Karyopherins: from nuclear-transport mediators to nuclear-function regulators

Mosammaparast, Nima; Pemberton, Lucy F.

doi:10.1016/j.tcb.2004.09.004

Cited by 294 publications

(275 citation statements)

References 91 publications

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“…Subnuclear compartmentalization may be a general regulatory theme in V(D)J recombination. In addition, there are now several examples of karyopherins acting as regulators of nuclear function outside of their roles in nuclear transport (48,49).…”

Section: Discussionmentioning

confidence: 99%

Biochemical and Folding Defects in a RAG1 Variant Associated with Omenn Syndrome

Simkus

Anand

Bhattacharyya

et al. 2007

The Journal of Immunology

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The RAG1 and RAG2 proteins are required to assemble mature Ag receptor genes in developing lymphocytes. Hypomorphic mutations in the gene encoding RAG1 are associated with Omenn syndrome, a primary immunodeficiency. We explored the biochemical defects resulting from a mutation identified in an Omenn syndrome patient which generates an amino acid substitution in the RAG1 RING finger/ubiquitin ligase domain (C325Y in murine RAG1) as well as an adjacent substitution (P326G). RAG1 C325Y demonstrated a 50-fold reduction in recombination activity in cultured pro-B cells despite the fact that its expression and localization to the nucleus were similar to the wild-type protein. The C325Y substitution severely abrogated ubiquitin ligase activity of the purified RAG1 RING finger domain, and the tertiary structure of the domain was altered. The P326G substitution also abrogated ubiquitin ligase activity but had a less severe effect on protein folding. RAG1 P326G also demonstrated a recombination impairment that was most pronounced when RAG1 levels were limiting. Thus, a correctly folded RAG1 RING finger domain is required for normal V(D)J recombination, and RAG1 ubiquitin ligase activity can contribute when the protein is present at relatively low levels.

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Section: Discussionmentioning

confidence: 99%

Biochemical and Folding Defects in a RAG1 Variant Associated with Omenn Syndrome

Simkus

Anand

Bhattacharyya

et al. 2007

The Journal of Immunology

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“…A third group consists of importin-␣ isoforms that function as adaptors, which facilitate cargo binding to importin-␤. Finally, functions of two karyopherins, RanBP6 and RanBP17, are still unknown (Mosammaparast and Pemberton, 2004;Pemberton and Paschal, 2005).…”

Section: Introductionmentioning

confidence: 99%

STRADα Regulates LKB1 Localization by Blocking Access to Importin-α, and by Association with Crm1 and Exportin-7

Dorfman

Macara

2008

MBoC

109

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LKB1, a serine/threonine kinase, regulates cell polarity, metabolism, and cell growth. The activity and cellular distribution of LKB1 are determined by cofactors, STRAD␣ and MO25. STRAD␣ induces relocalization of LKB1 from the nucleus to the cytoplasm and stimulates its catalytic activity. MO25 stabilizes the STRAD␣/LKB1 interaction. We investigated the mechanism of nucleocytoplasmic transport of LKB1 in response to its cofactors. Although LKB1 is imported into the nucleus by importin-␣/␤, STRAD␣ and MO25 passively diffuse between the nucleus and the cytoplasm. STRAD␣ induces nucleocytoplasmic shuttling of LKB1. STRAD␣ facilitates nuclear export of LKB1 by serving as an adaptor between LKB1 and exportins CRM1 and exportin7. STRAD␣ inhibits import of LKB1 by competing with importin-␣ for binding to LKB1. MO25 stabilizes the LKB1-STRAD␣ complex but it does not facilitate its nucleocytoplasmic shuttling. Strikingly, the STRAD␤, isoform which differs from STRAD␣ in the N-and C-terminal domains that are responsible for interaction with export receptors, does not efficiently relocalize LKB1 from the nucleus to the cytoplasm. These results identify a multifactored mechanism to control LKB1 localization, and they suggest that the STRAD␤-LKB1 complex might possess unique functions in the nucleus. INTRODUCTIONPeutz-Jeghers cancer syndrome is caused by mutations in a gene encoding a serine/threonine kinase called LKB1 (Hemminki et al., 1998). This kinase is closely related to PAR-4, a protein required for polarization of the Caenorhabditis elegans zygote, and it has recently been implicated in the apical/basal polarization of mammalian epithelial cells (Baas et al., 2004). LKB1 is also involved in numerous cell signaling pathways that regulate cellular metabolism (Shaw et al., 2004Liang et al., 2007), cell growth, and responses to DNA damage (Wei et al., 2005;Setogawa et al., 2006;Zeng and Berger, 2006). LKB1 can phosphorylate and activate 13 protein kinases from the AMP-activated protein kinase family (Lizcano et al., 2004). However, the biological significance of this phosphorylation is still unclear for many of these kinases. The cellular localization and activity of LKB1 is controlled through its interaction with Ste20 Related Adaptor (STRAD) and an adapter protein, MO25 . STRAD, a 48-kDa protein, is a pseudokinase that consists of a STE20-like kinase domain but lacks several residues that are indespensible for catalytic activity. STRAD resembles most closely the STE20 homologues SPAK (Johnston et al., 2000) and ILPIP (Sanna et al., 2002), or PAP kinase (Nishigaki et al., 2003). Whereas SPAK is a true kinase, it was later shown that ILPIP/PAPK is a pseudokinase, similarly to STRAD and that it also interacts with and activates LKB1. Therefore, it was termed STRAD␤, whereas the original STRAD became known as STRAD␣ . The complex of LKB1 and STRAD␣ or -␤ is stabilized by MO25, a 40-kDa protein composed of ␣-helical repeats that are distantly related to the armadillo repeat domain (Milburn et al., 2004). MO25 binds STRAD ...

