Regulation of prohormone convertase 1 (PC1) by thyroid hormone

The prohormone convertases (PCs) PC1 and PC2 are key enzymes capable of pro cessing a variety of prohormones to their bioactive forms. In this study, w e demonstrated that 6-n-propyl-2-thiouracil (PTU)-induced hypothyroidism st imulated, whereas triido-L-thyronine (T-3)-induced hyperthyroidism suppress ed, PC1 mRNA levels in the rat anterior pituitary. Using 5' deletions of th e human PC1 (hPC1) promoter transiently transfected into GH3 (a somatotroph cell line) cells, we found that T-3 negatively regulated hPC1 promoter act ivity and that this regulation required the region from -82 to +19 bp relat ive to the transcription start site. Electrophoretic mobility shift assays (EMSAs) using purified thyroid hormone receptor-alpha1 (TR alpha1) and reti noid X receptor-beta (RXR beta) proteins and GH3 nuclear extracts demonstra ted that the region from -10 to +19 bp of the hPC1 promoter bound TR alpha1 as both a monomer and a homodimer and bound TR alpha1/RXR beta as a hetero dimer and multimer. EMSAs with oligonucleotides containing point mutations of the putative negative thyroid response elements (TREs) exhibited diminis hed homodimer and loss of multimer binding. We conclude that there are mult iple novel TRE-like sequences in the hPC1 promoter located from -10 to +19 bp.