Using in vivo electroporation to identify hepatic LDL receptor promoter elements and transcription factors mediating activation of transcription by T(3)

The technique of in vivo electroporation was adapted to investigate the promoter elements and transcription factors mediating the rapid induction of hepatic LDL receptor expression in response to thyroid hormone. Direct comparisons between wild type and mutant promoter constructs were made within the same animal. It was demonstrated that both TREs at bp − 612 and − 156 were required for the l-triiodothyronine (T(3)) response. ChIP analysis showed that binding of TRβ1 to the − 612 and − 156 TREs was markedly stimulated by T(3)in vivo. Introduction of siRNAs against TRβ1/RXRα with LDL receptor promoter-luciferase construct by in vivo electroporation demonstrated that these transcription factors play the major physiological role in the activation of hepatic LDL receptor transcription. The findings agree with those made by transfecting H4IIE cells in vitro thus validating this technique for in vivo studies of mechanisms of transcriptional regulation. The findings reported herein also indicated, for the first time, that PPARα and USF-2 were required for maximum transcriptional activation of the LDL receptor in response to T(3) treatment.