Genetic Polymorphism of Estrogen Metabolizing Enzymes in Siberian Women with Breast Cancer

Abstract

Allelic variants of cytochrome P450: CYP1A1, CYP1A2, CYP19 (aromatase), and the II-phase enzyme sulfotransferase 1A1 (SULT1A1) genes are associated with a high risk of hormone-dependent cancers. We estimated the frequency of these allelic variants in the female population of the Novosibirsk district and their association with the elevated risk of breast cancer. A DNA bank of patients with gynecologic oncology, patients with breast cancer (n=335), and healthy women (n=530) was created, and the following single-nucleotide polymorphisms were examined: CYP1A1 M1 polymorphism, that is, T264-C transition in the 30-noncoding region; CYP1A2*1F polymorphism, that is, C734-A transversion in the CYP1A2 gene; C-T transition (Arg264Cys) in exon 7 of CYP19; and SULT1A1*2 polymorphism, that is, G638-A transition (Arg213His) in the SULT1A1 gene. The results of our study indicate that women with mutant allele C and genotypes C/T, C/C of the CYP1A1 gene, wild-allele C, and genotype C/C of the CYP1A2 gene, mutant allele A and genotypes A/G, A/A of the SULT1A1 gene have an increased risk of development of breast cancer. Women with body mass index ≥30 and the heterozygous genotype C/T of the CYP19 gene have an increased risk of breast cancer. The CYP1A2 heterozygous variant genotype C/A is associated with an increased risk of an estrogen receptor (ER⁺) tumor.

Introduction

Hormone-dependent cancers such as breast, endometrial, and ovarian cancer show a growing incidence rate all over the world, including Russia. Breast cancer is first among malignant neoplasms in Russia. In the Siberian region, the incidence of breast cancer in the female population is approximately 81.6 per 100,000.

It is estimated that the disease will develop in one of every eight women during her lifetime. Sufficient evidence indicates that breast cancer is a multifactorial disease where genetic susceptibility, environment, nutrition, and other lifestyle risk factors may play an important role in the etiology of the disease.

Estrogen is implicated in the development of breast cancer. Risk factors associated with breast cancer reflect cumulative exposure of the breast epithelium to estrogen. Two current hypotheses exist to explain this relationship. The first, binding of estrogens to the estrogen receptor (ER), stimulates proliferation of mammary cells, thus increasing the target cell number within the tissue, and the increase in cell division and DNA synthesis elevates the risk for replication errors, which may result in the acquisition of detrimental mutations that disrupt normal cellular processes such as apoptosis, cellular proliferation, or DNA repair. In the second hypothesis, estrogen metabolism leads to the production of genotoxic by-products that could directly damage DNA, again resulting in point mutations. There is evidence that estrogen may act through both mechanisms to initiate and/or promote mammary cancer (Deroo and Korach, 2006).

The genetic nature of hormone-dependent cancers may also contribute to the disease development. Feigelson and Henderson (2000) have proposed a multigenic model of breast cancer predisposition which includes genes that are involved in estrogen biosynthesis and intracellular binding. They hypothesized that a combination of functional germ line mutations in genes together with well-known hormonally related risk factors would help define a high-risk profile for breast cancer. They concentrated on genes responsible for the estrogen synthesis. In our proposal, we added a group of genes that play a very important role in estrogen catabolism.

The whole process of estrogen metabolism is quite complex, but it can be divided into three main stages: synthesis, metabolism, and detoxification. The key enzyme in the complex chain of biochemical reactions during the synthesis of estrogens from androgens is the cytochrome P450, subfamily 19 (CYP19 or aromatase) (Talbott et al., 2008). Estrogens are metabolized by several enzymes, including cytochrome P450 1A1 and 1A2 (CYP1A1 and CYP1A2), through hydroxylation resulting in reactive metabolites (Mueck et al., 2002). Further degradation of these metabolites via detoxification pathways involves participation of sulfotransferase 1A1 (SULT1A1) (Nagar et al., 2006). This enzyme catalyzes the sulfate conjugation of estrogen metabolites, forming hydrophilic sulfates of estrogens that are excreted in the urine. Endocrine system disturbances may occur through changes in the activities of enzymes involved. The CYP1A1, CYP1A2, CYP19, and SULT1A1 phenotypes vary between human individuals, thus suggesting the possibility of genetic component in the activities of these enzymes. This relationship has been confirmed by several studies.

The purpose of our study was to estimate a frequency of allelic variants of CYP19, CYP1A1, CYP1A2, and SULT1A1 and their association with the elevated risk of breast cancer in the female population of the Siberian region of Russia. The following functional polymorphisms were studied. CYP1A1 M1 variant has a T to C substitution located in the 3′- noncoding region, which is important in determining translational efficiency and mRNA stability (Levy et al., 1995; Tanguay and Gallie, 1996). The M1 variant is associated with CYP1A1 inducibility (Petersen et al., 1991). CYP1A2*1F (2163C>A) polymorphism at intron 1 position 734 was observed to be associated with a decrease in the protein activity (Goodman et al., 2003). The substitution C→A in the 264 codon for the CYP19 gene (Arg264Cys polymorphism) was observed to be associated with a change in the enzyme stability (Kagawa et al., 2004). Nucleotide substitution G638→A resulting in the Arg213His substitution for the SULT1A1 is associated with a significant decrease (as high as 85%) of enzyme activity (Raftogianis et al., 2000).

Materials and Methods

A DNA bank of patients with breast cancer and healthy women of the Novosibirsk region was created, utilizing an experimental group—patients with different stages of breast cancer (n=335, 19-55 years old) and a group of healthy controls over the age of 55 with an uncomplicated obstetric and gynecological history (n=530). Clinical diagnosis was performed by board-certified gynecologic oncologists from the Regional Clinical Oncological Hospital of Novosibirsk. Before study enrollment, the aims of the study were fully explained, and informed consent was obtained from each patient. The study protocol was reviewed and approved by the appropriate Institutional Review Boards.

Genotyping of the studied population utilized the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Exfoliated buccal cell samples were collected from patients as a source of genomic DNA for genotyping assays. DNA was isolated from buccal epithelium by using the MasterAmp Buccal Swab DNA Extraction Kit (BIOzym). After precipitation, DNA samples were dissolved in 10 mM Tris/1 mM EDTA, pH 8.0 and stored at 4°C. Respective PCR reactions for each gene were performed in a total volume of 50 mL of buffer solution containing PCR buffer (10 mM Tris-HCl, pH 8.3; 1.5 mM MgCl2; 50 mM KCl), 0.2 mM of each deoxynucleotide triphosphate, 20 pmol of each primer (in the primer pair), 100 ng of genomic DNA, and 2U of Taq DNA polymerase (purchased in Medigen). The PCR cycling conditions were as follows: denaturation at 95°C for 3 min followed by 35 cycles of denaturation at 95°C for 30 s, annealing at 62°C for 30 s, and extension at 72°C for 1 min. A final extension step at 72°C for 10 min was followed by cooling to 4°C. The oligonucleotide primers for CYP1A1, CYP1A2, CYP19, and SULT1A1 were synthesized by Medigen Company (www.medigen.ru) according to sequences chosen by using the PCR primer design software GeneRunner (available at www.generunner.com) to ensure specific and efficient amplification of target sequences. The oligonucleotide primer sequences were as follows:

CYP1A1 U, 5-TAGGAGTCTTGTCTCATGCC-3;

CYP1A1 R, 5-GCACTTAAGCAGTCTGTTTGAG-3;

CYP1A2 U, 5-TGAGGCTCCTTTCCAGCTCTCA-3;

CYP1A2 R, 5-AGAAGCTCTGTGGCCGAGAAGG-3;

CYP19 U, 5-CGCTAGATGTCTAAACTGAG-3;

CYP19 R, 5-CATATGTGGCATGGGAATTA-3;

SULT1A1 U, 5-GGGTCTCTAGGAGAGGTGGC-3;

SULT1A1 R, 5-GCTGTGGTCCATGAACTCCT-3.

