c-kit D816V Provides a Strong Signal for Myelomastocytic Differentiation and Cluster Formation in Murine Ba/F3 Cells.

The pathologic hallmark of systemic mastocytosis (SM) is differentiation and cluster formation of mast cells (MC) in hematopoietic tissues. The somatic c-kit mutation D816V is detectable in a majority of all SM patients independent of the proliferation-status of MC or subtype (indolent or aggressive) of disease. To investigate the role of c-kit D816V in the pathogenesis of SM, we established a Ba/F3 cell line with doxycycline-inducible expression of c-kit D816V. We found that c-kit D816V provides a strong signal for mast cell differentiation and cluster formation in Ba/F3 hematopoietic progenitor cells without enhancing their growth thereby resembling the clinical presentation of indolent SM (ISM). As assessed by gene chip analysis, induction of c-kit D816V resulted in expression of various differentiation antigens including mouse mast cell protease 5, mi transcription factor, histidine decarboxylase (HDC), secretory granule proteoglycan, IL-4 receptor, ICAM-1, and CD63 consistent with an early phase of mastopoiesis. By contrast, c-kit D816V did neither induce expression of granulo-monocytic antigens such as myeloperoxidase, IL-3 receptor, or GM-CSF receptor, nor expression of ‘late stage’ mast cell antigens such as FcεRI. The c-kit D816V-induced synthesis of histamine in Ba/F3 cells was confirmed by RIA. To examine the role of c-kit D816V in the pathogenesis of mastocytosis, we extended our analysis to bone marrow biopsy sections obtained from patients with ISM. In these experiments, the D816V-mutated form of c-kit was detected more frequently in micro-dissected tryptase-positive MC obtained from dense compact infiltrates (44.2%) than in diffusely spread MC in these patients (22.6%) (p<0.05). In summary, our data establish a role for c-kit D816V in differentiation and cluster formation of neoplastic (mast) cells. Additional genetic hits, apart from c-kit D816V, may be responsible for aggressive growth of MC in advanced MC neoplasms.