GSTP1 CpG island hypermethylation is responsible for the absence of GSTP1 expression in human prostate cancer cells.

GSTP1 CpG island hypermethylation is the most common somatic genome alteration described for human prostate cancer (PCA); lack of GSTP1 expression is characteristic of human PCA cells in vivo. We report here that loss of GSTP1 function may have been selected during the pathogenesis of human PCA. Using a variety of techniques to detect GSTP1 CpG island DNA hypermethylation in PCA DNA, we found only hypermethylated GSTP1 alleles in each PCA cell in all but two PCA cases studied. In these two cases, CpG island hypermethylation was present at only one of two GSTP1 alleles in PCA DNA. In one of the cases, DNA hypermethylation at one GSTP1 allele and deletion of the other GSTP1 allele were evident. In the other case, an unmethylated GSTP1 allele was detected, accompanied by abundant GSTP1 expression. GSTP1 CpG island DNA hypermethylation was responsible for lack of GSTP1 expression by LNCaP PCA cells: treatment of the cells with 5-azacytidine (5-aza-C), an inhibitor of DNA methyltransferases, reversed the GSTP1 promoter DNA hypermethylation, activated GSTP1 transcription, and restored GSTP1 expression. GSTP1 promoter activity, assessed via transfection of GSTP1 promoter-CAT reporter constructs in LNCaP cells, was inhibited by SssI-catalyzed CpG dinucleotide methylation. Remarkably, although selection for loss of GSTP1 function may be inferred for human PCA, GSTP1 did not act like a tumor suppressor gene, as LNCaP cells expressing GSTP1, either after 5-aza-C treatment or as a consequence of transfection with GSTP1 cDNA, grew well in vitro and in vivo. Perhaps, GSTP1 inactivation may render prostatic cells susceptible to additional genome alterations, caused by electrophilic or oxidant carcinogens, that provide a selective growth advantage.

GSTP1 CpG island DNA hypermethylation in hepatocellular carcinomas.

Glutathione S-transferases, enzymes that defend cells against damage mediated by oxidant and electrophilic carcinogens, may be critical determinants of cancer pathogenesis. We report here that the pathogenesis of hepatocellular carcinoma (HCC), one of the most common cancers in the world, frequently involves an accumulation of somatic DNA methylation changes at GSTP1, the gene encoding the pi-class glutathione S-transferase. For our study, Hep3B HCC cells and a cohort of 20 HCC tissue specimens were subjected to analysis for GSTP1 expression and for somatic GSTP1 alterations. GSTP1 DNA hypermethylation in HCC DNA was assessed by Southern blot analysis, via a polymerase chain reaction (PCR) assay, and by using a genomic sequencing approach. Hep3B HCC cells failed to express GSTP1 mRNA or GSTP1 polypeptides. Similarly, HCC cells in 19 of 20 HCC cases were devoid of GSTP1 polypeptides. By Southern blot analysis, DNA from Hep3B HCC cells displayed abnormal GSTP1 hypermethylation. Treatment of Hep3B HCC cells in vitro with the DNA methyltransferase inhibitor 5-aza-deoxycytidine both reversed GSTP1 DNA hypermethylation and restored GSTP1 expression. Using a PCR assay, somatic GSTP1 DNA hypermethylation was also detected in HCC DNA from 17 of 20 HCC cases. Genomic sequencing analyses, undertaken to map 5-methyldeoxycytidine nucleotides located at the GSTP1 transcriptional regulatory region, frequently detected somatic DNA hypermethylation near the gene promoter in HCC DNA. The data indicate that GSTP1 DNA hypermethylation changes appear frequently in human HCC. In addition, the data raise the possibility that somatic GSTP1 inactivation, via hypermethylation, may contribute to the pathogenesis of HCC.

Deletion mapping at 12p12-13 in metastatic prostate cancer.

