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Cancer Susceptibility and Prevention |
Authors' Affiliations: Departments of 1 Cellular and Structural Biology, 2 Pediatrics, 3 Pathology, and 4 Urology, The University of Texas Health Science Center, San Antonio, Texas and 5 Departments of Pathology and Preventive Medicine and Biometrics, University of Colorado at Denver and Health Sciences Center, Aurora, Colorado
Requests for reprints: Robin J. Leach, Department of Cellular and Structural Biology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900. Phone: 210-567-6947; Fax: 210-567-6781; E-mail: leach{at}uthscsa.edu.
| Abstract |
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Experimental Design: Two RNASEL common variants, located at amino acids 462 and 541, were genotyped in non-Hispanic Caucasian, Hispanic Caucasian, and African American prostate cancer cases and controls.
Results: The RNASEL 462 AA genotype was found to increase prostate cancer risk over 4-fold in Hispanic Caucasians [odds ratio (OR), 4.43; 95% confidence interval (95% CI), 1.68-11.68; P = 0.003] and over 10-fold in African Americans (OR, 10.41; 95% CI, 2.62-41.40; P = 0.001) when compared with the GG genotype. Analysis of the RNASEL 541 variant showed that Hispanic Caucasian patients with the GG genotype had a statistically significant increase in their risk for developing prostate cancer when compared with the TT and GT genotypes (OR, 1.91; 95% CI, 1.16-3.14; P = 0.01). A common G-T haplotype for the combination of the RNASEL 462 and 541 variants was found to occur more frequently in controls compared with cases in African Americans (P = 0.04) but not in non-Hispanic Caucasians or Hispanic Caucasians.
Conclusions: This is the first study that investigates the association of prostate cancer risk with RNASEL variants in Hispanic men. Our data support the role of RNASEL as a predisposition gene for prostate cancer and showed a significant association between the RNASEL 462 variant and prostate cancer risk in African Americans and Hispanic Caucasians.
Currently, elevated serum levels of prostate-specific antigen and/or an abnormal digital rectal exam are the main methods for diagnosing this disease (7). However, there is increased impetus for better understanding of the molecular processes involved in prostate carcinogenesis with the ultimate goal of discovering new biomarkers, which may be beneficial in the detection, prevention, and/or treatment of this disease (8). Only limited association studies on candidate genes and/or linkage analyses for susceptibility loci have consistently produced positive findings. In 1996, the first prostate cancer susceptibility locus, the hereditary prostate cancer (HPC) 1 locus (HPC1; MIM 601518), was mapped to chromosomal region 1q24-q25 by linkage analysis (9) and since this initial report, several prostate cancer susceptibility loci have been identified (10–18). Because the majority of these regions have not been consistently confirmed in independent populations, evidence has emerged that prostate cancer is a genetically complex and heterogeneous disorder, with multiple genetic and environmental factors contributing to the disease.
There is substantial evidence for a genetic component in the vulnerability to prostate cancer. A cohort study of twins reported by Lichtenstein et al. (19) indicated that the proportion of prostate cancer risk accounted for by heritable factors is estimated to be 42%. Prostate cancer is classified as hereditary (HPC) or sporadic and it is assumed that HPC might be caused by rare, highly penetrant alleles at single gene forms of the disease (20). Alternatively, the sporadic prostate cancer cases may involve some of the same genes and pathways that determine HPC incidence, but they most likely involve more common, low- to moderate-penetrant alleles in genes that are components of pathways that influence prostate function (21–23).
An important gene involved in innate immunity and apoptosis is the gene encoding 2'-5'-oligoadenylate (2-5A)–dependent RNASEL (RNASEL; MIM 180435). RNASEL, located at 1q25, regulates cell proliferation and apoptosis through the IFN-regulated 2-5A pathway (24) that mediates antiviral and antiproliferative activities (25–27) and has been suggested to be a candidate tumor suppressor gene. Previous studies indicated that germ-line mutations in the RNASEL gene segregate in prostate cancer families that show linkage to the HPC1 region (28). The investigators also found a truncating mutation (E265X) and an initiation-codon mutation (M1I) segregating with the disease in two HPC1-linked families. Functional studies show that both mutations were associated with a reduction in RNASEL activity (28). Furthermore, loss of the wild-type RNASEL allele was found in tumor tissue from an affected patient in a family with the E265X mutation, accompanied by absent protein expression. This E265X mutation was also associated with HPC in Finnish patients (29). Follow-up studies revealed a frameshift mutation, 471delAAAG, as a founder allele in Ashkenazi Jews (30).
