Control of cyclin B1 localization through regulated binding of the nuclear export factor CRM1.
Activation of the Cyclin B/Cdc2 kinase complex triggers entry into mitosis in all eukaryotic cells. Cyclin B1 localization changes dramatically during the cell cycle, precipitously transiting from the cytoplasm to the nucleus at the beginning of mitosis. Presumably, this relocalization promotes the phosphorylation of nuclear targets critical for chromatin condensation and nuclear envelope breakdown. We show here that the previously characterized cytoplasmic retention sequence of Cyclin B1, responsible for its interphase cytoplasmic localization, is actually an autonomous nuclear export sequence, capable of directing nuclear export of a heterologous protein, and able to bind specifically to the recently identified export mediator, CRM1. We propose that the observed cytoplasmic localization of Cyclin B1 during interphase reflects the equilibrium between ongoing nuclear import and rapid CRM1-mediated export. In support of this hypothesis, we found that treatment of cells with leptomycin B, which disrupted Cyclin B1-CRM1 interactions, led to a marked nuclear accumulation of Cyclin B1. In mitosis, Cyclin B1 undergoes phosphorylation at several sites, a subset of which have been proposed to play a role in Cyclin B1 accumulation in the nucleus. Both CRM1 binding and the ability to direct nuclear export were affected by mutation of these phosphorylation sites; thus, we propose that Cyclin B1 phosphorylation at the G2/M transition prevents its interaction with CRM1, thereby reducing nuclear export and facilitating nuclear accumulation.
Yang
J
J
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710 USA.
Bardes
E S
ES
Moore
J D
JD
Brennan
J
J
Powers
M A
MA
Kornbluth
S
S
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D019926:Cyclin B / Q000235:genetics / Q000378:metabolism*; D056744:Cyclin B1; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D028884:Karyopherins; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014981:Xenopus; D014982:Xenopus laevis; D020931:ran GTP-Binding Protein; D000097606:Exportin 1 Protein
D002352:Carrier Proteins; D019926:Cyclin B; D056744:Cyclin B1; D005231:Fatty Acids, Unsaturated; D006153:Guanosine Diphosphate; D047908:Intracellular Signaling Peptides and Proteins; D028884:Karyopherins; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D020931:ran GTP-Binding Protein; D000097606:Exportin 1 Protein; C534699:CCNB1 protein, human; C534700:Ccnb1 protein, mouse; C534701:Ccnb1 protein, rat; C015482:protein kinase modulator; C038753:leptomycin B