胃肠道间质瘤中伊马替尼耐药的信号转导机制

Oncogenic signaling mechanisms in imatinib-resistant gastrointestinal stromal tumor

目的 评价胃肠道间质瘤（GIST）中不同信号通路的特征,并初步探讨与伊马替尼耐药可能相关的信号通路.方法 选取2003年11月至2008年8月间复旦大学附属肿瘤医院收治的5例GIST患者8份手术新鲜标本,检测其KIT和PDGFRa基因突变情况,并采用Western blot法检测Ras/Raf/MAPK和PI3/AKT两种信号通路中的相关蛋白（KIT、P-KIT、MAPK、P-MAPK、p-AKT、p-MTOR、PCNA、BCL2）的表达.结果 伊马替尼治疗有效的3例患者均存在1次突变,其中2例为KIT基因第11外显子缺失突变,另1例为KIT基因第13外显子点突变;1例伊马替尼原发耐药患者无KIT基因突变,1例继发耐药患者存在KIT基因2次突变;所有标本均未见PDGFRa基因突变.伊马替尼耐药的肿瘤标本磷酸化（p）-KIT和p-AKT表达水平强于伊马替尼敏感的肿瘤标本;KIT、MAPK、p-MAPK及p-MTOR在GIST标本中均有较强的表达,其表达强度在伊马替尼耐药标本与敏感标本间并无明显区别;而PCNA和BCL2则在不同治疗时间及不同部位的标本中表达有所差异.结论 Ras/Raf/MAPK和PI3-K/AKT/MTOR两条信号通路在GIST形成过程中起着非常重要的作用：KIT基因2次突变及PI3-K/AKT/MTOR信号通路可能与伊马替尼继发耐药的形成密切相关.

Objective To characterize oncogenic KIT signaling mechanisms in gasrointestinal 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 hospotal.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 particalady relevant for therapeutic targeting in imatinib-resistant GIST.