There are numerous nucleotide variants identified in the RNASEL gene, with seven of them resulting in protein sequence changes (29). Six variants cause missense alterations and one rare variant creates a nonsense mutation. The two most commonly found variants in the U.S. non-Hispanic Caucasian population are the nonsynonymous variants: Arg462Gln (G
A) and Asp541Glu (T
G). The Arg462Gln variant reduces the ability of the cell to cause apoptosis in response to activation by 2-5 (A) and also has three times less enzymatic activity than normal (31), whereas the Asp541Glu variant has no known effect on RNASEL protein function (32). There continues to be much debate over whether these common variants increase the risk of prostate cancer. The Arg462Gln AA genotype has been associated with both increased prostate cancer in U.S. Caucasian sample groups (31, 32) and decreased prostate cancer risk in Caucasian and Japanese sample groups (33, 34). Previous studies using the Asp541Glu variant within RNASEL indicated that the GG and TT genotypes were associated with an increased risk for prostate cancer in Japanese (34) and European-American samples, respectively (17). On the other hand, a significant negative association of the TT genotype with prostate cancer in Swedish Caucasian samples was reported by Wiklund et al. (35).
In summary, several studies provide strong support, both functional and epidemiologic, that RNASEL plays a role in HPC, yet other studies have suggested that its role may be small. To date, no association study has been done using Hispanic Caucasian prostate cancer cases. Furthermore, no significant association has been reported in African American prostate cancer cases thus far. In this study, we analyzed an extended group of samples from three different racial/ethnic groups to determine whether a significant association exists between the allelic variants RNASEL 462 and/or RNASEL 541 and prostate cancer in non-Hispanic Caucasians, Hispanic Caucasians, and/or African Americans.
| Materials and Methods |
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15% of the control samples to check for error rates and found a 100% concordance rate for the genotyping results of RNASEL 462 and one mismatch for marker RNASEL 541. Both markers were in Hardy-Weinberg equilibrium in the control samples (P > 0.05).
Statistics. For each single nucleotide polymorphism (SNP), allele frequency was determined for the three ethnic groups individually and the frequencies among the ethnic sample groups were compared using the
2 test. The Hardy-Weinberg equilibrium test was done on the control population for both SNPs. To estimate the association between prostate cancer risk and each RNASEL SNP, age-adjusted odds ratios (OR) and 95% confidence intervals (95% CI) were determined using logistic regression models. For the purpose of these calculations, study age among controls was the age at last follow-up, whereas age among cases was the age at cancer diagnosis. All analyses were done using SAS statistical software version 9.1 (SAS Institute) and stratified by ethnicity. All statistical tests were two sided and significance was set at P < 0.05. Haplotypes and measures of linkage disequilibrium between the two markers were determined using Haploview version 3.26 (36) for each race/ethnicity.
| Results |
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Associations of RNASEL 462 and 541 SNPs with prostate cancer risk. Age-adjusted logistic regression analysis stratified by ethnicity showed a statistically significant association between the AA genotype of Arg462Gln and prostate cancer risk in Hispanic Caucasian men, with a >4-fold increase in prostate cancer risk (OR, 4.43; 95% CI, 1.68-11.68; P = 0.003) compared with the GG genotype (Table 3 ). Furthermore, a >10-fold increase in prostate cancer risk was observed for the AA genotype at Arg462Gln in the African American samples (OR, 10.41; 95% CI, 2.62-41.40; P = 0.001; Table 3). In the non-Hispanic Caucasian men, however, no significant association for the Arg462Gln variant could be found. Assuming a recessive model, age-adjusted ORs for the presence of the AA genotype in the RNASEL 462 SNP, compared with GG and AG genotypes, showed that the observed risk estimate is slightly decreased in both sample groups (OR, 4.03; 95% CI, 1.56-10.42 in Hispanic Caucasian men, P = 0.004; OR, 9.84; 95% CI, 2.51-38.54 in African American men, P = 0.001; Table 3). In the African American men, we also noticed a significant result under the dominant model (AA/AG versus GG genotypes), with a 2-fold increase in risk estimate (OR, 2.07; 95% CI, 1.06-4.05; P = 0.03; Table 3).
