Gain-of-function mutation at the extracellular domain of KIT in gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal tu mours of the human gastrointestinal tract. Previous studies of GISTs found gain-of-function mutations of the c-kit gene, which encodes a receptor tyro sine kinase (KIT). All the mutations were confined to exon II, which encode s the juxtamembrane domain. By further examination of the whole coding regi on of c-kit complementary DNA in 35 GISTs, two were found to show the ident ical mutation at exon 9, which encodes the extracellular domain, The aims o f the present study were to examine the frequency of the extracellular doma in mutation and to determine whether the mutation is a gain-of-function typ e or not, Genomic DNA was extracted from paraffin-embedded tissues of 133 G ISTs and exon 9 of the c-kit gene was amplified by polymerase chain reactio n. Screening of the mutation was carried out by single-strand conformation polymorphism analysis and direct sequencing was done. Mutant c-kit cDNA was transfected into 293T human embryonic kidney cells and the magnitude of au tophosphorylation of the mutant KIT was examined with or without the ligand of KIT, stem cell factor (SCF), In total, seven GIST cases (approximately 5%) were found with the identical mutation at exon 9, The mutant KIT exhibi ted constitutive autophosphorylation without SCF stimulation. The prognosis of the patients with the extracellular domain mutation was comparable to t hat of the patients with the juxtamembrane domain mutation, Copyright (C) 2 001 John Wiley & Sons, Ltd.