| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Regular Articles |
1 Center for Human Genomics, Wake Forest University School of Medicine, Winston-Salem, North Carolina, and 2 Department of Urology, Johns Hopkins Medical Institutions, Baltimore, Maryland
| ABSTRACT |
|---|
|
|
|---|
| INTRODUCTION |
|---|
|
|
|---|
Recently, in a study of 96 prostate cancer cases and 106 controls, Kibel et al. (6) reported an association between a nonsynonymous change of CDKN1B and the risk of advanced prostate cancer. The single nucleotide polymorphism (SNP) 326T/G changes a valine at codon 109 to glycine. Among men with the TT genotype, an association with increased risk of advanced prostate carcinoma was reported (odds ratio = 1.95; 95% confidence interval = 1.093.47), and the association was stronger in patients with androgen-independent disease (odds ratio = 2.88, 95% confidence interval = 1.196.97). Other results implicating CDKN1B and the risk for prostate cancer have come from linkage studies. The chromosomal region of CDKN1B (12p13) has been reported to be linked to prostate cancer susceptibility in several hereditary prostate cancer (HPC) family studies (7 , 8) . In our HPC study population, no evidence for linkage was observed at 12p13 in the complete set of the 188 HPC families based on the log of odds (LOD = 0); however, significant evidence for linkage at this region was found among the 34 families with the highest linkage score at 10q23 (the chromosomal region of PTEN), with a LOD score of 2.75 (P = 0.0002). This conditional linkage analysis was prompted by a mouse model, which demonstrated that the combined effects of both the Pten and Cdkn1b genes rather than a single gene cause prostate cancer in mice (9) . On the basis of the critical role CDKN1B plays in cell cycle control, the strong functional and clinical implications of this gene in prostate carcinogenesis, and the positive findings of association and linkage studies, we hypothesized that germ-line mutations or polymorphisms in CDKN1B may modify an individuals risk to prostate cancer, and this may lead to familial aggregation of prostate cancer. To test this hypothesis, we first screened for germ-line mutations in 96 probands from HPC families, followed by genotyping among all 188 HPC families for the identified mutations and polymorphisms that were either rare or of potential functional importance. To evaluate the risk CDKN1B imparts for HPC, cosegregation of the mutations and polymorphisms in the HPC families was evaluated using family-based linkage and association tests. This study is unique in describing the CDKN1B mutation spectrum and its implications in HPC.
| MATERIALS AND METHODS |
|---|
|
|
|---|
5 affected individuals was 28, 47, and 113, respectively. All individuals that participated in this study gave full informed consent. The family history for other types of cancers was also collected. For the diagnoses of other types of cancers, the majority was confirmed through interview with at least two relatives, and a small proportion (7%) was verified by medical records. Among the 188 HPC families, 68 (36.2%), 36 (19.1%), and 22 (11.7%) have at least one, two, and three or more other types of cancers in the family, respectively. Seventy-three of the prostate cancer cases were also diagnosed with another primary cancer. There were 148 other subjects diagnosed with other cancers. Colon cancer was the highest concurrent cancer (35 cases), followed by breast cancer (34 cases) and lung cancer (20 cases).
Sequencing and Genotyping Methods.
The PCR products of all three exons, exon-intron junctions, and
800-bp promoter region of CDKN1B were directly sequenced in 96 HPC probands. The primers used for PCR and the components and cycling conditions for PCR are available upon request. All PCR products were purified using the QuickStep PCR purification Kit (Edge BioSystems, Gaithersburg, MD) to remove deoxynucleoside triphosphates and excess primers. All sequencing reactions were performed using dye-terminator chemistry (BigDye; ABI, Foster City, CA), and separated in an ABI 3700 DNA Analyzer. SNPs were identified using Sequencher software version 4.0.5 (Gene Codes Corporation).
SNPs were genotyped using the MassARRAY system (Sequenom, Inc., San Diego, CA). All reaction components and conditions were performed according to the manufactures instruction (Sequenom, Inc.) and are available upon request.
Statistical Methods.
Hardy-Weinberg equilibrium tests and pairwise linkage disequilibrium tests for all possible pairs of the variants were performed using the Fisher probability test statistic, as described by Weir (10)
. For each test, 10,000 permutations were performed, and the test statistic of each replicate was calculated. Empirical Ps for each test were estimated as the proportion of replicates that are as probable as or less probable than the observed data, as implemented in the software package Genetic Data Analysis.
Family-based association tests were performed for the SNPs genotyped in the 188 HPC families, using the family-based association test software package (11) . Family-based association test uses data from nuclear families, sibships, or a combination of the two to test for linkage and linkage disequilibrium (association) between traits and genotypes. The test for linkage is valid when multiple affected members/pedigree are used, and the power to detect linkage is increased if there is an association. The test for association is valid if one affected member/pedigree is used (the genotypes of all of the affected members can be included) or if the empirical variance is used to account for correlation between transmissions in families when linkage is present.
