Born to be exported: COOH-terminal nuclear export signals of different strength ensure cytoplasmic accumulation of nucleophosmin leukemic mutants.

Abstract

Creation of a nuclear export signal (NES) motif and loss of tryptophans (W) 288 and 290 (or 290 only) at the COOH terminus of nucleophosmin (NPM) are both crucial for NPM aberrant cytoplasmic accumulation in acute myelogenous leukemia (AML) carrying NPM1 mutations. Hereby, we clarify how these COOH-terminal alterations functionally cooperate to delocalize NPM to the cytoplasm. Using a Rev(1.4)-based shuttling assay, we measured the nuclear export efficiency of six different COOH-terminal NES motifs identified in NPM mutants and found significant strength variability, the strongest NES motifs being associated with NPM mutants retaining W288. When artificially coupled with a weak NES, W288-retaining NPM mutants are not exported efficiently into cytoplasm because the force (W288) driving the mutants toward the nucleolus overwhelms the force (NES) exporting the mutants into cytoplasm. We then used this functional assay to study the physiologic NH(2)-terminal NES motifs of wild-type NPM and found that they are weak, which explains the prominent nucleolar localization of wild-type NPM. Thus, the opposing balance of forces (tryptophans and NES) seems to determine the subcellular localization of NPM. The fact that W288-retaining mutants always combine with the strongest NES reveals mutational selective pressure toward efficient export into cytoplasm, pointing to this event as critical for leukemogenesis.

• Authors: Niccolò Bolli, Ildo Nicoletti, M Felicetta De Marco, Barbara Bigerna, Alessandra Pucciarini, Roberta Mannucci, Maria Paola Martelli, Arcangelo Liso, Cristina Mecucci, Francesco Fabbiano, Massimo F Martelli, Beric R Henderson, Brunangelo Falini
• Journal: Cancer research (Cancer Res) Vol. 67 Issue 13 Pg. 6230-7 (Jul 01 2007) ISSN: 0008-5472 [Print] United States
• PMID: 17616680 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Npm1 protein, mouse
• Nuclear Proteins
• Nucleophosmin

Topics

• Amino Acid Motifs
• Animals
• Cell Transformation, Neoplastic
• Cytoplasm (metabolism)
• DNA Mutational Analysis
• Fibroblasts (metabolism)
• Gene Expression Regulation, Neoplastic
• Leukemia, Myeloid, Acute (metabolism)
• Mice
• Microscopy, Fluorescence
• Mutation
• NIH 3T3 Cells
• Nuclear Proteins (chemistry, genetics)
• Nucleophosmin
• Plasmids (metabolism)
• Protein Structure, Tertiary