NSC348884 cytotoxicity is not mediated by inhibition of nucleophosmin oligomerization

Oligomerization of the nucleolar phosphoprotein nucleophosmin (NPM) is mediated by its N-terminal domain. In acute myeloid leukemia, a frequent NPM mutation occurring at the C-terminus causes NPM delocalization to the cytoplasm. Due to formation of NPM heterooligomers, the wild-type NPM as well as many of NPM interaction partners are also delocalized. Proper localization and function of mislocalized proteins in the cells with mutated NPM may be restored by targeting NPM oligomerization. We introduce a reliable set of complementary methods for monitoring NPM oligomerization in both cell lysates and live cells. Using this methodological background we show that a putative inhibitor of NPM oligomerization, NSC348884, does not prevent formation of NPM oligomers in leukemia cells. Instead, we reveal that the observed cytotoxic effect of NSC348884 is associated with changes in cell adhesion signaling. * NPMwt : wild-type nucleophosmin NPMmut : nucleophosmin with AML-associated mutation type A C21 : Cysteine 21 in nucleophosmin C21A : substitution of C21 to Alanine C21F : substitution of C21 to Phenylalanine Δ25 : nucleophosmin with deletion of the first 25 amino acids Δ100 : nucleophosmin with deletion of the first 100 amino acids Δ117 : nucleophosmin with deletion of the first 117 amino acids G_ : eGFP-labeled protein at the N-terminus R_ : mRFP1-labeled protein at the N-terminus