Alternative titles; symbols
HGNC Approved Gene Symbol: XPO1
Cytogenetic location: 2p15 Genomic coordinates (GRCh38): 2:61,477,849-61,538,612 (from NCBI)
Human CRM1, or XPO1, is the homolog of yeast crm1 (named for 'required for chromosome region maintenance'), a nuclear protein essential for proliferation and chromosome region maintenance. Fornerod et al. (1997) used the oncogenic nucleoporin CAN (114350) to coprecipitate human CRM1. The complete cDNA encodes a predicted protein of 1,071 amino acids with a predicted molecular mass of 123 kD. The CRM1 protein migrates at 112 kD. Human CRM1 has 47% identity with S. cerevisiae crm1 and 52% identity with S. pombe crm1+. The N terminus of human CRM1 shares significant homology with the N terminus of importin-beta. Fornerod et al. (1997) identified a group of largely uncharacterized yeast and vertebrate proteins of similar size (110 to 120 kD) that share this homology domain, which they proposed to call the CRIME domain (for 'CRM1, importin-beta, etc.').
Kudo et al. (1997) cloned human CRM1 cDNA using sequence information from EST databases and a PCR-based strategy based on the sequence of S. pombe crm1+. Northern blot analysis using the C-terminal region of human CRM1 cDNA as a probe revealed a major transcript of 5.6 kb expressed in all tissues tested except kidney.
Kudo et al. (1997) found that Human CRM1 weakly complemented the cold-sensitive mutation of S. pombe crm1-809. Overproduction of human CRM1 suppressed cell proliferation in wildtype S. pombe in an expression level-dependent manner. Overexpression of native S. pombe crm1+ had the same effect. Northern blot analysis with RNAs isolated from synchronized mammalian cells showed that the expression of mammalian CRM1 was initiated in the late G1 phase and reached a peak at G2/M, although the protein level did not change during the cell cycle. Human CRM1 fused to green fluorescent protein (GFP) and transiently expressed in NIH 3T3 cells showed that human CRM1 was localized preferentially in the nuclear envelope, but was also detectable in the nucleoplasm and the cytoplasm. A crm1 mutation of S. pombe caused nuclear import of a GFP fusion protein containing a nuclear export signal (NES) but no change in the distribution of a GFP fusion protein containing a nuclear localization signal (NLS). These data suggested to Kudo et al. (1997) that CRM1 is a novel cell cycle-regulated gene that is essential for the NES-dependent nuclear export of proteins.
CRM1 protein binds CAN and NUP88 (602552), and its association with the nuclear pore is dynamic (Fornerod et al., 1997). To test whether CRM1 could be a nuclear export receptor, Fornerod et al. (1997) used Xenopus oocytes incubated in leptomycin B, a cytotoxin which blocks Rev export and Rev-mediated RNA export in tissue culture cells. Leptomycin B interacted directly with CRM1, as shown by gel shift assays, and blocked export of Rev and U snRNAs from Xenopus oocyte nucleus. Overexpression of CRM1 stimulated Rev and U snRNA export from the nucleus. Fornerod et al. (1997) found that an NES/CRM1/Ran complex forms in the presence of RanGTP. Leptomycin B blocks formation of this complex. Fornerod et al. (1997) concluded that CRM1 is an export receptor for leucine-rich NESs. Noting that CRM1 is a member of a family of proteins related to importin-beta, Fornerod et al. (1997) suggested the descriptive name 'exportins' for those family members involved in nuclear export.
Stade et al. (1997) characterized CRM1 as an essential nuclear export factor in S. cerevisiae and proposed that CRM1 be renamed 'exportin-1,' symbolized XPO1. XPO1 protein is localized in the nucleus at steady state but is capable of shuttling between the nucleus and cytoplasm. Stade et al. (1997) constructed an NES-GFP-NLS substrate which shuttled continuously between the nucleus and cytoplasm, but appeared largely cytoplasmic, presumably due to a higher rate of export. In yeast containing a temperature-sensitive mutation in CRM1, the substrate became nuclear within 5 minutes at high temperature, indicating that the mutation blocks NES export. High temperature also blocked mRNA export in yeast. A 2-hybrid analysis showed an interaction between NES and CRM1 and between Ran and CRM1.
