Methyl group metabolism gene polymorphisms and susceptibility to prostatic carcinoma

BACKGROUND

Alterations of DNA methylation are very frequent in prostatic carcinoma. A possible cause underlying altered DNA methylation could be an insufficient level of S-adenosylmethionine as a consequence of nutritional imbalances or of weaker alleles of genes for its synthesis, i.e., encoding methylene-tetrahydrofolate reductase (MTHFR), methionine synthase (MS), and beta-cystathione synthetase (CBS). Therefore, homozygosity or heterozygosity for such weaker alleles may underlie susceptibility to prostatic carcinoma.

METHODS

The distribution of the two most frequent MTHFR, MS, and CBS alleles was determined in 132 prostatic carcinoma patients and 150 population controls by restriction fragment length polymorphism-(RFLP) PCR.

RESULTS

In the controls, a Hardy-Weinberg equilibrium was observed for each allele pair. No significant differences were observed with respect to age or gender. No significant differences for single genes or combinations were found between prostatic carcinoma patients and controls, although the MTHFR Val allele was slightly overrepresented among the tumor patients. Neither did the allele distribution significantly differ among the prostatic carcinoma patients stratified according to age, clinical stage, or presence of metastases. However, the MTHFR Val allele tended to be associated with higher tumor grade.

CONCLUSIONS

In general, the data do not support the hypothesis that weaker alleles in methyl group metabolism genes constitute a major factor in the high prevalence of DNA methylation alterations found in prostatic carcinoma. However, a potential association with the MTHFR genotype deserves further study.

Glutathione transferase isozyme genotypes in patients with prostate and bladder carcinoma

Genotype distributions for GSTP1, GSTM1, and GSTT1 were determined in 91 patients with prostatic carcinoma and 135 patients with bladder carcinoma and compared with those in 127 abdominal surgery patients without malignancies. None of the genotypes differed significantly with respect to age or sex among controls or cancer patients. In the group of prostatic carcinoma patients, GSTT1 null allele homozygotes were more prevalent (25% in carcinoma patients vs. 13% in controls, Fisher P =0.02, chi2 P=0.02, OR=2.31, CI = 1.17-4.59) and the combined M1-/T1 -null genotype was also more frequent (9% vs. 3%, chi2 P=0.02, Fisher P = 0.03). Homozygosity for the GSTM1 null allele was more frequent among bladder carcinoma patients (59% in bladder carcinoma patients vs 45% in controls, Fisher P=0.03, chi2 P=0.02, OR=1.76, CI=1.08-2.88). In contrast to a previous report, no significant increase in the frequency of the GSTP1b allele was found in the tumor patients. Except for the combined GSTM1-/ T1-null genotype in prostatic carcinoma, none of the combined genotypes showed a significant association with either of the cancers. These findings suggest that specific single polymorphic GST genes, that is GSTM1 in the case of bladder cancer and GSTT1 in the case of prostatic carcinoma, are most relevant for the development of these urological malignancies among the general population in Central Europe.

Cyclin-dependent kinase inhibitor P27(KIP1) is expressed preferentially in early stages of urothelial carcinoma

OBJECTIVES

To evaluate the expression of p27(KIP1) and p21(CIP1) and the prognostic values of both markers in urothelial carcinoma. The expression of the cyclin-dependent kinase inhibitor p27(KIP1) characterizes early-stage and well-differentiated carcinomas of the colon, breast, and prostate and is associated with an improved prognosis. In urothelial carcinoma, its expression has not been as well investigated. Another cyclin-dependent kinase inhibitor, p21(CIP1), is expressed in early-stage bladder tumors, but published data on its prognostic value are contradictory.

METHODS

Expression of p27(KIP1) and p21(CIP1) was analyzed by immunohistochemistry in 114 urothelial carcinoma specimens from 77 patients. The Ki67 index was determined as an indicator of cell proliferation. The expression of the markers was correlated with tumor recurrence and progression during an average follow-up period of 3.9 years.

RESULTS

Expression of p27(KIP1) was significantly more frequent in superficial than in muscle-invasive tumors (chi-square test, P = 0.012; Fisher's exact test, P = 0.014). Although similar overall, the expression pattern of p21(CIP1) did not match on a tumor-by-tumor basis. No correlation was seen with the Ki67 index. Patients with tumors displaying strong positive staining for p27(KIP1) or p21(CIP1) had fewer recurrences and progression events, but the difference was not statistically significant. Instead, a Ki67 index of less than 10% was significantly (P = 0.0335) related to a lack of recurrence.