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Haplotype analysis of RNASEL 462 and 541 SNPs with prostate cancer risk. There was high linkage disequilibrium between the two polymorphisms in the three ethnic/racial sample groups with D-prime values >0.90 in both the Hispanic Caucasians and non-Hispanic Caucasians, indicating that both SNPs are in nearly complete linkage disequilibrium in these sample groups. The D-prime value in the African Americans was 0.79. In the non-Hispanic Caucasians, both SNPs are part of a haplotype block as defined by the Haploview program with the option of adopting block definition proposed by Gabriel et al. (38). A common G-T haplotype for the RNASEL 462 and 541 SNP combination was found to occur more frequently in controls compared with cases in African Americans (controls, 0.686; cases, 0.586; P = 0.04) but not in non-Hispanic Caucasians (controls, 0.444; cases, 0.448; P = 0.87) or in Hispanic Caucasians (control, 0.526; cases, 0.464; P = 0.08; Table 5 ).
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| Discussion |
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Previous studies using the Asp541Glu variant within RNASEL indicated that the GG genotype was associated with an increased risk for prostate cancer in a Japanese study (34). On the other hand, a study in European-American samples resulted in a significant positive association of the TT genotype with prostate cancer (17) and in a significant negative association of the TT genotype with prostate cancer in Swedish Caucasian samples (35). No association for the Asp541Glu variant was found in several other studies (29, 31, 33, 39). Furthermore, no study reported to date has examined/confirmed the role of RNASEL variants in the Hispanic Caucasian or African American population.
To test the hypothesis that RNASEL sequence variants are associated with prostate cancer risk, we did a case-control genotype analysis on two common variants of RNASEL in more than 1,500 men from the South Texas region including 933 non-Hispanic Caucasians, 214 African Americans, and 392 Hispanic Caucasians. We included African Americans and Hispanic Caucasians in the analysis because these ethnic study groups are of particular interest; African Americans have the highest risk and death rate, whereas Hispanics are the fastest growing minority population in the United States. The two RNASEL variants analyzed in this study have not been extensively evaluated in African American populations and have not been studied at all in Hispanic Caucasian populations.
The allelic frequencies for Arg462Gln are significantly different among the Hispanic Caucasians and African Americans. This suggests an ethnic-specific allele distribution and is a likely explanation why substantial differences in the incidence of prostate cancer are observed among populations.
The most significant finding was the association of the Arg462Gln genotype with increased prostate cancer risk in both the Hispanic Caucasian and African American samples. Age-adjusted ORs for Arg/Gln (AG) and Gln/Gln (GG) genotypes, compared with Arg/Arg (AA), showed that the Arg/Arg (AA) genotype increases prostate cancer risk over 4-fold in Hispanic Caucasians and over 10-fold in African Americans, which suggests a recessive model for the RNASEL 462 AA genotype. This is to our knowledge the first report on the significant association of Arg462Gln genotypes with increased prostate cancer risk in Hispanic Caucasian or African American men. Our results support the findings of Casey et al. (31) and Xiang et al. (32) showing that the AA genotype of the Gln462 variant is significantly associated with prostate cancer, although they differ from the findings of Casey et al. (31) in that we found the association in Hispanic Caucasians and African Americans but not in non-Hispanic Caucasians. Our results suggest that the role of the Arg462Gln variant in the development of prostate cancer is different across populations. From our sample group, we conclude that the genetic influence of the Arg462Gln variant within RNASEL on prostate cancer in the non-Hispanic Caucasian samples is relatively small, if there is any effect at all. Because it has been shown that the Gln462 AA genotype has three times less enzymatic activity than the wild-type protein (31), our data support the hypothesis that the less active RNASEL protein could leave viral infections intact, leading to inflammation, which eventually could lead to prostate cancer. Additional functional evidence for this variant's role in prostate cancer development comes from the observation that the Arg462Gln variant reduced the ability of RNASEL to cause apoptosis in response to activation by 2-5A (32) and suppresses antiviral effects of IFN (25–27). Furthermore, a strong association between infection with the xenotropic MuLV-related (XMRV) virus and homozygous mutant (Gln462 AA genotype) cases has been reported by Urisman et al. (40), which implicates that defects in RNASEL activity may lead to persistent viral infection in vivo.