We studied the following single-nucleotide polymorphisms: CYP1A1 M1 polymorphism, that is, T264-C in the 30-noncoding region giving rise to an MspI restriction site; C734-A transversion in the CYP1A2 gene abolishing an ApaI restriction site; C-T transition (Arg264Cys) in exon 7 of the CYP19 gene, which creates a recognition site for the SfaNI restriction enzyme; and a G638-A transition (Arg213His) in the SULT1A1 gene that eliminates an HhaI restriction site. The amplified DNA fragments were digested with MspI (for CYP1A1), ApaI (for CYP1A2), SfaNI (for CYP19), and HhaI (for SULT1A1) restriction enzymes (purchased from Sibenzyme) and subjected to electrophoresis on an 8% polyacrylamide gel followed by staining with ethidium bromide for UV visualization. Fragment sizes were estimated by comparison to standard DNA molecular ladders. Statistical analysis was performed with GraphPad (www.graphpad.com) and SISA (http://home.clara.net/sisa/) on-line calculators. The genotype data were analyzed by using the Fisher exact test. All polymorphisms examined in the current study were explored with regard to whether the genotype frequencies observed were in agreement with those predicted by the Hardy-Weinberg equilibrium.

Results

For the detection of germ-line mutations in genes, four selected estrogen-metabolizing enzymes encoding in the PCR-RFLP method were used. The genotype and allele distributions for CYP1A1, CYP1A2, CYP19, and SULT1A1 polymorphisms for both patients and controls are given in Table 1. There was no significant difference in both genotype and allele distribution for CYP19 polymorphism in patients with breast cancer. In contrast, significant differences in the genotype and allele distributions for CYP1A1, CYP1A2, and SULT1A1 polymorphisms between patients with breast cancer and controls were found.

Table 1.

Genotype and Allele Frequencies of CYP1A1, CYP1A2, CYP19, and SULT1A1 Polymorphisms

	Breast cancer
	n	OR (95% CI)	p-Value^a	Controls
CYP1A1
Allele frequencies
T	446			491
C	106	2.05 (1.45-2.90)	0.0000004	57
Genotype frequencies
T/T	179			218
T/C	88	1.95 (1.32-2.88)	0.001	55
C/C	9	10.96 (1.38-87.34)	0.0126	1
Total	276			274
CYP1A2
Allele frequencies
C	228			296
A	418	0.72 (0.58-0.89)	0.0023	756
Genotype frequencies
C/C	40			38
C/A	148	0.64 (0.39-1.04)	0.0946	220
A/A	135	0.48 (0.29-0.78)	0.0042	268
Total	323			527
CYP19
Allele frequencies
C	605			1011
T	41	1.12 (0.75-1.69)	0.651	61
Genotype frequencies
C/C	283			477
C/T	39	1.15 (0.75-1.78)	0.5933	57
T/T	1	0.84 (0.07-9.33)	0.6464	2
Total	323			536
SULT1A1
Allele frequencies
G	258			593
A	412	2.03 (1.66-2.47)	0.0000003	467
Genotype frequencies
G/G	47			166
G/A	164	2.22 (1.52-3.24)	0.00005	261
A/A	124	4.25 (2.80-6.45)	0.00000004	103
Total	335			530

n, Number of individuals in each category; bold values are statistically significant.

Fisher exact two-tailed p-values.

OR, odds ratio; CI, confidence interval.

Significant differences in the allele distributions for CYP1A1 M1 polymorphism between patients with breast tumors and controls were found (odds ratio [OR]=2.05, p=0.000004). A frequency of mutant T/C heterozygote genotypes (OR=1.95, p=0.001) and C/C homozygotes (OR=10.96; p=0.0126) was also higher in patients with breast cancer compared with controls.

Remarkable differences in the allele and genotype distribution for CYP1A2*1F polymorphism in patients with breast cancer were found. There is a deficiency of a mutant allele A of CYP1A2*1F in patients with breast cancer (OR=0.72, p=0.0023) as well as genotype A/A homozygotes (OR=0.048, p=0.0042), which exhibited a reduction of breast cancer risk.