The identification of homozygous deletions in malignant tissue is a powerful tool for the localization of tumor suppressor genes. Representational difference analysis (RDA) uses selective hybridization and the polymerase chain reaction (PCR) to isolate regions of chromosomal loss and has facilitated the identification of tumor suppressor genes, such as BRCA2 and PTEN. We have recently identified a 1-5-cM homozygous deletion on 12p12-13 in a prostate cancer xenograft and found that 47% of patients who died of prostate carcinoma demonstrate focal loss of heterozygosity (LOH) in this region in metastatic deposits. We have now characterized the region of interest by assembling a yeast artificial chromosome (YAC) contig spanning the homozygous deletion and identifying which known genes and expressed sequence tags (EST) lie within the homozygous deletion. A rib metastasis was harvested at autopsy and placed subcutaneously in a male SCID mouse. Genomic DNA from this xenograft and from the patient's normal renal tissue was extracted. Multiplex PCR, with the xenograft and normal DNA used as template, was performed using primers for loci on the Whitehead contig 12.1 believed to be near our region of interest. We found that our deletion lay in a 1-2-Mb interval between WI-664 and D12S358. We then used the same primers to construct a YAC contig across the homozygous deletion. PCR amplification of YAC DNA, using primers for the genomic sequences of known genes and ESTs reported to lie on 12p12-13, was used to identify candidate genes that lay within the deletion. Duplex PCR, with control primers known not to be deleted in the xenograft, was used to confirm that both the CDKN1B and ETV6 genes were homozygously deleted in the xenograft. Mutations in either or both of these genes may play an important role in metastatic prostate carcinoma.

No evidence for a role of BRCA1 or BRCA2 mutations in Ashkenazi Jewish families with hereditary prostate cancer.

BACKGROUND: Two genes responsible for hereditary breast cancer (BRCA1 and BRCA2) have been identified, and predisposing mutations identified. Several studies have provided evidence that germline mutations in BRCA1 and BRCA2 confer an increased risk of prostate cancer. Based on these findings, one might expect to find an increased frequency of mutations in these genes in family clusters of prostate cancer. The Ashkenazi Jewish population is unique in that it has an approximate 2% incidence of specific founder BRCA1 and BRCA2 mutations (i.e., 185delAG and 5382insC in BRCA1, and 6174delT in BRCA2). METHODS: To address the question of whether or not mutations in either of these genes were overrepresented in prostate cancer families, we searched for these mutations in germline DNA samples collected from affected and unaffected members of 18 Ashkenazi Jewish families, each having at least 3 first-degree relatives affected with prostate cancer. RESULTS: No mutations were found in the BRCA1 gene in any of the 47 individuals tested. One individual possessed a BRCA2 mutation (6174delT). This individual was unaffected at the time of analysis, but had an affected paternal uncle, and an affected first cousin, neither of whom harbored the mutant gene. CONCLUSIONS: In this sample of Ashkenazi prostate cancer families, the frequency of founder BRCA1 and BRCA2 mutations was not elevated, suggesting that such mutations will account for only a small, perhaps minimal, fraction of familial prostate cancer.

Evidence for a prostate cancer susceptibility locus on the X chromosome.

Over 200,000 new prostate cancer cases are diagnosed in the United States each year, accounting for more than 35% of all cancer cases affecting men, and resulting in 40,000 deaths annually. Attempts to characterize genes predisposing to prostate cancer have been hampered by a high phenocopy rate, the late age of onset of the disease and, in the absence of distinguishing clinical features, the inability to stratify patients into subgroups relative to suspected genetic locus heterogeneity. We previously performed a genome-wide search for hereditary prostate cancer (HPC) genes, finding evidence of a prostate cancer susceptibility locus on chromosome 1 (termed HPC1; ref. 2). Here we present evidence for the location of a second prostate cancer susceptibility gene, which by heterogeneity estimates accounts for approximately 16% of HPC cases. This HPC locus resides on the X chromosome (Xq27-28), a finding consistent with results of previous population-based studies suggesting an X-linked mode of HPC inheritance. Linkage to Xq27-28 was observed in a combined study population of 360 prostate cancer families collected at four independent sites in North America, Finland and Sweden. A maximum two-point lod score of 4.60 was observed at DXS1113, theta=0.26, in the combined data set. Parametric multipoint and non-parametric analyses provided results consistent with the two-point analysis. Significant evidence for genetic locus heterogeneity was observed, with similar estimates of the proportion of linked families in each separate family collection. Genetic mapping of the locus represents an important initial step in the identification of an X-linked gene implicated in the aetiology of HPC.

Interfocal heterogeneity of PTEN/MMAC1 gene alterations in multiple metastatic prostate cancer tissues.

