A NOVEL GAIN-OF-FUNCTION MUTATION OF C-KIT GENE IN GASTROINTESTINAL STROMAL TUMORS

Background & Aims: The c-kit gene encodes a receptor tyrosine kinase ( KIT). Recently, we found gain-of-function mutations of the c-hit gene in gastrointestinal stromal tumors (GISTs). All mutations were confine d within the 11 amino acids (Lys-550 to Val-560) in the juxtamembrane domain, but one GIST showed a novel deletion-type mutation at codon 57 9 (Asp) in the juxtamembrane domain. The aim of this study was to clar ify whether the mutation is activating. Methods: Mutant c-kit cDNA was transfected into an interleukin 3 (IL-3)-dependent Ba/F3 murine lymph oid cell line, and the magnitude of autophosphorylation of the mutant KIT was examined with or without stem cell factor (SCF), a ligand of K IT. An in vitro kinase assay was also performed. the biological behavi or of the transfectant was estimated by both an in vitro proliferation assay and in vivo transplantation to nude mice. Results: The mutant K IT exhibited constitutive phosphorylation and strong kinase activity w ithout SCF. The transfectant grew autonomously without IL-3 and SCF, a nd it formed tumors in nude mice. Conclusions: Deletion at codon 579 ( Asp) in the juxtamembrane domain of the c-kit gene is a novel gain-of- function mutation other than the region between Lys-550 and Val-560.