Significant differences were found in the genotype and allele distribution for SULT1A1 polymorphism between patients with breast cancer and controls. Women with mutant allele A (OR=2.03, p=0.0003) and genotypes SULT1A1 AG heterozygotes (OR=2.22, p=0.000005) and A/A homozygotes (OR=4.25, p=0.000004) of SULT1A1 gene exhibited an increase of breast cancer risk.

Table 2 shows the relation of investigated polymorphisms to body mass index (BMI) (limit value BMI ≥30). After BMI stratification of groups, interesting results were revealed. The frequency of mutant allele C (OR=2.88, p=0.00005) and genotypes C/T (OR=2.79, p=0.000005), C/C (OR=11.28, p=0.0114) of CYP1A1 gene was statistically higher in the women group with BMI <30. These results may support the idea that CYP1A1 M1 polymorphism results in a higher risk of breast cancer for women without obesity (BMI <30).

Table 2.

Genotype and Allele Frequencies of CYP1A1, CYP1A2, CYP19, and SULT1A1 Polymorphisms in Women With Breast Cancer Without Obesity and Women With Obesity

	Women without obesity				Women with obesity
	n	OR (95% CI)	p-Value^a	Controls	n	OR (95% CI)	p-Value^a	Controls
CYP1A1
Allele frequencies
T	345			377	101			114
C	87	2.88 (1.88-4.41)	0.000005	33	19	0.89 (0.46-1.73)	0.87	24
Genotype frequencies
T/T	138			173	41			45
T/C	69	2.79 (1.73-4.51)	0.00000003	31	19	0.87 (0.42-1.81)	0.851	24
C/C	9	11.28 (1.41-90.1)	0.0114	1	0		1	0
Total	214			205	60			69
CYP1A2
Allele frequencies
C	160			179	68			117
A	292	0.62 (0.48-0.80)	0.0002	531	128	0.98 (0.67-1.41)	0.985	225
Genotype frequencies
C/C	37			24	3			14
C/A	86	0.43 (0.24-0.76)	0.0055	131	62	3.25 (0.89-11.79)	0.106	89
A/A	103	0.33 (0.19-0.59)	0.0001	200	32		3.364	68
Total	227			356	97	2.2 (0.58-8.18)		171
CYP19
Allele frequencies
C	426			702	181			309
T	26	0.89 (0.55-1.46)	0.742	48	15	1.97 (0.91-4.23)	0.118	13
Genotype frequencies
C/C	201			328	82			149
C/T	24	0.85 (0.50-1.44)	0.638	46	15	2.47 (1.08-5.64)	0.045	11
T/T	1	1.63 (0.10-26.2)	0.703	1	0		0.999	1
Total	226			375	97			161
SULT1A1
Allele frequencies
G	192			385	66			208
A	284	1.81 (1.43-2.29)	0.0000004	315	128	2.65 (1.84-3.81)	0.000004	152
Genotype frequencies
G/G	7			100	10			66
G/A	118	1.72 (1.11-2.68)	0.02	185	46	3.99 (1.87-8.54)	0.0003	76
A/A	83	3.66 (2.23-6.00)	0.00003	65	41	7.12 (3.20-15.8)	0.000005	38
Total	238			350	97			180

n, Number of individuals in each category; bold values are statistically significant.

Fisher exact two-tailed p-values.

There were no significant differences in both genotype and allele distributions for CYP1A1 polymorphisms in patients with BMI ≥30. The comparison of the allele frequencies revealed a deficiency of allele C and genotypes C/T, C/C of CYP1A1 gene in patients with obesity compared with controls.

In contrast, significant differences in the genotype and allele distributions for CYP1A2 polymorphism association with the elevated risk of breast cancer in the female patients with different BMI were found. Statistically, a woman with BMI <30 has a significant deficiency of mutant allele A (OR=0.62, p=0.0002) as well as genotypes C/A and A/A (OR=0.43; p=0.0055 and OR=0.33; p=0.0001, respectively) in patients with compared with controls. Possibly, this mutation has a lower risk of developing breast cancer. There were no significant differences in increase of both genotype CA heterozygotes and CC homozygotes distributions for CYP1A2 polymorphisms in patients with BMI ≥30.

