Objective: To 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.
Methods: The 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.
Results: Three 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.
Conclusions: Ras/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.