The cyclin-dependent kinase inhibitor p27(KIP1) (CDKN1B; 600778) is degraded during the cell cycle by the ubiquitin-proteasome pathway. Using NIH-3T3 mouse fibroblasts and mouse embryonic fibroblasts, Kamura et al. (2004) found that a complex made up of Kpc1 (RNF123; 614472) and Kpc2 (UBAC1; 608129) ubiquitinated cytoplasmic p27(KIP1) at G1 phase and that cytoplasmic degradation of p27(KIP1) required p27(KIP1) nuclear export by Crm1.
A single transcript in its unspliced and spliced forms directs synthesis of all human immunodeficiency virus (HIV)-1 proteins. Although nuclear export of intron-containing cellular transcripts is restricted in mammalian cells, HIV-1 has evolved the viral Rev protein to overcome this restriction for viral transcripts. CRM1 is a cellular cofactor for Rev-dependent export of intron-containing HIV-1 RNA. Yedavalli et al. (2004) presented evidence that Rev/CRM1 activity uses the ATP-dependent RNA helicase DDX3 (300160). They showed that DDX3 is a nucleocytoplasmic shuttling protein that binds CRM1 and localizes to nuclear membrane pores. Knockdown of DDX3 using either antisense vector or dominant-negative mutants suppressed Rev-RRE (Rev response element) function in the export of incompletely spliced HIV-1 RNAs. Yedavalli et al. (2004) concluded that DDX3 is the human RNA helicase that functions in the CRM1 RNA export pathway analogously to the postulated role for Dbp5 (605812) in yeast mRNA export.
For a review of nuclear export receptors, see Ullman et al. (1997).
Kim et al. (2016) used a multigenomic data-driven approach based on 106 human non-small-cell lung cancer cell lines to interrogate 4,725 biological processes with 39,760 short interfering RNA pools for those selectively required for the survival of KRAS (190070)-mutant cells that harbor a broad spectrum of phenotypic variation. Nuclear transport machinery was the sole process-level discriminator of statistical significance. Chemical perturbation of the nuclear export receptor XPO1 with a clinically available drug revealed a robust synthetic-lethal interaction with native or engineered oncogenic KRAS both in vitro and in vivo. The primary mechanism underpinning XPO1 inhibitor sensitivity was intolerance to the accumulation of NFKBIA (164008) with consequent inhibition of NF-kappa-B (see 164011) transcription factor activity. Intrinsic resistance associated with concurrent FSTL5 (620128) mutations was detected and determined to be a consequence of YAP1 (606608) activation via a previously unappreciated FSTL5-Hippo pathway regulatory axis. This occurred in approximately 17% of KRAS-mutant lung cancers and could be overcome with the coadministration of a YAP1-TEAD (e.g., TEAD1, 189967) inhibitor.
Crystal Structure
Dong et al. (2009) presented a 2.9-angstrom resolution crystal structure of CRM1 bound to snurportin (SNUPN1; 607902). Snurportin-1 binds CRM1 in a bipartite manner by means of an N-terminal leucine-rich nuclear export signal (LR-NES) and its nucleotide-binding domain. The LR-NES is a combined alpha-helical-extended structure that occupies a hydrophobic groove between 2 CRM1 outer helices. The LR-NES interface explains the consensus hydrophobic pattern, preference for intervening electronegative residues, and inhibition by leptomycin B. The second nuclear export signal epitope is a basic surface on the snurportin-1 nucleotide-binding domain, which binds an acidic patch on CRM1 adjacent to the LR-NES site. Multipartite recognition of individually weak nuclear export signal epitopes may be common to CRM1 substrates, enhancing CRM1 binding beyond the generally low affinity LR-NES. Similar energetic construction is also used in multipartite nuclear localization signals to provide broad substrate specificity and rapid evolution in nuclear transport.
Monecke et al. (2009) presented the crystal structure of the SPN1-CRM1-RanGTP (see 601179) export complex at 2.5-angstrom resolution. SPN1 is a nuclear import adaptor for cytoplasmically assembled, m3G (5-prime-2,2,7-terminal trimethylguanosine)-capped spliceosomal U snRNPs. The structure showed how CRM1 can specifically return the cargo-free form of SPN1 to the cytoplasm. The extensive contact area includes 5 hydrophobic residues at the SPN1 amino terminus that dock into a hydrophobic cleft of CRM1, as well as numerous hydrophilic contacts of CRM1 to m3G cap-binding domain and carboxyl-terminal residues of SPN1. Monecke et al. (2009) concluded that RanGTP promotes cargo binding to CRM1 solely through long-range conformational changes in the exportin.
