ABSTRACT
Estrogen receptor (ER)-mediated effects have been associated with the modulation of myocardial hypertrophy in animal models and in humans, but the regulation of ER expression in the human heart has not yet been analyzed. In various cell lines and tissues, multiple human estrogen receptor alpha (hERalpha) mRNA isoforms are transcribed from distinct promoters and differ in their 5'-untranslated regions. Using PCR-based strategies, we show that in the human heart the ERalpha mRNA is transcribed from multiple promoters, namely, A, B, C, and F, of which the F-promoter is most frequently used variant. Transient transfection reporter assays in a human cardiac myocyte cell line (AC16) with F-promoter deletion constructs demonstrated a negative regulatory region within this promoter. Site-directed mutagenesis and electrophoretic mobility shift assays indicated that NF-kappaB binds to this region. An inhibition of NF-kappaB activity by parthenolide significantly increased the transcriptional activity of the F-promoter. Increasing NF-kappaB expression by tumor necrosis factor-alpha reduced the expression of ERalpha, indicating that the NF-kappaB pathway inhibits expression of ERalpha in human cardiomyocytes. Finally, 17beta-estradiol induced the transcriptional activity of hERalpha promoters A, B, C, and F. In conclusion, inflammatory stimuli suppress hERalpha expression via activation and subsequent binding of NF-kappaB to the ERalpha F-promoter, and 17beta-estradiol/hERalpha may antagonize the inhibitory effect of NF-kappaB. This suggests interplay between estrogen/estrogen receptors and the pro-hypertrophic and inflammatory responses to NF-kappaB.
