The evolving roles of cell surface proteases in health and disease: implications for developmental, adaptive, inflammatory, and neoplastic processes

Reduced transthyretin expression in sera of lung cancer

Lung cancer is a leading cause of cancer death worldwide, and very few specific biomarkers can be used in its clinical diagnosis. Using surface-enhanced laser desorption-ionization time-of-flight mass spectrometry (MS) to find novel serum biomarkers for lung cancer, we analyzed 227 serum samples, including 146 lung cancers, 41 benign lung diseases and 40 normal individuals. Three peaks, at 13.78, 13.90 and 14.07 k m/z, were significantly lower in lung cancer sera compared with sera from normal individuals (P < 0.001), whereas these peaks were higher than those in the sera of benign lung diseases (P < 0.001). The peaks were identified as native transthyretin (TTR) and its two variants by one-dimensional polyacrylamide gel electrophoresis, ESI-MS/MS, immunoprecipitation and western blot analysis. An enzyme-linked immunosorbent assay indicated that TTR levels were consistent with surface-enhanced laser desorption-ionization analysis in all groups tested. It gave 78.5% sensitivity and 77.5% specificity for lung cancer versus normal at the cut-off point 115 microg/mL, and 66.7% sensitivity and 64.4% specificity for lung cancer versus benign lung diseases at the cut-off point 88.5 microg/mL. Therefore, TTR may be useful as a biomarker to improve the diagnosis of lung cancer.

Classification of cancer types by measuring variants of host response proteins using SELDI serum assays

Protein expression profiling has been increasingly used to discover and characterize biomarkers that can be used for diagnostic, prognostic or therapeutic purposes. Most proteomic studies published to date have identified relatively abundant host response proteins as candidate biomarkers, which are often dismissed because of an apparent lack of specificity. We demonstrate that 2 host response proteins previously identified as candidate markers for early stage ovarian cancer, transthyretin and inter-alpha trypsin inhibitor heavy chain 4 (ITIH4), are posttranslationally modified. These modifications include proteolytic truncation, cysteinylation and glutathionylation. Assays using Surface Enhanced Laser Desorption/Ionization Time of Flight Mass Spectrometry (SELDI-TOF-MS) may provide a means to confer specificity to these proteins because of their ability to detect and quantitate multiple posttranslationally modified forms of these proteins in a single assay. Quantitative measurements of these modifications using chromatographic and antibody-based ProteinChip array assays reveal that these posttranslational modifications occur to different extents in different cancers and that multivariate analysis permits the derivation of algorithms to improve the classification of these cancers. We have termed this process host response protein amplification cascade (HRPAC), since the process of synthesis, posttranslational modification and metabolism of host response proteins amplifies the signal of potentially low-abundant biologically active disease markers such as enzymes.