Inadequate "caretaker" gene function and human cancer development.
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Cell Transformation, Neoplastic↗
Biomedical subjects
William G Nelson
Publications and source records attributed to William G Nelson.
Prostate cancer detection by GSTP1 methylation analysis of postbiopsy urine specimens.
PURPOSE: We assess the feasibility of a urinary test for prostate cancer detection in a high-risk patient cohort based on methylation-specific PCR analysis of the pi class glutathione S-transferase (GSTP1) gene promoter. EXPERIMENTAL DESIGN: A total of 45 men underwent transrectal ultrasound-guided biopsy of the prostate for suspected malignancy. Clean-catch voided urine specimens were prospectively collected from each patient immediately after biopsy. Genomic DNA was isolated from urine specimens and subjected to sodium bisulfite modification. Methylation of the GSTP1 promoter was examined in a blinded manner by methylation-specific PCR analysis and correlated with pathology results, and clinical information was obtained from the patient record. RESULTS: Methylation of GSTP1 in the urine was detected in a total of 18 of 36 (50%) informative cases. A total of 7 of 18 (39%) patients with prostate adenocarcinoma identified on their initial biopsy had detectable urinary GSTP1 methylation (58% sensitivity among informative cases). Abnormal urinary GSTP1 methylation was also detected in 7 of 21 (33%) patients without evidence of cancer on biopsy and in 4 of 6 (67%) patients diagnosed with atypia or high-grade prostatic intraepithelial neoplasia. CONCLUSIONS: We have demonstrated the feasibility of a novel, noninvasive molecular approach for the detection of epigenetic changes associated with prostate cancer. A screening test based on GSTP1 methylation in the urine specimens of patients with suspected prostate malignancy may be a useful adjunct to serum screening tests and digital rectal examination findings for identification of men at increased risk of harboring cancer despite a negative biopsy. This molecular assay has potential application for stratification of patients into low- and high-risk groups for surveillance versus repeat biopsy.
Aged↗
8-Hydroxyguanosine repair is defective in some microsatellite stable colorectal cancer cells.
Mutator phenotypes are involved in the carcinogenesis of some cancers, e.g., defects in mismatch repair produce a mutator phenotype that drives carcinogenesis and causes microsatellite instability in hereditary nonpolyposis colon cancers and some sporadic colorectal cancers (CRC). Less understood, however, is the potential role of mutator phenotypes in microsatellite stable (MSS) CRC carcinogenesis. A novel transversion mutator phenotype was reported recently in an MSS CRC cell line. We hypothesized that 8-hydroxyguanosine could be involved and found elevations in 5 of 15 (33%) MSS CRC cell lines analyzed. Repair of an adenine*8-hydroxyguanosine mispair was functionally defective in the same five cell lines. The human MutY homologue transcript and MutY homologue protein levels were also decreased. These findings may reflect a MSS mutator phenotype contributing to the development of CRC.
Adaptor Proteins, Signal Transducing↗
Transmission/disequilibrium tests of androgen receptor and glutathione S-transferase pi variants in prostate cancer families.
Population-based case-control studies have found relationships between risk of prostate cancer and genetic polymorphisms in the CAG repeat and GGC repeat of the X-linked androgen receptor gene (AR) as well as the autosomal gene coding for glutathione S-transferase pi (GSTP1). This family-based study utilized the transmission disequilibrium test to examine whether there was evidence that these polymorphisms could account for familial aggregation of prostate cancer. Seventy-nine North American pedigrees were studied. Most of these families had 3 or more affected first-degree relatives. Genotype information was obtained on 578 individuals. The reconstruction combined transmission disequilibrium test (RC-TDT) was used to test for linkage. There was no evidence of linkage to the CAG and GGC repeat sequences in the AR gene or the pentanucleotide (ATAAA) repeat in the GSTP1 gene when each allele was analyzed separately or when alleles were grouped by repeat length. Our findings do not support the hypothesis that familial clustering of prostate cancer in high-risk families is attributable to these genetic variants.
Adult↗
Methyl-CpG binding domain protein 2 represses transcription from hypermethylated pi-class glutathione S-transferase gene promoters in hepatocellular carcinoma cells.
