Analysis of the Plasma Peptidome from Pancreas Cancer Patients Connects a Peptide in Plasma to Overexpression of the Parent Protein in Tumors

Abstract

Blood circulates through nearly every organ including tumors. Therefore, plasma is a logical source to search for tumor-derived proteins and peptides. The challenge with plasma is that it is a complex bodily fluid composed of high concentrations of normal host proteins that obscure identification of tumor-derived molecules. To simplify plasma, we examined a low molecular weight (LMW) fraction (plasma peptidome) using liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. In the plasma peptidome of patients with ductal adenocarcinoma of the pancreas (DAP), a prominent peptide was identified from the QSOX1 parent protein. This peptide is stable in whole blood over 24 h and was present in 16 of 23 DAP patients and 4 of 5 patients with intraductal papillary mucinous neoplasm (IPMN). QSOX1 peptides were never identified in the plasma peptidome from 42 normal healthy donors using the same methods. Immunohistochemical staining of DAP tissue sections with anti-QSOX1 antibody shows overexpression of QSOX1 in tumor but not in adjacent stroma or normal ducts. Three of four pancreas tumor cell lines also express QSOX1 protein by Western blot analysis. This is the first report of QSOX1 peptides in plasma from DAP patients and makes the rare connection between a peptide in plasma from cancer patients and overexpression of the parent protein in tumors.

A well‐characterised peak identification list of MALDI MS profile peaks for human blood serum

“…Other comparisons including lists of endogenous plasma peptides 21 and other proteins showed similar results. In addition, none of these lists include any post-translational modifications (PTMs), and only recently a few phosphorylated endogenous serum peptides were reported 22 .…”

The Dendritic Cell Major Histocompatibility Complex II (MHC II) Peptidome Derives from a Variety of Processing Pathways and Includes Peptides with a Broad Spectrum of HLA-DM Sensitivity

“…Recently, a number of reports have analyzed the half-life and overall stability of peptides in biological fluids and shown that most peptides are bound to carrier proteins, including albumin, lipoproteins, immunoglobulins, and transthyretin. The peptides exist in equilibrium between their free and bound form, and their half-life varies between 1 and 20 days, directly proportional to the half-life of the carrier protein (3,25). The prolonged half-life and continuing production of these carrierbound peptides support an available amount of biological fluids far superior to the steady-state concentration of free peptide.…”

“…Conventional dendritic cells (cDC) 3 are a heterogeneous population of antigen-presenting cells involved in different aspects of tolerogenic and immunogenic T cell responses. They are subclassified as resident cDC, which reside in secondary lymphatic organs (spleen and lymph node), and migratory cDC, which traffic from peripheral tissues to the draining lymph nodes and the thymus (30 -33).…”

Mining the proteome: the application of tandem mass spectrometry to endocrine cancer research

“…These results were confirmed by western blotting, suggesting that these markers may be useful adjuncts to the existing biomarkers, CA19-9 and CEA. Despite using similar methods, another study reported the presence of a peptide chain from sulphhydryl oxidase 1 as their only significant finding and linked this to the expression of protein in pancreatic tumour cell lines (Antwi et al 2009). These studies highlight the fact that proteomic research using MS/MS can yield very variable results even though the methodology may be similar.…”