CONCLUSIONS

Neither p27(KIP1) nor p21(CIP1) appear to be good predictors of tumor progression in urothelial carcinoma, even though their expression is strongly decreased in muscle-invasive tumors.

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.

Novel mutations of the von hippel-lindau tumor-suppressor gene and rare DNA hypermethylation in renal-cell carcinoma cell lines of the clear-cell type

Renal-cell carcinoma (RCC) is the most common neoplasm of the kidney, accounting for about 3% of all adult malignancies. Histopathologically, 80% of all cases can be classified as clear-cell RCC. Of these, approximately 55% to 70% are associated with mutations in the von Hippel-Lindau (VHL) tumor-suppressor gene. Here, new mutations of the VHL gene were defined by the use of temperature gradient gel electrophoresis and subsequent sequencing. In addition, DNA hypermethylation, an alternative mechanism of VHL gene silencing, was evaluated by methylation-specific PCR. Twenty-six clear-cell, 3 chromophilic, and 2 chromophobic RCC cell lines were analyzed. Among the clear-cell RCC cell lines tested, 12 (47%) contained 13 mutations overall: 8 (62%) in exon 1, 3 (23%) in exon 2, and 2 (15%) in exon 3. Ten of these mutations have thus far not been described. All single base pair changes were transversions. Six mutations led to alteration of a single amino acid. Seven mutations generated a frameshift or a stop codon. One cell line contained a complex duplication of 36 bp. All cell lines with mutations showed loss of heterozygosity in the VHL gene. No mutations could be detected in the chromophilic or chromophobic RCC samples. Significant hypermethylation was not observed in any of the cell lines. These data provide further evidence that distinct mutations in the VHL gene are a characteristic feature of clear-cell RCC. In contrast, hypermethylation of the gene is probably a rare event. The high frequency of transversion mutations suggests a role for exogenous carcinogens in the etiology of clear-cell RCCs.

Decreased expression of p57(KIP2)mRNA in human bladder cancer

To identify targets of genetic and epigenetic alterations on chromosome 11p15.5 in human bladder cancer, expression of the imprinted KIP2, IGF2 and H19 genes was studied by quantitative RT-PCR in 24 paired samples of urothelial carcinomas and morphologically normal mucosa obtained by cystectomy, and in bladder carcinoma cell lines. The most frequent alteration in tumour tissue was decreased expression of KIP2 identified in 9/24 (37%) specimens. Decreased IGF2 and H19 mRNA levels were found in five (21%) and three (13%) tumours, respectively. One tumour each overexpressed IGF2 and H19. Loss of H19 expression was only found associated with loss of KIP2 expression, whereas decreased expression of IGF2 mRNA occurred independently. Almost all bladder carcinoma cell lines showed significant changes in the expression of at least one gene with diminished expression of KIP2 mRNA as the most frequent alteration. IGF2 mRNA levels were diminished in several lines, but increased in others. The KIP2 gene could be an important target of genetic and epigenetic alterations in bladder cancer affecting the maternal chromosome 11p15.5. However, reminiscent of the situation in Wilms' tumours, expression of the IGF2 gene on the paternal chromosome can also be disturbed in bladder cancers.

Delineation of the 6p22 amplification unit in urinary bladder carcinoma cell lines

Eight cell lines from transitional cell carcinoma of the urinary bladder were analyzed by comparative genomic hybridization. All tumor lines exhibited frequent chromosome gains (11.5/cell line) and losses (8.4/cell line). In six cell lines, gain of chromosome 5p was associated with gains of 6p and 20q. In five of these cell lines, amplification of parts of 6p was observed. Cytogenetic investigation combined with fluorescence in situ hybridization analysis revealed typical marker chromosomes with homogeneously staining regions (HSRs) containing material from 6p. By hybridizing individual yeast artificial chromosome probes from a chromosome 6p contig to these HSRs, a contig of three yeast artificial chromosomes common to all 6p HSRs was identified that spans less than 2 Mb. The genes SOX4 and PRL were shown to map to this region and to be coamplified in the cell lines. However, SOX4 was not overexpressed in any cell line and PRL was not expressed at all. Thus, the presumptive 6p oncogene remains to be conclusively identified.

