| Popis: |
Estrogen replacement therapy in women decreases hepatic lipase (HL) activity, which may account for the associated increase in HDL cholesterol. To investigate whether estrogen decreases HL transcription, transient cotransfection assays with HL promoter and estrogen receptor-α (ERα) expression constructs were performed in HepG2 cells. 17β-estradiol (E2) decreased transcription driven by the −1557/+41 human HL promoter by up to 50% at 10−7 M. Mutation of ERα by deletion of its transactivation domains or ligand-binding domain eliminated E2-induced repression of the promoter, whereas deletion of the DNA-binding domain of ERα resulted in a 7-fold activation by E2. The E2-induced repression was maintained after mutation of a potential estrogen-response element in the promoter. The region of estrogen responsiveness was localized to −1557/ −1175 of the HL promoter by deletion analysis. Mutation of an AP-1 site at −1493 resulted in a partial loss of E2-induced repression, similar to that caused by deletion of nucleotides −1557 to −1366. Gel shift assays with nuclear extracts from E2-treated HepG2 cells stably expressing ERα demonstrated an increase in binding to an AP-1 consensus oligonucleotide. The AP-1 activator, phorbol 12-myristate 13-acetate, inhibited the HL promoter by greater than 50%. Collectively, the data suggest that estrogen represses the transcription of the HL gene, possibly through an AP-1 pathway. —Jones, D. R., R. J. Schmidt, R. T. Pickard, P. S. Foxworthy, and P. I. Eacho. Estrogen receptor-mediated repression of human hepatic lipase gene transcription. |
