Biologia, Bratislava, 55/Suppl. 8: 19-22, 2000.
ISSN 0006-3088 (Biologia). ISSN 1335-6399 (Biologia. Section Cellular and Molecular Biology).
Thyroid hormone and retinoic acid receptors – ligand inducible transcription factors: up- or down-regulation of nuclear receptor expression in vivo.
Institute of Experimental Endocrinology, Slovak Academy of Sciences, Vlarska 3, SK-83306 Bratislava, Slovakia; fax: ++421 7 5477 4247, e-mail: email@example.com
Received: July 10, 2000 / Accepted: October 24, 2000
Regulation of gene expression by both thyroid hormones and vitamin A-derived “retinoid hormones“ is a critical component in controlling many aspects of higher vertebrate development and metabolism. The functions of retinoids and thyroid hormones are mediated by nuclear receptors, which comprise a large superfamily of ligand-inducible transcription factors. Four major functional domains have been identified in all members of the receptor superfamily. The carboxy-terminal domain is responsible for hormone binding and dimerization of nuclear receptors, and it is critical in transcriptional activation and repression. The ligand-nuclear receptor complexes regulate gene expression through binding to short cis-acting DNA sequences - hormone responsive elements. Both thyroid hormone receptors (TR) and all-trans retinoic acid receptors (RAR) are capable to function as transcriptional repressors in the absence of specific ligands and potent activators upon binding thyroid hormone or all-trans retinoic acid. 9-cis retinoic acid receptors (RXR) play a central role in the regulation of many intracellular signalling pathways and can mediate ligand-dependent transcription as well. In this study data are presented on a possible modulation of either the TR or the RAR concentration and/or expression in the rat liver or spleen in different experimental models (partial hepatectomy, laparotomy, adjuvant arthritis, immobilization stress or 2-deoxy-D-glucose-induced intracellular glucopenia).
Key words: nuclear receptors, thyroid hormone receptors, all-trans retinoic acid receptors, rat liver and spleen nuclei, gene expression.