Search and characterization of nucleocytoplasmic transport signals in the c-CBL oncoprotein
Abstract
[EN] Most proteins cannot cross the nuclear envelope by diffusion, instead they need to be actively
transported by specific nuclear transport (import or export) receptors that recognize and bind specific
nucleocytoplasmic transport signals in proteins. Nuclear import receptors recognize Nuclear Localization Signals
(NLSs) and transport their cargo proteins to the nucleus, while nuclear export receptors recognize Nuclear Export
Signals (NESs) and transport cargos to the cytoplasm. The best-studied export receptor is CRM1, which mediates
the nuclear export of cargos bearing “leucine-rich” NES motifs. CRM1-mediated nuclear export is crucial for
proper protein localization and to maintain cellular homeostasis. Therefore, CRM1 malfunction can be a trigger
for different human diseases, and identifying CRM1 cargo proteins might be important to better understand related
pathologies. However, the full CRM1 cargo spectrum is not yet completely clear. A global proteomics analysis,
proposed a long list of potential CRM1 cargoes, but many remain to be validated. In the present work, a protein
from this list, c-CBL, was selected for further study, as the mechanisms and signals that might modulate its
subcellular distribution are still unkown. We aimed to identify novel nucleocytoplasmic transport signals in this
protein. For that purpose, in silico predictions and nuclear export assays were carried out. We report here two
novel functional NESs in c-CBL, and discuss the importance of this finding in the context of c-CBL’s transport,
stressing the need for further research on c-CBL’s nucleocytoplasmic transport to better understand and use c-
CBL as a novel target for different therapies. [EU] Proteina gehienek ezin dute gaineztadura nuklearra difusioz zeharkatu, eta nukleoko garraio-
hartzaile espezifikoen bidez igaro behar dute modu aktiboan (inportazioz edo esportazioz). Hartzaile horiek
proteinen garraio nukleozitoplasmatikorako seinale espezifikoak ezagutu eta lotzen dituzte. Zehazki, inportazio-
hartzaileek nukleorako kokapen-seinaleak (NLS) ezagutzen dituzte eta proteinak nukleora garraiatzen dituzte;
esportazio-hartzaileek, berriz, nukleotiko esportazio-seinaleak (NESak) ezagutu eta proteinak zitoplasmara
garraiatzen dituzte. Gehien ikertu den esportazio-hartzailea CRM1 da, “leuzinatan aberatsak diren NESak”
dituzten proteinak zitoplasmara esportatzen dituena. CRM1 bidezko esportazioa ezinbestekoa da proteinen
kokapen egokirako eta zelulako homeostasia mantentzeko. Ondorioz, CRM1-en akatsek zenbait giza gaixotasun
eragin ditzakete. Horregatik, CRM1-en bidez esportatzen diren proteinak identifikatzea garrantzizkoa izan daiteke
horiei loturiko gaixotasunak hobeto ulertzeko. Hala ere, CRM1-en bidez esportatzen diren proteinen espektroa
(zein proteina garraiatzen diren CRM1 bidez) ez da guztiz argia oraindik. Proteomika-analisi global batek CRM1-
en bidez esportatzen diren proteina potentzialen zerrenda proposatu zuen, baina horietako asko balioztatzeke
daude. Lan honetan, zerrendako proteina bat, c-CBL, hautatu zen sakonago ikertzeko. Izan ere, proteina horren
kokapen zelularra eraentzen duten mekanismo eta sekuentziak ezezagunak dira eta beraz, gure helburua proteina
honetan garraio nukleozitoplasmatikorako sekuentzia berriak bilatzea zen. Horretarako, in silico iragarpenak egin
genituen, esportazio-entseguekin batera. Lan honetan bi NES funtzional berri deskribatu dira eta aurkikuntza
honek c-CBL-ren garraioan duen garrantziaz eztabaidatzen da. Azkenik, c-CBL terapia ezberdinetan itu berri gisa
erabili ahal izateko, bere garraioaren inguruko ikerketa gehiagoren beharra azpimarratzen da.