Salivary proteome profiling of oral squamous cell carcinoma in a Hungarian population

Abstract

Oral squamous cell carcinoma (OSCC) is the seventh most common malignancy and the ninth most frequent cause of cancer death in Europe. Within Europe, Hungary has one of the highest rates of OSCC incidence and mortality. Thus, there is an urgent need to improve early detection. Saliva, as a readily available body fluid, became an increasingly important substance for the detection of biomarkers for many diseases. Different research groups have identified salivary biomarkers specific for OSCC for different countries. In this study, saliva samples of Hungarian patients with OSCC were studied to discover disease-specific and perhaps region-specific biomarkers. LC-mass spectrometry (MS)/MS analysis on a linear ion trap-Orbitrap mass spectrometer was used for qualitative and quantitative salivary protein profiling. More than 500 proteins were identified from saliva by shotgun proteomics. The up- and downregulated proteins in the saliva of patients with OSCC highlighted the importance of protein-protein interaction networks involving the immune system and proteolysis in disease development. Two potential biomarkers from our shotgun analysis and a third candidate reported earlier by a Taiwanese group were further examined by ELISA on a larger reference set of samples. Resistin, a biomarker reported in Taiwan but not validated in our study, highlights the necessity of application of standardized analysis methods in different ethnic or geographical populations to identify biomarkers with sufficient specificity and sensitivity.

Keywords: ELISA; biomarker; oral squamous cell carcinoma; proteomics analysis.

Figure 1

Cluster analysis and heat map of proteins identified in the CTL and OSCC groups. The relative peptide count (%), characteristic of each sample, is shown.

Figure 2

The protein–protein interaction network and functional classification of up‐ and downregulated proteins in OSCC. The network of downregulated (A) and upregulated (C) proteins in OSCC displayed by String 10.4 using default settings and medium stringency. Each node represents a protein and the edges represent protein–protein interactions based on different levels of evidence collected by String. The enrichment table of GO terms calculated by String in the case of downregulated (B) and upregulated (D) proteins is shown indicating the number of the proteins belonging to each term and the false discovery rate calculated by String.

Figure 3

Examination of potential salivary biomarkers using ELISA. The concentration of SERPIND1 (A), resistin (B), and complement C5 (C) proteins in the saliva samples collected from patients with OSCC, YCTL, and MCTL. The P value is indicated; * refers to P < 0.05.