The long arm of chromosome 10 is frequently affected by allelic loss in prostate cancer. PTEN/MMAC1, a candidate tumor suppressor gene located at 10q23.3, a region commonly deleted in prostate cancer, was recently identified and found to be deleted or mutated in cancer cell lines derived from a variety of human tissues including prostate. To examine the role of PTEN/MMAC1 in the progression of prostate cancer, we screened a unique set of 50 metastatic prostate cancer tissues from 19 cancer-death patients for alterations in the PTEN/MMAC1 gene, using single-strand conformational polymorphism analysis and direct sequencing to identify sequence changes and microsatellite analysis to examine allelic loss in the vicinity of PTEN/MMAC1. Overall, gene alterations (deletions or point mutations) were observed in at least 1 metastatic site in 12 of the 19 patients studied. Two cases had homozygous deletions that were confirmed by fluorescence in situ hybridization analysis. Four patients harbored point mutations, with one mutation being found in all four tumors (a primary lesion and three different metastases) from the same patient. The remaining three mutations were detected in only one of multiple metastases. Loss of heterozygosity was found in 10 of 18 informative cases, with 1 case showing a unique pattern of microsatellite instability in each of six different metastases examined. Loss of the same allele was found in all metastases in a given patient in 9 of 10 cases. These results indicate that PTEN/MMAC1 gene alterations occur frequently in lethal prostate cancer, although a substantial amount of mutational heterogeneity is found among different metastatic sites within the same patient. These latter findings emphasize the potentially complex genetic relationship that can exist between various clonal lineages of prostate cancer cells as they evolve during the metastatic process and suggest a molecular basis for phenotypic heterogeneity of different prostate cancer foci in patients with disseminated disease.

Early age at diagnosis in families providing evidence of linkage to the hereditary prostate cancer locus (HPC1) on chromosome 1.

In a recent study of 91 families having at least three first degree relatives with prostate cancer, we reported the localization of a major susceptibility locus for prostate cancer (HPC1) to chromosome 1 [band q24; J. R. Smith et al., Science (Washington DC), 274: 1371-1373, 1996]. There was significant evidence for locus heterogeneity, with an estimate of 34% of the families being linked to this locus. In this report, we investigate the importance of age at diagnosis of prostate cancer and number of affected individuals within a family as variables in the linkage analysis of an expanded set of markers on 1q24. Under two different models for the prostate cancer locus, we find that the evidence for linkage to HPC1 is provided primarily by large (five or more members affected) families with an early average age at diagnosis. Specifically, for 40 North American families with an average age at diagnosis <65 years, the multipoint lod score is 3.96, whereas for 39 families with an older average age at diagnosis, this value is -0.84. Assuming heterogeneity, the proportion of families linked is 66% for the 14 families with the earliest average ages at diagnoses, but it decreases to 7% for the families with the latest ages at diagnoses. A similar age effect is observed in 12 Swedish pedigrees analyzed. To test the hypotheses generated by these analyses, we examined an additional group of 13 newly identified prostate cancer families. Overall, these families provided additional evidence for linkage to this region (nonparametric linkage Z = 1.91; P = 0.04 at marker D1S1660), contributed primarily by the families in this group with early age at diagnosis [nonparametric linkage Z = 2.50 (P = 0.01) at D1S422]. These results are consistent with the existence of a locus in this region that predisposes men to develop early-onset prostate cancer.

Characteristics of prostate cancer in families potentially linked to the hereditary prostate cancer 1 (HPC1) locus.

CONTEXT: Approximately 9% of prostate cancer cases have been estimated to result from inheritance of mutated prostate cancer susceptibility genes. Few data exist as to whether there are clinical differences between prostate cancers that are inherited and those that occur in the general population. OBJECTIVE: To investigate phenotypic characteristics of families potentially linked to the hereditary prostate cancer 1 (HPC1) locus on chromosome 1q24-25. DESIGN: Retrospective case study in which clinical data were extracted from medical and pathological records. FAMILIES: A total of 74 North American families with hereditary prostate cancer. Prostate cancer cases from the National Cancer Data Base were used as a reference population for comparison. MAIN OUTCOME MEASURES: The families were divided into 2 groups: either potentially linked (33 families with 133 men with prostate cancer), and thus likely to be carrying an altered HPC1 gene, or potentially unlinked (41 families with 172 men with prostate cancer), on the basis of haplotype analysis in the region of HPC1. The age at diagnosis of prostate cancer, serum prostate-specific antigen levels, digital rectal examination status, stage, grade, primary treatment of prostate cancers, and occurrence of other cancers were compared between the groups. RESULTS: The mean age at diagnosis of prostate cancer for men in potentially linked families was significantly lower than for men in potentially unlinked families (63.7 vs 65.9 years, respectively, P=.01; mean age at diagnosis in the reference population was 71.6 years). Higher-grade cancers (grade 3) were more common in potentially linked families, and advanced-stage disease was found in 41% of the case patients in potentially linked families compared with 31% in both the potentially unlinked families and the reference groups (P=.03 for the latter comparison). In the other clinical parameters, we found no significant differences between the groups. A modest excess of breast cancer and colon cancer was found in potentially linked families in comparison with potentially unlinked families, but this difference was not statistically significant. CONCLUSIONS: Families that provide evidence for segregation of an altered HPC1 gene are characterized by multiple cases of prostate cancer that, in most respects, are indistinguishable from nonhereditary cases. However, 3 characteristics were observed: younger age at diagnosis, higher-grade tumors, and more advanced-stage disease. Our study shows that a significant fraction of hereditary prostate cancers are diagnosed in advanced stages, emphasizing the clinical importance of early detection in men potentially carrying prostate cancer susceptibility genes. These findings support the current recommendations to screen men with a positive family history of prostate cancer beginning at age 40 years.

