Nucleophosmin Is Required for Macrophage Function and Maturation.

Abstract 238

Nucleophosmin (NPM1) is a multifunctional phosphoprotein predominantly localized in the nucleolus that is involved in numerous cellular processes. The NPM1 gene is frequently a target of genetic alteration in hematological tumors and recent published reports have highlighted the importance of NPM1 in malignancies that affect predominantly the myeloid lineage. Complete inactivation of Npm1 in the mouse disrupts primitive hematopoiesis and results in embryonic lethality. Npm1 heterozygosity produces features similar to those of MDS patients, and can progress to overt leukemia. Here we generated a conditional mousemutant to inactivate Npm1 in the myeloid compartment crossing mice carrying a floxed conditional allele of Npm1 (Npm1^fl/fl) with the MRP8-Cre transgenic mouse model. Specific deletion of the Npm1 allele in Npm1^fl/fl;MRP8-Cre+ mice resulted in complete loss of Npm1 at the protein level in 40% of peritoneal macrophages analyzed by immunofluorescence. In vitro analysis demonstrates that Npm1 deletion altered peritoneal macrophage functions and influenced monocytic differentiation in Npm1^fl/fl;MRP8-Cre+ mice. Specifically we demonstrate that (i) superoxide production was significantly attenuated over time in Npm1^fl/fl;MRP8-Cre+ compared with Npm1^fl/fl;MRP8-Cre- macrophages; (ii) The chemotactic response was decreased by up to 46% ± 9.6 in Npm1^fl/fl;MRP8-Cre+ macrophages when compared to controls; and (iii) Phagocytic index of Npm1^fl/fl;MRP8-Cre+ macrophages dropped to 40% of that for the control Npm1^fl/fl;MRP8-Cre- macrophages. Analysis of monocyte transcriptional regulators revealed a significant reduction of Maf-b and Irf-8 mRNA expression in Npm1 deficient macrophages, demonstrating an altered maturation process in the absence of Npm1. Our analysis demonstrates that Npm1 loss in the myeloid compartment affects macrophage function and profoundly alters gene expression patterns required for proper monocyte/macrophage development and maturation.