POLYMORPHISMS OF ESTROGEN BIOSYNTHESIS AND METABOLIZING GENES IN EGYPTIAN WOMEN WITH BREAST CANCER

* Wafaa Tolba 1 , Rizk El Baz 2 , Azza I Othman 3 , Sameh Roshdy 4 and Ahmad Settin 5 . 1. PH D candidate, Physiology, Zoology Department, Faculty of science, Mansoura University; Egypt. 2. Asst Professor, Molecular Biology, Genetics Unit, Mansoura University; Egypt. 3. Professor , Physiology, Zoology Department , Faculty of science , Mansoura University; Egypt. 4. Asst Professor, Department of General Surgery & Oncology , Faculty of Medicine, Mansoura University; Egypt. 5. Professor, Molecular Biology, Genetics Unit, Mansoura University; Egypt. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


ISSN: 2320-5407
Int. J. Adv. Res. 5 (5), 453-464 454 menarche), alcohol, smoking, postmenopausal obesity in addition fatty diet (Fredslund et al.;. Estrogen metabolism is affected by four possible pathways that might contribute to cancer evolution. These include the 16 alpha hydroxylation pathway, the pathway of 2-hydroxylation, the pathway of 4-hydroxylation through redox cycling, besides 4-hydroxyestradiolquinone-adenine/guanine adduct depurination pathway (yue, et al; 2013). Single nucleotide polymorphisms (SNPs) in genes of estrogen biosynthesis and metabolism might have an effect on levels of circulating estrogen and affect the susceptibility of breast cancer (Bozina, et al;2009). The human CYP17 gene found on 10q24.3 chromosome (Fan, et al;1992), encodes for cytochrome p450c17A that mediates activities vital for the endogenous steroid hormones production, such as estrogen and androgen (Miller, 1998). The most studied single nucleotide polymorphism (SNP) in CYP17 gene was a T to C (A1 to A2) substitution at 34 bp (base pair) upstream of the translation initiation site of CYP17 (rs 743572) (Cary et al;1994). This substitution might create an additional SP1-type (CCACC box) binding site in promoter region, enhancing transcription, and expression of CYP17, hence an increased estrogen level 1994, Feigelson et al;1998).
The Cytochrome P450 1A1 (CYP1A1) gene, located at 15q22-q24, (Kawajiri et al;. It is used in estrone and estradiol conversion to 2-hydroxyestradiol 2001). It also activates metabolism of polycyclic aromatic hydrocarbons to aryl epoxides by its aryl hydrocarbon hydroxylase activity (Law, 1990). A well-known single nucleotide polymorphism affecting this gene is the 6235T>C also known as CYP1A1*2A polymorphism in the 3'untranslated region, could be identified by Msp I restriction enzyme . This polymorphism was more studied in association with risk of breast cancer (dos Santos, et al;2011, da Fonte de Amorim, et al;2002). The CYP1B1 gene is located at 2p21-p22 chromosome. It encodes for the main cytochrome p450 enzyme which catalyzing the formation of estrogen metabolite called 4-hydroxy estrogen, that has carcinogenic effect in animal models due to its high hormonal activity (Kristensen, et al;2000). Moreover, 4-hydroxyestradiol can undergo redox cycling ) that causes the formation of free radicals as well as reactive semiquinone/ quinone intermediates which are potentially noxious to the DNA 1997). Val 432 Leu (G > C) polymorphism of the cytochrome p450 1B1 (CYP1B1) gene was 2.4-to 3.4-fold higher catalytically active than the wild type one (Mitrunen, Hirvonen , 2003).
Catechol-O-Methyltransferase enzyme (COMT) activates the O-methylation of 2-and 4-OHE2 (Yager, Liehr, 1996). COMT activity is found highly in kidney and liver, and it is also present at high levels in RBCs, brain, the mammary gland and uterine endometrium. The COMT gene, found on 22q11.1-q11.2 chromosome, has a G>A single-nucleotide polymorphism in codon 158/108 of the membrane bound/cytosolic form (Butterworth , Dragunow, 1996). It causes an amino acid change, Val>Met , which determining high-and low-activity alleles of the enzyme (Lachman, et al;. It was proved that the COMT Met allele, the low-activity and heat-labile enzyme, was four to five fold less effective in catechol substrates methylation in vitro (Scanlon, et al;1979) . The decreased COMT activity might cause accumulation of 4-OHE2 which may confer high breast cancer risk, however, the results remained controversial (He, et al;).
This study is aiming to test for the association between polymorphisms of CYP17 MspA1I, CYP1A1 MspI, CYP1B1 G>C, and COMT G>A genes and breast cancer in Egyptian women.

Materials and Methods:-
This work is a case controlled study involving 152 Egyptian women with breast cancer admitted in the Oncology Center, College of Medicine, Mansoura University, Egypt. Breast cancer cases were compared to 100 unrelated healthy women which are age and locality matched. All these participants were exposed to thorough history analysis of items like age, socioeconomic level, education, work, nutrition, smoking habits, consanguinity, family history, parity, abortion, age at menarche, menopause, breast feeding, use of oral contraceptives, stage and grade of cancer, number of lymph nodes, estrogen receptors, progesterone receptors and site of metastases. Statistical Analysis:-SPSS program version 17 was used for analyzing the data statistically. Comparing genotype and allele frequencies among cases and controls was done using the Fisher's Exact and Chi square tests with the odds ratio (OR) and 95% 455 confidence intervals (95% CI). Testing for genetic equilibrium was done using Hardy-Weinberg Equilibrium (HWE). p value <0.05 was considered significant.

Discussion:-
This study, to our knowledge is the first report of testing the association of polymorphic genetic variants involved in biosynthesis and metabolism of estrogen with breast cancer among Egyptian women. The results showed a significant increase of the frequency of certain genotypes among patients compared to controls.
The highest degree of association was found with C allele carriage of CYP1B1 polymorphism. The same was reported among American CC homozygous women (Sigurdson, (Sun , et al;. On the contrary, a reverse association with the G; and not the C allele was observed among American women of African ethnicity (Van Emburgh, et al; 2008). A reduced risk was also observed among African American women with the CYP1B1 CC genotype in comparison with those who had at least one G allele (Kato, et al;2009).
The second gene to show positive association with breast cancer was COMT low production allele A carriage. Also COMT AG+AA genotypes were common in cases with positive lymphadenopathy and in premenopausal women. The same positive association was observed among American premenopausal women specially the heaviest ones (Thompson, et al;1998); Turkish premenopausal women with sporadic breast cancer (Sazci, et  These wide variations in genetic associations might be due to genomic diversity in subjects of different ethnicities; nonetheless it might also arise from biased selection criteria and low power studies. Although this study might also suffer some limitations related to a relatively small sample size and lack of expression analysis, we could conclude that cancer breast in Egyptian women is associated with rare alleles of estrogen biosynthesis and metabolizing genes including CYP1B1 G>C, and COMT G>A followed by CYP1A1 MspI, and CYP17 MspA1I.