Abstract
The 5' region of BRCA1 contains multiple regulatory sequences flanking the two alternative promoters α and β and two alternative, non-coding exons, 1a and 1b. Aberrations within the 5' region BRCA1 (encompassing two alternative promoters α and β and exons 1a and 1b) may be associated with an increased risk of breast and ovarian cancer. In this study we screened 150 patients for polymorphism and mutations in this region of BRCA1. All probands came from familial breast and/or ovarian cancer that had been found to be mutation-negative in a previous search for founder mutations in BRCA1 (185delAG, C61G, 4153delA, 5382insC) or BRCA2 (6174delT, 9631delC). In our study we found several sequence alterations within the non-coding region of BRCA1 by using direct DNA sequencing and allele-specific PCR amplification. Three families with a polymorphic deletion in BRCA1 exon 1b (2223delAAAAA, Acc. U37574) were found. Moreover, two linked nucleotide substitutions (2642A>T, 2743T>C, Acc. U37574) in BRCA1 intron 1 were detected in 16 patients. In order to assess the functional significance of these two sequence variants, we constructed a reporter vector encoding firefly luciferase under the transcriptional and translational control of wild type and altered BRCA1 promoter region. The reporter assay was performed using a lung cancer cell line (NCI-H1299) and a breast cancer cell line (MCF7). We have demonstrated that the analysed sequence variants have no functional significance in our experimental system. However, we have found that the BRCA1 promoter has lower relative activity in the breast cancer cell line compared with the lung cancer cell line. Based on the results of our functional experiments we conclude that the polymorphic deletion 2223delAAAAA and two linked substitutions 2642A>T and 2743T>C do not significantly alter BRCA1 expression and are probably not disease-causing mutations.
Highlights
The human BRCA1 gene is under the transcriptional control of two different promoters, α and β that drive the transcription of exon 1a and 1b, respectively [22].At the RNA level each of the alternative first exons is linked by splicing with exon 2 [21]
Eighty-seven patients diagnosed with breast and/or ovarian cancer were selected for BRCA1 promoter/5’UTR
One hundred and fifty patients with breast and/or ovarian cancer from Upper Silesia in Poland were screened for sequence alterations in the 5’ region of BRCA1
Summary
The human BRCA1 gene is under the transcriptional control of two different promoters, α and β that drive the transcription of exon 1a and 1b, respectively [22].At the RNA level each of the alternative first exons is linked by splicing with exon 2 [21]. The human BRCA1 gene is under the transcriptional control of two different promoters, α and β that drive the transcription of exon 1a and 1b, respectively [22]. The translational initiation site is the same for the two mRNA variants and is located in exon 2 [11]. The BRCA1 5`UTR region coded by exon 1b contains three. BRCA1 contains multiple transcription factor binding sites identified in 5` flanking regions of exon 1a and exon 1b [17, 18]. The different transcripts of the BRCA1 gene are present at different levels in various normal and tumour tissues and may have distinct biological functions [21]. Expression of transcripts α and β of the BRCA1 gene may be co-regulated by use of a dual promoter system. The two mRNAs may differ in their stability or translational efficiency [21]
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