Estrogen response element and the promoter context of the human and mouse lactoferrin genes influence estrogen receptor alpha-mediated transactivation activity in mammary gland cells

Stokes, K.; Alston-Mills, B.; Teng, C.

Journal of Molecular Endocrinology 33(2): 315-334

2004


ISSN/ISBN: 0952-5041
PMID: 15525592
DOI: 10.1677/jme.1.01456
Accession: 012052341

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Abstract
A critical step in estrogen action is the recognition of estrogen responsive elements (EREs) by liganded estrogen receptor. Our current studies were designed to determine whether an extended estrogen response element half-site (ERRE) contributes to the differential estrogen responses of the human and mouse lactoferrin overlapping chicken ovalbumin upstream promoter/ERE sequences (estrogen response modules, ERMs) in the context of their natural promoters. Transient transfections of MCF-7 cells show that liganded estrogen receptor alpha (ERalpha) activates transcription of the human lactoferrin ERM fourfold higher than the mouse lactoferrin ERM in the context of their natural promoters. Since the ERRE of the human lactoferrin gene naturally occurs 18 bp upstream from the ERM and is absent in the mouse lactoferrin gene promoter, we created a chimeric mouse lactoferrin CAT reporter, which now encodes the ERRE in tie identical location as in the human lactoferrin gene. The addition of the ERRE in the mouse lactoferrin gene rendered this reporter extremely responsive to estrogen stimulation. Using limited protease digestions and electrophoretic mobility shift assays, we showed that the binding and protease sensitivity of ERalpha bound to the mouse ERM with or without the ERRE, differed. Importantly, occupancy of additional nuclear receptors at the ERRE may contribute to ERalpha binding and activation. Furthermore, the presence of ERRE influences the selectivity of coactivators in liganded ERalpha-mediated transcriptional activity. When the receptor is bound to human and mouse plus genes, which contain the ERRE, steroid receptor coactivator (SRC)-2 was preferred, while SRC-1 and SRC-3 coactivators selectively enhanced the mouse lactoferrin gene activity. Moreover, peroxisome proliferator activated receptor-gamma coactivator-1 (PGC-1alpha) and PGC-1-related estrogen receptor coactivator (PERC) robustly increase the transcriptional function of ERalpha in the presence of the ERRE. In conclusion, these data show that the context of the lactoferrin gene influences the ERalpha-mediated transcriptional activity.