Phenol sulphotransferase SULT1A1 polymorphism in prostate cancer: lack of association

Preliminary evidence suggests that genetic polymorphisms in certain enzymes involved in xenobiotic metabolism and chemical defense could modify a susceptibility to prostate cancer. In the present study, two recently described phenol sulphotransferase SULT1A1 alleles (SULT1A1*1, SULT1A1*2) were investigated using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) approach. Genotyping was performed on DNA isolated from white blood cells from 134 patients with prostate cancer and 184 healthy control subjects. Both the prostate cancer patients and the controls demonstrated similar frequencies of the variant allele SULT1A1*2 (35.1% vs 39.1%). Homozygosity for the variant allele was slightly less frequent in cancer patients than controls (12.7% vs 17.4%). Our study does not support the hypothesis that the phenol sulphotransferase variant allele SULT1A1*2 with a G/A transition at nucleotide 638 is a risk modifier for prostate cancer in the Caucasian population.

DNA methylation and expression of LINE-1 and HERV-K provirus sequences in urothelial and renal cell carcinomas

Since DNA methylation is considered an important mechanism for silencing of retroelements in the mammalian genome, hypomethylation in human tumours may lead to their reactivation. The methylation status of LINE-1 retroposons was determined in 73 samples of urinary bladder cancers, 34 specimens of renal cell carcinoma and in the corresponding normal tissues by Southern blot analysis. LINE-1 sequences were strongly methylated in normal tissues and were significantly hypomethylated in 69 (95%) urothelial carcinomas, but in none of the renal carcinomas. Hypomethylation in bladder cancers was independent of stage and tended to increase with grade. The methylation status of HERV-K proviral DNA in normal and transformed urothelial cells paralleled that of LINE-1 sequences (r2 = 0.87). It was shown by ligation-mediated polymerase chain reaction that hypomethylation also extended to the LINE-1 promoter sequence located at the 5'-ends of full-length elements which is repressed by methylation in somatic tissues. Accordingly, full-length LINE-1 transcripts were detected by Northern blot analysis in two urothelial carcinoma cell lines. In contrast, transcripts from HERV-K proviruses were restricted to teratocarcinoma cell lines. Our data indicate that genome-wide DNA hypomethylation is an early change in urothelial carcinoma, but is absent from renal cell carcinoma. The coordinate changes of LINE-1 and HERV-K DNA methylation suggest that hypomethylation in urothelial cancer affects a variety of different retroelements to similar extents. We speculate that decreased methylation of LINE-1 retroelements, in particular, may contribute to genomic instability in specific human tumours such as urothelial carcinoma by rendering these normally repressed sequences competent for transcription and recombination.

High frequency of alterations in DNA methylation in adenocarcinoma of the prostate

BACKGROUND

Alterations of DNA methylation have been reported in many human cancers. In prostatic carcinoma, hypermethylation of the GST P gene promoter and an overall decrease in methylcytosine content have been reported. The aim of the present study was to investigate the frequency and extent of these alterations in relation to tumor stage and grade, in order to explore their clinical relevance and to determine their relationship to each other.

METHODS

DNA from 32 histologically verified adenocarcinomas of the prostate was analyzed for GST P hypermethylation by a semiquantitative PCR method and for overall DNA methylation by quantitative Southern blot analysis or LM-PCR of LINE-1 repetitive sequence methylation.

RESULTS

GST P hypermethylation was detected in 24/32 (75%) specimens, and LINE-1 hypomethylation in 17/32 (53%). Both alterations tended to increase in frequency and extent with tumor stage. All but 1 of 8 carcinomas with lymph node involvement were positive for GST P hypermethylation. Six of these as compared to 2 out of 24 showed strong hypomethylation (P = 0.005). Hypermethylation and hypomethylation did not show a quantitative correlation, but all except two samples with weak LINE-1 hypomethylation also displayed GST P hypermethylation.

CONCLUSIONS

GST P hypermethylation is an extremely frequent change in prostatic carcinoma which most probably precedes genome-wide hypomethylation. It appears useful for sensitive detection of prostatic carcinoma, whereas pronounced LINE-1 hypomethylation may be associated with progressive tumors.

