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目的：在明确 7q32- ter区域等位基因杂合性丢失最小共同缺失区位于以 D7S509为中心的 D7S500- D7S509- D7S495的基础上，筛选和克隆位于该区内鼻咽癌相关的候选抑瘤基因。方法：应用定位—候选克隆策略筛选位于该最小共同缺失区的 3′末端 ESTs(expressed sequence tags,ESTs),RT- PCR和 Northern杂交筛选出在鼻咽癌细胞株和活检组织中表达下调的 ESTs,采用 cDNA克隆测序和生物信息学资源获取候选 EST的全长 cDNA。 Southern杂交和甲基化分析研究候选基因表达下调的机制。结果：筛选 D7S500- D7S495区域内的 12个代表新基因的 3′末端 ESTs序列，发现一个 EST（ AI290024）在鼻咽癌细胞株及 50％（ 6/12）的鼻咽癌活检组织中表达下调， Multiple Tissue Northern(MTNTM) Blot杂交结果显示该 EST在心、肝、肾等多种组织中存在大小 2.0 kb的转录本。通过测定包含该 EST的 cDNA克隆，获得该新基因（命名为 NAG- 22基因） 2.3 kb转录本的全长 cDNA(GenBank登录号： AF247820),编码 77AA，含有 disintegrin的结构域。 NAG22在 NPC中表达下调的机制不是高甲基化和基因拷贝数的丢失。结论： NAG22是定位于 7q32- ter最小共同缺失区的一个与鼻咽癌相关的抑瘤基因候选者。
OBJECTIVE: To screen and clone nasopharyngeal carcinoma-associated candidate tumor suppressor genes in this region based on D7S500-D7S509-D7S495, a D7S509-D7S495 centered on D7S509, . Methods: The ESTs expressed in the 3 ’end of the smallest common deletion region were screened by the strategy of location-candidate cloning. The ESTs down-regulated in NPC cell lines and biopsies were screened by RT-PCR and Northern blotting , CDNA cloning sequencing and bioinformatics resources were used to obtain full-length cDNAs of candidate ESTs. Southern hybridization and methylation analysis of candidate gene expression down regulation mechanism. Results: Twelve ESTs representing the new gene in 12 regions of D7S500-D7S495 were screened and one EST (AI290024) was found to be downregulated in nasopharyngeal carcinoma cell lines and in 50% (6/12) NPC tissues , Multiple Tissue Northern (MTNTM) Blot hybridization results showed that this EST in the heart, liver, kidney and other tissues exist 2.0 kb in size transcripts. The full-length cDNA (GenBank accession number: AF247820) encoding the 2.3 kb transcript of the new gene (designated as NAG-22 gene) was obtained by assaying the cDNA clone containing the EST and encoding 77AA, a domain containing disintegrin. The mechanism by which NAG22 is down-regulated in NPC is not hypermethylation and loss of gene copy number. Conclusion: NAG22 is a nasopharyngeal carcinoma-associated tumor suppressor gene candidate located in the 7q32-ter minimal common deletion region.