A combination of proteomics, principal component analysis and transcriptomics is a powerful tool for the identification of biomarkers for macrophage maturation in the U937 cell line

The monocyte‐like human histiocytic lymphoma cell line U937 can be induced by phorbol 12‐myristate 13‐acetate (PMA) to undergo differentiation into a macrophage‐like phenotype. We have used two‐dimensional gel electrophoresis (2‐DE), oligonucleotide microarrays and principal component analysis (PCA) to characterize the U937 cell line as a model system for the differentiation of monocytes into macrophages. A total of 226 differentially expressed proteins were found, of which 41 were selected by PCA for identification using matrix‐assisted laser desorption/ionization tandem mass spectrometry. Based on the PCA results, three marker proteins were selected for confirmation of differential expression using Western blot and quantitative real time‐PCR. The selected marker proteins were: gamma interferon inducible lysosomal thiol reductase, cathepsin D and adipocyte‐fatty acid binding protein. All three proved to be good differentiation markers for macrophage maturation of U937 cells as well as peripheral blood‐derived macrophages. The transcriptomics data revealed a large number of additional putative differentiation markers in U937 macrophages, many of which are known to be expressed in peripheral blood‐derived macrophages. These include osteospontin, matrix metalloproteinase 9, and HC‐gp39. Our results show that the characteristics of U937 macrophages resemble those of inflammatory (exudate) macrophages, exemplified by the down‐regulation of 5' nucleotidase and the up‐regulation of leucine aminopeptidase mRNAs. In conclusion, using the powerful combination of transcriptomics, 2‐DE and PCA, our results show that U937 cells differentiated by PMA treatment are an excellent model system for monocyte derived macrophage generation from blood.