Activity of Fgr protein-tyrosine kinase is reduced in neutrophils of patients with myelodysplastic syndromes and chronic myelogenous leukemia.

The Fgr protein-tyrosine kinase, p55(c-fgr), is specifically expressed and functions in cells of myelomonocytic lineages. We examined levels of expression and enzymatic activity of p55(c-fgr) peripheral blood neutrophils of patients with myelodysplastic syndromes (MDS) and chronic myelogenous leukemia (CML) by comparison with those of normal individuals. While neutrophils of eight normal subjects gave uniform results, the specific enzymatic activity of p55(c-fgr), a ratio of the total kinase activity versus the protein level was reduced in seven out of eight patients with MDS and all of five patients with CML. The specific kinase activity of p55(c-fgr) correlated significantly with the activity of neutrophil alkaline phosphatase (NAP) which has been considered to be a marker of neutrophil maturity (r=0.568, P<0.01). The reduced activity of this tyrosine kinase was considered to be a biological parameter for immaturity and to reflect dysfunction of neutrophils of patients with MDS and with CML.