Kinase domain mutation of NTRK3 gene is uncommon in gastric carcinomas

Abstract

Protein kinases regulate intracellular signal-trans-duction pathway mediating cell proliferation, differ-entiation and survival [1]. Protein kinase family isone of the most frequently mutated gene familyfound in human cancers and thus are potentialtherapeutic targets for human cancers [1]. Neuro-trophic tyrosine kinase receptor type 3 (NTRK3),also referred to as TrkC, is a receptor tyrosine kinaseand plays an important role in the development ofneural tissues [2]. NTRK3 expression is not re-stricted to neural tissues, and various types of tissues,including the gastrointestinal epithelia (stomach,small intestine and colon), have also been shown toexpress NTRK3 [3]. These data suggest a role ofNTRK3 in the growth and maintenance of thegastrointestinal cells.Recently, Bardelli et al. [4] analyzed 138 tyrosinekinase genes in 147 colorectal cancer tissues for thedetection of the somatic mutations. They identified46 mutations in 14 genes. Of those, seven genes(NTRK3,FES,KDR,EPHA3,NTRK2, MLK4andGUCY2F) were mutated in more than one tumor.NTRK3 gene mutations were found in six (4.1%) ofthe 147 colorectal cancers. Of note, the NTRKmutations were exclusively identified in the kinasedomain. Because NTRK3 is expressed in gastricepithelium as well as in colorectal epithelium [3], wehypothesized that gastric carcinomas might alsoharbor NTRK3 mutation. To see whether alterationof NTRK3 gene is involved in the tumorigenesis ofgastric carcinoma, we analyzed NTRK3 gene for thedetection of somatic mutations in gastric carcinomasby polymerase chain reaction (PCR)-based singlestrand conformation polymorphism (SSCP) assay.We analyzed methacarn-fixed tissues of 140 gas-tric carcinomas. All of the patients of the cancerswere Asians (Koreans). The gastric carcinomasconsisted of 60 diffuse-type, 49 intestinal-type and31 mixed-type gastric adenocarcinomas by Lauren’sclassification, and 25 early and 115 advanced gastriccarcinomas according to the depth of invasion.Malignant cells and normal cells from the samepatients were selectively procured from hematoxylinand eosin-stained slides using a 30G1/2 hypodermicneedle (Becton Dickinson, Franklin Lakes, NJ)affixed to a micromanipulator, as described pre-viously [5]. DNA extraction was performed by amodified single-step DNA extraction method [5].Because NTRK3 mutations were previously de-tected only in the exons 15