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Nuclear import of the thyroid hormone receptor ?1 is mediated by importin 7, importin ?1, and adaptor importin ?1.

ABSTRACT: The thyroid hormone receptor ?1 (TR?1) is a nuclear receptor for thyroid hormone that shuttles rapidly between the nucleus and cytoplasm. Our prior studies showed that nuclear import of TR?1 is directed by two nuclear localization signals, one in the N-terminal A/B domain and the other in the hinge domain. Here, we showed using in vitro nuclear import assays that TR?1 nuclear localization is temperature and energy-dependent and can be reconstituted by the addition of cytosol. In HeLa cells expressing green fluorescent protein (GFP)-tagged TR?1, knockdown of importin 7, importin ?1 and importin ?1 by RNA interference, or treatment with an importin ?1-specific inhibitor, significantly reduced nuclear localization of TR?1, while knockdown of other importins had no effect. Coimmunoprecipitation assays confirmed that TR?1 interacts with importin 7, as well as importin ?1 and the adapter importin ?1, suggesting that TR?1 trafficking into the nucleus is mediated by two distinct pathways.

SUBMITTER: Roggero VR

PROVIDER: S-EPMC4684427 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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Nuclear import of the thyroid hormone receptor α1 is mediated by importin 7, importin β1, and adaptor importin α1.

Roggero Vincent R VR Zhang Jibo J Parente Laura E LE Doshi Yazdi Y Dziedzic Rose C RC McGregor Emma L EL Varjabedian Arev D AD Schad Sara E SE Bondzi Cornelius C Allison Lizabeth A LA

Molecular and cellular endocrinology 20151023

The thyroid hormone receptor α1 (TRα1) is a nuclear receptor for thyroid hormone that shuttles rapidly between the nucleus and cytoplasm. Our prior studies showed that nuclear import of TRα1 is directed by two nuclear localization signals, one in the N-terminal A/B domain and the other in the hinge domain. Here, we showed using in vitro nuclear import assays that TRα1 nuclear localization is temperature and energy-dependent and can be reconstituted by the addition of cytosol. In HeLa cells expre ...[more]

PMID: 26525414

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Project description:Bovine ephemeral fever virus (BEFV) is an arthropod-borne rhabdovirus that is classified as the type species of the genus Ephemerovirus. In addition to the five canonical rhabdovirus structural proteins (N, P, M, G, and L), the large and complex BEFV genome contains several open reading frames (ORFs) between the G and L genes (α1, α2/α3, β, and γ) encoding proteins of unknown function. We show that the 10.5-kDa BEFV α1 protein is expressed in infected cells and, consistent with previous predictions based on its structure, has the properties of a viroporin. Expression of a BEFV α1-maltose binding protein (MBP) fusion protein in Escherichia coli was observed to inhibit cell growth and increase membrane permeability to hygromycin B. Increased membrane permeability was also observed in BEFV-infected mammalian cells (but not cells infected with an α1-deficient BEFV strain) and in cells expressing a BEFV α1-green fluorescent protein (GFP) fusion protein, which was shown by confocal microscopy to localize to the Golgi complex. Furthermore, the predicted C-terminal cytoplasmic domain of α1, which contains a strong nuclear localization signal (NLS), was translocated to the nucleus when expressed independently, and in an affinity chromatography assay employing a GFP trap, the full-length α1 was observed to interact specifically with importin β1 and importin 7 but not with importin α3. These data suggest that, in addition to its function as a viroporin, BEFV α1 may modulate components of nuclear trafficking pathways, but the specific role thereof remains unclear. Although rhabdovirus accessory genes occur commonly among arthropod-borne rhabdoviruses, little is known of their functions. Here, we demonstrate that the BEFV α1 ORF encodes a protein which has the structural and functional characteristics of a viroporin. We show that α1 localizes in the Golgi complex and increases cellular permeability. We also show that BEFV α1 binds importin β1 and importin 7, suggesting that it may have a yet unknown role in modulating nuclear trafficking. This is the first functional analysis of an ephemerovirus accessory protein and of a rhabdovirus viroporin.

Dataset Information

Nuclear import of the thyroid hormone receptor ?1 is mediated by importin 7, importin ?1, and adaptor importin ?1.

Publications

Nuclear import of the thyroid hormone receptor α1 is mediated by importin 7, importin β1, and adaptor importin α1.

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