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Vanderbilt-Ingram Cancer Center and Vanderbilt Center for Health Services Research, Vanderbilt University, Nashville, Tennessee 37232-8300 [W. Z., W. W.]; School of Public Health, University of South Carolina, Columbia, South Carolina [D. X.]; Mayo Clinic Cancer Center, Rochester, Minnesota 55905 [J. R. C., T. A. S.]; and School of Public Health, University of Minnesota, Minneapolis, Minnesota 55454 [A. R. F.]
| Abstract |
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A transition at codon 213 (CGC/Arg
to CAC/His) of the SULT1A1 gene
was reported recently, and individuals homozygous for the
His allele have a substantially lower activity of this
enzyme than those with other genotypes. We hypothesized that the
His allele may be a risk factor for breast cancer,
particularly among women who had risk factors related to higher
endogenous estrogen exposure. This hypothesis was investigated in a
case-control study conducted in a cohort of postmenopausal Iowa women
who completed a mailed questionnaire in 1986 on lifestyle factors
including information on major breast cancer risk factors. DNA samples
and information related to well-done meat intake were obtained from
breast cancer cases diagnosed between 1992 and 1994 and a random sample
of cancer-free cohort members. Multivariate analysis was performed on
data from 156 cases and 332 controls who donated a blood sample. The
frequency of the His allele was 41.6% in cases and
34.1% in controls (P = 0.03), and the risk of
breast cancer was increased with the number of His
alleles (P for trend = 0.02). Compared with women
with the Arg/Arg genotype, an 80% elevated risk was
observed among women homozygous for the His allele (95%
confidence interval, 1.03.2; P = 0.04). This
positive association was more pronounced among women who drank alcohol
and had a high body mass index, early age at menarche, and late age at
menopause, factors related to high endogenous estrogen exposure, than
among those who did not have these risk factors. The risk of breast
cancer was elevated with increasing doneness level of red meat intake
among women with the Arg/Arg genotype (P
for trend, 0.01) or the Arg/His genotype
(P for trend, 0.10), whereas this association was not
evident for women with the His/His genotype. The results
from this study suggest that homozygosity for the SULT1A1
His213 allele may be a risk factor for breast
cancer, and its effect may be modified by the exposure level of
endogenous estrogens and heterocyclic amines. | Introduction |
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The polymorphic nature of SULTs has long been recognized (1, 2, 3
, 9)
. Because of a strong correlation of enzyme activity and
thermal stability between SULTs from platelets and those from other
organs such as liver, brain, and intestine, platelets were used, for
convenience, in many previous biochemical pharmacogenetic studies of
human SULTs (1
, 2
, 9)
. These studies have demonstrated a
large individual variation (about 50-fold in some studies) in the
activity of platelet SULTs in humans (1
, 2
, 9
, 10)
. It was
reported recently that a large portion of this variability could be
explained by a newly identified common polymorphism (a G
A
transition) in the coding region (nucleotide 638) of the
SULT1A1 gene (10)
. This base change in the gene
sequence results in an arginine to histidine substitution at codon 213,
and individuals homozygous for the His allele had only about
15% of the SULT activity in platelets of those with other genotypes.
The His allele is common in the Caucasian population, and
the frequency of this allele was reported to be about 3035%
(11
, 12)
. Given the role of SULT1A1 in the
metabolism of estrogens and environmental carcinogens, we hypothesized
that the SULT1A1 polymorphism and its interaction with
relevant lifestyle factors may be associated with the risk of breast
cancer. We have designed a PCR-based RFLP assay to investigate the
association of the SULT1A1 polymorphism with breast cancer
risk in a case-control study conducted in the Iowa Womens Health
Study.
