Oral cavity squamous cell carcinoma (OSCC), which is frequently associated with poor prognosis and mortality, is a leading cause of cancer-related death worldwide. Discovery of body fluid accessible biomarkers is needed to improve OSCC screening. To this end, we profiled proteomes of saliva from the healthy volunteers, the individuals with oral potentially malignant disorders (OPMD), and the OSCC patients by means of SDS-PAGE coupled with LC-MS/MS. In the control, the OPMD, and the OSCC groups, 958, 845, and 1030 salivary proteins were detected, respectively. With spectral counting-based label-free quantification, 22 overexpressed salivary proteins were identified in the OSCC group compared with the healthy controls and the OPMD individuals. Among them, resistin (RETN) was subjected to further validation with an independent cohort using ELISA. The data confirmed that the salivary RETN levels in the OSCC patients were significantly higher than that in the healthy or in the OPMD group. Moreover, the elevated levels of salivary RETN were highly correlated with late-stage primary tumors, advanced overall stage, and lymph-node metastasis. Our results not only reveal that profiling of saliva proteome is feasible for discovery of OSCC biomarkers, but also identify RETN as a potential salivary biomarker for OSCC detection.

Oral cancer is one of the most common cancers worldwide. To identify biomarkers for oral cancer diagnosis, salivary proteins differentially expressed in oral cancer patients have been identified with iTRAQ-based MS analyses. The candidates were further selected using MRM-MS and validated with the immunoassays. The results suggest that three proteins (CFH, FGA, and SERPINA1) have the potential as diagnosis and prognosis biomarkers of oral cancer, and analysis of salivary proteome is a feasible strategy for biomarker discovery.

Staphylococcus aureus is a bacterial pathogen that produces and exports many virulence factors that cause diseases in humans. PrsA, a membrane-bound foldase, is expressed ubiquitously in Gram-positive bacteria and required for the folding of exported proteins into a stable and active structure. To understand the involvement of PrsA in posttranslocational protein folding in S. aureus, a PrsA-deficient mutant of S. aureus HG001 was constructed. Using isobaric tags for relative and absolute quantification (iTRAQ)-based mass spectrometry analyses, the exoproteomes of PrsA mutant and wild type S. aureus were comparatively profiled, and 163 cell wall-associated proteins and 67 exoproteins with altered levels have been identified in the PrsA-deficient mutant. Bioinformatics analyses further reveal that prsA deletion altered the amounts of proteins that are potentially involved in the regulation of cell surface properties and bacterial pathogenesis. To determine the relevancy of our findings, we investigated the functional consequence of prsA deletion in S. aureus. PrsA deficiency can enhance bacterial autoaggregation and increase the adhesion ability of S. aureus to human lung epithelial cells. Moreover, mice infected with PrsA-deficient S. aureus had a better survival rate compared with those infected with the wild-type S. aureus. Collectively, our findings reveal that PrsA is required for the posttranslocational folding of numerous exported proteins and critically affects the cell surface properties and pathogenesis of S. aureus.

Purpose: To identify aberrantly expressed proteins contributing to pathogenesis of canine mammary tumors (CMTs) which are the most prevalent neoplasms in female dogs and include different types. Experimental design: Frozen tissue specimens of normal mammary gland (n = 7), lobular hyperplasia (n = 6), simple carcinoma (n = 6), and complex carcinoma (n = 6) are collected from 11 CMT cases. Tissue homogenates are comparatively analyzed by the isobaric tags for relative and absolute quantification (iTRAQ) combined with LC-MS/MS to identify proteins differentially expressed in different-type CMT tissues. Results: Among 3795 proteins identified and quantified among all groups, 133, 127, and 98 proteins are particularly overexpressed in simple carcinoma, complex carcinoma, and both types, respectively, compared with normal and hyperplastic tissues. Moreover, collagen type II alpha 1 chain (COL2A), myeloperoxidase (MPO), thymidylate synthetase (TYMS), and insulin-like growth factor-binding protein 5 (IGFBP5) are validated to be highly expressed in different-type CMT tissues using immunoblotting and immunohistochemistry. Notably, COL2A1 and IGFBP5 levels are correlated with clinical stages. Conclusions and clinical relevance: COL2A1, MPO, TYMS, and IGFBP5 protein levels are positively associated with CMT development. Data expedite further investigations to improve treatment regimens for CMT.

The Michael addition reaction is a spontaneous and quick chemical reaction that is widely applied in various fields. This reaction is performed by conjugating an addition of nucleophiles with α, β-unsaturated carbonyl compounds, resulting in the bond formation of C-N, C-S, C-O, and so on. In the development of molecular materials, the Michael addition is not only used to synthesize chemical compounds but is also involved in the mechanism of drug action. Several covalent drugs that bond via Michael addition are regarded as anticarcinogens and anti-inflammatory drugs. Although drug development is mainly focused on pharmaceutical drug discovery, target-based discovery can provide a different perspective for drug usage. However, considerable time and labor are required to define a molecular target through molecular biological experiments. In this review, we systematically examine the chemical structures of current FDA-approved antiviral drugs for potential Michael addition moieties with α, β-unsaturated carbonyl groups, which may exert an unidentified broad-spectrum inhibitory mechanism to target viral or host factors. We thus propose that profiling the targets of antiviral agents, such as Michael addition products, can be achieved by employing a high-throughput LC-MS approach to comprehensively analyze the interaction between drugs and targets, and the subsequent drug responses in the cellular environment to facilitate drug repurposing and/or identify potential adverse effects, with a particular emphasis on the pros and cons of this shotgun proteomic approach.