Variants in the Prostate-Specific Antigen (PSA) Gene and Prostate Cancer Risk, Survival, and Circulating PSA

Association between three genetic variants in kallikrein 3 and prostate cancer risk

Background: Epidemiological studies have assessed the association between kallikrein 3 (KLK3) polymorphisms and prostate cancer (PCa) susceptibility. However, published data on this association are somewhat inconclusive. Methods: Articles investigating the association between three KLK3 (rs1058205, rs2735839, and rs266882) variants and PCa susceptibility were searched from online databases, which included 35,838 patients and 36,369 control participants. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to demonstrate the strength of the association. We also utilized ELISA to detect serum expression of KLK3. In addition, in silico tools were adopted to evaluate the relationship of KLK3 expression and PCa survival time. Results: The overall results indicated that polymorphism T>C of rs1058205 was associated with decreased risk of PCa (allele contrast: OR = 0.75, 95% CI = 0.64–0.88, P_{heterogeneity} < 0.001; homozygote comparison: OR = 0.58, 95% CI = 0.42–0.81, P_{heterogeneity} < 0.001), particularly in Caucasian population (allele contrast: OR = 0.77, 95% CI = 0.65–0.91, P_{heterogeneity} < 0.001; homozygote comparison: OR = 0.58, 95% CI = 0.41–0.82, P_{heterogeneity} < 0.001). No association was observed between the polymorphism A>G of rs2735839 and risk of PCa. In addition, no association was observed between polymorphism A>G of rs266882 and risk of PCa. Serum KLK3 levels in PCa patients carrying CC/CT genotypes were statistically lower than those carrying TT genotypes. Conclusion: This meta-analysis suggests that rs1058205 polymorphism of KLK3 is a risk factor for PCa development, polymorphism T>C of rs1058205 is associated with decreased susceptibility to PCa particularly in Caucasian population.

Genome-wide association studies on prostate cancer: the end or the beginning?

Prostate cancer (PCa) is the second most frequently diagnosed malignancy in men. Genome-wide association studies (GWAS) has been highly successful in discovering susceptibility loci for prostate cancer. Currently, more than twenty GWAS have identified more than fifty common variants associated with susceptibility with PCa. Yet with the increase in loci, voices from the scientific society are calling for more. In this review, we summarize current findings, discuss the common problems troubling current studies and shed light upon possible breakthroughs in the future. GWAS is the beginning of something wonderful. Although we are quite near the end of the beginning, post-GWAS studies are just taking off and future studies are needed extensively. It is believed that in the future GWAS information will be helpful to build a comprehensive system intergraded with PCa prevention, diagnosis, molecular classification, personalized therapy.

The genomic landscape of prostate cancer

By the age of 80, approximately 80% of men will manifest some cancerous cells within their prostate, indicating that prostate cancer constitutes a major health burden. While this disease is clinically insignificant in most men, it can become lethal in others. The most challenging task for clinicians is developing a patient-tailored treatment in the knowledge that this disease is highly heterogeneous and that relatively little adequate prognostic tools are available to distinguish aggressive from indolent disease. Next-generation sequencing allows a description of the cancer at an unprecedented level of detail and at different levels, going from whole genome or exome sequencing to transcriptome analysis and methylation-specific immunoprecipitation, followed by sequencing. Integration of all these data is leading to a better understanding of the initiation, progression and metastatic processes of prostate cancer. Ultimately, these insights will result in a better and more personalized treatment of patients suffering from prostate cancer. The present review summarizes current knowledge on copy number changes, gene fusions, single nucleotide mutations and polymorphisms, methylation, microRNAs and long non-coding RNAs obtained from high-throughput studies.

Contribution of genetic variation rs266882 to prostate-specific antigen levels in healthy controls with serum PSA below 2.0 ng/ml

We evaluated the impact of genetic variation in the prostate-specific antigen (PSA) gene (rs266882) on serum PSA levels in healthy men as well as risk factors for benign prostate hypertrophy (BPH) and prostate cancer. The study population comprised 91 men with PSA levels below 2.0 ng/ml as healthy controls, 78 men with PSA 2-10 ng/ml as a BPH group, and 128 prostate cancer patients, all in Korea. DNA was amplified by polymerase chain reaction and the product was sequenced. We found that PSA levels were associated with a G/A polymorphism only in healthy controls. The transition, however, was not associated with PSA levels of BPH and cancer patients, nor was it a risk factor. In conclusion, this genetic factor is important for determining serum PSA levels in the naive group, whereas the disruption of prostatic architecture in BPH or prostate cancer may be a major determining factor for PSA levels.

