title: Nuclear cytoplasmic shuttling by thyroid hormone receptors. multiple protein interactions are required for nuclear retention.
abstract: In this report, we have studied the intracellular dynamics and distribution of the thyroid hormone receptor-beta (TRbeta) in living cells, utilizing fusions to the green fluorescent protein. Wild-type TRbeta was mostly nuclear in both the absence and presence of triiodothyronine; however, triiodothyronine induced a nuclear reorganization of TRbeta. By mutating defined regions of TRbeta, we found that both nuclear corepressor and retinoid X receptor are involved in maintaining the unliganded receptor within the nucleus. A TRbeta mutant defective in DNA binding had only a slightly altered nuclear/cytoplasmic distribution compared with wild-type TRbeta; thus, site-specific DNA binding is not essential for maintaining TRbeta within the nucleus. Both ATP depletion studies and heterokaryon analysis demonstrated that TRbeta rapidly shuttles between the nuclear and the cytoplasmic compartments. Cotransfection of nuclear corepressor and retinoid X receptor markedly decreased the shuttling by maintaining unliganded TRbeta within the nucleus. In summary, our findings demonstrate that TRbeta rapidly shuttles between the nucleus and the cytoplasm and that protein-protein interactions of TRbeta with various cofactors, rather than specific DNA interactions, play the predominant role in determining the intracellular distribution of the receptor.
authors.affiliation: Laboratory of Receptor Biology and Gene Expression, NCI and Molecular Regulation and Neuroendocrinology Section, Clinical Endocrinology Branch, NIDDKD, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: C T
authors.initials: CT
authors.lastname: Baumann
authors.forename: P
authors.initials: P
authors.lastname: Maruvada
authors.forename: G L
authors.initials: GL
authors.lastname: Hager
authors.forename: P M
authors.initials: PM
authors.lastname: Yen
mesh_terms: D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D011485:Protein Binding; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D011988:Receptors, Thyroid Hormone; D004247:DNA