Discovery and application of colorectal cancer protein markers for disease stratification

Colorectal cancer (CRC) is a major cause of cancer mortality. Whereas some patients respond well to therapy, others do not, and thus more precise methods of CRC stratification are needed. The intracellular protein expression from 28 CRC primary tumours and corresponding normal intestinal mucosa was analysed using saturation-DIGE/MS and Explorer antibody microarrays. Changes in protein abundance were identified at each stage of CRC. Proteins associated with proliferation, glycolysis, reduced adhesion, endoplasmic reticulum stress, angiogenesis, and response to hypoxia represent changes to CRC and its microenvironment during development. Molecular changes in CRC cells and their microenvironment can be incorporated into clinic-pathological data to help sub-classify tumours and personalise treatment. DotScan antibody microarray analysis was used to profile the surface proteome of cells derived from 50 CRC samples and corresponding normal intestinal mucosa. Fluorescence multiplexing enabled the analysis of two different sub-populations of cells from each sample: EpCAM+ cells (CRC cells or normal epithelial cells in normal mucosa) and CD3+ T-cells (tumour-infiltrating lymphocytes). Unsupervised hierarchical clustering of the CRC and T-cell surface profiles defined four clinically relevant clusters, which showed some correlation with histopathological and clinical characteristics such as cancer cell differentiation, peri-tumoural inflammation and stimulation of infiltrating T-cells. The observed relationship between the surface antigen expression profiles of patients’ CRC cells and their corresponding tumour infiltrating T-cells suggests that CRC surface proteins may play a direct role in influencing the activity (and hence surface protein expression) of neighbouring T-cells and/or vice versa. We conclude that the application of surface profiling may provide improved patient stratification, allowing more reliable prediction of disease progression and patient outcome

Clostridioides difficile phosphoproteomics shows an expansion of phosphorylated proteins in stationary growth phase

In this paper, we present a comprehensive analysis of protein phosphorylation in the Gram-positive enteropathogen Clostridioides difficile. To date, only limited evidence on the role of phosphorylation in the regulation of this organism has been published; the current study is expected to form the basis for research on this posttranslational modification in C. difficile.Phosphorylation is a posttranslational modification that can affect both housekeeping functions and virulence characteristics in bacterial pathogens. In the Gram-positive enteropathogen Clostridioides difficile, the extent and nature of phosphorylation events are poorly characterized, though a protein kinase mutant strain demonstrates pleiotropic phenotypes. Here, we used an immobilized metal affinity chromatography strategy to characterize serine, threonine, and tyrosine phosphorylation in C. difficile. We find limited protein phosphorylation in the exponential growth phase but a sharp increase in the number of phosphopeptides after the onset of the stationary growth phase. Our approach identifies expected targets and phosphorylation sites among the more than 1,500 phosphosites, including the protein kinase PrkC, the anti-sigma-F factor antagonist (SpoIIAA), the anti-sigma-B factor antagonist (RsbV), and HPr kinase/phosphorylase (HprK). Analysis of high-confidence phosphosites shows that phosphorylation on serine residues is most common, followed by threonine and tyrosine phosphorylation. This work forms the basis for a further investigation into the contributions of individual kinases to the overall phosphoproteome of C. difficile and the role of phosphorylation in C. difficile physiology and pathogenesis. IMPORTANCE In this paper, we present a comprehensive analysis of protein phosphorylation in the Gram-positive enteropathogen Clostridioides difficile. To date, only limited evidence on the role of phosphorylation in the regulation of this organism has been published; the current study is expected to form the basis for research on this posttranslational modification in C. difficile.Molecular basis of bacterial pathogenesis, virulence factors and antibiotic resistanc

Revised model for the type A glycan biosynthetic pathway in Clostridioides difficile strain 630Δerm based on quantitative proteomics of cd0241-cd0244 mutant strains

The bacterial flagellum is involved in a variety of processes including motility, adherence, and immunomodulation. In the Clostridioides difficile strain 630 Delta erm, the main filamentous component, FliC, is post-translationally modified with an O-linked Type A glycan structure. This modification is essential for flagellar function, since motility is seriously impaired in gene mutants with improper biosynthesis of the Type A glycan. The cd0240-cd0244 gene cluster encodes the Type A biosynthetic proteins, but the role of each gene, and the corresponding enzymatic activity, have not been fully elucidated. Using quantitative mass spectrometry-based proteomics analyses, we determined the relative abundance of the observed glycan variations of the Type A structure in cd0241, cd0242, cd0243, and cd0244 mutant strains. Our data not only confirm the importance of CD0241, CD0242, and CD0243 but, in contrast to previous data, also show that CD0244 is essential for the biosynthesis of the Type A modification. Combined with additional bioinformatic analyses, we propose a revised model for Type A glycan biosynthesis.Molecular basis of bacterial pathogenesis, virulence factors and antibiotic resistanc

Oxonium ion guided analysis of quantitative proteomics data reveals site-specific O-glycosylation of anterior gradient protein 2 (AGR2)