Inherited susceptibility for aggressive prostate cancer

Whether or not there is inherited basis for prostate cancer aggressiveness is not clear, but advances in DNA analysis should provide an answer to this question in the very near future.

Evaluation of multiple risk-associated single nucleotide polymorphisms versus prostate-specific antigen at baseline to predict prostate cancer in unscreened men

BACKGROUND

Although case-control studies have identified numerous single nucleotide polymorphisms (SNPs) associated with prostate cancer, the clinical role of these SNPs remains unclear.

OBJECTIVE

Evaluate previously identified SNPs for association with prostate cancer and accuracy in predicting prostate cancer in a large prospective population-based cohort of unscreened men.

DESIGN, SETTING, AND PARTICIPANTS

This study used a nested case-control design based on the Malmö Diet and Cancer cohort with 943 men diagnosed with prostate cancer and 2829 matched controls. Blood samples were collected between 1991 and 1996, and follow-up lasted through 2005.

MEASUREMENTS

We genotyped 50 SNPs, analyzed prostate-specific antigen (PSA) in blood from baseline, and tested for association with prostate cancer using the Cochran-Mantel-Haenszel test. We further developed a predictive model using SNPs nominally significant in univariate analysis and determined its accuracy to predict prostate cancer.

RESULTS AND LIMITATIONS

Eighteen SNPs at 10 independent loci were associated with prostate cancer. Four independent SNPs at four independent loci remained significant after multiple test correction (p<0.001). Seven SNPs at five independent loci were associated with advanced prostate cancer defined as clinical stage≥T3 or evidence of metastasis at diagnosis. Four independent SNPs were associated with advanced or aggressive cancer defined as stage≥T3, metastasis, Gleason score≥8, or World Health Organization grade 3 at diagnosis. Prostate cancer risk prediction with SNPs alone was less accurate than with PSA at baseline (area under the curve of 0.57 vs 0.79), with no benefit from combining SNPs with PSA. This study is limited by our reliance on clinical diagnosis of prostate cancer; there are likely undiagnosed cases among our control group.

CONCLUSIONS

Only a few previously reported SNPs were associated with prostate cancer risk in the large prospective Diet and Cancer cohort in Malmö, Sweden. SNPs were less useful in predicting prostate cancer risk than PSA at baseline.

Genetics of prostate cancer risk

For decades, physicians and researchers have recognized that family history is a significant risk factor for prostate cancer. The identification of the genes responsible for inherited risk, however, proved difficult. With the sequencing of the human genome and the completion of the initial phases of the International HapMap Project, the tools are available to scan the entire genome and find genetic markers for disease. Since 2006, more than 30 inherited variants strongly associated with prostate cancer have been reported. As the inherited component of the disease is revealed, efforts are ongoing to translate genetic findings into the clinic.

Association of KLK3 (PSA) genetic variants with prostate cancer risk and PSA levels

Genome-wide association studies have identified genetic markers in kallikrein-related peptidase 3 (KLK3) associated with prostate cancer. However, some of these markers are also associated with prostate-specific antigen (PSA) levels, so it is unclear whether the polymorphisms are causal or if the association with risk is solely due to detection bias through PSA screening. PSA is a biologically active serine protease, cleaving insulin-like growth factor-binding protein. We examined the association of single-nucleotide polymorphisms (SNPs) in KLK3 with prostate cancer risk, disease-specific survival and pre-diagnostic PSA levels in a case-control study nested within the Physicians' Health Study, which began in 1982, with over 27 years of follow-up. We genotyped SNPs spanning the entire KLK3 locus to capture common variation at high resolution. Six polymorphisms were significantly associated with prostate cancer incidence (P < 0.05); the odds ratios per minor allele ranged from 0.88 to 0.73. For four of these, the odds ratios were lower when restricting to cases diagnosed in the pre-PSA screening era (before 1989). The four alleles significantly associated with lower PSA levels were also associated with lower prostate cancer risk. KLK3 variants were not significantly associated with stage at diagnosis, risk of lethal cancer or survival. Our results suggest that detection bias due to the association of KLK3 variants with PSA levels cannot completely explain the association with prostate cancer risk. Understanding the mechanism by which genetic variation in KLK3 affects prostate cancer risk has important implications for study of the biological role of PSA in prostate tumorigenesis.

