Gene Chip Technology For Nasopharyngeal Carcinoma And Its Sensitivity To Radiotherapy

Nasopharyngeal carcinoma (NPC), most of them are poorly differentiated, is one of epithelial origin malignant tumors. The cancer cells will be metastasis in the lymph dens covering the whole body, and the death rate is very high. In some regions, notably the southern parts of China, this cancer occurs in an endemic form with an incidence10-to30-fold higher than the other regions. The etiology of NPC involves multiple factors including genetic susceptibility, exposure to chemical carcinogens, and Epstein-Barr virus (EBV) infection. Radiotherapy is the major treatment modality for NPC, but in some cases, the disease is radiation resistant. The5-year survival rate after treatment is only50-60%. Hence, radiation resistance remains a serious obstacle to successful treatment in many cases. This study aims to screen the differently expressed genes based on cDNA microarrays NPC, then to estimate the probably mechanism of NPC radiation resistance.The total RNA of20NPC patient biopsy specimens, containing8radiation sensitive NPC and12radiation resistant NPC, and a pool of nasopharyngeal chronic inflammation (NPCI) tissues, as common reference for microarray experiments, was isolated by Trizol and then hybridized through cDNA Expression Profiling Panels. Then the microarrays were scanned using ScanArray4000Software.The method of Significance Analysis of Microarrays (SAM, version3.02) was performed involving one class comparison. Nine genes were found significantly aberrant expression in more than17(85%) NPC patients (q<0.01) with higher than2-fold change, included1over-expression gene and8under-expression genes. For further research, CR2and MXLIP expression were detected by real-time RT-PCR in additional50NPC specimens. Compared with3independent nasopharyngeal chronic phlogistic tissues, CR2was lower expression in41(82%) specimens and MXLIP was over expression in42(84%) specimens. This result was consistent with our microarray data.Then, the method of SAM was performed involving two class unpaired comparison to identified differentially expressed genes in radiation resistant NPC patients. The results of cDNA microarrays were verified by real time RT-PCR using17the other independent NPC tissues.111genes were detected as differentially expressed, in which108genes (ZNF608, PIZEO2, and CSF1R et al) were up-regulated, while3genes (ATP2C1, MUDENG and OLA1) were down-regulated in radiation resistant NPC tissue. Furthermore, we identified26enriched pathways (9categories) through GenMAPP analysis. Reflected by the targets, the results indicated that these differentially expressed genes were highly correlated with cell ion homeostasis, cytokines and inflammatory, humoral immune, cell proliferation et al. Here, we suggest the radiation resistant capacity of NPC was mostly due to the change of cell Ca2+homeostasis, which promoting anti-apoptosis, DNA repair and rescuing tumor cell under radiation therapy. Moreover, cell proliferation promotion which induced by extracellular and intracellular factors may maintain tumor size under radiotherapy, and lead to recurrence after treatment.