A high prevalence of functional inactivation by methylation modification of p16INK4A/CDKN2/MTS1 gene in primary urothelial cancers

Molecular biomarker in prostate cancer: the role of CpG island hypermethylation

CpG island hypermethylation may be one of the earliest somatic genome alterations to occur during the development of multiple cancers. Recently, aberrant methylation patterns for different tumors have been reported. We present a comprehensive review of the literature describing the role of CpG island hypermethylation of DNA from prostatic tissue and bodily fluids from men with prostate cancer. We reviewed the literature to evaluate CpG island hypermethylation in tissue and bodily fluids of men with primary and metastatic prostate cancer. Additionally, we reviewed the literature with respect to CpG island hypermethylation patterns in other urological malignancies. Using modern analytic methods, CpG island hypermethylation detection can be achieved. In men with prostate cancer, correlations between specific gene regulatory region hypermethylation analyses and Gleason score, pathologic stage and tumor recurrence have been demonstrated. CpG island hypermethylation may serve as a useful molecular biomarker for the detection and diagnosis of patients with prostate cancer.

Expression and regulation of MIM (Missing In Metastasis), a novel putative metastasis suppressor gene, and MIM-B, in bladder cancer cell lines

It has been proposed that a 356 amino acid protein encoded by the MIM (Missing In Metastasis) gene on Chromosome 8q24.1, is a bladder cancer metastasis suppressor. Recently, Machesky and colleagues [Biochem. J. 371 (2003) 463] identified MIM-B, a 759 amino acid protein, of which the C-terminal 356 amino acids are almost identical to MIM. Importantly, PCR primers and Northern Blotting probes used in the studies of MIM in bladder cancer did not distinguish between sequences specific for MIM or MIM-B, thus the importance of either protein to bladder cancer remains unclear. We have used primer sequences specific for either MIM or MIM-B to explore the possible functional significance of MIM and MIM-B to bladder cancer cell behaviour. We have compared MIM and MIM-B mRNA levels in a non-tumourigenic, non-invasive, transformed uro-epithelial cell line versus 15 bladder cancer cell lines of differing in vitro invasive abilities, as well as in five cell lines clonally isolated from the BL17/2 bladder tumour cell line, whose in vitro and in vivo invasive abilities have been determined. MIM and MIM-B mRNA levels varied widely between cell lines. Down-regulation of MIM and MIM-B occurred in 6/15 (40%) lines but lines showing down-regulation differed between MIM and MIM-B. Reduced levels of MIM and MIM-B in BL17/2 were further reduced in 2/5 (40%) sublines (MIM and MIM-B). Importantly, there was no association between MIM or MIM-B expression and invasive behaviour in vivo or in vitro. Treatment of representative cell lines with 5-aza-2-deoxycytidine failed to induce MIM or MIM-B expression. Furthermore, there was no association between MIM or MIM-B mRNA levels and p53 functional status. Our data indicate that down-regulation of MIM and/or MIM-B expression can occur in bladder cancer cell lines but is not associated with increased invasive behaviour. Our data also suggest that in those cell lines with reduced levels of MIM and MIM-B mRNA, down-regulation is unlikely to be due to promoter hypermethylation or loss of p53 function.

Methylation of a CpG island within the uroplakin Ib promoter: a possible mechanism for loss of uroplakin Ib expression in bladder carcinoma

Uroplakin Ib is a structural protein on the surface of urothelial cells. Expression of uroplakin Ib mRNA is reduced or absent in many transitional cell carcinomas (TCCs) but molecular mechanisms underlying loss of expression remain to be determined. Analysis of the uroplakin Ib promoter identified a weak CpG island spanning the proximal promoter, exon 1, and the beginning of intron 1. This study examined the hypothesis that methylation of this CpG island regulates uroplakin Ib expression. Uroplakin Ib mRNA levels were determined by reverse transcription polymerase chain reaction and CpG methylation was assessed by bisulfite modification of DNA, PCR, and sequencing. A correlation was demonstrated in 15 TCC lines between uroplakin Ib mRNA expression and lack of CpG methylation. In support of a regulatory role for methylation, incubating uroplakin Ib-negative lines with 5-aza-2'-deoxycytidine reactivated uroplakin Ib mRNA expression. A trend between uroplakin Ib mRNA expression and CpG methylation was also observed in normal urothelium and bladder carcinomas. In particular, loss of uroplakin Ib expression correlated with methylation of a putative Sp1/NFkappaB binding motif. The data are consistent with the hypothesis that methylation of specific sites within the uroplakin Ib promoter may be an important factor in the loss of uroplakin Ib expression in TCCs.

Changes produced in the urothelium by traditional and newer therapeutic procedures for bladder cancer

A handful of traditional and newer therapeutic procedures, such as chemotherapy, immunotherapy, radiotherapy, photodynamic and laser treatment, and gene therapy, are used to treat epithelial malignancies of bladder origin. These treatment modalities, used either intravesically or systemically, produce morphological changes in the urothelial mucosa that can be mistaken for carcinoma. The pathologist must be able to separate toxic and drug related alterations from tumour related changes. The clinical history is usually invaluable in this assessment.