Association of prostate cancer risk Loci with disease aggressiveness and prostate cancer-specific mortality

Genome-wide association studies have detected more than 30 inherited prostate cancer risk variants. While clearly associated with risk, their relationship with clinical outcome, particularly prostate cancer-specific mortality, is less well known. We investigated whether the risk variants are associated with various measures of disease aggressiveness and prostate cancer-specific mortality. In a cohort of 3,945 men of European ancestry with prostate cancer, we genotyped 36 single nucleotide polymorphisms (SNP): 35 known prostate cancer risk variants and one SNP (rs4054823) that was recently reported to be associated with prostate cancer aggressiveness. The majority of subjects had a diagnosis of prostate cancer between 1995 and 2004, and the cohort included a total of 580 prostate cancer-specific deaths. We evaluated associations between the 36 polymorphisms and prostate cancer survival, as well as other clinical parameters including age at diagnosis, prostate-specific antigen (PSA) at diagnosis, and Gleason score. Two SNPs, rs2735839 at chromosome 19q13 and rs7679673 at 4q24, were associated with prostate cancer-specific survival (P = 7 × 10(-4) and 0.014, respectively). A total of 12 SNPs were associated with other variables (P < 0.05): age at diagnosis, PSA at diagnosis, Gleason score, and/or disease aggressiveness based on D'Amico criteria. Genotype status at rs4054823 was not associated with aggressiveness or outcome. Our results identify two common polymorphisms associated with prostate cancer-specific mortality.

Meta-analysis of genome-wide and replication association studies on prostate cancer

BACKGROUND

Genome-wide and replication association studies (GWAs) have identified multiple loci at which common variants modestly influence the risk of developing prostate cancer (PCa). To enhance the power to identify loci associated with PCa, we constructed a meta-analysis of GWAs on PCa.

METHODS

Articles evaluating the effects of genome-wide SNPs on PCa were identified by searching the PubMed database. After extraction of relevant data, main and subgroup meta-analyses were performed to assess the effects of relevant SNPs on PCa.

RESULTS

21 eligible articles containing 71 subgroups were included in this meta-analysis. Significant associations were found between 31 SNPs and PCa. They were rs445114, rs620861, rs983085, rs1016343, rs1447295, rs1859962, rs2660753, rs2710646, rs2735839, rs3760511, rs4242382, rs4430796, rs4962416, rs5945572, rs5945619, rs6470494, rs6501455, rs6983267, rs6983561, rs7000448, rs7214479, rs7501939, rs7920517, rs7931342, rs9364554, rs9623117, rs10090154, rs10486567, rs10896449, rs10993994, and rs16901979. The weighted odds ratios for above SNPs ranged between 0.64 and 1.88 (all P < 0.05). Subgroup analysis further indicated that the significant associations of some SNPs existed only in specific ancestry population (P < 10⁻⁵).

CONCLUSIONS

The current meta-analysis demonstrated the moderate effects of above 31 SNPs on PCa and 14 independent PCa risk loci were identified.

Kallikreins on steroids: structure, function, and hormonal regulation of prostate-specific antigen and the extended kallikrein locus

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and putative proteolytic functions. The kallikrein family is also emerging as a rich source of disease biomarkers with KLK3, commonly known as prostate-specific antigen, being the current serum biomarker for prostate cancer. The kallikrein locus is also notable because it is extraordinarily responsive to steroids and other hormones. Indeed, at least 14 functional hormone response elements have been identified in the kallikrein locus. A more comprehensive understanding of the transcriptional regulation of kallikreins may help the field make more informed hypotheses about the physiological functions of kallikreins and their effectiveness as biomarkers. In this review, we describe the organization of the kallikrein locus and the structure of kallikrein genes and proteins. We also focus on the transcriptional regulation of kallikreins by androgens, progestins, glucocorticoids, mineralocorticoids, estrogens, and other hormones in animal models and human prostate, breast, and reproductive tract tissues. The interaction of the androgen receptor with androgen response elements in the promoter and enhancer of KLK2 and KLK3 is also summarized in detail. There is evidence that all kallikreins are regulated by multiple nuclear receptors. Yet, apart from KLK2 and KLK3, it is not clear whether all kallikreins are direct transcriptional targets. Therefore, we argue that gaining more detailed information about the mechanisms that regulate kallikrein expression should be a priority of future studies and that the kallikrein locus will continue to be an important model in the era of genome-wide analyses.