| Materials and Methods |
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From 1995 to 1996, a case-control study was conducted in the Iowa Womens Health Study to collect DNA samples and additional information on meat consumption habits (17, 18, 19, 20, 21) . Eligible cases for this case-control study were cohort members who were diagnosed with breast cancer between January 1, 1992 and December 31, 1994 (n = 456). Controls were randomly selected from women who were cancer free as of January 1, 1992 (n = 900). Of the 900 controls, 24 were excluded from the control group because they were later found either to have a breast cancer diagnosis (n = 3) or to have been selected to participate in other Iowa Womens Health Study ancillary projects (n = 21). All eligible women were asked to complete a self-administered questionnaire on meat consumption habits during the reference year (1991, 1992, or 1993). The reference year for cases was the year immediately before breast cancer diagnosis. Controls were divided randomly into three approximately equal groups for each reference year and answered the same questionnaire. In addition, a series of color photographs used to represent the various doneness levels of hamburger, beefsteak, and bacon was included in the questionnaire to facilitate the assessment of usual doneness levels of meat consumed by the study participants (17) . Of all women selected for the study, 273 cases and 657 controls responded, representing approximately 60% and 75% response rates, respectively. The major reasons for nonparticipation were refusal (29.1% of cases and 18.7% of controls), inability to locate subject (4.9% of cases and 3.8% of controls), and subject death before contact (5.7% of cases and 2.5% of controls).
Exfoliated buccal cell samples were collected through the mail as a source of genomic DNA for genotyping assays for this study. About 96.6% of women (267 cases and 631 controls) who completed the supplemental questionnaire provided a sample of exfoliated buccal cells using the cytobrush method (22) . Genomic DNA from buccal cells were extracted using the NaOH method described by Richards et al. (22) . Blood samples were also collected through the mail from 488 women (156 cases and 332 controls), reflecting an overall response rate of 53% (57% for cases and 50% for controls; Refs. 18, 19, 20 ). Specifically, a blood collection kit including vacutainer tubes, biological specimen packaging containers and envelopes, and instructions was mailed to all women who agreed to donate a blood sample. Study participants were instructed to contact their physicians to have their blood drawn and to return samples via overnight express mail using preaddressed, prepaid envelopes provided by the study. Because of an unsatisfactory quality and quantity of DNA extracted from buccal cells, this study was restricted to those whose blood samples were collected.
Genomic DNA was extracted from peripheral blood leukocytes using a standard protocol and stored at a low temperature for subsequent assays (18, 19, 20) . Most assays for the SULT1A1 genotypes were completed in the summer of 1998 using a PCR RFLP-based assay. According to the published sequence of the human SULT1A1 gene (10 , 23) , we designed two primers (forward primer, 5'-GGGTCTCTAGGAGAGGTGGC; reverse primer, 5'-GCTGTGGTCCATGAACTCCT) to amplify a 270-bp fragment) of exon 7 that included the polymorphic site (codon 213, His/CAC to Arg/CGC) of the gene. The PCR reactions were performed on a Perkin-Elmer GeneAmp System 9700 according to the manufacturers protocol. Specifically, these reactions were carried out in 50 µl of 20 mM Tris-HCl (pH 8.4), 50 mM KCl, 1.5 mM MgCl2, 0.2 mM deoxynucleotide triphosphate, and 1 unit of Taq polymerase. The reactions were heated to 94°C for 1 min followed by 35 cycles of 94°C for 30 s, 62°C for 30 s, and 72°C for 30 s. At the end, the reactions were extended 7 min at 72°C. The PCR products (270 bp) were digested with HhaI and analyzed by gel electrophoresis [3% (2:1) Nusiev/SeaKem agarose]. Digestion of each PCR product with HhaI gives rise to 155- and 115-bp fragments for the Arg/CGC allele and a single 270-bp fragment for the His/CAC allele. The SULT1A1 genotypes were successfully identified for all but one case and four controls, resulting in 155 cases and 328 controls for data analysis.
ORs were calculated to measure the strength of the association of
breast cancer risk with SULT1A1 genotypes. Unconditional
logistic regression was used to control for potential confounding
variables assessed in the baseline survey in 1986 and to derive
adjusted ORs and 95% CIs. In addition to the study variables,
covariates included in multiple logistic models were age
(continuously), WHR (<0.85,
0.85), and live births (<4,
4),
variables that were significantly associated with the risk of breast
cancer in this study population. Trend tests for dose-response
relationships across levels of the exposure variables were performed by
treating ordinal score variables (with values of 1, 2, 3, ... ) as
continuous variables in logistic regression models. Tests for
interaction used the likelihood ratio test by adding the interaction
term(s) (genotype by exposure) to the model that already included the
main effect variables (genotype, exposure) and confounding variables.