Destabilization of chromosome 9 in transitional cell carcinoma of the urinary bladder

The most frequent genetic alteration in transitional cell carcinoma of the urinary bladder (TCC) is loss of chromosome 9 which targets CDKN2A on 9p. The targets on 9q are not confirmed. Here, 81 advanced TCC specimens were investigated for loss of heterozygosity (LOH) and homozygous deletions (HD) on chromosome 9q using multiplex analysis of microsatellite markers. 41/81 tumours (51%) showed LOH on 9q, with LOH at all markers in 33 cases. Eight partial losses involved three regions in 9q12, 9q22.3, and 9q33- 9q34. No mutations were identified in the candidate tumour suppressor gene DBCCR1 in three tumours showing restricted LOH at 9q32-33. 22% of the specimens had HD at CDKN2A, but no HD was found on 9q. Two tumours had lost 9p only and five 9q only. 9q LOH was not related to tumour grade or stage and present or absent with equal frequency in recurrent TCC. LOH on 9q correlated with the extent of genome-wide hypomethylation (P < 0.0001) which extended into satellite sequences located in 9q12 juxtacentromeric heterochromatin. While the high frequency of chromosome 9q loss in TCC may reflect destabilization of the chromosome related to hypomethylation of repetitive DNA, the data are compatible with the existence of tumour suppressor genes on this chromosome arm.

DNA methylation and the mechanisms of CDKN2A inactivation in transitional cell carcinoma of the urinary bladder

Alterations of the CDKN2A locus on chromosome 9p21 encoding the p16INK4A cell cycle regulator and the p14ARF1 p53 activator proteins are frequently found in bladder cancer. Here, we present an analysis of 86 transitional cell carcinomas (TCC) to elucidate the mechanisms responsible for inactivation of this locus. Multiplex quantitative PCR analysis for five microsatellites around the locus showed that 34 tumors (39%) had loss of heterozygosity (LOH) generally encompassing the entire region. Of these, 17 tumors (20%) carried homozygous deletions of at least one CDKN2A exon and of flanking microsatellites, as detected by quantitative PCR. Analysis by restriction enzyme PCR and methylation-specific PCR showed that only three specimens, each with LOH across 9p21, had bona fide hypermethylation of the CDKN2A exon 1alpha CpG-island in the remaining allele. Like most other specimens, these three specimens displayed substantial genome-wide hypomethylation of DNA as reflected in the methylation status of LINE L1 sequences. The extent of DNA hypomethylation was significantly more pronounced in TCC with LOH and/or homozygous deletions at 9p21 than in those without (26% and 28%, respectively, on average, versus 11%, p < 0.0015). No association of LOH or homozygous deletions at 9p21 with tumor stage or grade was found. The data indicate that DNA hypermethylation may be rare in TCC and that deletions are the most important mechanism for inactivation of the CDKN2A locus. The predominance of allelic loss may be explained by its correlation with genome-wide DNA hypomethylation, which is thought to favor chromosomal instability and illegitimate recombination.

Mutation of cell cycle regulators and their impact on superficial bladder cancer

Early cytogenetic studies in bladder cancer identify regions of chromosomal gain or loss that can be candidate loci for oncogenes and tumor suppressor genes. Oncogenes with potential prognostic significance identified in bladder cancer the RAS family, epidermal growth factor receptor, ERBB-2, MDM2, and cyclin D1. The TP53 gene has been the most thoroughly characterized tumor suppressor gene in bladder cancer, with correlation of TP53 alterations with type of carcinogenic exposure, tumor stage and grade, as well as prognosis. Studies evaluating alterations of the retinoblastoma pathway have identified the retinoblastoma gene, RB, p161NK4A/CDKN2, and E2F-1 as tumor suppressor genes with potential prognostic significance in patients with bladder cancer. Better understanding of the genetic mechanisms underlying bladder tumor development and progression will allow better prevention, diagnosis, and treatment strategies.

Evidence for two candidate tumour suppressor loci on chromosome 9q in transitional cell carcinoma (TCC) of the bladder but no homozygous deletions in bladder tumour cell lines

The most frequent genetic alterations in transitional cell carcinoma (TCC) of the bladder involve loss of heterozygosity (LOH) on chromosome 9p and 9q. The LOH on chromosome 9p most likely targets the CDKN2 locus, which is inactivated in about 50% of TCCs. Candidate genes that are the target for LOH on chromosome 9q have yet to be identified. To narrow the localization of one or more putative tumour suppressor genes on this chromosome that play a role in TCC of the bladder, we examined 59 tumours with a panel of microsatellite markers along the chromosome. LOH was observed in 26 (44%) tumours. We present evidence for two different loci on the long arm of chromosome 9 where potential tumour suppressor genes are expected. These loci are delineated by interstitial deletions in two bladder tumours. Our results confirm the results of others and contribute to a further reduction of the size of these regions, which we called TCC1 and TCC2. These regions were examined for homozygous deletions with EST and STS markers. No homozygous deletions were observed in 17 different bladder tumour cell lines.