Identification of glycoproteins from mouse skin tumors and plasma

Introduction: Plasma has been the focus of testing different proteomic technologies for the identification of biomarkers due to its ready accessibility. However, it is not clear if direct proteomic analysis of plasma can be used to discover new marker proteins from tumors that are associated with tumor progression. In this paper, we reported that such proteins can be detected in plasma in a chemical-induced skin cancer model in mice. Materials and Methods: We analyzed glycoproteins from both benign papillomas and malignant carcinomas from mice using our recently developed platform, solid-phase extraction of glycopeptides and mass spectrometry, and identified 463 unique N-linked glycosites from 318 unique glycoproteins. These include most known extracellular proteins that have been reported to play roles in skin cancer development such as thrombospondin, cathepsins, epidermal growth factor receptor, cell adhesion molecules, cadherins, integrins, tuberin, fibulin, and TGFβ receptor. We further investigated whether these tumor proteins could be detected in plasma from tumor-bearing mice using isotope labeling and 2D liquid chromatography/matrix-assisted laser desorption/ionization tandem mass spectrometry. Results and Discussion: Two tumor glycoproteins, Tenascin-C and Arylsulfatase B, were identified and quantified successfully in plasma from tumor bearing mice. This result indicates that analysis of tumor-associated proteins in tumors and plasma by a method using glycopeptide capture, isotopic labeling, and mass spectrometry can be used as a discovery tool to identify candidate tumor proteins that may be detected in plasma.