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Endothelial cells (ECs) express 2 members of the cadherin family, VE and N-cadherin. Although VE-cadherin induces EC homotypic adhesion, N-cadherin function in ECs remains largely unknown. EC-specific inactivation of either VE or N-cadherin leads to early fetal lethality suggesting that these cadherins play a nonredundant role in vascular development. We report here that VE-cadherin negatively controls junctional localization and expression of N-cadherin by limiting p120-catenin availability and reducing β-catenin transcriptional activity. Using EC lines expressing either VE or N-cadherin we found that both cadherins inhibit cell proliferation and apoptosis. Both trigger the phosphatidylinositol-3-OH-kinase (PI3K)-AKT-Forkhead-box protein-O1 (FoxO1) pathway and reduce β-catenin transcriptional activity. The extent of signaling correlates with the total level of cadherins regardless of the type of cadherin expressed. In contrast, basal and fibroblast growth factor (FGF)-induced cell motility is promoted by N-cadherin and strongly inhibited by VE-cadherin. This opposite effect is partly because of the ability of VE-cadherin to associate with FGF receptor and the density-enhanced phosphatase-1 (Dep-1) which, in turn, inhibits receptor signaling. We conclude that VE and N-cadherin have both additive and divergent effects on ECs. Differences in signaling are due, in part, to cadherin association with growth factor receptors and modulation of their downstream signaling.

Nucleophosmin (NPM) exon-12 mutations occur in 50% to 60% of adult acute myeloid leukemia (AML) with normal karyotype and are predictors of favorable prognosis. We evaluated bone marrow or peripheral blood samples from 450 adult patients with AML of the GIMEMA (Gruppo Italiano Malattie Ematologiche Maligne dell'Adulto)/AML12 EORTC (European Organization for Research and Treatment of Cancer) trial to (1) search for new exon-12 NPM mutations; (2) determine whether NPM immunostaining on paraffin-embedded biopsies predicts NPM mutations; and (3) investigate altered nucleocytoplasmic NPM traffic in primary AML cells. Fourteen NPM mutations, including 8 new variants, were identified. All 200 AML cases expressing cytoplasmic NPM (NPMc(+) AML) carried NPM mutations. None of the 250 cases with nucleus-restricted NPM (NPMc(-) AML) was mutated. At the C-terminus, NPM leukemic mutants carried mutations of only tryptophan 290 or of both tryptophans 288 and 290 and a new nuclear export signal (NES) motif, which appear to underlie their nuclear export. The specific Crm1/exportin-1 inhibitor leptomycin-B relocated NPM mutants from cytoplasm to nucleus of primary NPMc(+) AML cells, demonstrating that nuclear export is NES dependent. NPM mutants bound and recruited wild-type NPM into leukemic cell cytoplasm. Because alterations at C-terminus of leukemic NPM mutants are similar, immunohistochemistry detects all exon-12 NPM mutations and is a valuable, inexpensive tool in the diagnostic-prognostic work-up of patients with AML with normal karyotype.

Approximately one third of acute myeloid leukemias (AMLs) are characterized by aberrant cytoplasmic localization of nucleophosmin (NPMc+ AML), consequent to mutations in the NPM putative nucleolar localization signal. These events are mutually exclusive with the major AML-associated chromosomal rearrangements, and are frequently associated with normal karyotype, FLT3 mutations, and multilineage involvement. We report the gene expression profiles of 78 de novo AMLs (72 with normal karyotype; 6 without major chromosomal abnormalities) that were characterized for the subcellular localization and mutation status of NPM. Unsupervised clustering clearly separated NPMc+ from NPMc- AMLs, regardless of the presence of FLT3 mutations or non-major chromosomal rearrangements, supporting the concept that NPMc+ AML represents a distinct entity. The molecular signature of NPMc+ AML includes up-regulation of several genes putatively involved in the maintenance of a stem-cell phenotype, suggesting that NPMc+ AML may derive from a multipotent hematopoietic progenitor.