Transportin 1

Transportin 1
PDB rendering based on 1qbk.
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 1QBK​, 2H4M​, 2OT8​, 2QMR​, 2Z5J​, 2Z5K​, 2Z5M​, 2Z5N​, 2Z5O​, 4FDD​, 4FQ3​, 4JLQ​, 4OO6​
Identifiers
Symbols	TNPO1 ; IPO2; KPNB2; MIP; MIP1; TRN
External IDs	OMIM: 602901 MGI: 2681523 HomoloGene: 5358 GeneCards: TNPO1 Gene
Gene ontology Molecular function • protein binding • nuclear localization sequence binding • Ran GTPase binding • poly(A) RNA binding Cellular component • nucleus • cytoplasm • cytosol • extracellular exosome • primary cilium Biological process • protein import into nucleus, translocation • organelle organization • gene expression • viral process Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	3842	238799
Ensembl	ENSG00000083312	ENSMUSG00000009470
UniProt	Q92973	Q8BFY9
RefSeq (mRNA)	NM_002270	NM_001048267
RefSeq (protein)	NP_002261	NP_001041732
Location (UCSC)	Chr 5: 72.82 – 72.92 Mb	Chr 13: 98.84 – 98.93 Mb
PubMed search

Transportin-1 (or Importin-β 2) is a protein that in humans is encoded by the TNPO1 gene.^[1][2][3]

Function

This protein is a karyopherin which interacts with nuclear localization sequence to target nuclear proteins to the nucleus. The classical karyopherin receptor complex, such as the complex that uses Importin-β1 (encoded by gene KPNB1), is a heterodimer of an alpha subunit which recognizes the nuclear localization signal and a beta subunit which docks the complex at nucleoporins. However, Transportin-1 can directly bind to the cargo proteins and may not need importin alpha subunit to do it.^[4]

Transportin-1 is thought to use the same principal mechanism to carry out nuclear transport as other Importins. It mediates docking to the nuclear pore complex through binding to nucleoporin and is subsequently translocated through the pore by an energy requiring mechanism. Then, in the nucleus Ran binds to Transportin-1, it dissociates from cargo, and Transportin-1 is re-exported from the nucleus to the cytoplasm where GTP hydrolysis releases Ran. Then Transportin-1 is free to bind new cargo.

In addition, Transportin-1 is implicated in helping protein transport into primary cilium.^[5] The function of Transportin-1 in this case is thought to be similar to carrying proteins into the nucleus through a nuclear pore. Transportin-1 binds cargo and then is helping this cargo to pass through a pore at the base of the cilium. Ran and nucleoporins are also implicated in this mechanism.^[6]

Alternate splicing of this gene results in two transcript variants encoding different proteins.^[3]

Targets

Transportin 1 (TRN1) is part of the non-classical nuclear import pathway. In conjunction with the RanGTP hydroysis cascade TRN1 acts to import a selection of proteins into the nucleus of cells. These targets typically contain a PY-motif otherwise known as a M9 nuclear localisation signal. Well described examples include hnRNP A1.^[7]

The type of cargo proteins that Transportin 1 can carry into the nucleus include RNA-binding proteins (such as hnRNP A1 and hnRNP F) and also ribosomal proteins.^[8]

Clinical Significance

TRN1 has been implicated in the pathogenesis of two neurodegenerative diseases namely Amyotrophic lateral sclerosis and frontotemporal dementia.^[9]

Interactions

Transportin 1 has been shown to interact with:

• RGPD5^[10] and
• Ran (biology).^[11][12]