Analysis of the RNASEL Asp541Glu variant in the three racial/ethnic groups revealed a statistically significant increase in the risk for developing prostate cancer for the RNASEL 541 Glu/Glu (GG) genotype versus the combined Asp/Asp and Asp/Glu genotypes in the Hispanic Caucasian samples. An association of the GG genotype at RNASEL 541 with a slightly increased prostate cancer risk was also reported by Noonan-Wheeler et al. (17) among Caucasian individuals. However, we observed the finding in the Hispanic Caucasian group, whereas non-Hispanic Caucasians did not show a significant positive association for the GG genotype. Our data suggest that susceptibility to develop prostate cancer at this variant is likely ethnic specific and that the RNASEL Asp541Glu variant does not seem to have a major effect on the development of prostate cancer in our non-Hispanic Caucasian or African-American population, whereas it seems to play a role in the Hispanic Caucasian cancer cases. Alternatively, because the Asp541Glu variant had similar enzymatic activity as wild-type RNASEL (32), the substitution of the amino acid Glu by Asp might not be of any functional significance and it is therefore possible that the RNASEL 541 variant may be in linkage disequilibrium with a nearby functional polymorphism(s) within the RNASEL gene or within another gene nearby such that the actual causal variant(s) resides on diverse haplotypes in different study populations. Therefore, additional studies are needed to confirm and clarify the functional significance of these findings in the vulnerability/etiology of prostate cancer.
A common G-T haplotype for the combination of the RNASEL 462 and 541 variants was found to occur more frequently in controls compared with cases in African Americans but not in non-Hispanic Caucasians or in Hispanic Caucasians. These findings are consistent with the observation of Wiklund et al. (35) who found that in sporadic cancer cases, the frequency of the haplotype significantly associated with prostate cancer risk (containing the G-T alleles for RNASEL 462 and 541, respectively) also occurred at higher frequencies among controls compared with sporadic prostate cancer cases.
In conclusion, we confirm the likely involvement of RNASEL in the etiology of prostate cancer and we further provide the first evidence for an association of the RNASEL gene with prostate cancer in Hispanic Caucasian and African American men. The prostate cancer risk differs widely between racial/ethnic groups, indicating that race/ethnicity plays a role in the development of prostate cancer. This is likely because each individual brings with them genetic material that sets each race and ethnicity apart. Furthermore, there may be different exposures to environmental factors between the populations. Involvement of environmental factors combined with genetic background may result in the differences in incidence of prostate cancer observed in these populations.
| Footnotes |
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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.
6 http://www.broad.mit.edu/mpg/haploview/ ![]()
Received 3/27/07; revised 6/ 6/07; accepted 7/11/07.
| References |
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gene polymorphism and the risk of prostate cancer in black men. J Urol 2006;175:523–7.[CrossRef][Medline]This article has been cited by other articles:
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S. Kim, N. Kim, B. Dong, D. Boren, S. A. Lee, J. Das Gupta, C. Gaughan, E. A. Klein, C. Lee, R. H. Silverman, et al. Integration Site Preference of Xenotropic Murine Leukemia Virus-Related Virus, a New Human Retrovirus Associated with Prostate Cancer J. Virol., October 15, 2008; 82(20): 9964 - 9977. [Abstract] [Full Text] [PDF] |
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L. M. Dong, J. D. Potter, E. White, C. M. Ulrich, L. R. Cardon, and U. Peters Genetic Susceptibility to Cancer: The Role of Polymorphisms in Candidate Genes JAMA, May 28, 2008; 299(20): 2423 - 2436. [Abstract] [Full Text] [PDF] |
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