By fluorescence in situ hybridization, Fornerod et al. (1997) mapped the CRM1 gene to chromosome 2p16.
Dong, X., Biswas, A., Suel, K. E., Jackson, L. K., Martinez, R., Gu, H., Chook, Y. M. Structural basis for leucine-rich nuclear export signal recognition by CRM1. Nature 458: 1136-1141, 2009. Note: Erratum: Nature 461: 550 only, 2009. [PubMed: 19339969] [Full Text: https://doi.org/10.1038/nature07975]
Fornerod, M., Ohno, M., Yoshida, M., Mattaj, I. W. CRM1 is an export receptor for leucine-rich nuclear export signals. Cell 90: 1051-1060, 1997. [PubMed: 9323133] [Full Text: https://doi.org/10.1016/s0092-8674(00)80371-2]
Fornerod, M., van Baal, S., Valentine, V., Shapiro, D. N., Grosveld, G. Chromosomal localization of genes encoding CAN/Nup214-interacting proteins--human CRM1 localizes to 2p16, whereas Nup88 localizes to 17p13 and is physically linked to SF2p32. Genomics 42: 538-540, 1997. [PubMed: 9205132] [Full Text: https://doi.org/10.1006/geno.1997.4767]
Fornerod, M., van Deursen, J., van Baal, S., Reynolds, A., Davis, D., Murti, K. G., Fransen, J., Grosveld, G. The human homologue of yeast CRM1 is in a dynamic subcomplex with CAN/Nup214 and a novel nuclear pore component Nup88. EMBO J. 16: 807-816, 1997. [PubMed: 9049309] [Full Text: https://doi.org/10.1093/emboj/16.4.807]
Kamura, T., Hara, T., Matsumoto, M., Ishida, N., Okumura, F., Hatakeyama, S., Yoshida, M., Nakayama, K., Nakayama, K. I. Cytoplasmic ubiquitin ligase KPC regulates proteolysis of p27(Kip1) at G1 phase. Nature Cell Biol. 6: 1229-1235, 2004. [PubMed: 15531880] [Full Text: https://doi.org/10.1038/ncb1194]
Kim, J., McMillan, E., Kim, H. S., Venkateswaran, N., Makkar, G., Rodriguez-Canales, J., Villalobos, P., Neggers, J. E., Mendiratta, S., Wei, S., Landesman, Y., Senapedis, W., and 11 others. XPO1-dependent nuclear export is a druggable vulnerability in KRAS-mutant lung cancer. Nature 538: 114-117, 2016. [PubMed: 27680702] [Full Text: https://doi.org/10.1038/nature19771]
Kudo, N., Khochbin, S., Nishi, K., Kitano, K., Yanagida, M., Yoshida, M., Horinouchi, S. Molecular cloning and cell cycle-dependent expression of mammalian CRM1, a protein involved in nuclear export of proteins. J. Biol. Chem. 272: 29742-29751, 1997. [PubMed: 9368044] [Full Text: https://doi.org/10.1074/jbc.272.47.29742]
Monecke, T., Guttler, T., Neumann, P., Dickmanns, A., Gorlich, D., Ficner, R. Crystal structure of the nuclear export receptor CRM1 in complex with snurportin 1 and RanGTP. Science 324: 1087-1091, 2009. [PubMed: 19389996] [Full Text: https://doi.org/10.1126/science.1173388]
Stade, K., Ford, C. S., Guthrie, C., Weis, K. Exportin 1 (Crm1p) is an essential nuclear export factor. Cell 90: 1041-1050, 1997. [PubMed: 9323132] [Full Text: https://doi.org/10.1016/s0092-8674(00)80370-0]
Ullman, K. S., Powers, M. A., Forbes, D. J. Nuclear export receptors: from importin to exportin. Cell 90: 967-970, 1997. [PubMed: 9323123] [Full Text: https://doi.org/10.1016/s0092-8674(00)80361-x]
Yedavalli, V. S. R. K., Neuveut, C., Chi, Y., Kleiman, L., Jeang, K.-T. Requirement of DDX3 DEAD box RNA helicase for HIV-1 Rev-RRE export function. Cell 119: 381-392, 2004. [PubMed: 15507209] [Full Text: https://doi.org/10.1016/j.cell.2004.09.029]