OBJECTIVETo characterize oncogenic KIT signaling mechanisms in gastrointestinal stromal tumor(GIST), and to determine which signaling pathway might be of potential relevance to imatinib acquired resistance.

METHODSThe mutations of KIT and PDGFRa gene were evaluated and KIT downstream signaling profiles were evaluated in 8 specimen from 5 GIST patients who were evaluated treated between 2003 and 2008 in our hospital. Biochemical inhibition of the expression of related proteins in Ras/Raf/MAPK and PI3-K/AKT pathways, such as KIT, mitogen-activated protein kinase(MAPK),mammalian target of rapamycin(MTOR), AKT, Proliferating cell nuclear antigen (PCNA) and BCL-2, were determined by Western blotting for protein activation.

RESULTSThree cases who showed response to imatinib carried primary mutations in KIT gene, with 2 cases possessing mutation in exon 11, 1 case in exon 13. One case with imatinib-resistance developed KIT secondary mutation, but all the cases had no PDGFRa mutation. p-KIT and p-AKT expressions were higher in the samples of imatinib-resistant GIST than those of imatinib-responsive GIST. Total KIT, MAPK, p-MAPK, p-MTOR expressions were strong and comparable in all varied GISTs, which had no significant difference between imatinib-resistant and imatinib-responsive samples. PCNA and BCL-2 expression varied in samples of different therapy cycles and different location.

CONCLUSIONSRas/Raf/MAPK and PI3-K/AKT/MTOR pathways are essential to GIST pathogenesis. The KIT secondary mutation and PI3-K/AKT/MTOR pathway are particularly relevant for therapeutic targeting in imatinib-resistant GIST.