Loss of function of the tissue specific transcription factor HNF1 alpha in renal cell carcinoma and clinical prognosis

BACKGROUND

Human renal cell carcinogenesis is associated with loss of expression of tissue-specific genes and loss of function of tissue-specific transcription factors such as HNF(hepatic nuclear factor)1 alpha.

MATERIALS AND METHODS

In this study HNF1 alpha DNA-binding activities and protein amounts were determined by gel retardation assay and Western blot analysis, respectively, in 42 non-metastasized renal cell carcinomas and paired normal tissues.

RESULTS

36 tumors out of 42 (86%) showed diminished binding activity of HNF1 alpha. In most cases (26 out of 42) this appeared to be due to decreased amounts of HNF1 alpha protein, but 10 tumors contained equal or even higher amounts of HNF1 alpha, in spite of reduced binding to DNA. Only 6 tumors out of 42 had unaltered HNF1 alpha binding activity. A clinical follow-up was obtained for 40 patients. Over an average follow-up period of 39 months no significant differences in the survival rate were observed between patients having lost or retained HNF1 alpha function. However, since most of the patients with retained function are still alive, long-term follow-up might be warranted.

CONCLUSIONS

The very high incidence of loss of HNF1 alpha function indicates the important biological role of this change in renal cell carcinoma.

Over-expression and amplification of the c-myc gene in human urothelial carcinoma

To understand the mechanisms underlying increased expression of Myc protein in human urinary bladder cancer, expression of c-myc mRNA and the copy number of the c-myc gene were determined. Expression of mRNA was measured by quantitative RT-PCR in 40 urothelial carcinomas and in 18 histologically normal mucosae. Mean expression in tumors was significantly increased (3.23+/-2.63 AU vs. 1.90+/-0.95 AU, p < 0.023) and exceeded the highest level in normal mucosa in 15 (37.5%) tumors. The c-myc gene copy number was higher than in leukocytes and normal bladder mucosa in 14 of 40 tumors, but only 3 among these showed a more than 4-fold increase indicative of gene amplification. Most, but not all, tumors with elevated expression displayed an increased gene copy number (p < 0.0001). In line with other studies of the protein level, no significant association either of c-myc mRNA over-expression or of increased gene copy number with tumor stage or grade was observed. The data indicate that elevated mRNA expression as a consequence of increases in c-myc gene copy number often underlies Myc protein over-expression in bladder cancer. This increase may be a consequence of, most frequently, chromosome 8q gain and, occasionally, gene amplification, while in some tumors deregulation of mRNA expression occurs without evident changes in the c-myc gene copy number.

Loss of HNF1alpha function in human renal cell carcinoma: frequent mutations in the VHL gene but not the HNF1alpha gene

Human renal cell carcinoma (RCC) is a common malignant disease of the kidney characterized by dedifferentiation of renal epithelial cells. Our previous experiments showed that most RCCs have a loss of function of the tissue-specific transcription factor hepatocyte nuclear factor (HNF) 1alpha. Detailed analyses of the 10 exons encoding HNF1alpha in 32 human RCCs by single-strand conformation polymorphism analysis and direct DNA sequencing revealed no tumor-associated mutation, whereas with the same probes we frequently found mutations in the von Hippel-Lindau tumor suppressor gene. No mutation leading to loss of HNF1alpha function was detected by analyzing the integrity of the HNF1alpha transcripts in the RNA derived from RCCs by the protein truncation test. Investigating human RCC cell lines by western blotting and gel retardation assays showed a dramatic loss in the expression of the tissue-specific transcription factor HNF1alpha in eight of 10 cell lines. As the HNF1alpha-related transcription factor HNF1beta was expressed in all these tumor cell lines, the loss of HNF1alpha expression was a specific event and was maintained in RCC cell lines. The loss of HNF1alpha expression in RCC cell lines on the RNA level was confirmed by reverse transcription polymerase chain reaction. We propose that tumor-associated mutations in the HNF1alpha gene do not occur in human RCC and that the loss of function is partially due to a transcriptional inactivation of the HNF1alpha gene.