There were no significant differences in both genotype and allele distributions for CYP19 polymorphism in patients with breast cancer without obesity. The frequency of mutant CYP19 heterozygote genotype C/T was higher in patients with obesity compared with women with BMI <30 (OR=2.47; p=0.045).

Significant differences were found in the genotype and allele distribution for SULT1A1 polymorphism between patients with BMI <30 and controls as well as between patients with BMI ≥30 and controls. Comparison of allele frequencies A and genotypes A/G, A/A of SULT1A1*2 revealed an increase in patients with BMI <30 (OR=1.81, p=0.0000004; OR=1.72; p=0.02; OR=3.66, p=0.00003 respectively) and with BMI ≥30 (OR=2.65, p=0.0000004 OR=3.99; p=0.0003 OR=7.12, p=0.0000005 respectively) compared with controls. Interestingly, obese women had a two-fold increased OR compared with women without obesity.

The examined genotype was related to the risk of developing an ER-positive (ER⁺) and progesterone receptor (PR)-positive (PR⁺) breast cancer tumor.

As shown in Table 3, the risk of an ER⁺ breast tumor seemed to be smaller for individuals with the CYP1A1, CYP19, and SULT1A1 variant allele and genotypes (OR (C)=0.82; OR (T/C)=0.78; OR (C/T)=0.66; OR (A)=0.68), which was not found to be statistically significant. Further, an increased risk of an ER⁺ tumor might be associated with the CYP1A2 heterozygote variant genotype C/A (OR=3.82; p=0.05).

Table 3.

The Genotype Was Related to the Risk of Developing an Estrogen Receptor (ER)-Positive and Progesterone Receptor (PR)-Positive Breast Cancer Tumor

	estrogen receptor (ER+)				progesterone receptor (PR+)
	n	OR (95% CI)	p-Value^a	ER−	n	OR (95% CI)	p-Value^a	PR−
CYP1A1
Allele frequencies
T	102			51	87			66
C	18	0.82 (0.36-1.86)	0.7907	11	21	1.59 (0.70-3.61)	0.3566	10
Genotype frequencies
T/T	2			20	34			28
T/C	18	0.78 (0.31-1.96)	0.7682	11	19	1.56 (0.63-3.91)	0.4627	10
C/C	1		0.68	0	1		0.55	0
Total	61			31	54			38
CYP1A2
Allele frequencies
C	81			40	74			48
A	145	1.05 (0.65-1.69)	0.9274	68	132	1.07 (0.68-1.69)	0.8616	80
Genotype frequencies
C/C	5			7	4			7
C/A	71	3.82 (1.11-13.11)	0.050	26	66	3.4 (0.93-12.42)	0.1087	34
A/A	38	2.53 (0.71-8.98)	0.252	21	33	2.51 (0.66-9.58)	0.2963	23
Total	114			54	103			64
CYP19
Allele frequencies
C	217			94	196			120
T	11			7	10	0.77 (0.29-1.99)	0.7642	8
Genotype frequencies
C/C	103			47	93			56
C/T	11	0.66 (0.24-1.81)	0.5828	7	10	0.75 (0.28-2.01)	0.7574	8
T/T	0		0.5	0	0			0
Total	114			54	103			64
SULT1A1
Allele frequencies
G	102			45	82			58
A	136	0.68 (0.25-1.81)	0.6086	63	124	1.25 (0.80-1.95)	0.3801	70
Genotype frequencies
G/G	18			9	16			12
G/A	56	1.04 (0.41-2.61)	0.8738	27	50	1.1 (0.46-2.62)	0.4653	34
A/A	40	1.11 (0.42-2.94)	0.9694	18	37	1.54 (0.60-3.93)	0.505	18
Total	114			54	103			64

n, Number of individuals in each category; bold values are statistically significant.

Fisher exact two-tailed p-values.

The risk of a PR⁺ breast tumor seemed to be smaller for women with the CYP19 variant allele and genotypes (OR (T)=0.77; (C/T) 0.75), which was not found to be statistically significant.

