Inactivation of TPEF Gene by Aberrant Methylation in Hepatocellular Carcinoma

BACKGROUND: Abnormalities of genomic methylation patterns have been shown to play a role in the development of carcinoma, and the silencing of tumor suppressor genes is related to local de novo methylation. METHODS: Using methylation specific arbitrarily primed-Polymerase Chain Reaction (Ms AP-PCR), we identified a 322 bp sequence that contained a 5' un-translated and exon1 regions of the TPEF gene. To evaluate the inactivation of the TPEF gene through hypermethylation in hepatocellular carcinoma (HCC), we investigated the correlation between methylation patterns and TPEF expression in tumor tissues of human HCC and cell lines via a Combined Bisulfite Restriction Assay (CoBRA) and RT-PCR. RESULTS: A dense methylation pattern of the TPEF was detected in most cell lines, as well as in 10 of the 14 (71.4%) HCC tissues. In addition, loss of heterozygosity (LOH) from the TPEF gene was observed in 5 of the 14 (36%) HCC tissues. Furthermore, RT-PCR analysis revealed TPEF expression in 5 of 8 (62.5%) cell lines. Finally, treatment with a demethylating agent, 5-Aza- 2'-deoxycitidine (5-AzaC), increased the expression of TPEF mRNA. CONCLUSION: These results indicate that inactivation of the TPEF gene through hypermethylation may be a mechanism by which tumorigenesis occurs in HCC.

DNA Hypermethylation of Tumor-Related Genes in Gastric Carcinoma

The hypermethylation of the CpG islands is a common mechanism for the inactivation of tumor-related genes. In the present study, we analyzed the methylation status of genes for cell repair such as hMLH1, MGMT, and GSTP1, and a gastric cancer-specifically methylated DNA fragment, MINT 25 in gastric cancer cases and control groups. The study population consisted of 100 gastric cancer patients (50 distal and 50 proximal carcinomas), and 238 healthy controls. All genes showed more frequent hypermethylation in the cases than in the control group (p<0.0001). We investigated the association between promoter hypermethylation and relevant parameters including age, gender, alcohol consumption, smoking, and family history. There was a common hypermethylation of hMLH1 (p=0.008), MGMT (p= 0.0001), and GSTP1 (p=0.0003) in females. This study also demonstrates that hypermethylation was strongly associated with non-drinkers (MGMT, p=0.046 and MINT 25, p=0.049) and non-smokers (hMLH1, p=0.044; MGMT, p=0.0003; MINT 25, p=0.029). Moreover, the frequency of MINT 25 hypermethylation increased with age (p=0.037), and MGMT methylation was frequently detected in distal gastric cancer than in proximal type (p=0.038). Our study suggested that promoter hypermethylation of the genes involved in cell repair system and MINT 25 is associated strongly with some subgroups of primary gastric carcinoma.

Hypermethylation of Tumor-related Genes in Genitourinary Cancer Cell Lines

Hypermethylation of CpG island is a common mechanism for the inactivation of tumor-related genes. In the present study, we analyzed 13 genitourinary cancer cell lines for aberrant DNA methylation of 5 tumor-related genes using methylation- specific polymerase chain reaction (MSP). GSTP1 was methylated in 5 (38.5%), E-cadherin in 1 (8%), VHL in 1 (8%), and MGMT and hMLH1 in none (0%). Six out of thirteen genitourinary cancer cell lines had methylation of at least one of five genes; 5 had one gene methylated, and, 1 had two genes methylated. Methylation of these 5 genes was not detected in any of the bladder cancer cell lines. GSTP1 was methylated in all of the 3 prostate cancer cell lines. We conclude that aberrant hypermethylation may be an important mechanism for the inactivation of cancer-related genes in kidney and prostate cancer cell lines.