Predisposition towards urolithiasis associated with the NQO1 null-allele

The distribution of two alleles of the NQO1 gene encoding NADP(H):quinone oxidoreductase was studied in 140 urolithiasis patients and 271 control individuals. The minor allele encoding a protein lacking quinone reductase activity was significantly more frequent (q = 0.214) among these patients than in control individuals (P = 0.135) indicating an increased risk for kidney stone formation among heterozygotes (odds ratio 1.83, confidence interval 1.17-2.86) and homozygotes for the null-allele (odds ratio 2.97, confidence interval 0.78-11.33). Since NADP(H):quinone oxidoreductase is thought to participate in activation of vitamin K for protein gamma-carboxylation, decreased activity of the enzyme in heterozygotes or in null-allele homozygotes may disturb the post-translational modification of urinary calcium-binding proteins protective against kidney stone formation. The NQO1 null-allele might therefore be a determinant in enhanced risk of urolithiasis.

Predictive value of molecular alterations for the prognosis of urothelial carcinoma

Accumulation of p53 and C-Myc overexpression are frequently found in advanced urothelial carcinomas. The prevalence and predictive value of both molecular alterations was investigated in 61 patients with superficial urothelial tumors. Distinct patterns of p53 accumulation and C-Myc overexpression were observed in superficial urothelial carcinoma of different stages. For instance, 67% of carcinomata in situ displayed accumulation of p53, but only 44% showed C-Myc overexpression, whereas in pT1 tumors the corresponding percentages were 25 and 75%. Similarly, while p53 accumulation was significantly (p = 0.02) associated with tumor grade, C-Myc overexpression did not correlate with grade. In multivariate analysis, p53 accumulation was found to be an independent predictor of tumor progression (p = 0.0096), whereas C-Myc overexpression did not correlate with the course of disease. Alterations in both markers together predicted neither tumor recurrence nor tumor progression better than p53 accumulation on its own. Sufficient expression of C-Myc may be a general requirement for proliferative competence in urothelial tumors, barring its use as a predictive marker. The predictive value of p53 accumulation for tumor progression was further underlined by the finding that in a distinct group of 52 patients with progressive urothelial carcinoma 73% of the recurrent tumors displayed p53 accumulation.

Regulation of CD95 (Apo-1/Fas) ligand and receptor expression in human embryonal carcinoma cells by interferon gamma and all-trans retinoic acid

Expression of CD95 (Apo-1/Fas) ligand and its two receptor isoforms, in response to all-trans retinoic acid and interferon gamma (IFNgamma), was analyzed atthe mRNA and protein levels in human Tera-2 embryonal carcinoma cells. Exposure of Tera-2 cells to all-trans retinoic acid for up to 16 days led to a decrease of CD95 ligand expression when compared to the control conditions, whereas expression of both CD95 isoforms increased. These changes were functionally significant since Tera-2 cells treated with all-trans retinoic acid for six to 16 days were more susceptible to CD95-mediated apoptosis. On the other hand, Tera-2 cells lost their capacity to induce apoptosis in CD95 receptor bearing Jurkat T lymphocytes after six days of incubation with all-trans retinoic acid. When Tera-2 cells were treated with IFNgamma, expression of CD95 ligand and both CD95 receptor isoforms increased within 24 hours. Tera-2 cells were then more susceptible to CD95 mediated apoptosis but also killed more CD95 receptor bearing Jurkat T lymphocytes via CD95 ligation compared to the control conditions. The results are indicative of differential regulation of CD95-mediated apoptosis by all-trans retinoic acid and IFNgamma in Tera-2 embryonal carcinoma cells, with likely impact on antitumor immunity.

DNA methylation in urological malignancies (review)

