Identification of genes differentially expressed in human primary lung squamous cell carcinoma

To identify differentially expressed genes in lung squamous cell carcinomas (SCCs), the suppression subtractive hybridization method (SSH) was performed comparing six lung tumour tissues and 10 morphologically normal bronchial epithelial tissues. A cDNA library consisting of 220 upregulated genes in tumour tissue was established and named as LSCC (lung squamous cell carcinoma). Of them, six were tested using semi-quantitative reverse transcription-PCR on 27 pairs of tumour tissue and normal lung tissue. Differential expression was confirmed in five of these six genes, including IGFBP5, SQLE, RAP2B, CLDN1, and TBL1XR1. The elevated mRNA expression of RAP2B, CLDN1 and TBL1XR1, three genes located on chromosome 3q, were further validated in 64.3% (18/28), 82.1% (23/28), and 75.0% (21/28) of lung SCC tumour tissues, respectively, by quantitative real-time reverse transcription-PCR analysis. Moreover, western blot analysis showed that the protein expression of TBL1XR1 was also upregulated in 53.3% (8/15) of lung SCC tumour samples, as well as in five lung cancer cell lines and in one human immortalized bronchial epithelial cell line. All the initial characteristics of these genes were first reported in the lung SCCs. The differentially expressed genes reported in this study will provide a valuable resource for understanding the pathogenesis of lung SCCs and for discovery of novel diagnostic or therapeutic targets.