Figure 5.

T₃-dependent silencing of PLB gene expression is localized to the conserved core promoter region. A, Alignment of mammalian PLB core promoter sequences. Nucleotide sequences from mouse (36), rat (37), and human (38) are shown. Numbers indicate relative nucleotide positions upstream of the transcription start site (+1). B, rat PLB core promoter sequences showing potential TR-binding half-sites (underlined arrows), potential TATA boxes (italics), GATA element (bold), CCAAT element (boxed), and an E-box (bold and italics). Numbers indicate relative nucleotide positions up- and downstream of the transcription start site (+1). C, HL-1 cells were transfected with either the rat pGL3-PLB (−156 to +64) promoter luciferase vector or an empty pGL3 vector along with pSV-β-gal as an internal control. The cells were then cultured with or without T₃ (1 μm) for additional 24 h and then harvested for determination of luciferase activity via a luminometer. Luciferase activity was normalized for both protein concentration as well as β-galactosidase activity. Error bars represent the ±sd calculated from three separate experiments. *, Statistical significant difference, P < 0.01.