Colony-stimulating factor-1 (CSF-1) receptor-mediated macrophage differentiation in myeloid cells: a role for tyrosine 559-dependent protein phosphatase 2A (PP2A) activity

M1 myeloid cells transfected with the wild-type (WT) colony-stimulating fac tor-1 (CSF-1) receptor (CSF-1R; M1/WT cells) undergo CSF-1-dependent macrop hage differentiation. By mutation studies, we have provided prior evidence that tyrosine 559 in the CSF-1R cytoplasmic domain governs the Src-dependen t differentiation pathway. Further components of this pathway were then sou ght. We report that the extent of CSF-1-mediated tyrosine phosphorylation o f protein phosphatase 2A (PP2A), and the associated loss of its activity we re reduced in MI cells transfected with the CSF-IR with a tyrosine-to-pheny lalanine mutation at position 559 (M1/559 cells), compared with the corresp onding responses in CSF-1-treated M1/WT cells. This evidence for an involve ment of a reduction in PP2A activity in the differentiation process was sup ported by the restoration of the defect in the CSF-1-mediated differentiati on of M1/559 cells by the addition of the PP2A inhibitor, okadaic acid. It was also found that the degree of activation of extracellular-signal-regula ted kinase (ERK) activities by CSF-1 was reduced in M1/559 cells, suggestin g their involvement in the differentiation process. These data suggest that PP2A and ERK form part of the Src-dependent signal-transduction cascade go verning CSF-1-mediated macrophage differentiation in M1 cells.