Transportin Is a Major Nuclear Import Receptor for c-Fos

Arnold, Marc; Nath, Annegret; Wohlwend, Daniel; Kehlenbach, Ralph H.

doi:10.1074/jbc.m513281200

Cited by 33 publications

(52 citation statements)

References 52 publications

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“…The fact that CD44 binds several proteins from the importin family, but that only one of them is sufficient for nuclear translocation is not surprising. It has been shown that the transcription factor c-Fos binds several importins, including importin ␤ and transportin1 (27). Detailed analysis showed that transportin1 plays the key role in the import of c-Fos.…”

Section: Discussionmentioning

confidence: 99%

Transportin Regulates Nuclear Import of CD44

Janiszewska

Vito

Bitoux

et al. 2010

Journal of Biological Chemistry

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CD44 is a facultative cell surface proteoglycan that serves as the principal cell surface receptor for hyaluronan (HA). Studies have shown that in addition to participating in numerous signaling pathways, CD44 becomes internalized upon engagement by ligand and that a portion of its intracellular domain can translocate to the nucleus where it is believed to play a functional role in cell proliferation and survival. However, the mechanisms whereby fragments of CD44 enter the nucleus have not been elucidated. Here we show that CD44 interacts with two import receptors of the importin ␤ superfamily, importin ␤ itself and transportin. Inhibition of importin ␤-dependent transport failed to block CD44 accumulation in the nucleus. By contrast, inhibition of the transportin-dependent pathway abrogated CD44 import. Mutagenesis of the intracellular domain of CD44 revealed that the 20 membrane-proximal residues contain sequences required for transportin-mediated nuclear transport. Our observations provide evidence that CD44 interacts with importin family members and identify the transportin-dependent pathway as the mechanism whereby full-length CD44 enters the nucleus.Proteins cross the double membrane of the nuclear envelope through nuclear pores. To traverse this barrier, proteins larger than 40 kDa must bind to soluble transport factors or carrier molecules that shuttle between the cytoplasm and the nucleus (1). Most of the nuclear transport factors belong to the ␤-karyopherin family and are classified, according to their function, as importins or exportins (2). In the cytoplasm, cargo proteins containing a nuclear localization signal (NLS) 2 are usually bound by the adaptor protein importin ␣, followed by the carrier importin ␤ (2), although in some cases, importin ␣ binding is not required (3). Importin-bound cargo is then translocated through the nuclear pore complex and is released in the nucleus following binding of importin ␤ to RanGTP protein (2). The importin-Ran complex is exported to the cytoplasm where it dissociates upon RanGTP conversion to RanGDP. An analogous mechanism is used by mRNA-binding proteins, where cargo is recognized by the transportin1 carrier (2). Interestingly, it has also been shown that some proteins, including ␤-catenin, SMAD, and ERK2, can be imported into the nucleus without involvement of importins and RanGTP (4).Nuclear export is analogous to the import mechanism. There is a single karyopherin protein, Crm1, that upon recognition of a nuclear export sequence binds the target protein in the nucleus and upon stimulation by Ran protein releases the cargo into the cytoplasm (2). The mechanisms described above are common for cytoplasmic proteins, but there is also some evidence that the same pathways might be used for nuclear translocation of the full-length transmembrane receptors (5, 6).Growth factor receptor signaling proceeds as a cascade of intracellular events. Receptor engagement by ligand on the cell surface typically results in receptor clustering and, depending on the receptor type...

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Section: Discussionmentioning

confidence: 99%

Transportin Regulates Nuclear Import of CD44

Janiszewska

Vito

Bitoux

et al. 2010

Journal of Biological Chemistry

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“…The canonical Trn1 import signal (M9) was initially described for hnRNP A1, and analogous domains have been described for several other proteins that associate with Trn1/2 (3,22,26,31,37,41,43,54,67,68,(72)(73)(74)76). hnRNP F was previously shown to interact with and be imported by Trn1 (43,73), and hnRNP H was shown to interact with Trn1/2 (31).…”

Section: Discussionmentioning

confidence: 99%

A Glycine-Rich Domain of hnRNP H/F Promotes Nucleocytoplasmic Shuttling and Nuclear Import through an Interaction with Transportin 1

