associated methylation is common in pancreatic adenocarcinoma and is a late event in pancreatic neoplastic development.     

食管鳞癌组织中TSLC1基因启动子甲基化状态检测的临床意义

目的:探讨肺癌抑癌基因1（TSLC1）在食管鳞癌组织中基因启动子甲基化状态及其与临床病理参数的关系。方法:应用甲基化特异性PCR检测TSLC1基因启动子在98例食管鳞癌组织及相应癌旁组织中的甲基化状态并结合临床病理资料进行分析。结果:在食管鳞癌组织中TSLC1基因甲基化阳性率（55.1%,54/98）显著高于癌旁组织（4.1%,4/98）（P<0.01）。TSLC1甲基化与食管鳞癌临床分期和浸润深度显著相关（P=0.035和0.001）。结论:TSLC1基因甲基化可能是参与食管鳞癌发展的重要分子事件。     

Inactivation of the INK4a/ARF locus and p53 in sporadic extrahepatic bile duct cancers and bile tract cancer cell lines.

The tumor-suppressor genes p14(ARF), p16(INK4a) and Tp53 are commonly inactivated in many tumors. We investigated their role in the pathogenesis of 9 bile tract cancer cell lines and 21 primary sporadic extrahepatic bile duct carcinomas. p53 and p16 protein expression was examined by Western blot analysis and immunohistochemistry. Mutation screening of p53 was done by SSCP and direct sequencing. Inactivating mechanisms of p14 and p16 were addressed by screening for mutations, homozygous deletions, chromosomal loss of 9p21 (loss of heterozygosity [LOH] analysis) and promoter hypermethylation of the p14/p16 genes. p53 overexpression could be detected in 7 of 9 cell lines and 7 of 21 primary tumors, but mutations were found in 3 cell lines only. p16 expression was absent in all cell lines, due to homozygous deletion of the gene in 8 of 9 cell lines and hypermethylation of the p16 promoter in one cell line (CC-LP-1). p14 exon 1beta was homozygously deleted in 6 of 9 cell lines, while retained in CC-LP-1 and 2 additional lines. No p14 promoter hypermethylation could be detected. p16 expression was lost in 11 of 21 primary tumors. p16 promoter hypermethylation was present in 9 of 21 primary tumors, all with lost p16 expression. Allelic loss at 9p21 was detected in 13 of 21 primary tumors, 10 of 11 with lost p16 expression and 8 of 9 with methylated p16 promoter. No p14 promoter hypermethylation or p14/p16 mutations could be detected. Neither Tp53 nor p16 alterations showed obvious association with histopathologic or clinical characteristics. In conclusion, inactivation of the p16 gene is a frequent event in primary sporadic extrahepatic bile duct cancers, 9p21 LOH and promoter hypermethylation being the principal inactivating mechanisms. Therefore, p16, but not p14, seems to be the primary target of inactivation at the INK4a locus in bile duct cancers. Other mechanisms than Tp53 mutations seems to be predominantly responsible for stabilization of nuclear p53 protein in bile duct cancers.