Identification of differentially expressed genes in oral squamous cell carcinoma (OSCC): Overexpression of NPM, CDK1 and NDRG1 and underexpression of CHES1

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Abstract
To identify cellular genes that could potentially serve as predictive molecular markers for human oral cancer, we employed differential display analysis to compare the gene expression profiles between oral squamous cell carcinoma (OSCC) and histopathologically normal epithelium tissues. Comparative real-time RT-PCR was used to confirm the gene expression in 52 OSCC patients, and a 2-fold difference was defined as over- or underexpression. A total of 7 genes were identified: NPM, CDK1, NDRG1, HMGCR, EF1A, NAC and CHES1. In the cancer tissues, NPM, CDK1 and NDRG1 were significantly overexpressed (an average of 7.6-, 17.2- and 12.9-fold, respectively), and CHES1 was underexpressed (15-fold). The frequencies of the differential expression were 40, 56, 67 and 46%, respectively in NPM, CDK1, NDRG1 and CHES1. In Western blot analysis, the protein expressions of NPM, CDK1 and NDRG1 were also increased in the cancer tissues, consistent with the mRNA expression results. To further evaluate clinicopathological associations in these genes, Pearson chi-square analysis was employed. Levels of CDK1 and NDRG1 were associated with poorly differentiated tumors (p = 0.043 and 0.023), suggesting that these genes participate in the mechanism of tumor transformation. Expressions of CDK1 and NDRG1, and CDK1 and CHES1 were mutually statistically correlated (p = 0.001 and 0.014), indicating that these genes share a very close regulatory relationship or interact synergistically in oncogenesis. In conclusion, we identified 7 genes that are differentially expressed in OSCC, and we provide the first evidence that NPM, CDK1 and NDRG1 are overexpressed and CHES1 is underexpressed in oral cancer. These results serve as a fundamental base for employing these genes in future clinical applications.