Reported P values are based on two-tailed probability tests.
BMI, age at menarche, age at menopause, and alcohol consumption were evaluated as potential modifiers of SULT1A1 genotypes because they are related to endogenous estrogen exposure. Although WHR, age at first live birth, and parity are also hormonally related, their association with breast cancer risk is thought to be mainly through mechanisms other than cumulative endogenous estrogen exposure (24 , 25) . These variables were also considered in stratified analyses. Exposure to well-done meat was measured by assessing usual doneness levels of hamburgers, beefsteaks, and bacon. Doneness levels of rare or medium, well-done, and very well-done meat were given scores of 1, 2, or 3, respectively, for each food to describe the eating habits of participants on the basis of their responses to the color photographs in the questionnaire. A doneness score, defined as the sum of the usual doneness level for each of these three meats, was then calculated (17) . The scores ranged from 3 to 9, with 3 for consistently rare/medium doneness, and 9 for consistently very well-done meat. To enhance the stability of risk estimates, several levels of the doneness score were combined to form the following three groups: (a) rare/medium, scores of 34; (b) mostly well-done meat, score of 5; and (c) consistently well- or very well-done meat, scores of 69 (17) . Information on SULT1A1 genotype was analyzed along with estrogen-related factors and well-done meat intake to evaluate potential joint effects of genetic and lifestyle factors in the etiology of breast cancer.
| Results |
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| Discussion |
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Our finding of a positive association between the His allele (encoding a low activity allozyme) and breast cancer risk is consistent with the role of SULT1A1 in the inactivation of estrogens, the hormones believed to play a central role in the etiology of breast cancer (24 , 25) . This finding was further supported by the observation that the positive association with the His allele was more evident among women who had risk factors related to higher endogenous estrogen exposure. It has been reported that the level of endogenous estrogen is positively related to age at menopause and inversely related to age at menarche (24 , 25) . Alcohol drinking also increases blood estrogen levels (24, 25, 26) . After menopause, adipose tissue is the major source of estrogen production from androgens (24 , 25 , 27) , and high body weight, often measured using BMI, has been demonstrated to be a risk factor for postmenopausal breast cancer (19 , 23) . It was intriguing to find that the association of breast cancer with the His/His genotype was stronger among women who had a high BMI, earlier age at menarche, later age at menopause, and a regular alcohol consumption history than it was among those who did not have these factors.
The strong association of breast cancer risk with the His allele observed in this study among women with a low WHR is puzzling because a high WHR is a risk factor for breast cancer. In a cross-sectional study of 88 participants of the Iowa Womens Health Study, we found that WHR was positively correlated with blood level of insulin and inversely related to the blood level of sex hormone-binding globulin (28) . However, WHR was not correlated with blood estrogens (r = -0.16 for estrone; r = 0.13 for estradiol), even free estradiol (r = 0.14). Recently, Tchernof et al. (29) reviewed published data from previous epidemiological studies and concluded that there is an increase in central body fatness during the transition period of menopause, and this increase may be due to estrogen deficiency as a result of a progressive loss of ovarian function in estrogen production. Intervention studies have shown that estrogen replacement therapy reduces central fat distribution in postmenopausal women (29) . The association of breast cancer with the His/His genotype also appears to be stronger among women who had an earlier age at first live birth and lower parity than it is among those who did not have these factors. It appears that this observation cannot simply be explained by the cumulative estrogen exposure hypothesis. During a pregnancy, particularly during the first pregnancy, breast cells proliferate rapidly and differentiate into mature cells prepared for lactation (24 , 25) . Mature breast cells have a longer cell cycle and spend more time in G1, the phase that allows for DNA repair, and are thus less susceptible to carcinogens (24) . Early age at first live birth is believed to reduce the susceptibility of mammary tissue at an early stage of a womens life, and additional live births may confer further benefits by increasing mature cells (and thus decreasing susceptible cells) of the breast.
