The c-kit proto-oncogene encodes a receptor tyrosine kinase that is known to play a crucial role in hematopoiesis, especially in mast cell growth and differentiation. Although a number of dominant loss-of- function mutations of c-kit gene have been well characterized in mice, rats, and humans, little is known about the c-kit mutations contributing to ligand-independent activation of the c-kit receptor tyrosine kinase (KIT). In a murine mastocytoma cell line, P-815, KIT has been found to be constitutively phosphorylated on tyrosine and activated in a ligand-independent manner. Sequencing of the whole coding region of c-kit cDNA showed that c-kit cDNA of P-815 cells carries a point mutation in codon 814, resulting in amino acid substitution of Tyr for Asp. Murine wild-type c-kit cDNA and mutant- type c-kit cDNA encoding Tyr in codon 814 were expressed in cells of a human embryonic kidney cell line, 293T. In the transfected cells, mutant-form KITTyr814 was strikingly phosphorylated on tyrosine and activated in immune complex kinase reaction regardless of stimulation with a ligand for KIT (stem cell factor), whereas tyrosine phosphorylation and activation was barely detectable in wild-form KIT. The data presented here provide evidence for a novel activating mutation of c-kit gene that might be involved in neoplastic growth or oncogenesis of some cell types, including mast cells.
Expression of KIT Receptor Tyrosine Kinase in Endothelial Cells of Juvenile Brain Tumors