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“…In eukaryotic cells the nucleocytoplasmic transport of most proteins and some RNAs is mediated by an evolutionarily conserved family of soluble transport factors, the karyopherins (also referred to as importins and exportins; reviewed in Weis, 2003;Harel and Forbes, 2004;Mosammaparast and Pemberton, 2004). After synthesis in the cytoplasm, most nuclear protein cargoes are bound by a member of the karyopherin family, through direct interaction with a nuclear localization sequence contained in the cargo protein.…”

Section: Introductionmentioning

confidence: 99%

“…Once in the nucleus, the karyopherin encounters a high concentration of RanGTP, which acts as a regulator of transport. Interaction of the karyopherin with RanGTP leads to dissociation of the karyopherin from its nuclear cargo (Weis, 2003;Harel and Forbes, 2004;Mosammaparast and Pemberton, 2004). In some circumstances, nuclear-binding partners of the cargo appear to also play a role in stimulating the dissociation of Kap and cargo (Senger et al, 1998;Lee and Aitchison, 1999;Pemberton et al, 1999).…”

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confidence: 99%

Nuclear Import of TFIIB Is Mediated by Kap114p, a Karyopherin with Multiple Cargo-binding Domains

Hodges

Leslie

Mosammaparast

et al. 2005

MBoC

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Nuclear import and export is mediated by an evolutionarily conserved family of soluble transport factors, the karyopherins (referred to as importins and exportins). The yeast karyopherin Kap114p has previously been shown to import histones H2A and H2B, Nap1p, and a component of the preinitiation complex (PIC), TBP. Using a proteomic approach, we have identified several potentially new cargoes for Kap114p. These cargoes include another PIC component, the general transcription factor IIB or Sua7p, which interacted directly with Kap114p. Consistent with its role as a Sua7p import factor, deletion of KAP114 led to specific mislocalization of Sua7p to the cytoplasm. An interaction between Sua7p and TBP was also detected in cytosol, raising the possibility that both Sua7p and TBP can be coimported by Kap114p. We have also shown that Kap114p possesses multiple overlapping binding sites for its partners, Sua7p, Nap1p, and H2A and H2B, as well as RanGTP and nucleoporins. In addition, we have assembled an in vitro complex containing Sua7p, Nap1p, and histones H2A and H2B, suggesting that this Kap may import several proteins simultaneously. The import of more than one cargo at a time would increase the efficiency of each import cycle and may allow the regulation of coimported cargoes. INTRODUCTIONIn eukaryotic cells the nucleocytoplasmic transport of most proteins and some RNAs is mediated by an evolutionarily conserved family of soluble transport factors, the karyopherins (also referred to as importins and exportins; reviewed in Weis, 2003;Harel and Forbes, 2004;Mosammaparast and Pemberton, 2004). After synthesis in the cytoplasm, most nuclear protein cargoes are bound by a member of the karyopherin family, through direct interaction with a nuclear localization sequence contained in the cargo protein. Transport through the nuclear pore complex occurs via transient interactions of the karyopherin with the NPC. Once in the nucleus, the karyopherin encounters a high concentration of RanGTP, which acts as a regulator of transport. Interaction of the karyopherin with RanGTP leads to dissociation of the karyopherin from its nuclear cargo (Weis, 2003;Harel and Forbes, 2004;Mosammaparast and Pemberton, 2004). In some circumstances, nuclear-binding partners of the cargo appear to also play a role in stimulating the dissociation of Kap and cargo (Senger et al., 1998;Lee and Aitchison, 1999;Pemberton et al., 1999). In yeast, there are 14 members of the karyopherin family, with Ͼ20 members in mammalian cells (Mosammaparast and Pemberton, 2004). Karyopherins appear to function in either nuclear import or nuclear export, with only two examples of a Kap that works in both directions (Weis, 2003;Harel and Forbes, 2004;Mosammaparast and Pemberton, 2004). In yeast, 11 members of the karyopherin family must import at least 1500 nuclear proteins, suggesting that each receptor must have many cargoes. To date specific transport receptor-cargo pairs have only been shown for ϳ30 cargoes; in addition the NLS sequences recognized by most Kaps is n...

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Karyopherins: from nuclear-transport mediators to nuclear-function regulators

Cited by 294 publications

References 91 publications

Biochemical and Folding Defects in a RAG1 Variant Associated with Omenn Syndrome

Biochemical and Folding Defects in a RAG1 Variant Associated with Omenn Syndrome

STRADα Regulates LKB1 Localization by Blocking Access to Importin-α, and by Association with Crm1 and Exportin-7

Nuclear Import of TFIIB Is Mediated by Kap114p, a Karyopherin with Multiple Cargo-binding Domains

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