KIT GNNK splice variants: Expression in systemic mastocytosis and influence on the activating potential of the D816V mutation in mast cells.
Stem cell factor-dependent KIT activation is an essential process for mast cell homeostasis. The two major splice variants of KIT differ by the presence or absence of four amino acids (GNNK) at the juxta-membrane region of the extracellular domain. We hypothesized that the expression pattern of these variants differ in systemic mastocytosis, and that transcripts containing the KIT D816V mutation segregate preferentially to one GNNK variant. A quantitative real-time PCR assay to assess GNNK- and GNNK+ transcripts from bone marrow mononuclear cells was developed. The GNNK-/GNNK+ copy number ratio showed a trend towards a positive correlation with % neoplastic mast cell involvement, and KIT D816V containing transcripts displayed a significantly elevated GNNK-/GNNK+ copy number ratio. Relative expression of only the GNNK- variant correlated with increasing % neoplastic mast cell involvement. A mast cell transfection system revealed that the GNNK- isoform of wild type KIT was associated with increased granule formation, histamine content and growth. When accompanying the KIT D816V mutation, the GNNK- isoform enhanced cytokine-free metabolism and moderately reduced sensitivity to the tyrosine kinase inhibitor, PKC412. Together, these data suggest that neoplastic mast cells favor a GNNK- variant predominance, which in turn enhances the activating potential of the KIT D816V mutation and thus may influence therapeutic sensitivity in systemic mastocytosis.
Copyright © 2013 ISEH – Society for Hematology and Stem Cells. Published by Elsevier Inc. All rights reserved.