There was no significant difference in genotype and allele distributions for CYP1A1, CYP1A2, and SULT1A1 polymorphisms for PR⁺ breast tumors.

Discussion

By the present time, the hormonal origin for many forms of breast cancer and female reproductive organs has been proved. It is also beyond any doubt that excessive production of estrogens, in particular estradiol, is needed for both development and growth of a tumor. There are many reasons for overproduction of hormones. One of the key reasons is the disruption of estrogen metabolism that can be due to both endogenous and environmental factors. In this work, we studied genetic factors, in particular, genes of steroid-metabolizing enzymes playing important roles in the susceptibility to hormonal carcinogenesis. We found that the frequency distribution for mutant alleles and genotypes of some of these enzymes is different for breast cancer.

A significant difference in genotypes and allele distributions was obtained for three studied genes. The cytochrome P450 1A1 allele variants can be considered a risk factor for breast cancer.

CYP1A1 is involved in the metabolism of environmental carcinogens or estrogens. Two polymorphisms of the CYP1A1 gene are important for breast cancer: M1, a T→C substitution at nucleotide 3801, giving rise to an MspI restriction site in the 3'-noncoding region and M2, nucleotide 2455 A→G, resulting in an amino acid change at codon 462 of isoleucine to valine within the heme-binding domain of exon 7 (Sergentanis and Economopoulos, 2010). Both mutations cause an increase of enzyme activity. Msp1 genetic polymorphism (M1) of this enzyme may be a susceptibility factor for breast cancer in Thailand (Huang et al., 1999). Recently, Li et al. (2004) suggested that CYP1A1 M1-containing and M3-containing genotypes increased the risk of breast cancer associated with a long duration (>20 years) of cigarette smoking, but the effects of the CYP1A1 genotype appear to be quite weak. In our case, mutant allele C and genotypes T/C and C/C are appropriate candidates for studying the contribution of genetic factors to breast cancer susceptibility.

The cytochrome P450 1A2 allele variants can be considered a risk factor for many human cancers. This is a major phase I enzyme, and it accounts for about 15% of total liver P450 content (Sangrajrang et al., 2009). This enzyme is the most active in catalyzing 2-hydroxylations of 40%-50% of circulating estrogens (Qiu et al., 2010). Increased formation of 2-hydroxylated estrogens would be consistent with a reduced risk for breast cancer under a “receptor-mediated” hypothesis, because 2-hydroxyestrogens can weakly bind only the estrogen receptor (Curcic et al., 2009). In our study, the frequency of A allele and genotypes C/A and A/A of CYP1A2*1F was higher in controls, in agreement with female breast cancer. These results suggest that women with the C allele of CYP1A2*1F, which is associated with a decrease in CYP1A2 enzyme activity, have a higher risk of developing breast cancer.

Aromatase or CYP19 is a major enzyme in estrogen synthesis (Xita et al., 2010) and genetic polymorphism, this enzyme contributes to the development of many hormonal cancers (Mikhailova et al., 2006). Transition C→T in exon 7 (Arg264Cys) of the aromatase gene showed the increased risk for prostate cancer among Caucasian patients (Modugno et al., 2001). For the study of predisposition to breast cancer, we are offering to study C→T substitution (Arg264Cys) in exon 7. This mutation may increase aromatase enzymatic activity (Wang et al., 2011).

Women with BMI ≥30 and heterozygote genotype C/T of the CYP19 gene have an increased risk of breast cancer. It is important to note that the contribution of a genetic component in aromatase activity is not the only factor for cancer development. The concept of local estrogen biosynthesis due to an increased aromatase activity is one of the leading factors for the development of estrogen-depending tumors for today (Bulun and Simpson, 2008). According to this concept, the local synthesis of estrogens in single cells results in the variation of estrogen content and, as a consequence, enhancement of proliferation processes (Cleary et al., 2010; Lønning et al., 2011). It appears that alternative activation of tissue-specific promoters by cell-specific and ubiquitously expressed transcription factors controls CYP19 expression in various human tissues. In estrogen-dependent pathologic tissues such as breast cancer, aromatase is upregulated via inappropriate activation of aberrant promoters (Bulun et al., 2005). From this point of view, it is rather difficult to predict the behavior of this enzyme; so, we need more scientific information about the regulation of this enzyme. At the moment, there is evident call for identification by fine methods of proteomics of new classes of tumor-associated biomarkers, particularly for breast cancer. One of the approaches is determination of the protein profile by mass-spec analysis in breast ductal fluid for the prediction of cancer development. In this case, there is the probability to detect the increase of aromatase activity and consider it as a risk factor.

