Characterisation of the promoter region of the human DNA-repair gene Rad51

Purpose of investigation: Regulatory elements of the 5'-flanking region of the DNA-repair gene Rad51 were analysed to characterise pathological alterations of Rad51 mRNA expression during tumour development.

Methods: Various fragments of the Rad51 promoter were cloned into the pGL3 reporter vector and the respective promoter activity was determined by luciferase assays in transfected U2-OS cells. Transcription factor binding was identified using Protein/DNA arrays.

Results: The region encompassing base pairs -204 to -58 was identified as crucial for Rad51 gene transcription. Down regulator sequences are present upstream (-305 to -204) and downstream (-48 and +204) of this core promoter element. Promoter activity is significantly enhanced by substituting G at the polymorphic positions +135 and +172 for C and T, respectively. Transcription factors Ets1/PEA3, E2F1, p53, EGR1, and Stat5 were identified as relevant for regulating expression of Rad51.

Conclusion: We identified three separate cis-sequence elements within the Rad51 transcriptional promoter, one ensuring basal levels of expression and two elements limiting expression to relatively low levels. The characterisation of transcription factor binding might help to explain high-level expression of Rad51 in a variety of solid tumours. The polymorphic sites appear important for the increased risk of breast and/or ovarian cancer for BRCA2 mutation carriers.

Recombination factor Rad51; Promoter analysis; Gynaecological tumours; Single nucleotide polymorphism

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