Blood biomarker levels to aid discovery of cancer-related single-nucleotide polymorphisms: kallikreins and prostate cancer

Polymorphisms associated with prostate cancer include those in three genes encoding major secretory products of the prostate: KLK2 (encoding kallikrein-related peptidase 2; hK2), KLK3 (encoding prostate-specific antigen; PSA), and MSMB (encoding beta-microseminoprotein). PSA and hK2, members of the kallikrein family, are elevated in sera of men with prostate cancer. In a comprehensive analysis that included sequencing of all coding, flanking, and 2 kb of putative promoter regions of all 15 kallikrein (KLK) genes spanning approximately 280 kb on chromosome 19q, we identified novel single-nucleotide polymorphisms (SNP) and genotyped 104 SNPs in 1,419 cancer cases and 736 controls in Cancer Prostate in Sweden 1, with independent replication in 1,267 cases and 901 controls in Cancer Prostate in Sweden 2. This verified prior associations of SNPs in KLK2 and in MSMB (but not in KLK3) with prostate cancer. Twelve SNPs in KLK2 and KLK3 were associated with levels of PSA forms or hK2 in plasma of control subjects. Based on our comprehensive approach, this is likely to represent all common KLK variants associated with these phenotypes. A T allele at rs198977 in KLK2 was associated with increased cancer risk and a striking decrease of hK2 levels in blood. We also found a strong interaction between rs198977 genotype and hK2 levels in blood in predicting cancer risk. Based on this strong association, we developed a model for predicting prostate cancer risk from standard biomarkers, rs198977 genotype, and rs198977 x hK2 interaction; this model had greater accuracy than did biomarkers alone (area under the receiver operating characteristic curve, 0.874 versus 0.866), providing proof in principle to clinical application for our findings.

Replication of prostate cancer risk loci on 8q24, 11q13, 17q12, 19q33, and Xp11 in African Americans

BACKGROUND

Prostate cancer (Pca) is a common malignancy that disproportionately affects African American men (AA). Recently there have been several genome-wide association studies (GWAS) implicating new prostate cancer risk loci along chromosomes 2, 3, 6, 7, 8, 10, 11, 12, 17, 19, and X in populations of European ancestry. Given the higher incidence and mortality for AAs, and differences in allele frequencies and haplotype structures between African and European descent populations, it is important to assess the impact of these candidate risk loci in AAs.

METHODS

Here we evaluated 20 single nucleotide polymorphisms (SNPs) associated with prostate cancer risk in recent GWAS studies, in AA prostate cancer cases and controls.

RESULTS

We replicated five of the SNPs in our AA population, rs10896449 on 11q13.2 (P = 0.009), rs2735839 on 19q33.33 region, (P = 0.04), rs443076 on chromosome 17q12 (P = 0.008), rs5945572 on Xp11.22 (P = 0.05), as well as the rare variant specific to west African ancestry, bd11934905 in region 2 of 8q24 (P = 1 x 10(-4)).

CONCLUSIONS

While we were able to replicate a few of the previous GWAS SNPs, we were not able to confirm the vast majority of these associations in our AA population. This finding further supports the need to perform GWAS and additional fine mapping in AAs to locate additional susceptibility loci.

Association of reported prostate cancer risk alleles with PSA levels among men without a diagnosis of prostate cancer

BACKGROUND

Prostate specific antigen (PSA) is widely used for prostate cancer screening but its levels are influenced by many non cancer-related factors. The goal of the study is to estimate the effect of genetic variants on PSA levels.

METHODS

We evaluated the association of SNPs that were reported to be associated with prostate cancer risk in recent genome-wide association studies with plasma PSA levels in a Swedish study population, including 1,722 control subjects without a diagnosis of prostate cancer.

RESULTS

Of the 16 SNPs analyzed in control subjects, significant associations with PSA levels (P < or = 0.05) were found for six SNPs. These six SNPs had a cumulative effect on PSA levels; the mean PSA levels in men were almost twofold increased across increasing quintile of number of PSA associated alleles, P-trend = 3.4 x 10(-14). In this Swedish study population risk allele frequencies were similar among T1c case patients (cancer detected by elevated PSA levels alone) as compared to T2 and above prostate cancer case patients.

CONCLUSIONS

Results from this study may have two important clinical implications. The cumulative effect of six SNPs on PSA levels suggests genetic-specific PSA cutoff values may be used to improve the discriminatory performance of this test for prostate cancer; and the dual associations of these SNPs with PSA levels and prostate cancer risk raise a concern that some of reported prostate cancer risk-associated SNPs may be confounded by the prevalent use of PSA screening.

