Interaction of oestrogen and peroxisome proliferator-activated receptors with apolipoprotein(a) gene enhancers.
A high plasma concentration of lipoprotein(a) [Lp(a)] confers an increased risk for the development of coronary heart disease. Hormones, such as oestrogen, are some of the few compounds known to reduce plasma Lp(a) levels. A putative enhancer region, located at the DHII DNase I hypersensitive site approx. 28 kb upstream of the apolipoprotein(a) [apo(a)] gene, contains a number of sequences similar to the binding half-sites for nuclear hormone receptors, such as the oestrogen receptor and the peroxisome proliferator-activated receptor (PPAR). The 180 bp core DHII enhancer increased the activity of the apo(a) promoter by over 7-fold in reporter-gene assays in HepG2 cells in vitro. Almost 60% of this increase was lost in the presence of co-transfected oestrogen receptor and oestrogen. In contrast, co-transfection with PPARalpha increased the effect of the DHII enhancer on apo(a) transcriptional activity by approx. 70% and could overcome the inhibitory effect of the oestrogen receptor on apo(a) transcription. Gel mobility-shift assays showed that oestrogen receptor protein bound to one half of a sequence corresponding to a predicted oestrogen receptor response element. PPARalpha also bound to this site and competed with oestrogen receptors for binding. In addition, PPARalpha bound to a separate site that comprised part of a direct repeat of nuclear hormone receptor half-sites. The results suggest that nuclear hormones affect plasma Lp(a) concentrations by binding to the sequences within the DHII enhancer, thereby altering the amount by which the enhancer increases the transcription of the apo(a) gene.
Puckey
Loretto H
LH
Lipoprotein Group, MRC Clinical Sciences Centre, Faculty of Medicine, Imperial College, Hammersmith Hospital, DuCane Road, London W12 ONN, U.K.
Knight
Brian L
BL
D001054:Apolipoproteins A / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001667:Binding, Competitive; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004742:Enhancer Elements, Genetic; D004967:Estrogens / Q000378:metabolism*; D017930:Genes, Reporter; D005822:Genetic Vectors; D006801:Humans; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
D001054:Apolipoproteins A; D002843:Chromatin; D004967:Estrogens; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors