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1 Division of Endocrinology, Department of Medicine, Cedars-Sinai Research Institute- University of California at Los Angeles (UCLA) School of Medicine, Los Angeles 90048; 2 Division of Endocrinology, Charles R. Drew University of Medicine and Sciences- UCLA School of Medicine, Los Angeles 90059; 3 Division of Endocrinology, Department of Medicine, West Los Angeles Veterans Affairs Medical Center, Los Angeles, CA 90073; and 4 Laboratory for Molecular Oncology, Center for Human Genetics, University of Leuven and the Flanders Interuniversity Institute for Biotechnology, B-3000 Leuven, Belgium
The prohormone convertases (PCs) PC1 and PC2 are key enzymes capable of
processing a variety of prohormones to their bioactive forms. In this
study, we demonstrated that 6-n-propyl-2-thiouracil (PTU)-induced hypothyroidism stimulated, whereas
triido-L-thyronine (T3)-induced hyperthyroidism
suppressed, PC1 mRNA levels in the rat anterior pituitary. Using 5'
deletions of the human PC1 (hPC1) promoter transiently transfected into
GH3 (a somatotroph cell line) cells, we found that T3
negatively regulated hPC1 promoter activity and that this regulation
required the region from
82 to +19 bp relative to the transcription
start site. Electrophoretic mobility shift assays (EMSAs) using
purified thyroid hormone receptor-
1 (TR
1) and retinoid X
receptor-
(RXR
) proteins and GH3 nuclear extracts demonstrated
that the region from
10 to +19 bp of the hPC1 promoter bound TR
1
as both a monomer and a homodimer and bound TR
1/RXR
as a
heterodimer and multimer. EMSAs with oligonucleotides containing point
mutations of the putative negative thyroid response elements (TREs)
exhibited diminished homodimer and loss of multimer binding. We
conclude that there are multiple novel TRE-like sequences in the hPC1
promoter located from
10 to +19 bp.
posttranslational processing; negative thyroid response element; hypothyroidism; processing enzyme; pituitary; regulation; triiodo-L-thyronine
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