During the pathogenesis of human hepatocellular carcinoma (HCC), the CpG island encompassing the pi-class glutathione S-transferase gene (GSTP1) becomes hypermethylated. Repression of transcription accompanying CpG island hypermethylation has been proposed to be mediated by methyl-CpG binding domain (MBD) proteins. We report here that inhibition of transcription from hypermethylated GSTP1 promoters in Hep3B HCC cells, which fail to express GSTP1 mRNA or GSTP1 polypeptides, appears to be mediated by MBD2. Treatment of Hep3B cells with 5-azadeoxycytidine (5-aza-dC), a methyltransferase inhibitor, activated GSTP1 expression, whereas treatment with trichostatin A, a histone deacetylase inhibitor, had little effect. To more precisely assess the contribution of the pattern of GSTP1 CpG island methylation on GSTP1 mRNA expression, Hep3B cells were treated for 72 h with 5-aza-dC and then subjected to limiting dilution cloning. Bisulfite sequencing was used to map the methylation patterns of the GSTP1 promoter region in GSTP1-expressing and -non-expressing clones. In the clone that expressed GSTP1 mRNA determined by Northern blot analysis and quantitative reverse transcriptase (RT)-PCR, widespread demethylation of at least one GSTP1 allele was evident. Chromatin immunoprecipitation experiments revealed the presence of MBD2, but not Sp1, at the GSTP1 promoter in Hep3B cells. In contrast, Sp1 was detected at the GSTP1 promoter in a GSTP1-expressing Hep3B 5-aza-dC subclone. To test whether MBD2 might be responsible for the inhibition of GSTP1 transcription from hypermethylated GSTP1 promoters, siRNAs were used to reduce MBD2 polypeptide levels in Hep3B cells. SssI-catalyzed methylation of GSTP1 promoter sequences resulted in diminished luciferase reporter activity after transfection into Hep3B cells. However, when hypermethylated GSTP1 promoter sequences were transfected into Hep3B cells that had been treated with siRNA-targeting MBD2 mRNA, no repression of luciferase reporter expression was evident. These findings implicate MBD2 in the repression of GSTP1 expression associated with GSTP1 CpG island hypermethylation in HCC cells.
Alleles↗
The diet, prostate inflammation, and the development of prostate cancer.
Evidence that somatic inactivation of GSTP1, encoding the human pi-class glutathione S-transferase, may initiate prostatic carcinogenesis is reviewed along with epidemiological evidence implicating several environment and lifestyle factors, including the diet and sexually transmitted diseases, as prostate cancer risk factors. An integrated model is presented featuring GSTPI function as a 'caretaker' gene during the pathogenesis of prostate cancer, in which the early loss of GSTPI activity renders prostate cells vulnerable to genome damage associated with chronic prostatic inflammation and repeated exposure to carcinogens. The model predicts that the critical prostate carcinogens will be those that are substrates for GSTP1 detoxification and are associated with high prostate cancer risk diet and lifestyle habits.
Cell Transformation, Neoplastic↗
The design of a randomized, placebo-controlled trial of celecoxib in preprostatectomy men with clinically localized adenocarcinoma of the prostate.
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Adenocarcinoma↗
Treatment and prevention of intraepithelial neoplasia: an important target for accelerated new agent development.
Precancer or intraepithelial neoplasia (IEN) is a noninvasive lesion that has genetic abnormalities, loss of cellular control functions, and some phenotypic characteristics of invasive cancer and that predicts for a substantial likelihood of developing invasive cancer. The AACR Task Force on the Treatment and Prevention of IEN has delineated the relationship between IEN and cancer risk as well as the clinical benefit that can be derived from reducing IEN burden. Although several effective endoscopic and surgical treatments for IEN have become standard medical practice, these interventions can confer morbidity and do not treat the entire epithelial field at risk. The incidence of many epithelial cancers is continuing to rise, the number of individuals at risk is increasing with the aging population, and the rapid advancement of imaging and molecular diagnostics is bringing to light precancers that were heretofore clinically silent. There is therefore an urgent need to rapidly develop new treatment and prevention agents for IEN. The AACR IEN Task Force recommends focusing on established precancers as the target for new agent development because of the close association between dysplasia and invasive cancer and because a convincing reduction in IEN burden provides patient benefit by reducing cancer risk and/or by decreasing the need for invasive interventions. The IEN Task Force proposes several clinical trial designs that provide practical and feasible approaches to the rapid development of new agents to treat and prevent precancer.
Antineoplastic Agents↗
Prostate-specific antigen as a marker of disease activity in prostate cancer.
Despite the impact of prostate-specific antigen (PSA) testing on the detection and management of prostate cancer, controversy about its usefulness as a marker of disease activity continues. This review, based on a recent roundtable discussion, examines whether PSA measurements can be used rationally in several clinical settings. Following radical prostatectomy and radiation therapy, prediction of survival by PSA level is most reliable in high-risk patients. PSA doubling time after radiation therapy is the strongest predictor of biochemical failure. PSA measurements have been associated with inconsistent results following hormonal treatment; reduced PSA levels may result from antiandrogen treatment, which decreases expression of the PSA gene, and therefore, the level of PSA production. In the setting of primary and secondary cancer prevention, PSA is important in risk stratification when selecting patients for studies. Part 1 of this two-part article, which concludes in the September issue, focuses on the physiology of PSA, its measurement and use in clinical practice, and its predictive value following radical prostatectomy and radiation therapy.
