cytidylyl-3--5--guanosine and Urinary-Bladder-Neoplasms

XIAP-associated factor 1 (XAF1) is a new candidate tumor suppressor, which has been known to exert proapoptotic effects by interfering with the caspase-inhibiting activity of XIAP. To explore the XAF1's candidacy for a suppressor in urogenital tumorigenesis, we investigated the XAF1 status in a series of cancer cell lines and primary tumors derived from the bladder, kidney and prostate. Expression of XAF1 transcript was undetectable or extremely low in 60% (3/5) of bladder, 66% (10/15) of kidney, and 100% (3/3) prostate cancer cell lines. Abnormal reduction of XAF1 was also found in 33% (18/55) of primary bladder and 40% (8/20) of primary kidney tumors, and showed a correlation with advanced stage and high grade of bladder tumor. Hypermethylation at 14 CpG sites in the 5' proximal region of the XAF1 promoter was highly prevalent in cancers versus adjacent normal or benign tissues and tightly associated with reduced gene expression. XAF1 expression enhanced the apoptotic response of tumor cells to chemotherapeutic agents, such as etoposide or 5-FU. While XAF1 expression did not influence the subcellular distribution or expression of XIAP, it elevated the protein stability of p53 and its target gene expression. Moreover, the apoptosis-sensitizing and growth suppression function of XAF1 was markedly impeded by blockade of p53 function. Collectively, our study demonstrates that epigenetic alteration of XAF1 is frequent in human urogenital cancers and may contribute to the malignant progression of tumors by rendering tumor cells a survival advantage partially through the attenuated p53 response to apoptotic stresses.

Topics: Adaptor Proteins, Signal Transducing; Apoptosis Regulatory Proteins; Dinucleoside Phosphates; DNA Methylation; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Intracellular Signaling Peptides and Proteins; Kidney Neoplasms; Male; Neoplasm Proteins; Promoter Regions, Genetic; Prostatic Neoplasms; Reverse Transcriptase Polymerase Chain Reaction; Tumor Suppressor Protein p53; Urinary Bladder Neoplasms; Urogenital Neoplasms

4-aminobiphenyl (4-ABP) is a major etiological agent of human bladder cancer, and its metabolites are able to form DNA adducts that may induce mutation and initiate bladder carcinogenesis. Thirty to sixty percent of human bladder cancer has a mutation in the p53 gene, and the mutational spectrum bears two characteristics: compared with other cancers, the pattern of mutations is more evenly distributed along the p53 gene, and the mutational hotspots occur at both CpG sites, such as codons 175, 248 and 273, and non-CpG sites, such as codons 280 and 285, the latter two being unique mutational hotspots for bladder and other urinary tract cancers. These findings raise the possibility that the special p53 mutational features in human bladder cancer are due to the unique binding spectrum of metabolically activated 4-ABP in bladder cells. To address this question, here we have mapped the 4-ABP-DNA adduct distribution in the p53 gene at the nucleotide sequence level in human bladder cells. We found that, unlike benzo[a]pyrene trans-7,8-dihydrodiol-9,10-epoxide-DNA adduction, which preferentially occurs at CpG sites, 4-ABP-DNA adduction is not biased for CpG sites, and the adducts are more evenly distributed along the p53 gene; nonetheless, the p53 mutational hotspots in bladder cancer at codons 175, 248, 280 and 285 are also the preferential sites for 4-ABP adduct formation. These results strongly suggest that the unique binding spectrum of 4-ABP contributes greatly to the unique mutational spectrum in the p53 gene of human bladder cancer, and provide further molecular evidence to directly link 4-ABP to bladder cancer.

Topics: Aminobiphenyl Compounds; Base Sequence; Carcinogens; Cell Line; Codon; Dinucleoside Phosphates; DNA Adducts; Exons; Genes, p53; Humans; Lung; Molecular Sequence Data; Mutation; Urinary Bladder; Urinary Bladder Neoplasms; Urologic Neoplasms

Topics: Dinucleoside Phosphates; DNA Methylation; Genes, Tumor Suppressor; Humans; Receptor, Endothelin B; Receptors, Endothelin; Tumor Cells, Cultured; Urinary Bladder Neoplasms

We have developed a rapid quantitative method (Ms-SNuPE) for assessing methylation differences at specific CpG sites based on bisulfite treatment of DNA followed by single nucleotide primer extension. Genomic DNA was first reacted with sodium bisulfite to convert unmethylated cytosine to uracil while leaving 5-methylcytosine unchanged. Amplification of the desired target sequence was then performed using PCR primers specific for bisulfite-converted DNA and the resulting product isolated and used as a template for methylation analysis at the CpG site(s) of interest. This methylation-sensitive technique has several advantages over existing methods used for detection of methylation changes because small amounts of DNA can be analyzed including microdissected pathology sections and it avoids utilization of restriction enzymes for determining the methylation status at CpG sites.

Topics: Dinucleoside Phosphates; DNA; DNA Methylation; DNA Primers; Genetic Techniques; Humans; Indicators and Reagents; Microchemistry; Polymerase Chain Reaction; Restriction Mapping; Sulfates; Tumor Cells, Cultured; Urinary Bladder Neoplasms

Cytosine methylation at CpG dinucleotides is thought to cause more than one-third of all transition mutations responsible for human genetic diseases and cancer. We investigated the methylation status of the CpG dinucleotide at codon 248 in exon 7 of the p53 gene because this codon is a hot spot for inactivating mutations in the germ line and in most human somatic tissues examined. Codon 248 is contained within an HpaII site (CCGG), and the methylation status of this and flanking CpG sites was analyzed by using the methylation-sensitive enzymes CfoI (GCGC) and HpaII. Codon 248 and the CfoI and HpaII sites in the flanking introns were methylated in every tissue and cell line examined, indicating extensive methylation of this region in the p53 gene. Exhaustive treatment of an osteogenic sarcoma cell line, TE85, with the hypomethylating drug 5-aza-2'-deoxycytidine did not demethylate codon 248 or the CfoI sites in intron 6, although considerable global demethylation of the p53 gene was induced. Constructs containing either exon 7 alone or exon 7 and the flanking introns were transfected into TE85 cells to determine whether de novo methylation would occur. The presence of exon 7 alone caused some de novo methylation to occur at codon 248. More extensive de novo methylation of the CfoI sites in intron 6, which contains an Alu sequence, occurred in cells transfected with a vector containing exon 7 and flanking introns. With longer time in culture, there was increased methylation at the CfoI sites, and de novo methylation of codon 248 and its flanking HpaII sites was observed. These de novo-methylated sites were also resistant to 5-aza-2'-deoxycytidine-induced demethylation. The frequent methylation of codon 248 and adjacent Alu sequence may explain the enhanced mutability of this site as a result of the deamination of the 5-methylcytosine.

Topics: Base Sequence; Blotting, Southern; Bone Neoplasms; Carcinoma, Transitional Cell; Cell Line; Codon; Dinucleoside Phosphates; DNA; DNA, Neoplasm; Fetus; Genes, p53; Humans; Introns; Lymphocytes; Male; Methylation; Molecular Sequence Data; Muscles; Neoplasms; Osteosarcoma; Point Mutation; Polymerase Chain Reaction; Spermatozoa; Transfection; Tumor Cells, Cultured; Urinary Bladder Neoplasms