The Kit-activating mutation D816V enhances stem cell factor-dependent chemotaxis

The D816V mutation of c-kit has been detected in patients with mastocytosis . This mutation leads to constitutive tyrosine kinase activation of Kit. Be cause stem cell factor (SCF), the ligand for Kit (CD117(+)), is a chemoattr actant for CD117+ cells and one feature of mastocytosis is an abnormal coll ection of mast cells in tissues derived from CD34(+)CD117(+) mast cell prec ursors, the hypothesis was considered that the D816V mutation would enhance chemotaxis of these precursor cells. Constructs encoding wild-type Kit or Kit bearing the D816V mutation were transfected into Jurkat cells, labeled with Calcein-AM, and migration to SCF assessed in the presence or absence o f tyrosine kinase inhibitors. Chemotaxis to SCF was enhanced in D816V trans fectants compared to wild-type Kit transfectants (P < .002). Migration of b oth transfectants was inhibited by tyrosine kinase inhibitors, although D81 6V transfectants were more sensitive. Chemotaxis was next performed on CD34 (+)CD117(+) circulating mast cell precursors obtained from patients with ma stocytosis. Analysis of prechemotaxis and migrated cells showed that wherea s less than 10% in the prechemotaxis sample had the D816V mutation, 40% to 80% of migrated cells had this mutation. These results demonstrate that the D816V Kit mutation enhances chemotaxis of CD117(+) cells, offering one exp lanation for increased mast cells observed in tissues of patients with mast ocytosis.