Biomarkers, Tumor↗
Identification of potential prostate cancer preventive agents through induction of quinone reductase in vitro.
Human prostate cancer is characterized by an early and near-universal loss of expression of the phase 2 enzyme glutathione S-transferase-pi (GSTP1). We hypothesize that a mechanism-based prostate cancer preventive strategy could involve induction of phase 2 enzymes within the prostate to compensate for the loss of GSTP1 expression. NAD[P]H:(quinone-acceptor) oxidoreductase (quinone reductase or QR) enzymatic activity, a surrogate of phase 2 enzyme response, was measured after treating the human prostate cancer cell line LNCaP with known phase 2 enzyme-inducing agents from 10 distinct chemical classes. QR enzymatic activity was assayed in microtiter plates using the menadione-coupled reduction of tetrazolium dye. Degree of induction was expressed as fold-increase over control and corrected for toxicity. Compounds were also tested in LNCaP-5-aza-C, an LNCaP subline selected in 5-aza-cytidine that expresses GSTP1, and in the human liver cell line HepG2. LNCaP showed robust induction of QR enzymatic activity after treatment with a subset of the phase 2 enzyme-inducing agents. All Michael acceptors were effective at inducing QR activity in LNCaP. Some phenolic antioxidants, heavy metal salts, and quinones also significantly increased QR activity, although inducer potency varied widely within these classes of compounds. Some of the isothiocyanates, mercaptans, bifunctional inducers, and trivalent arsenicals also produced modest QR induction, but peroxides and dithiolethiones were inactive. LNCaP-5-aza-C and LNCaP responded similarly to all compounds, but the pattern of response for HepG2 differed significantly. The differences in QR responsiveness between the prostate cell lines and HepG2 suggest that prostate tissues may have a unique pattern of response to phase 2-inducing agents distinct from other tissue types. Our data suggest that measurement of QR induction in prostate cancer cell lines may help identify potential cancer chemopreventive agents effective in the prostate.
Anticarcinogenic Agents↗
Prostate-specific antigen as a marker of disease activity in prostate cancer.
Despite the impact of prostate-specific antigen (PSA) testing on the detection and management of prostate cancer, controversy about its usefulness as a marker of disease activity continues. This review, based on a recent roundtable discussion, examines whether PSA measurements can be used rationally in several clinical settings. Following radical prostatectomy and radiation therapy, prediction of survival by PSA level is most reliable in high-risk patients. PSA doubling time after radiation therapy is the strongest predictor of biochemical failure. PSA measurements have been associated with inconsistent results following hormonal treatment; reduced PSA levels may result from antiandrogen treatment, which decreases expression of the PSA gene, and therefore, the level of PSA production. In the setting of primary and secondary cancer prevention, PSA is important in risk stratification when selecting patients for studies. Part 2 of this two-part article, which began in the August issue, discusses the role of PSA in hormonal and drug therapies and in primary and secondary chemoprevention.
Biomarkers, Tumor↗
Specific inhibition of DNMT1 by antisense oligonucleotides induces re-expression of estrogen receptor-alpha (ER) in ER-negative human breast cancer cell lines.
Recent studies have shown that changes in epigenetic regulation, such as DNA methylation and histone acetylation, are associated with silencing of the estrogen receptor a (ER) gene in ER-negative human breast cancer cells. Treatment of these cells with the general DNMT inhibitor, 5-aza-2'deoxycytidine, led to reactivation of functional ER protein. This study addresses the hypothesis that specific inhibition of the maintenance DNA methyltransferase, DNMT1, by antisense oligonucleotides (DNMT1 ASO) is sufficient to re-express the ER gene in ER-negative human breast cancer cell lines. MDA-MB-231 and Hs578t cells were transfected with 100 nM and 150 nM DNMT1 ASO respectively for three consecutive days and evidence of DNMT1 downregulation and functional ER re-expression was sought. Significant growth reduction was observed within 48 hr and persisted after 96 hr. DNMT1 expression was blocked after exposure to DNMT1 ASO as detected by RT-PCR, Western blot and enzymatic assay whereas a mutant DNMT1 ASO had little effect. This was associated with enhanced ER mRNA and protein expression and restoration of estrogen responsiveness in MDA-MB-231 cells as demonstrated by the ability of the induced ER protein to elicit ERE-regulated reporter activity from a luciferase reporter construct. Methylation specific PCR showed that the ER CpG island was minimally demethylated, suggesting that other epigenetic events, introduced by specific DNMT1 inhibition, might also be involved in ER re-expression. Our results suggest that specific inhibition of DNMT1 expression alone is sufficient to re-express ERa in human breast cancer cell lines.
Azacitidine↗