Abstract
We have previously reported that transcription from a distal promoter (promoter B) of the estrogen receptor alpha (ERalpha) gene is responsible for the increased expression of ERalpha in human breast carcinomas. This paper first characterized the promoter B region in terms of transient transfection experiments with luciferase using MCF-7 cells. Gradual deletions from the 5'-end of promoter B resulted in a decrease in promoter activity corresponding to the deleted lengths; a deletion of 39 bp in a non-coding exon 1a, drastically diminished the activity, indicating existence of an important cis -element. Furthermore, electrophoretic mobility shift assay and subsequent mutational analysis indicated that this element containing nucleotide sequence CTGGAAAG forms a specific DNA-protein complex. This element was capable of transactivating a heterogeneous SV40 promoter in MCF-7 cells, confirming that the element is a transcriptional enhancer; the trans -acting factor binding to the element was named ERBF-1 (estrogen receptor promoter B associated factor-1). The ERBF-1 was exclusively expressed in those cells expressing ERalpha mRNA transcribed from promoter B. Our findings indicate that ERBF-1 plays an important role in the expression of the ERalpha gene transcribed from promoter B, which is selectively utilized in breast cancer.
Full Text
The Full Text of this article is available as a PDF (233.9 KB).