An isolated human nucleophosmin protein (NPM) comprising a loss of a tryptophan residue at position 290 and comprising a signal motif of nuclear export (NES) beginning at position 287 of the human nucleophosmin protein, wherein the NES comprises the amino acid sequence YxxxYxxYxY (SEQ ID No 56) wherein Y is a hydrophobic amino acid selected from the group consisting of leucine, isoleucine, methion