Burned meat contains a wide variety of potentially carcinogenic compounds (4 , 7 , 8 , 30) , including heterocyclic amines and PAH procarcinogens that can be activated by SULT1A1 and other SULT variants (2, 3, 4) . Despite some inconsistent findings (31) , high intakes of fried foods and a preference for well-done meats have been shown to be associated with an increased risk of breast cancer in several epidemiological studies (17 , 21 , 32, 33, 34, 35, 36, 37) , including a prospective study reported recently (37) . We recently reported a dose-response relationship between doneness levels of meat consumption and the risk of breast cancer, with a nearly 5-fold elevated risk observed among women who consistently consumed very well-done meat (17) . We showed in this report that the positive association was evident only among women with the Arg/Arg or Arg/His genotype and not among those with the His/His genotype. This finding is biologically plausible because the former two genotypes are associated with higher phenol SULT activity and hence greater bioactivation of procarcinogens than the latter genotype.
A consideration in this study may be the low response rate for blood sample collection. The survival rate for breast cancer, however, is very high in our study population. As such, only 5.7% of patients died before we contacted them for the supplemental survey and sample collection. Therefore, the potential influence of selective survival due to genotypes is unlikely to be substantial in our study. The response rate for buccal cell collection for studying genetic factors was reasonably high, indicating that the low response in blood collection is unlikely to be related to the genetic characteristics of study subjects. Women who donated a blood sample to the study were not atypical because virtually all established risk factors for breast cancer were found to be positively associated with the risk of breast cancer in our study, although some of the associations were not statistically significant due to the small sample size. Data on factors related to endogenous estrogen exposure were collected before cancer diagnosis. The prospective nature of the study design for these factors eliminates potential recall bias. The information on well-done meat intake was collected in this case-control study retrospectively. An individuals intake preference for meat doneness level, however, is likely to be related to a personal habit, which may be recalled with relatively high accuracy. At the time this study was conducted, the hypothesis for a potential link between well-done meat intake and breast cancer risk was relatively new. Therefore, there is no reason to speculate that the breast cancer patients would differentially recall intake of well-done meat as compared with controls, particularly because consumption of well-done hamburger is recommended in the news media to reduce the risk of Escherichia coli infection.
In summary, this case-control study found that postmenopausal women who were homozygous for the His allele at codon 213 of the SULT1A1 gene may be at an increased risk of breast cancer, particularly if they have risk factors related to higher endogenous estrogen exposure. Our data also suggest a potentially modifying effect of the SULT1A1 polymorphism on the association of well-done meat intake and breast cancer. The dual effect of SULT1A1 in the inactivation of estrogens and activation of environmental carcinogens complicates the association between SULT1A1 genotype and breast cancer risk. Because endogenous estrogen exposure is believed to play a more important role in the etiology of breast cancer than heterocyclic amine and PAH exposure, it is conceivable that low activity of SULT1A1 (the His allele) may be a risk factor for breast cancer for most women. The high frequency of this risk allele and the involvement of this enzyme in estrogen, heterocyclic amine, and PAH metabolism suggest that SULT1A1 polymorphism may be important in the etiology of breast cancer. The sample size of this study is small, and additional studies will be needed to replicate the findings.
| Acknowledgments |
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| Footnotes |
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1 Supported in part by USPHS Grants RO1CA39742 and
R01CA64277 from the NIH and by Supplementary Grant OWH-284 from the
National Action Plan on Breast Cancer, Office on Womens Health,
USPHS. ![]()
2 To whom requests for reprints should be
addressed, at Vanderbilt University Medical Center, Center for Health
Services Research, Medical Center East, 6th Floor,
Nashville, TN 37232-8300. ![]()
3 The abbreviations used are: SULT,
sulfotransferase; CI, confidence interval; OR, odds ratio; PAH,
polycyclic aromatic hydrocarbon; BMI, body mass index; WHR, waist:hip
ratio. ![]()
Received 4/12/00; revised 11/ 9/00; accepted 11/16/00.
| References |
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