MICROSATELLITE INSTABILITY AND p53 GENE MUTATION IN ORAL SQUAMOUS CELL CARCINOMA

Germ-line mutations at DNA repair loci confer susceptibility to colon cancer in hereditary non-polypopsis colorectal cancer. Somatic loss of DNA mismatch repair gene has been reported in a large variety of other tumor types. Replication errors(RERs) judged by microsatellite instability(MSI) and its associated mutations have been recognized as an important mechanism in various tumor types. To investigate associations between MSI and oral squamous cell carcinoma, the frequency of MSI using 12 microsatellite markers were analyzed for the series of oral tumors. Of 17 tumors, 8 cases(47%) did not show instability at any of the 12 loci; 5(29%) showed instability at 2~3 loci; and 4(24%) showed instability above 4 loci. The 4 cases showing widespread MSI did not differ from those without evidence of instability in terms of age at diagnosis, degree of differentiation, metastasis to lymph node, tumor location or the presence of mutations in the p53 tumor suppressor gene. DCC and D17S 796 were the most frequently detected in MSI analysis. There were no correlation between smoking and MSI frequency, instead, smoking was suggested to increase the mutation rate of p53 and development of oral carcinomas.

Molecular Genetic Alteration and Loss of Genes on the Short Arm of the Chromosome 11 in Bladder Tumor / 대한비뇨기과학회지

Although bladder transitional cell carcinoma (TCC) is common, the underlying molecular events remain ill-defined. So we attempted to define the role of tumor suppressor genes in the pathogenesis of bladder tumor through a molecular genetic study. For 15 bladder TCC (6 gradeII, 1 gradeIII, and 8 grade IV), we performed the restriction fragment length polymorphism (RFLP) analysis for 6 loci of suspected or established tumor suppressor regions (3p21, 3p24-25, llp15, 13q14, and 17p13). Our data confirm that allelic losses are highly common in bladder tumors. We found that alleles from each of the four chromosomal arms tested were lost in most of the tumors. Reduction of allele occured at 3p21 (13%), 3p24~25 (50%), and 13q14 (38%). However, the greatest frequency of allelic loss was seen for 17p 13 (100% of informative cases) and llp15.5 (87% informative cases). Severe allelic losses of chromosome 17p and pADJ762 on lip were seen only in grade IV, not in grade II. Amplification of 3p21 was seen six out of eight. Amplification of 3p21 has not been previously observed on the other study. Addition to this, we observe the loss of H-ras allele on 11p in one case which was associated with duplication of the retained allele as was demonstrated in Wilms'tumors. The results of out study suggest that deletions of pADJ762 on chromosome 11p and 17p13 occur in high grade bladder tumor and may contribute to the progression of this disease. But, there was no apparent correlation between tumor grade and the loss of 3p or 13q14 alleles although they had some deletions. The role of these genetic alterations in the prognosis of bladder transitional cell carcinoma will require additional follow-up and further studies.

Altered Expressions and Point Mutations of p53 in Human Bladder Transitional Cell Carcinomas / 대한비뇨기과학회지

The objective of this study was to characterise the pattern of p53 mutations in bladder tumor. In this study, 25 bladder transitional cell carcinomas were analyzed by immunohisochemistry (IHC) for p53 nuclear overexpression, and the results were compared with those of polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) analysis in exon 5-8 of the p53 gene and DNA sequencing analysis. 15 out of 20 cases (75%) showed p53 nuclear immunoreactivities on IHC. On PCR-SSCP analysis, 10 out of 25 cases (40%) had abnormal shifts in mobility. 62% of the mutations were in exon 8. Direct DNA sequencing analysis were performed in these 10 cases to confirm the presence of mutated p53 genes and to determine the type of mutations. Sixteen point mutations were detected in 10 cases. Two specimens had double mutations and another two had triple mutations. G:C-->A:T transitions were the most frequent patterns (62.5%). One mutation was a premature stop codon and two were silent mutations. Three out of 10 had a point mutation at codon 285 (GAG/Glu-->AAG/Lys) and two had at codon 280 (AGA/Arg-->AAA/Lys). One of 16 mutations was transition at hot spot codon 273 with CpG site. These results suggest that altered expressions and point mutations of p53 occured in all grade of bladder cancer, but are more associated with high grade bladder tumors. To elucidate the carcinogenesis of bladder cancer, further studies should be carried out.