The Effects of Colony-Stimulating Factor-1 Receptor Tyrosine Kinase Mutations on Macrophage Motility and Functionality
Bazzell, Brian G.
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Macrophages play vital roles in normal tissue development and immune function, but also are involved in the pathogenesis of many diseases. Colony-stimulating factor 1 (CSF-1) helps regulate macrophage proliferation, differentiation, and motility by binding and signaling via the CSF-1 receptor tyrosine kinase (CSF-1R). The CSF-1R has seven tyrosine residues (denoted by Y) that are known to be phosphorylated following CSF-1 binding; several are involved in macrophage functionality. In this study tyrosines 721 (Y721) and 706 (Y706), believed to play roles in macrophage motility, are compared to the wild-type receptor (WT) and to a receptor that only allows cell survival (DAB). To look at motility, cells were globally stimulated with CSF-1; the Y721F, Y706F, and DAB mutants all demonstrated significantly reduced ruffling compared to the WT, which was indicative of reduced macrophage movement. In addition, the ability of the mutants to migrate across an endothelial barrier was also analyzed; results indicated that DAB mutants migrated independent of the cytokine tumor necrosis factor alpha (TNFα). The differentiation state of the cell lines, indicative of their being more macrophage-like or monocyte-like, was hypothesized to be the cause. To test this, the ability of each mutant to internalize particles via phagocytosis was investigated. While not statistically significantly different, the WT seemed to phagocytose more than the mutants. DAB cells were then stimulated with a well-characterized inducer of differentiation, phorbol 12-myristate 13-acetate (PMA). PMA-treated DAB macrophages were found to act more like the WT, though further analysis is needed to verify this. These results suggest that Y721 and Y706 are required for CSF-1 induced macrophage function, and that the differentiation state of each mutant may be playing a significant role in their function.