Nuclear export signals: small domains with large impact
Engelsma, D.H.
Citation
Engelsma, D. H. (2008, October 16). Nuclear export signals: small domains with large impact. Retrieved from https://hdl.handle.net/1887/13258
Version: Corrected Publisher’s Version
License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden
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Nucleocytoplasmic traffic is one of the hallmarks of the eukaryoc cell. To a large extent, this process is mediated by nuclear import and export receptors.
Study of nuclear import and export has had wide im- plicaons for many cellular processes including basic cell metabolism, cellular differenaon and disease (Chapter 1). In this thesis I have studied the nuclear export receptor CRM1/exporn1 and its interacon with various transport substrates and the nuclear pore complex (NPC), the supramolecular structure through which receptor-mediated nucleocytoplasmic transport takes place.
First, I have studied the nature of the Nuclear Export Signal (NES), the amino acid sequence present in pro- teins that directly mediates CRM1-dependent nuclear export. NESs have always been very difficult to iden-
fy due to their loose consensus and poor receptor binding affinies. This has resulted in the publicaon of mulple ‘pseudo’-NESs. In Chapter 2 of this thesis, we redefine the NES and explain its weak consensus and binding characteriscs. Key to this understanding was the idenficaon of the supraphysiological NES (supraNES), a synthec pepde NES that binds CRM1 with an unusual high affinity. Interesngly, we found that supraphysiological NES (supraNES) do not only exist as synthec pepdes, but are present in certain viruses, where they are required for export of the viral parcle from the nucleus (Chapter 3). In the course of the study of the supraNES-containing protein par- vovirus NS2, we also discovered that this protein is necessary and sufficient to cause an inhibion of
nuclear export of host cell mRNAs, possibly contrib- ung to the virus’s cytotoxicity (Chapter 4). We de- scribe in Chapter 5 the idenficaon of an NES in the chromosomal passenger protein Survivin, an essenal protein for mitoc progression and a protein respon- sible for escape from programmed cell death. This NES has previously been difficult to detect, because it appears to be regulated by intermolecular mask- ing, as a consequence of the formaon of Survivin homodimers. NPCs are the gateways to and from the nucleus, and it is an important queson how different transport routes ulize this gateway. In Chapter 6 we find that one component of the NPC, namely Nup214, is specifically required for CRM1-mediated export of the large (60S) pre-ribosomal subunit. This chapter also touches upon a highly controversial subject in the field, the funcon of the CRM1-Nup214 interacon, which has also been described to be responsible for CRM1-mediated export in general. This will be further discussed in Chapter 7, the General Discussion of this thesis. Also in this chapter, the general consequences and applicaons of supraNESs will be discussed, in- cluding currently emerging supraNESs in other viruses Furthermore, the hypothesis that supraNESs could be responsible for export of large cargo in general will be discussed.
