Mechanism of carcinogenesis by the mutations of c-kit gene

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The c-kit receptor tyrosine kinase (KIT) is constitutively activated by naturally occurring mutations in either the juxtamembrane domain or the kinase domain. Although the juxtamembrane domain mutations led to ligand-independent KIT dimerization, the kinase domain mutations (Asp^<814>* Val or Tyr) did not. In an effort to determine if the kinase domain mutant could transfer oncogenic signaling without receptor dimerization, we have constructed the truncated types of c-kit^<wild> and c-kit^<Tyr814>cDNAs (c-kit^<Del-wild> and c-kit^<Del-Try814> cDNAs, respectively), in which ligand-binding and ligand induced dimerization domains were deleted. When c-kit^<Del-wild> and c-kit^<Del-Tyr814> genes were introduced into a murine interleukin (IL)-3-dependent cell line Ba/F3, KIT^<Del-Tyr814> was constitutively phosphorylated on tyrosine and activated., whereas KIT^<Del-wild> was not. In addition, Ba/F3 cells expressing KJT^<Del-Tyr814> (Ba/F3^<Del-Tyr814>) grew in suspension culture wihout the a … More ddition of exogenous growth factor, whereas Ba/F3 cells expressing KIT^<Del-wild> (Ba/F3^<Del-wild>) required IL-3 for growth. To test the possibility that KfIT^<Tyr814> may yield homodimeric and heterodimeric association of KIT not in the extracellular region, 293T cells were transfected with the combinations of various c-kit genes, and then the association of KIT was examined. KIT^<Tyr814> was found to be co-immunoprecipitated with KiT by an ACK2 monoclonal antibody directed against the extracellular domain of KIT.Moreover, KIT was constitutively associated with a chimericFMS/KIT^<Tyr814> receptor containing the ligand-binding and receptor dimerization domain of c-fms receptor (FMS) fused to the transmembrane and cytoplasmic domain of KIT^<Tyr814>, but not with a chimeric EMS/KIT^<wild> receptor even after stimulation with FMS-ligand. These results suggest that constitutively activating mutation of c-kit at the Asp^<814> codon may cause a conformation change that leads to receptor self-association not in the extracellular domain, and that the receptor self-association of the Asp^<814> mutant may be important for activation of downstream effectors that are required for factor-independent growth and tumorigenicity. Less