Dusen

Yee

McNally

et al. 2010

Molecular and Cellular Biology

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Heterogeneous nuclear ribonucleoprotein (hnRNP) H and F are members of a closely related subfamily of hnRNP proteins that are implicated in many aspects of RNA processing. hnRNP H and F are alternative splicing factors for numerous U2-and U12-dependent introns. The proteins have three RNA binding domains and two glycine-rich domains and localize to both the nucleus and cytoplasm, but little is known about which domains govern subcellular localization or splicing activity. We show here that the central glycine-tyrosine-arginine-rich (GYR) domain is responsible for nuclear localization, and a nonclassical nuclear localization signal (NLS) was mapped to a short, highly conserved sequence whose activity was compromised by point mutations. Glutathione S-transferase (GST) pulldown assays demonstrated that the hnRNP H NLS interacts with the import receptor transportin 1. Finally, we show that hnRNP H/F are transcription-dependent shuttling proteins. Collectively, the results suggest that hnRNP H and F are GYR domain-dependent shuttling proteins whose posttranslational modifications may alter nuclear localization and hence function.Most genes in metazoans contain multiple introns that need to be removed by mRNA splicing to generate mature mRNA. Alternative splicing, the process whereby multiple mRNAs (and thus proteins) are produced from the same gene through inclusion/exclusion of various exons (7), is widespread, and it has become clear that alternative splicing plays a large role in regulated gene expression and accounts for enormous protein diversity (9,38,62). The heterogeneous nuclear ribonucleoprotein (hnRNP) family of factors represents an important group of proteins that bind splicing regulatory elements to positively and negatively influence alternative splicing; hnRNP A1 and hnRNP H/F are particularly important in this regard (16-18, 42, 48, 50, 51). Binding to exonic splicing silencers and oligomerization of hnRNP A1 along the exon are thought to sterically displace positively acting factors, such as serine-arginine (SR) proteins (61, 82), or alternatively, hnRNP A1 may operate to repress splicing by binding to intronic splicing silencers, which may loop out the exon (8, 60). This looping mechanism might also account for a positive role for hnRNP A1 and H/F in splicing control through interactions with sites at each end of long introns, thus bringing splice sites together (24,47).In addition to their influence on splicing through recognition of specific binding sites within target RNAs, subcellular localization of hnRNP proteins has emerged as a mechanism to regulate splicing. While essentially nuclear at steady state, several hnRNP proteins (hnRNP A1/A2, K, D, E, and I) continuously shuttle between the nucleus and cytoplasm (55). hnRNP A1 is particularly well studied in this regard and shuttles through the action of a bidirectional transport peptide called M9 (65). While the export activity of M9 is not well understood, nuclear import of hnRNP A1 is mediated by the interaction of the M9 peptide with the imp...

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“…We also showed that the nuclear import of protein pVII could be reconstituted in digitonin-permeabilized cells by using either cytosol or the receptors that bound to pVII in vitro. The apparent promiscuity of protein pVII in exploiting several nuclear import pathways has been observed for several other transport cargoes (3,14,21,37). Some of these cargoes are highly basic and are capable of nucleic acid binding and, like pVII, appear to use the same NLS region for more than one import receptor (21,37).…”

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confidence: 99%

Adenovirus Core Protein pVII Is Translocated into the Nucleus by Multiple Import Receptor Pathways

Wodrich

Cassany

D’Angelo

et al. 2006

J Virol

102

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Adenoviruses are nonenveloped viruses with an ϳ36-kb double-stranded DNA genome that replicate in the nucleus. Protein VII, an abundant structural component of the adenovirus core that is strongly associated with adenovirus DNA, is imported into the nucleus contemporaneously with the adenovirus genome shortly after virus infection and may promote DNA import. In this study, we evaluated whether protein VII uses specific receptor-mediated mechanisms for import into the nucleus. We found that it contains potent nuclear localization signal (NLS) activity by transfection of cultured cells with protein VII fusion constructs and by microinjection of cells with recombinant protein VII fusions. We identified three NLS-containing regions in protein VII by deletion mapping and determined important NLS residues by site-specific mutagenesis. We found that recombinant protein VII and its NLS-containing domains strongly and specifically bind to importin ␣, importin ␤, importin 7, and transportin, which are among the most abundant cellular nuclear import receptors. Moreover, these receptors can mediate the nuclear import of protein VII fusions in vitro in permeabilized cells. Considered together, these data support the hypothesis that protein VII is a major NLS-containing adaptor for receptor-mediated import of adenovirus DNA and that multiple import pathways are utilized to promote efficient nuclear entry of the viral genome.Adenoviruses (Ads) are nonenveloped, double-stranded DNA viruses with a diameter of ϳ90 nm. They contain an outer capsid shell with icosahedral symmetry composed of 12 vertices and 20 facets surrounding the viral core with the genomic DNA. Extending from each of the 12 vertices of the capsid is the spike-like fiber protein, which is anchored to the vertices by the penton protein. Ad infection of cells is initiated by attachment of the fiber to the Coxsackie adenovirus receptors of cells, followed by association of the penton with ␣V integrins. This secondary penton interaction is required for fiber release and viral uptake into clathrin-coated pits of the early endosomal pathway (10, 43, 51; reviewed in references 9 and 34). In the early endosome, a poorly understood mechanism involving a drop in pH induces conformational changes in the capsid, which appears to release proteins of the vertex region, including protein VI and penton (17). An amphipathic helix at the N terminus of protein VI is thought to mediate disruption of the endosomal membrane and aid in the release of the remaining partially uncoated capsid into the cytoplasm (52). The nucleocapsid then moves toward the nucleus in a microtubule-and dynein-dependent mechanism (26) and docks at the nuclear pore complex (NPC), the proteinaceous channel that mediates transport across the nuclear envelope. Finally, the viral genome is imported into the nucleus prior to initiation of viral replication (16,44).In contrast to the Ad capsid, the core does not display a well-ordered symmetry or the coaxial coiling of DNA previously observed with most bacteriopha...

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Transportin Is a Major Nuclear Import Receptor for c-Fos

Cited by 33 publications

References 52 publications

Transportin Regulates Nuclear Import of CD44

Transportin Regulates Nuclear Import of CD44

A Glycine-Rich Domain of hnRNP H/F Promotes Nucleocytoplasmic Shuttling and Nuclear Import through an Interaction with Transportin 1

Adenovirus Core Protein pVII Is Translocated into the Nucleus by Multiple Import Receptor Pathways

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