Study of the role of estrogen receptor alpha gene polymorphism in prostate cancer among egyptians

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STUDY OF THE ROLE OF

ESTROGEN RECEPTOR ALPHA GENE POLYMORPHISM

IN PROSTATE CANCER AMONG EGYPTIANS

Ola Hussein Elgaddar

Assistant lecturer of Chemical Pathology

Medical Research Institute

Alexandria University

Professor Dr. Thanaa Fathy Moghazy Professor of Clinical Pathology

Department of Chemical Pathology

University of Alexandria

Professor Dr. Saad Mohammed Saad Professor of Urology

Department of Urology

Faculty of Medicine

Professor Dr. Amel Abd El-Fattah Kamel Professor of Chemical Pathology

Dr. Moyassar Ahmad Zaki Assistant Professor of Chemical Pathology

Types of Estrogen

Estrogen receptors:

Estrogens induce cellular changes

through binding to its specific receptors.

There are two described types of

estrogen receptors (ERs) in humans:

ER alpha (ERα)

ER beta (ERβ)

Comparison of the structures and homology between ERα and ERβ

Estrogen receptor genes:

ERα and ERβ are encoded by ESR1

and ESR2 genes, present on

chromosomes 6q25.1 and 14q23-24.1,

respectively.

ESR1 and ESR2 comprise eight exons

separated by seven intronic regions and

spans more than 140 kilo-bases and

approximately 40 kilobases, respectively

Genomic format and domain structure of human ERα and ERβ

Estrogens – ER signaling pathways:

Classified in two pathways; genomic

and non-genomic

A. Genomic (Classical) Pathway:

E2 binds to nuclear or cytoplasmic receptors.

E2 actions occur over the course of hours.

B. Non-Genomic Pathway:

E2 binds to ER located in or adjacent to the

plasma membrane

E2 actions occur within few minutes

ER gene variants:

The DNA variants (polymorphisms) are

common, occurring in more than 1% of the

population.

The most common type of polymorphisms is a

single nucleotide change in DNA sequence

and is referred to as single nucleotide

polymorphisms (SNPs).

SNPs may account for many well-

characterized phenotypes, including disease

susceptibility and resistance.

Another type of polymorphisms is the

tandemly repeated DNA sequences.

They represent variation in the number of

copies of a tandemly repeated motif at each

locus.

These repeats differ in length to form variable

number tandem repeat (VNTR)

ERα gene polymorphism:

The most widely studied are:

T397C (PvuII: rs2234693)

A351G (XbaI: rs9340799)

Both named after the relevant restriction enzyme

Both lie in intron I in the ERα gene

They are in strong linkage disequilibrium

(TA)n variable number of tandem repeats

within the promoter region of the gene

Though both PvuII and XbaI polymorphisms

lie in intronic (apparently non-functioning) part

of the gene, they have been widely studied in

many diseases as they thought to be:

In linkage disequilibrium with causal

polymorphisms elsewhere in the ERα gene or

in an adjacent gene.

In linkage disequilibrium with the upstream

TA repeat polymorphism in the promoter

region of the ERα gene, having a significant

influence on transcriptional regulation

THE PROSTATE GLAND:

The prostate is the major accessory sex

gland of the male.

Its secreted fluid comprises 15% of the

ejaculate.

The gland has been the subject of much

study being susceptible to infection as well as

neoplastic transformation.

Carcinoma of the prostate: The 6th most common cancer in the world

and the 3rd in importance in men.

The prostate cancer is genetically

heterogeneous, with several genes having

different frequencies and penetrance.

Environmental factors may have a role in

inducing different genetic processes and

molecular pathways.

Heterogeneity of both environmental factors

and susceptibility genes could explain the

discrepancies of prostate cancer incidence

between populations.

The final diagnosis of prostate cancer is

done by histopathological examination of a

biopsy and it is graded by the Gleason system

(score).

Staging of the tumor is done using the tumor

node metastases (TNM) system, that had been

adopted by the American Joint Committee for

Cancer Staging.

