title: Implication of BRCA2 -26G>A 5' untranslated region polymorphism in susceptibility to sporadic breast cancer and its modulation by p53 codon 72 Arg>Pro polymorphism.
abstract: BACKGROUND
  The absence of mutation or promoter hypermethylation in the BRCA2 gene in the majority of breast cancer cases has indicated alternative ways of its involvement, deregulated expression being one possibility. We show how a polymorphism in the 5' untranslated region (UTR) of BRCA2 can serve as one such factor. Based on the hypothesis that variants of genes involved in the same pathway can influence the risk provided for breast cancer, the status of p53 codon 72 polymorphism was also investigated and a possible interaction between the polymorphisms was examined.
  
  
  METHODS
  The luciferase reporter assay followed by RNA secondary structure analysis was used for the functional characterization of -26 5' UTR G>A polymorphism in BRCA2. The genotype and the allele frequency for the polymorphisms were determined and relative risk adjusted for age was calculated in a case-control study of 576 individuals (243 patients and 333 controls) from north India.
  
  
  RESULTS
  -26 G>A polymorphism in the 5' UTR of BRCA2 was found to be functional whereby the A allele increased the reporter gene expression by twice that of the G allele in MCF-7 (P = 0.003) and HeLa (P = 0.013) cells. RNA secondary structure analysis by two different programs predicted the A allele to alter the stability of a loop in the vicinity of the translation start site. Its direct implication in breast cancer became evident by a case-control study in which the heterozygous genotype was found to be protective in nature (P heterozygote advantage model = 0.0005, odds ratio [OR] = 0.5, 95% confidence interval [CI] = 0.4 to 0.8), which was further supported by trends observed in a genomic instability study. The p53 codon 72 Arg homozygous genotype was found to be over-represented in patients (P = 0.0005, OR = 2.3, 95% CI = 1.4 to 3.6). The interaction study indicated an increased protection under simultaneous presence of protector genotypes of both the polymorphic loci (P = 0.0001, OR = 0.2, 95% CI = 0.1 to 0.4).
  
  
  CONCLUSIONS
  Our study shows that -26 5' UTR polymorphism in BRCA2 can modulate the fine-tuned regulation of the multifunctional gene BRCA2 and renders risk or protection according to the genotype status in the sporadic form of breast cancer, which is further influenced by the germline genetic backgrounds of codon 72 polymorphism of p53.
authors.affiliation: National Centre of Applied Human Genetics, School of Life Sciences, Jawaharlal Nehru University, Aruna Asafali Road, New Delhi-110067, India.
authors.forename: Sailesh
authors.initials: S
authors.lastname: Gochhait
authors.forename: Syed Irfan Ahmad
authors.initials: SI
authors.lastname: Bukhari
authors.forename: Narendra
authors.initials: N
authors.lastname: Bairwa
authors.forename: Shivani
authors.initials: S
authors.lastname: Vadhera
authors.forename: Katayoon
authors.initials: K
authors.lastname: Darvishi
authors.forename: Mohammad
authors.initials: M
authors.lastname: Raish
authors.forename: Pawan
authors.initials: P
authors.lastname: Gupta
authors.forename: Syed Akhtar
authors.initials: SA
authors.lastname: Husain
authors.forename: Rameshwar N K
authors.initials: RN
authors.lastname: Bamezai
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics*; D051017:Apoptosis Regulatory Proteins; D024682:BRCA2 Protein / Q000235:genetics*; D001943:Breast Neoplasms / Q000453:epidemiology / Q000235:genetics*; D016022:Case-Control Studies; D003062:Codon / Q000235:genetics*; D004252:DNA Mutational Analysis; D005260:Female; D017930:Genes, Reporter; D020022:Genetic Predisposition to Disease; D018095:Germ-Line Mutation; D006801:Humans; D007194:India / Q000453:epidemiology; D011110:Polymorphism, Genetic / Q000235:genetics*; D015995:Prevalence; D012307:Risk Factors; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*
chemical_list: D020121:5' Untranslated Regions; D051017:Apoptosis Regulatory Proteins; C118024:BLID protein, human; D024682:BRCA2 Protein; C551750:BRCA2 protein, human; D003062:Codon; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53