Major susceptibility locus for prostate cancer on chromosome 1 suggested by a genome-wide search.

Despite its high prevalence, very little is known regarding genetic predisposition to prostate cancer. A genome-wide scan performed in 66 high-risk prostate cancer families has provided evidence of linkage to the long arm of chromosome 1 (1q24-25). Analysis of an additional set of 25 North American and Swedish families with markers in this region resulted in significant evidence of linkage in the combined set of 91 families. The data provide strong evidence of a major prostate cancer susceptibility locus on chromosome 1.

Identification of a second pseudoautosomal region near the Xq and Yq telomeres.

The telomeres of Xq and Yq have been observed to associate during meiosis, and in rare cases a short synaptonemal complex is present. Molecular cloning of loci from Xqter and Yqter has revealed that their sequence homology extends over 400 kilobases, which suggests the possibility of genetic exchange. This hypothesis was tested by the development of two highly informative microsatellite markers from yeast artificial chromosome clones that carried Xqter sequences and the following of their inheritance in a set of reference pedigrees from the Centre d'Etude du Polymorphisme Humain in Paris, France. From a total of 195 informative male meioses, four recombination events between these loci were observed. In three cases, paternal X alleles were inherited by male offspring, and in one case a female offspring inherited her father's Y allele. These data support the existence of genetic exchange at Xq-Yq, which defines a second pseudoautosomal region between the sex chromosomes.

A 1.6-Mb contig of yeast artificial chromosomes around the human factor VIII gene reveals three regions homologous to probes for the DXS115 locus and two for the DXYS64 locus.

Two yeast artificial chromosome (YAC) libraries were screened for probes in Xq28, around the gene for coagulation factor VIII (F8). A set of 30 YACs were recovered and assembled into a contig spanning at least 1.6 Mb from the DXYS64 locus to the glucose 6-phosphate dehydrogenase gene (G6PD). Overlaps among the YACs were determined by several fingerprinting techniques and by additional probes generated from YAC inserts by using Alu-vector or ligation-mediated PCR. Analysis of more than 30 probes and sequence-tagged sites (STSs) made from the region revealed the presence of several homologous genomic segments. For example, a probe for the DXYS64 locus, which maps less than 500 kb 5' of F8, detects a similar but not identical locus between F8 and G6PD. Also, a probe for the DXS115 locus detects at least three identical copies in this region, one in intron 22 of F8 and at least two more, which are upstream of the 5' end of the gene. Comparisons of genomic and YAC DNA suggest that the multiple loci are not created artifactually during cloning but reflect the structure of uncloned human DNA. On the basis of these data, the most likely order for the loci analyzed is tel-DXYS61-DXYS64-(DXS115-3-DXS115-2)-5'F8-(D XS115-1)-3'F8-G6PD.

Yeast artificial chromosome-based genome mapping: some lessons from Xq24-q28.

Yeast artificial chromosomes (YACs) have recently provided a potential route to long-range coverage of complex genomes in contiguous cloned DNA. In a pilot project for 50 Mb (1.5% of the human genome), a variety of techniques have been applied to assemble Xq24-q28 YAC contigs up to 8 Mb in length and assess their quality. The results indicate the relative strength of several approaches and support the adequacy of YAC-based methods for mapping the human genome.