| Nasopharyngeal carcinoma (NPC) is one of the most common malignant tumors in South China and Southeast Asia. As many other tumors development, NPC also involves multiple genes and stages, including some oncogenes and antioncogenes. However, till now, its carcinogenic molecular mechanism is not well clarified. Several studies have shown loci of high loss of heterozygosity (LOH) in NPC are located at 3p14-25, 9p, 11q et al. In particular, the frequency of LOH at 3p21-26 reaches to 66.70%. It suggested some known or unknown NPC-associated genes harbored in this region, which may correlate with the occurrence and development of NPC. Therefore, it is essential of cloning these tumor-associated genes in NPC.On the other hand, with the progress and actualization of Human Genome Project, large amount of sequences, maps and functional researchdata are accumulated and deposited into public databases. Bioinformatic approaches play a more and more important role in gene cloning and gene identification. Since expressed sequence tags (ESTs) represented the expressed genes, EST markers mapped at 3p14.2 and 3p21 were screened for identifying the NPC-associated genes through differential expression analysis. By using RT-PCR and Northern blots, First ESTs at 3pl4.2 and 3p21 were detected for differentially expressed gene fragments in nasopharyngeal biopsies and NPC cell lines, which can be taken as candidates of tumor suppressor genes for further studies.By differential expression analysis with RT-PCR, 2 ESTs were found to be down-regulated expression in primary NPC biopsies and NPC cell lines at 3p21. The rate of down-regulated expression of EST N31985 was 47.06% (16/34) in primary NPC and 60%(3/5) in NPC cell lines (CNE2, HONE1 and HNE1). In 3 cases of primary culture NPC samples, 2 of 3 cases whose expression of N31985 were down-regulated grew more rapidly. However, the proliferation and growth of the other case was slow, as its expression was normal. The results of the current study strongly suggest that N31985 candidate a gene might be a tumor suppressor gene. The rate of down-regulated Expression of EST BG772301 was 41.18% (14/34) in primary NPC, 20%(l/5) in NPC cell lines (CNE2) and in 1 leukaemia cell line(HL-60).Result of MTETmArray2 Northern Blot showed that the hybridizationpositive signal of EST N31985 was weaker in 8 tumor cell lines than that in normal tissues. The weakest positive signal was in Burkitt's lymphoma cell line (Daudi). Its down-regulated expression was not noly in carcinoma (NPC), but also in sarcoma (lymphoma). Hybridization positive signal of BG772301 was weaker in 8 tumor cell lines than that in normal tissues by Northern blot hybridization. There was no positive expression signal of BG772301 in leukaemia cell line (HL-60). Those suggest that the 2 ESTs might candidate novel tumor suppressor genes closely associated with NPC and many other tumor cell lines.In order to isolate and clone the negatively-related NPC gene, plasmid cDNA sequencing and 5', 3'-RACE were used to get 2 full length cDNA sequences, 1271bp and 2377bp respectively. One was named as STGC3 (EST N31985) gene (GenBank accession number AY078383), the other named as NPCEDRG (EST BG772301) gene (GenBank accession number AF538150) by HUGO. STGC3 contains an open reading frame of 438bp, encoding 146 amino acids. By Blasting with lately released HTGS sequence (NT 034535), STGC3 gene was mapped on chromosome 3p21. It was made up of 1 exon. NPCEDRG gene contains an open reading frame of 507bp, encoding 169 amino acids. By Blasting with lately released HTGS sequence (NT 022439), NPCEDRG gene was mapped on chromosome 3p21. It was made up of 6 exons and 5 introns.In order to characterize STGC3 and NPCDERG, PEGFP-C2/STGC3and PEGFP-C2/NPCEDRG fusion mammalian expression vectors were constructed and introduced into the. COS7 and CNE2 cell lines by lipofectin transfection. Observation under the fluorescent microscope after 24-48 hours of transfection showed that STGC3 protein expressed in cellular nuclei...
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