Three different kinds of alterations in DNA methylation have been observed in urological malignancies. DNA hypermethylation of CpG-rich promoter regions is an important mechanism involved in the inactivation of tumor suppressor and other genes in prostate, renal cell, and bladder carcinoma. Genome-wide hypomethylation is most pronounced in urothelial carcinoma, but also occurs in prostatic cancer. Loss of imprinting may be a primary event in the aetiogenesis of Wilms' tumor and probably contributes to testicular cancer. With respect to alterations in DNA methylation three tumor categories are distinguished: in the development of embryonic tumors, e.g. Wilms' tumor, loss of imprinting is important probably by upsetting the balance between genes promoting or inhibiting proliferation. In tumors with faulty DNA methylation, e.g. renal cell carcinoma, occasional errors in DNA methylation are selected for during tumor development. In tumors with deranged methylation, e. g. in most bladder and prostate carcinomas, the mechanisms establishing methylation patterns are fundamentally disturbed and multiple alterations in DNA methylation are observed. At least one of the enzymes establishing methylation patterns, viz. DNA methyltransferases and demethylases, may be deregulated. Moreover, changes in methyl group metabolism need to be considered. DNA hypermethylation and loss of imprinting act by altering the expression of selected genes, whereas hypomethylation may facilitate transcription and recombination throughout the genome by its effect on the chromatin structure. The combination of all three types of alterations may create genomic instability in tumors with deranged DNA methylation. Regarding a potential clinical use, detection of hypermethylation appears most promising in cancer diagnosis, while parameters reflecting genome-wide hypomethylation may prove useful in the prediction of prognosis. Inhibitors of DNA methylation are being improved and will presumably first be employed against tumors with hypermethylated key tumor suppressor genes.

Expression of G1-->S transition regulatory molecules in human urothelial cancer

Growth of cancer cells is characterized by accelerated passage through the cell cycle, which is often caused by deregulation of the G1-->S transition. In this study the expression of G1-->S transition regulatory molecules was analyzed in 32 transitional cell carcinoma specimens and fifteen normal tissues obtained by cystectomy or nephroureterectomy of mainly locally advanced tumors, as well as six bladder cancer cell lines. Expression of mRNAs for cyclins D1 and D2 and cyclin-dependent kinases (CDK) 2 and 4 was investigated by quantitative reverse transcription-polymerase chain reaction. Overexpression of cyclin D1 compared to normal mucosa was observed in 3 tumors (9.4%), but in neither of the cell lines. All tumors with overexpression were moderately differentiated (G2) pT1 or pT2 tumors, and thus among the less advanced specimens. Cyclin D2 was not expressed in normal bladder mucosa or in tumors. The expression of CDK4 mRNA varied within the same range in mucosa, tumors, and cell lines. CDK2 mRNA expression varied more strongly and was diminished in individual tumors and in four cell lines. It is concluded that cyclin D1 overexpression can play an important role in the early stage of urothelial tumorigenesis, driving cell proliferation. Ectopic expression of cyclin D2 or amplification of CDK4 does not occur at a significant frequency in urothelial carcinomas. Different expression patterns of cyclin D1 and CDK2 indicate heterogeneity in the mechanisms of G1-->S transition deregulation in individual bladder tumors which may elicit differences in their biological and clinical behavior.

WAF1/p21 regulates proliferation, but does not mediate p53-dependent apoptosis in urothelial carcinoma cell lines

The WAF1/p21 gene product is an inhibitor of cyclin-dependent kinases which can be induced by the tumor suppressor p53 and mediate some of its effects, or function in p53-independent pathways of cell cycle regulation. Although a potential tumor suppressor gene, WAF1/p21 is expressed in bladder cancer. To elucidate the function of p21 in tumor cells we have investigated in urothelial carcinoma cell lines: i) WAF1/p21 mRNA and protein expression, ii) the biological effects of p21 overexpression or down-regulation and (iii) whether p21 can be induced by p53. WAF1/p21 mRNA levels examined in four cell lines were comparable to bladder mucosa. One cell line, HT1376, failed to express p21 protein due to a frame shift mutation. Overexpression of WAF1/p21 cDNA inhibited clone formation in three cell lines, whereas transfection with antisense WAF1 increased clone sizes and numbers. WAF1 sense clones showed diminished cell proliferation compared to the parental cell line. Apoptosis- induced wild-type p53 was not inhibited by overexpression of antisense WAF1/p21. In a cell clone derived from line VMCub1 by stable transfection with wild-type p53 under the control of a metallothionein promotor, p21 was induced along with p53 upon activation of the promoter with zinc chloride. This induction was accompanied by a decrease in cell proliferation but by little apoptosis. These data suggest that p21 inhibits proliferation in a p53-dependent or independent manner but does not mediate p53-induced apoptosis in urothelial carcinoma cells.