References

1. Pollard VW, Michael WM, Nakielny S, Siomi MC, Wang F, Dreyfuss G (Dec 1996). "A novel receptor-mediated nuclear protein import pathway". Cell 86 (6): 985–94. doi:10.1016/S0092-8674(00)80173-7. PMID 8808633.
2. Bonifaci N, Moroianu J, Radu A, Blobel G (Jun 1997). "Karyopherin beta2 mediates nuclear import of a mRNA binding protein". Proc. Natl. Acad. Sci. U.S.A. 94 (10): 5055–60. doi:10.1073/pnas.94.10.5055. PMC 24630. PMID 9144189.
3. "Entrez Gene: TNPO1 transportin 1".
4. R.A. Fridell (1997). Nuclear import of hnRNP A1 is mediated by a novel cellular cofactor related to karyopherin-beta. Journal of Cell Science 1997 110: 1325-1331;
5. Toby W. Hurd (2011). Localization of retinitis pigmentosa 2 to cilia is regulated by Importin β2. J Cell Sci 2011 124: 718-726; doi: 10.1242/jcs.070839
6. Kee HL (2012). A size-exclusion permeability barrier and nucleoporins characterize a ciliary pore complex that regulates transport into cilia.. Nat Cell Biol. 2012 Mar 4;14(4):431-7. doi: 10.1038/ncb2450.
7. Dormann D, Rodde R, Edbauer D, Bentmann E, Fischer I, Hruscha A, Than ME, Mackenzie IR, Capell A, Schmid B, Neumann M, Haass C (August 2010). "ALS-associated fused in sarcoma (FUS) mutations disrupt Transportin-mediated nuclear import". EMBO J. 29 (16): 2841–57. doi:10.1038/emboj.2010.143. PMC 2924641. PMID 20606625.
8. Anne-Christine Ström (2001). Importin-beta-like nuclear transport receptors. Genome Biol. 2001; 2(6): reviews3008.1–reviews3008.9.
9. Brelstaff J, Lashley T, Holton JL, Lees AJ, Rossor MN, Bandopadhyay R, Revesz T (November 2011). "Transportin1: a marker of FTLD-FUS". Acta Neuropathol. 122 (5): 591–600. doi:10.1007/s00401-011-0863-6. PMID 21847626.
10. Cai Y, Miao SY, Wang LF (October 2001). "[Determination of the binding site of testis-specific nucleoporin BS-63 to transportin (karopherin beta 2) and the proof of their combination in vitro]". Zhongguo Yi Xue Ke Xue Yuan Xue Bao (in Chinese) 23 (5): 462–6. PMID 12905863.
11. Chook YM, Blobel G (May 1999). "Structure of the nuclear transport complex karyopherin-beta2-Ran x GppNHp". Nature 399 (6733): 230–7. doi:10.1038/20375. PMID 10353245.
12. Shamsher MK, Ploski J, Radu A (October 2002). "Karyopherin beta 2B participates in mRNA export from the nucleus". Proc. Natl. Acad. Sci. U.S.A. 99 (22): 14195–9. doi:10.1073/pnas.212518199. PMC 137860. PMID 12384575.

