Influence of estrogen and variations at the BRCA1 promoter region on transcription and translation

We analyzed wild-type (WT) and four sequence variants of the BRCA1 promoter region—found in patients selected for hereditary breast and ovarian cancer syndrome—in respect to their influence on transcription and translation efficiencies in transient transfection assays in the presence or absence of estrogen. Five types of plasmids containing the EGFP reporter gene proceeded by WT 5′UTR-a, WT 5′UTR-b, and the three 5′UTR-b variants were constructed to evaluate their influence on translation. Plasmids containing the firefly luciferase reporter gene were constructed with the WT BRCA1 promoter region (containing promoter α, 5′UTR-a, promoter β, and 5′UTR-b) and with the four promoter variants for evaluating their influence on transcription and translation. All constructs were transfected in MCF7 cells maintained with and without estrogen. Expression of EGFP plasmids with WT 5′UTR-a was six to sevenfold higher than of plasmids with WT 5′UTR-b, expression of WT and the three variant 5′UTR-b plasmids showed slight differences in EGFP expression, and the presence or absence of estrogen result in non-significant changes in expression. Promoter’s constructs that carry the variants WT or g.3988C showed a higher firefly luciferase activity when estrogen is present; conversely, no significant differences were found in the transcription efficiency of the reporter gene indicating that estrogen affect the translation rather than transcription. The presence or absence of estrogen did not affect the activity of firefly luciferase for constructs with the other promoter variants, being the transcription efficiencies equivalent in both conditions.