Estrogens and their receptors in

cancer prostate: Prostate expresses both ER-α (mainly

stromal) and ER-β (mainly epithelial)

Evidence demonstrates a clear dichotomy

between ER-α and ER-β actions. The adverse

effects of estrogen, via ER-α, are specifically

related to the development of prostatic

proliferation and inflammation as well as

prostate cancer. In contrast, the beneficial

effects of estrogens reside with the activation of

ER-β, which appears to mediate the anti-

proliferative, anti-inflammatory and, potentially,

anti-carcinogenic effects of estrogen.

Estrogen receptor-α, coded by the ESR1

gene, has been examined in several studies for

the presence of polymorphic sites and their

relation to cancer prostate.

Among the most commonly studied

polymorphisms are the ESR1 T397C (PvuII) and

A351G (XbaI) restriction fragment length

polymorphism (RFLP) markers.

Results regarding the presence or absence of

an association between these two

polymorphisms and the presence of cancer

prostate are controversial among different

populations.

The present study aimed at

studying the role of T397C and

A351G polymorphisms of

estrogen receptor alpha gene in

the occurrence of prostate

cancer among Egyptians.

100 Egyptian males

Group III

Cancer prostate

N = 45

Group II

N = 20

Group I

Controls

N = 35

To all studied subjects the

following was done:

I) Full clinical examination

II) Laboratory investigations: Preliminary tests in serum.

(Creatinine, ALT, ALP, ACP; total & prostatic)

Serum tPSA

Serum Estradiol (E2)

Molecular studies for the detection of T397C

(PvuII) and A351G (XbaI) polymorphisms in

estrogen receptor α gene

Molecular study:

1) DNA extraction

2) PCR

3) RFLP

346 bp PCR

product

ERα T397C (PvuII) genotype distribution, according to the

Hardy-Weinberg equilibrium among the studied groups

CC CT TT CC CT TT CC CT TT

Control group BPH group Cancer prostate group

Observed frequency

Expected frequency

Chi-sq: 0.031

P-value: 0.985

Chi-sq: 0.312

P-value: 0.876

Chi-sq: 2.212

P-value: 0.331

ERα T397C (PvuII) genotype distribution

among the studied groups

TT CT CC TT CT CC TT CT CC

30 26.7

51.4 55

15 13.3

48.60% 51.40%

ERα T397C (PvuII) allele frequencies in

the control group

57.50% 42.50%

the BPH group

56.70% 43.30%

the cancer prostate group

the studied groups

T C T C T C

57.5 56.7

42.5 43.3

ERα A351G (XbaI) genotype distribution, according to the

Hardy-Weinberg equilibrium among the studied groups

AA / AG GG AA / AG GG AA /AG GG

Observed frequency

Expected frequency

Chi-sq: 0.141

P-value: 0.707

Chi-sq: 0.317

P-value: 0.573

Chi-sq: 0.915

P-value: 0.339

ERα A351G (XbaI) genotype distribution

among the studied groups

AA AG GG AA AG GG AA AG GG

50 53.3

50 46.7

17.10%

82.90%

ERα A351G (XbaI) allele frequencies in

the control group

the BPH group

75% A G

the cancer prostate group

26.70%

73.30% A

the studied groups

A G A G A G

25 26.7

75 73.3

1) No statistically significant difference

could be detected in both T397C (PvuII)

and A351G (XbaI) polymorphisms of the

ERα gene, between the three studied

groups of Egyptians; namely cancer

prostate patients, benign prostatic

hyperplasia patients and healthy controls.

Thus, the development of cancer prostate

among Egyptian males cannot be

attributed to these two polymorphisms.

2) No association could be found

between the presence of variant alleles

(C allele of PvuII and G allele of XbaI

polymorphisms of ERα gene), and the

development of cancer prostate among

the studied sample of Egyptian male.

Larger population based studies are

needed to assess the association

between T397C (PvuII) and A351G

(XbaI) polymorphisms of the ERα

gene, and the occurrence of cancer

prostate in Egyptians.

Other polymorphisms may be

studied in ER α, in relation to the

development of cancer prostate,

such as TA repeats in the promoter

region.

Study of the role of estrogen receptor alpha gene polymorphism in prostate cancer among egyptians

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