Requirement of Sp1 and Estrogen Receptor Interaction in 17 -Estradiol-Mediated Transcriptional Activation of the Low Density Lipoprotein Receptor Gene Expression

Abstract

Estrogen is one of the most important physiological regulators of low density lipoprotein receptor (LDLR) expression. Despite many studies conducted in animals and humans showing increased expressions of LDLR messenger RNA by hormone treatment, the molecular basis of the effect of estrogen on LDLR transcription has not been clearly elucidated. By using HepG2 cells that transiently express functional estrogen receptorα (ERα) and LDLR promoter constructs, we show that the specific interaction of ERα with the transcription factor Sp1 bound to the LDLR promoter is responsible for the activation of LDLR transcription by estrogen. We demonstrate that 1) mutations to abrogate the binding of Sp1 to its recognition sequences present in repeat 1 and repeat 3 elements of the LDLR promoter completely abolish the ERα-mediated activation of the LDLR promoter activity; 2) mutations that abolish the selective DNA-binding activity or inactivate the C-terminal transcription activation function (AF2) of ERα had no effect on the ability of ERα to activate LDLR transcription; however, transcriptional activation was completely lost by deletion of the N-terminal transcription activation region (AF1); 3) a subregion of AF1 (amino acids 67–139) was further identified to be important for ERα to activate the LDLR promoter; and 4) ERα enhanced the formation of Sp1-repeat 3 DNA complexes. We also show that mutation at the sterol-responsive element-1 site diminishes the activity of ERα on LDLR transcription, thereby suggesting that the sterol-responsive element-1-binding protein may interact with the Sp1-ERα complex to trans-activate LDLR gene transcription. This study for the first time provides a molecular basis for an understanding of the regulation of LDLR transcription by estrogens.