Frequent and heterogeneous expression of cyclin-dependent kinase inhibitor WAF1/p21 protein and mRNA in urothelial carcinoma

The inhibitor of cyclin-dependent kinases WAF1/p21 has been shown to mediate cell cycle arrest by p53 and other factors. We have studied its expression in urothelial carcinoma. Immunohistochemistry of paraffin-embedded tissues revealed no detectable p21 protein in normal mucosa, whereas 8 of 17 (47%) carcinomata in situ, 41 of 62 (66%) pTa, 14 of 30 (47%) pT1 and 5 of 15 (33%) muscle-invasive tumours stained positive, usually with a heterogeneous pattern. Expression of p21 was associated with low grade tumours. In contrast, the frequency of p53 accumulation increased with grade and stage as did the frequency of staining for the proliferation marker Ki67. The level of WAF1 mRNA was determined relative to beta-actin mRNA by quantitative reverse transcriptase polymerase chain reaction (RT-PCR) in 15 freshly frozen invasive tumours. In eight samples obtained from normal bladder mucosa, the values ranged from 0.93 to 2.19 arbitrary units (AU) (mean 1.54+/-0.37 AU), but varied widely from non-detectable to 16.21 AU (mean 3.02+/-4.44 AU) in the tumour specimens. In accord with the immunohistochemical findings, WAF1 mRNA expression was elevated over the range found in normal mucosa in 5 of 15 advanced tumours. In addition, RNA analysis revealed a decrease in expression in six tumours. No mutations were observed in the WAF1/p21 gene in these tumours, but two were heterozygous for the codon 31 polymorphism. These data indicate that p21 is frequently expressed in superficial, well differentiated urothelial carcinomas, but less often in muscle-invasive urothelial carcinomas, irrespective of their p53 status. The expression of p21 and its prevalence in low-stage tumours may reflect residual growth-regulatory influences potentially impeding but not necessarily inhibiting tumour development.

p53 and MDM2 in the development and progression of bladder cancer

OBJECTIVE

Earlier investigations have demonstrated that inactivation of the p53 tumor suppressor gene might play a role in the development and progression of bladder cancer. Complex formation with the MDM2 oncogene product is one mechanism inactivating the p53 protein. Therefore, the MDM2 and the p53 protein were investigated to study potential interactions in bladder cancer.

METHOD

200 archival bladder tissue specimens from 92 patients were studied by immunohistochemistry using monoclonal antibodies DO-1 against p53 and IF2 against MDM2.

RESULTS

No staining was observed for p53 or MDM2 in normal urothelium. Alterations of both genes were rare in dysplasia. p53 accumulation was observed in 27-44% of the tumor stages examined. MDM2 overexpression increased from 18% in carcinoma in situ to 49% in T1 tumors, but was present in only 22% of the advanced tumors. Alterations of both genes were more frequent in high-grade lesions. To investigate the prognostic impact of these alterations 61 patients with superficial bladder tumors were followed for at least 2 years (mean 51 months). Multivariate analysis demonstrated that multifocal disease and p53 accumulation were significantly correlated with tumor progression (p = 0.0099 and 0.0135). MDM2 overexpression alone had no prognostic significance. Patients with alterations of both genes had a very high risk of tumor progression (p = 0.0064).

CONCLUSION

These results demonstrate a positive correlation between p53 accumulation and MDM2 overexpression in the progression of bladder cancer which may have prognostic value.

Increased frequency of a null-allele for NAD(P)H: quinone oxidoreductase in patients with urological malignancies

The NQO1 locus on chromosome 16q2.2 encodes NAD(P)H:quinone oxidoreductase, an enzyme implicated in detoxication and protection against redox cycling. Two alleles have been identified in the human population, the rarer one, termed the null-allele, coding for a nonfunctional enzyme. Since lack of NQOR activity has been suggested to increase susceptibility to certain cancers, the distribution of the two alleles was determined by polymerase chain reaction-restriction fragment length polymorphism analysis in patients with renal cell carcinoma (n = 131) and urothelial carcinoma (n = 99) compared with a normal population (n = 260). Allele distribution in the normal population followed a Hardy-Weinberg distribution with frequencies of 0.867 for the major allele and 0.133 for the null-allele. Increased frequencies of the null-allele were found in the tumour patient groups (0.191 and 0.182, respectively) due to an increased number of both homo- and heterozygotes. The odds ratios for homozygous null-allele vs. wild-type genotypes were 1.7 and 3.6 for renal cell carcinoma and urothelial carcinoma, respectively. These data are compatible with the assumption that diminished activity of NQOR in some individuals increases susceptibility to certain cancers.