Both carboxy-terminus NES motif and mutated tryptophan(s) are crucial for aberrant nuclear export of nucleophosmin leukemic mutants in NPMc+ AML.
We recently identified aberrant cytoplasmic expression of nucleophosmin (NPM) as the immunohistochemical marker of a large subgroup of acute myeloid leukemia (AML) (about one-third of adult AML) that is characterized by normal karyotype and mutations occurring at the exon-12 of the NPM gene. In this paper, we have elucidated the molecular mechanism underlying the abnormal cytoplasmic localization of NPM. All 29 AML-associated mutated NPM alleles so far identified encode abnormal proteins which have acquired at the C-terminus a nuclear export signal (NES) motif and lost both tryptophan residues 288 and 290 (or only the residue 290) which determine nucleolar localization. We show for the first time that both alterations are crucial for NPM mutant export from nucleus to cytoplasm. In fact, the cytoplasmic accumulation of NPM is blocked by leptomycin-B and ratjadones, specific exportin-1/Crm1-inhibitors, and by reinsertion of tryptophan residues 288 and 290, which respectively relocate NPM mutants in the nucleoplasm and nucleoli. NPM leukemic mutants in turn recruit the wild-type NPM from nucleoli to nucleoplasm and cytoplasm. These findings indicate that potential therapeutic strategies aimed to retarget NPM to its physiological sites will have to overcome 2 obstacles, the new NES motif and the mutated tryptophan(s) at the NPM mutant C-terminus.
Falini
Brunangelo
B
Institute of Hematology, University of Perugia, 06122 Perugia, Italy. faliniem@unipg.it
Bolli
Niccolò
N
Shan
Jing
J
Martelli
Maria Paola
MP
Liso
Arcangelo
A
Pucciarini
Alessandra
A
Bigerna
Barbara
B
Pasqualucci
Laura
L
Mannucci
Roberta
R
Rosati
Roberto
R
Gorello
Paolo
P
Diverio
Daniela
D
Roti
Giovanni
G
Tiacci
Enrico
E
Cazzaniga
Giovanni
G
Biondi
Andrea
A
Schnittger
Suzanne
S
Haferlach
Torsten
T
Hiddemann
Wolfgang
W
Martelli
Massimo F
MF
Gu
Wei
W
Mecucci
Cristina
C
Nicoletti
Ildo
I
D021581:Active Transport, Cell Nucleus / Q000235:genetics*; D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D007938:Leukemia / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D049790:Nuclear Export Signals / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D000090243:Nucleophosmin; D014162:Transfection; D014364:Tryptophan / Q000235:genetics*
C000716967:NPM1 protein, human; D049790:Nuclear Export Signals; D009687:Nuclear Proteins; D000090243:Nucleophosmin; D014364:Tryptophan