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ABOUT BREAST CANCER-2
BRCA2: Breast Cancer 2, early onset
INTRODUCTION:
BRCA2 abbreviated as Breast Cancer 2, early onset is a protein which is
encoded by the BRCA2 gene in humans. [1] It is a gene which belongs to the
family of tumor suppressing gene[2][3] and BRCA2 protein encoded by this
gene is responsible for the repair of chromosomal damage which plays an
important role in the error-free repairing of DNA double strand breaks.
Position of the gene: long arm denoted by ‘q' of chromosome 13 at position
12.3 (totally represented as 13q12.3) from base pair 31, 787,616 to the base
pair 31,871, 804. [1]
BRCA plays a major role in cloning, gene structure and mapping, gene
function, DNA repair, and some molecular biology aspects such as
susceptibility to familial Breast-Ovarian cancer 2, prostate cancer and other
cancers, etc.
The BRCA genes are in general of 2 types, namely, BRCA 1 and BRCA 2. the
structure of these 2 genes varies although some of their functions are
correlated. The proteins that are encoded by these genes play a major role in
repair of damaged DNA. The BRCA2 protein fixes breaks in DNA by binding
to and regulating the protein produced by RAD51 gene. The breaks in DNA
are generally caused by exposure to natural and medical radiation or to other
environmental exposures. It also occurs during meiosis where the
chromosomes exchange genetic material. The BRCA1 is also involved in this
process as it interacts with RAD51 protein. In general, these three genes play
an important in the maintenance of stability in the human genome by
repairing DNA and thereby preventing dangerous gene re-arrangements that
can lead to hematologic cancer. [4]
As BRCA2 plays a very important role in fixing of DNA repair, any defect or
mutation may lead to increased risk of cancer. It was observed that most cells
having defective BRCA2 genes are sensitive to gamma radiations which
results in the increased risk of cancer. It was also observed that patients who
are inherited with BRCA mutations are generally more sensitive to radiations
compared to other patients suffering from breast cancer. [5]
BRCA2 promotes homologous recombination which involves 1 major pathway
of double stranded DNA repair. In comparison to BRCA1, BRCA2 does not
have any impact on multiple DNA repair or in other words to nonhomologous
end joining. The specific regulation over homologous recombination by BRCA
maintains the genomic integrity and also suppresses the tumor development
in proliferating cells.[6]
There are hundreds of variations that have been observed in BRCA2 gene.
The variations are nothing but the addition or deletion of small piece of DNA
from the gene. Due to this, the protein produced or encoded by this gene is
abnormal and hence does not function properly. When the protein is
abnormal it is not able to repair DNA properly or in other words able to fix the
repair properly in other genes. The abnormality gets accumulated and results
in the formation of tumor.