Association of prostate-specific antigen promoter genotype with clinical and histopathologic features of prostate cancer

The serum test for the secreted protease prostate-specific antigen (PSA) is the most widely used screening tool for prostate cancer. The PSA gene contains multiple functional and nonfunctional single nucleotide polymorphisms (SNP) in its promoter. We showed previously that the rs925013 G/A SNP, but not the rs266882 G/A SNP, was significantly associated with serum PSA in healthy men. In this study, we evaluated the association of the PSA promoter genotype with clinical data in a cohort of 1,224 men with prostate cancer. Previous work with a subset of this cohort has shown that percent high-grade (Gleason grades 4 and 5) cancer was the strongest predictor of biochemical recurrence (PSA relapse). We found a statistically significant association (P < 0.05) of the rs925013 SNP with several clinical and histomorphologic variables. The G allele was associated with higher serum PSA at diagnosis, higher percent Gleason grade 3 cancer, and lower percent high-grade and Gleason grade 4 cancer. The rs266882 SNP was modestly associated with PSA at diagnosis in a dominant model but was not associated with cancer grade. Neither SNP was associated with biochemical recurrence. The statistically significant predictors of biochemical recurrence were tumor location in the peripheral zone [odds ratio (OR), 10.71; 95% confidence interval (95% CI), 3.15-36.49], presence of any Gleason grade 4/5 cancer (OR, 4.26; 95% CI, 1.30-14.00), presence of any intraductal cancer (OR, 1.03; 95% CI, 1.00-1.04), and serum PSA at diagnosis (OR, 2.04; 95% CI, 1.50-2.77).

Effects of G/A polymorphism, rs266882, in the androgen response element 1 of the PSA gene on prostate cancer risk, survival and circulating PSA levels

Prostate-specific antigen (PSA) is a protease produced in the prostate that cleaves insulin-like growth factor binding protein-3 and other proteins. Production is mediated by the androgen receptor (AR) binding to the androgen response elements (ARE) in the promoter region of the PSA gene. Studies of a single nucleotide polymorphism (PSA -158 G/A, rs266882) in ARE1 of the PSA gene have been conflicting for risk of prostate cancer and effect on plasma PSA levels. In this nested case-control analysis of 500 white cases and 676 age- and smoking-matched white controls in the Physicians' Health Study we evaluated the association of rs266882 with risk and survival of prostate cancer and prediagnostic total and free PSA plasma levels, alone or in combination with AR CAG repeats. We used conditional logistic regression, linear regression and Cox regression, and found no significant associations between rs266882 (GG allele vs AA allele) and overall prostate cancer risk (RR=1.21, 95% confidence intervals (CI): 0.88-1.67) or prostate cancer-specific survival (RR=0.94, 95%CI: 0.56-1.58). Similarly, no associations were found among high grade or advanced stage tumours, or by calendar year of diagnosis. There was no significant association between rs266882 and baseline total or free PSA levels or the AR CAG repeats, nor any interaction associated with prostate cancer risk. Meta-analysis of 12 studies of rs266882 and overall prostate cancer risk was null.

Multiple newly identified loci associated with prostate cancer susceptibility

Prostate cancer is the most common cancer affecting males in developed countries. It shows consistent evidence of familial aggregation, but the causes of this aggregation are mostly unknown. To identify common alleles associated with prostate cancer risk, we conducted a genome-wide association study (GWAS) using blood DNA samples from 1,854 individuals with clinically detected prostate cancer diagnosed at </=60 years or with a family history of disease, and 1,894 population-screened controls with a low prostate-specific antigen (PSA) concentration (<0.5 ng/ml). We analyzed these samples for 541,129 SNPs using the Illumina Infinium platform. Initial putative associations were confirmed using a further 3,268 cases and 3,366 controls. We identified seven loci associated with prostate cancer on chromosomes 3, 6, 7, 10, 11, 19 and X (P = 2.7 x 10(-8) to P = 8.7 x 10(-29)). We confirmed previous reports of common loci associated with prostate cancer at 8q24 and 17q. Moreover, we found that three of the newly identified loci contain candidate susceptibility genes: MSMB, LMTK2 and KLK3.

Tagging SNPs in the kallikrein genes 3 and 2 on 19q13 and their associations with prostate cancer in men of European origin

Two of the classical kallikrein genes KLK3 and KLK2 on 19q13.4 are plausible candidates in prostate cancer susceptibility. They are expressed almost exclusively in prostate tissue. We have performed a comprehensive analysis of association of variants in these two genes with prostate cancer among men of European descent using a tagging SNP approach. Thirteen SNPs selected from the HapMap database were analyzed in a sample of 596 histologically verified prostate cancer cases and 567 ethnically matched controls. Five SNPs showed significant association at single marker level. Linkage disequilibrium (LD) analysis revealed four LD blocks. We performed a haplotype analysis within each LD block. A major haplotype in block 1 that contains the first two significantly associated SNPs was significantly underrepresented in the prostate cancer cases; a second haplotype in block 3 also showed significant frequency differences between cases and controls. Four of the studied SNPs show positive associations with serum PSA levels. A structure analysis revealed no population stratification in our samples that could have confounded the association results. These findings suggest a plausible role of kallikrein gene variants in the etiology of prostate cancer among men of European ancestry.