| RESULTS AND DISCUSSION |
|---|
|
|
|---|
800 bp promoter region, all three exons, and the exon-intron junctions among 96 HPC probands (Table 1)
|
To assess whether the identified nonsynonymous changes and other sequence variants are associated with prostate cancer risk, we genotyped 9 of these 10 variants among all 188 HPC families. The SNP -987C/T was excluded because a reliable assay could not be developed. Hardy-Weinberg equilibrium and pairwise linkage disequilibrium tests were performed among unrelated probands of non-Ashkenazi whites. Eight of the 9 remaining SNPs were in Hardy-Weinberg equilibrium (P > 0.05). The SNP -838C/A significantly deviated from Hardy-Weinberg equilibrium (P < 0.005) and therefore was dropped from additional analysis. The family-based association test was used to test whether the sequence variants in CDKN1B are associated with prostate cancer risk. Three SNPs were rare (114C/T, 258G/C, and 356T/C) and were uninformative for this analysis. Among the five remaining SNPs, -79C/T in the 5'-untranslated region was significantly associated with prostate cancer, and the C allele was found to be overtransmitted from parents to affected offspring (nominal P = 0.0005; Table 2
). Eighty HPC families were informative for the test of this SNP. We further explored this result by performing a stratified analysis based on age of diagnosis. Interestingly, the association was primarily observed among affected offspring with age at diagnosis < 65 years (P = 0.0015). There was no significant association among affected offspring with age at diagnosis
65 years (P = 0.34). It is worth noting that age of diagnosis is a crude indicator for age of onset and is not a good surrogate for clinically aggressive disease. Because the empirical variance, which accounts for correlation between transmission in families when linkage is present (13)
, was used in the statistical test, this significant result reflects an association between SNP -79C/T and prostate cancer. The significant association remained when the analysis was limited to non-Ashkenazi white families only (P = 0.02). None of the other SNPs was significantly linked or associated with prostate cancer.
|
The SNP -79C/T is located in the 5'-regulatory CpG island. Previous studies indicate that methylation of the CDKN1B promoter, although occurring in some cancer cells (14) , is rare in prostate carcinomas (15 , 16) , and the methylation that does occur in prostate cancer typically does not affect this particular CpG dinucleotide. Although a primary focus of CDNK1B gene regulation studies has been the increase in protein degradation rates mediated by SKP2 ubiquitin ligase complex, ultimately decreasing CDKN1B protein in prostate cancer (17) , CDKN1B protein levels can also be affected by the rates of gene transcription (18) as well as mRNA translation rates. Interestingly, this latter mechanism has been shown to be affected by sequences in the 5'-untranslated region of the CDKN1B transcript (19, 20, 21) . Whether the basal transcription or transcript translation rates are affected by the -79C/T polymorphism is unknown at present.
The evidence for cosegregation of the two rare nonsynonymous mutations with prostate cancer in our HPC families is inconclusive. For the SNP 258G/C (E86D), the variant allele C was only identified in a proband but not in other family members available for study. For the SNP 356T/C (I119T), all four affected siblings were found to be carriers of the variant allele C. In addition, one of the sisters of the proband was diagnosed with lung cancer and found to be a C allele carrier. However, the unaffected brother and three unaffected nephews (ages 42, 60, and 65 years) of the proband also carried the C allele. Additional follow-up studies on these two rare variants may clarify their roles in HPC.
Recently, in a study by Kibel et al. (6)
, which included 96 cases and 106 controls from a European-American population, the SNP 326T/G (V109G) was found to be associated with the risk of advanced prostate cancer, with the genotype TT significantly increasing the risk of advanced disease (odds ratio = 1.95; 95% confidence interval = 1.093.47). In their study, the variant T allele frequency was found to be 72.4% in controls and 82.3% in cases. We observed a similar frequency for the variant T allele in our collection of unrelated probands of non-Ashkenazi white families with HPC (81%; Table 1
). Furthermore, the T allele at SNP 326T/G was found to be overtransmitted, although not significantly, to affected offspring (observed S statistics = 334, expected statistics = 331.9, P = 0.74) in our family based association test. It is also possible that the SNP 326T/G may play an important role in sporadic cases but less so in the etiology of high-risk hereditary cases, where -79C/T may be more relevant.
Given the biological relevance of cell cycle controls to cancer etiology, as well as the recent findings of association between prostate cancer and cell cycle regulation candidate genes (CHEK2 and CDKN1B), additional studies are warranted. Specifically, follow-up studies should either evaluate the existing results in other populations or expand the analyses to other candidate genes in the same pathway. For CDKN1B, additional studies that evaluate interaction effects with PTEN among human populations will be interesting because these may build upon the biological mechanism already described in prostate cancer mouse models.
| ACKNOWLEDGMENTS |
|---|
| FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Requests for reprints: Jianfeng Xu, Center for Human Genomics, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157. Phone: (336) 716-5700; Fax: (336) 716-7575; E-mail: jxu{at}wfubmc.edu
Received 7/29/03. Revised 12/18/03. Accepted 1/20/04.
| REFERENCES |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
J. Healy, H. Belanger, P. Beaulieu, M. Lariviere, D. Labuda, and D. Sinnett Promoter SNPs in G1/S checkpoint regulators and their impact on the susceptibility to childhood leukemia Blood, January 15, 2007; 109(2): 683 - 692. [Abstract] [Full Text] [PDF] |
||||
![]() |
C Hughes, A Murphy, C Martin, O Sheils, and J O'Leary Molecular pathology of prostate cancer J. Clin. Pathol., July 1, 2005; 58(7): 673 - 684. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |