Analysis of Protein Expression Profile of Oral Squamous Cell Carcinoma by MALDI-TOF-MS

In this study, two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF-MS) technology was used to examine differentially expressed proteins in oral squamous cell carcinoma (OSCC) tissues from Norway (n=15) and the UK (n=45). Twenty-nine proteins were found to be significantly overexpressed in the OSCCs examined compared to the normal controls. Identified proteins included, family of annexin proteins that play important roles in signal transduction pathways and regulation of cellular growth, keratin-1, heat-shock proteins (HSP), squamous cell carcinoma antigen (SCC-Ag), cytoskeleton proteins, and proteins involved in mitochondrial and intracellular signalling pathways. The expression of four selected proteins (annexin II and V, HSP-27, and SCC-Ag) was verified using western blot analysis of 76 fresh tissue biopsy specimens in total, from Norway (n=53) and the UK (n=23). Proteomic analysis of OSCCs examined here demonstrated involvement of several proteins that might function as potential biomarkers and molecular targets for early cancer diagnostics, and may contribute to a novel approach to therapeutics and for predicting prognosis of OSCC. Oral squamous cell carcinoma (OSCC) represents one of the most common types of cancers of the head and neck region, and is a major health problem in Central, Eastern and Southeast Asia (1). This aggressive neoplasm afflicts about 500,000 new cases worldwide each year with approximately 62% of those occurring in developing countries, the disease is found more frequently in males than females (2). Worldwide, the frequency of the disease varies between 1% and 40% of all malignancies (2). Although the incidence of OSCC seems to be higher in many developing countries compared with industrial ones, there has been a rising trend in incidence and mortality in several Western countries during the past decades (2, 3). Regular use of tobacco and excessive alcohol consumption together account for about 75% of all cases of OSCCs. Increasing use of these substances might be an important reason for the overall increase in the incidence rates that have been recently reported in some European countries (4). In Britain, OSCC accounts for approximately 3% of all new cancer cases, and is the 15th most common type of cancer, with an increase in incidence since the mid-1970s (5-7). In males, it is the 12th most common types of cancer in the UK (5), and among women, it is the 16th. In Norway, the relative frequencies of head and neck cancer (HNSCC), including OSCC, reported in the period from 1996-2001 was slightly higher than in the UK, affecting approximately 6.1% of male and 2.5% of female patients, and is linked to the social habits of tobacco smoking and alcohol consumption (8). Since the 5- year survival of patients diagnosed with oral cancer still remains low (maximum 50%), and the possibility of regional recurrence of the disease is high, there is a need for specific molecular biomarkers for early diagnosis and better therapeutic strategies. The most common anatomical sites for oral cancer are the tongue and the buccal mucosa. The life-styles associated with increased risk of oral cancer are now well- characterized (4, 9-12) for different populations of the globe. Study of cancer genomics, as well as proteomics, has emerged as a powerful tool allowing for investigation of protein profiles and signatures for the purpose of screening, diagnosis, better understanding of OSCC pathogenesis, and possibly for improving therapeutics (13-20). Proteomics have