Further reading

• Bukrinsky MI, Haffar OK (1997). "HIV-1 nuclear import: in search of a leader". Front. Biosci. 2: d578–87. doi:10.2741/A213. PMID 9366553.
• Bukrinsky MI, Haffar OK (1998). "HIV-1 nuclear import: matrix protein is back on center stage, this time together with Vpr". Mol. Med. 4 (3): 138–43. PMC 2230352. PMID 9562972.
• Bukrinsky MI, Sharova N, Dempsey MP, Stanwick TL, Bukrinskaya AG, Haggerty S, Stevenson M (1992). "Active nuclear import of human immunodeficiency virus type 1 preintegration complexes". Proc. Natl. Acad. Sci. U.S.A. 89 (14): 6580–4. doi:10.1073/pnas.89.14.6580. PMC 49545. PMID 1631159.
• Moroianu J, Hijikata M, Blobel G, Radu A (1995). "Mammalian karyopherin alpha 1 beta and alpha 2 beta heterodimers: alpha 1 or alpha 2 subunit binds nuclear localization signal and beta subunit interacts with peptide repeat-containing nucleoporins". Proc. Natl. Acad. Sci. U.S.A. 92 (14): 6532–6. doi:10.1073/pnas.92.14.6532. PMC 41552. PMID 7604027.
• Bukrinsky MI, Haggerty S, Dempsey MP, Sharova N, Adzhubel A, Spitz L, Lewis P, Goldfarb D, Emerman M, Stevenson M (1993). "A nuclear localization signal within HIV-1 matrix protein that governs infection of non-dividing cells". Nature 365 (6447): 666–9. doi:10.1038/365666a0. PMID 8105392.
• Michael WM, Choi M, Dreyfuss G (1995). "A nuclear export signal in hnRNP A1: a signal-mediated, temperature-dependent nuclear protein export pathway". Cell 83 (3): 415–22. doi:10.1016/0092-8674(95)90119-1. PMID 8521471.
• Nakielny S, Siomi MC, Siomi H, Michael WM, Pollard V, Dreyfuss G (1996). "Transportin: nuclear transport receptor of a novel nuclear protein import pathway". Exp. Cell Res. 229 (2): 261–6. doi:10.1006/excr.1996.0369. PMID 8986607.
• Fridell RA, Truant R, Thorne L, Benson RE, Cullen BR (1997). "Nuclear import of hnRNP A1 is mediated by a novel cellular cofactor related to karyopherin-beta". J. Cell. Sci. 110 (11): 1325–31. PMID 9202393.
• Gallay P, Hope T, Chin D, Trono D (1997). "HIV-1 infection of nondividing cells through the recognition of integrase by the importin/karyopherin pathway". Proc. Natl. Acad. Sci. U.S.A. 94 (18): 9825–30. doi:10.1073/pnas.94.18.9825. PMC 23276. PMID 9275210.
• Siomi MC, Eder PS, Kataoka N, Wan L, Liu Q, Dreyfuss G (1997). "Transportin-mediated nuclear import of heterogeneous nuclear RNP proteins". J. Cell Biol. 138 (6): 1181–92. doi:10.1083/jcb.138.6.1181. PMC 2132560. PMID 9298975.
• Henderson BR, Percipalle P (1997). "Interactions between HIV Rev and nuclear import and export factors: the Rev nuclear localisation signal mediates specific binding to human importin-beta". J. Mol. Biol. 274 (5): 693–707. doi:10.1006/jmbi.1997.1420. PMID 9405152.
• Efthymiadis A, Briggs LJ, Jans DA (1998). "The HIV-1 Tat nuclear localization sequence confers novel nuclear import properties". J. Biol. Chem. 273 (3): 1623–8. doi:10.1074/jbc.273.3.1623. PMID 9430704.
• Vodicka MA, Koepp DM, Silver PA, Emerman M (1998). "HIV-1 Vpr interacts with the nuclear transport pathway to promote macrophage infection". Genes Dev. 12 (2): 175–85. doi:10.1101/gad.12.2.175. PMC 316441. PMID 9436978.
• Popov S, Rexach M, Zybarth G, Reiling N, Lee MA, Ratner L, Lane CM, Moore MS, Blobel G, Bukrinsky M (1998). "Viral protein R regulates nuclear import of the HIV-1 pre-integration complex". EMBO J. 17 (4): 909–17. doi:10.1093/emboj/17.4.909. PMC 1170440. PMID 9463369.
• Popov S, Rexach M, Ratner L, Blobel G, Bukrinsky M (1998). "Viral protein R regulates docking of the HIV-1 preintegration complex to the nuclear pore complex". J. Biol. Chem. 273 (21): 13347–52. doi:10.1074/jbc.273.21.13347. PMID 9582382.
• Fouchier RA, Meyer BE, Simon JH, Fischer U, Albright AV, González-Scarano F, Malim MH (1998). "Interaction of the human immunodeficiency virus type 1 Vpr protein with the nuclear pore complex". J. Virol. 72 (7): 6004–13. PMC 110405. PMID 9621063.