A major pathway for estrogen metabolism in humans is sulfate conjugation catalyzed by SULT enzymes that enhance the water solubility and the renal excretion of steroids. Thus, steroid sulfation contributes to the control of levels of biologically active hormone in target tissues. Inherited low activity of SULT can increase the risk of breast cancer. For the SULT1A1, a nucleotide substitution G638→A has been shown, thus resulting in the Arg213His substitution. Such a mutation leads to a significant decrease (as high as 85%) of the enzyme activity among homozygous persons (Jiang et al., 2010).

In contrast to expected results, patients with breast cancer had a higher frequency of A allele and genotypes A/G, A/A of SULT1A1*2 compared with healthy women. This may indicate that women with tumors have decreased SULT1A1 activity compared with healthy women. SULT1A1 catalyzes the sulfonation of estrogens to form water-soluble and biologically inactive estrogen sulfates, thus reducing the level of estrogen exposure in their target tissues (Zheng et al., 2001). Although sulfonation is, in general, considered a detoxification reaction, several SULTs, particularly SULT1A1, are involved in the bioactivation of certain procarcinogens, including heterocyclic amines and polyaromatic hydrocarbons (PAHs) (Tyapochkin et al., 2011). The sulfate esters of these compounds are highly reactive and can bind to DNA to form adducts (Glatt, 2000). 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. Since 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 risky allele and the involvement of this enzyme in estrogen, heterocyclic amine, and PAH metabolisms suggest that SULT1A1 polymorphism may be important in the etiology of breast cancer (Kotnis et al., 2008; Wang et al., 2010).

We studied female patients with breast cancer in order to evaluate the risk of ER⁺ or PR⁺ tumors associated with polymorphisms in specific CYP1A1, CYP1A2, CYP19, and SULT1A1 genes. There is increasing evidence that hormones are important in the development of hormone-dependent and hormone-independent breast cancer tumors. Women with ER⁻ tumors have a worse prognosis and fewer available treatment modalities. There was not a significant difference in genotype and allele distributions for CYP1A1, CYP19, and SULT1A1 polymorphisms in patients with ER⁺ and PR⁺ tumors. Sparks et al. (2004) and Miyoshi et al. (2003) found similar results in the study of polymorphism SULT1A1 and CYP1A1. In contrast, significant differences in the genotype for patients with CYP1A2 polymorphism with ER⁺ tumors and controls were found. The CYP1A2 heterozygous variant genotype C/A (OR=3.82; p=0.05) is associated with a more favorable prognosis because of increased risk of an ER⁺ tumor. Possibly, these results can account for reduced 4-hydroxylations as a result of changes in the enzymes CYP1B1 and CYP1A1. On the other hand, we have to acknowledge that, although our results have shown significant association, the definitive experiments should be performed by using large sample size. The p-value could be expected to lose significance in larger sample size.

In conclusion, the results of our study indicate that women with mutant allele C and genotypes C/T, C/C of the CYP1A1 gene, wild-allele C, and genotype C/C of the CYP1A2 gene, mutant allele A and genotypes A/G, A/A of the SULT1A1 gene have an increased risk of development of breast cancer. Women with BMI ≥30 and the heterozygous genotype C/T of CYP19 gene have an increased risk of breast cancer. Women with the CYP1A2 heterozygote variant genotype C/A may be associated with an increased risk of an ER⁺ tumor.

Footnotes

Acknowledgment

This work was supported by the Russian Federal Program of the Ministry of Education and Science of the Russian Federation “Scientific and pedagogical manpower of innovational Russia” to L.F.G. (GK_P600).

Disclosure Statement

No competing financial interests exist.

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