Developments in mass spectrometry (MS)-based analyses of glycoproteins have been important to study changes in glycosylation related to disease. Recently, the characteristic pattern of oxonium ions in glycopeptide fragmentation spectra had been used to assign different sets of glycopeptides. In particular, this was helpful to discriminate between O-GalNAc and O-GlcNAc. Here, we thought to investigate how such information can be used to examine quantitative proteomics data. For this purpose, we used tandem mass tag (TMT)-labeled samples from total cell lysates and secreted proteins from three different colorectal cancer cell lines. Following automated glycopeptide assignment (Byonic) and evaluation of the presence and relative intensity of oxonium ions, we observed that, in particular, the ratio of the ions at m/z 144.066 and 138.055, respectively, could be used to discriminate between O-GlcNAcylated and O-GalNAcylated peptides, with concomitant relative quantification between the different cell lines. Among the O-GalNAcylated proteins, we also observed anterior gradient protein 2 (AGR2), a protein which glycosylation site and status was hitherto not well documented. Using a combination of multiple fragmentation methods, we then not only assigned the site of modification, but also showed different glycosylation between intracellular (ER-resident) and secreted AGR2. Overall, our study shows the potential of broad application of the use of the relative intensities of oxonium ions for the confident assignment of glycopeptides, even in complex proteomics datasets.Proteomic

Fc gamma receptor IIIb binding of individual antibody proteoforms resolved by affinity chromatography-mass spectrometry

The crystallizable fragment (Fc) of immunoglobulin G (IgG) activates key immunological responses by interacting with Fc gamma receptors (Fc gamma R). Fc gamma RIIIb contributes to neutrophil activation and is involved in antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). These processes present important mechanisms-of-actions of therapeutic antibodies. The very low affinity of IgG toward Fc gamma RIIIb (K-D similar to 10 mu M) is a technical challenge for interaction studies. Additionally, the interaction is strongly dependent on IgG glycosylation, a major contributor to proteoform heterogeneity. We developed an affinity chromatography-mass spectrometry (AC-MS) assay for analyzing IgG-Fc gamma RIIIb interactions in a proteoform-resolved manner. This proved to be well suited to study low-affinity interactions. The applicability and selectivity of the method were demonstrated on a panel of nine different IgG monoclonal antibodies (mAbs), including no-affinity, low-affinity and high-affinity Fc-engineered or glycoengineered mAbs. Thereby, we could reproduce reported affinity rankings of different IgG glycosylation features and IgG subclasses. Additional post-translational modifications (IgG1 Met252 oxidation, IgG3 hinge-region O-glycosylation) showed no effect on Fc gamma RIIIb binding. Interestingly, we observed indications of an effect of the variable domain sequence on the Fc-binding that deserves further attention. Our new AC-MS method is a powerful tool for expanding knowledge on structure-function relationships of the IgG-Fc gamma RIIIb interaction. Hence, this assay may substantially improve the efficiency of assessing critical quality attributes of therapeutic mAbs with respect to an important aspect of neutrophil activation.Proteomic

Healthy cells functionally present TAP-independent SSR1 peptides: implications for selection of clinically relevant antigens

Tumors with an impaired transporter associated with antigen processing (TAP) present several endoplasmic reticulum-derived self-antigens on HLA class I (HLA-I) which are absent on healthy cells. Selection of such TAP-independent antigens for T cell-based immunotherapy should include analysis of their expression on healthy cells to prevent therapy-induced adverse toxicities. However, it is unknown how the absence of clinically relevant antigens on healthy cells needs to be validated. Here, we monitored TAP-independent antigen presentation on various healthy cells after establishing a T cell tool recognizing a TAP-independent signal sequence receptor 1-derived antigen. We found that most but not all healthy cells present this antigen under normal and inflammatory conditions, indicating that TAP-independent antigen presentation is a variable phenomenon. Our data emphasize the necessity of extensive testing of a wide variety of healthy cell types to define clinically relevant TAP-independent antigens that can be safely targeted by immunotherapy.Immunobiology of allogeneic stem cell transplantation and immunotherapy of hematological disease

Proteasomal Degradation of Proinsulin Requires Derlin-2, HRD1 and p97

Nephrolog

PAKC: a novel panel of HLA class I antigen presentation machinery knockout cells from the same genetic origin

A single model system for integrative studies on multiple facets of antigen presentation is lacking. PAKC is a novel panel of ten cell lines knocked out for individual components of the HLA class I antigen presentation pathway. PAKC will accelerate HLA-I research in the fields of oncology, infectiology, and autoimmunity.Proteomic

ST6Gal1 targets the ectodomain of ErbB2 in a site-specific manner and regulates gastric cancer cell sensitivity to trastuzumab

The clinical performance of the therapeutic monoclonal antibody trastuzumab in the treatment of ErbB2-positive unresectable gastric cancer (GC) is severely hampered by the emergence of molecular resistance. Trastuzumab's target epitope is localized within the extracellular domain of the oncogenic cell surface receptor tyrosine kinase (RTK) ErbB2, which is known to undergo extensive N-linked glycosylation. However, the site-specific glycan repertoire of ErbB2, as well as the detailed molecular mechanisms through which specific aberrant glycan signatures functionally impact the malignant features of ErbB2-addicted GC cells, including the acquisition of trastuzumab resistance, remain elusive. Here, we demonstrate that ErbB2 is modified with both alpha 2,6- and alpha 2,3-sialylated glycan structures in GC clinical specimens. In-depth mass spectrometry-based glycomic and glycoproteomic analysis of ErbB2's ectodomain disclosed a site-specific glycosylation profile in GC cells, in which the ST6Gal1 sialyltransferase specifically targets ErbB2 N-glycosylation sites occurring within the receptor's trastuzumab-binding domain. Abrogation of ST6Gal1 expression reshaped the cellular and ErbB2-specific glycomes, expanded the cellular half-life of the ErbB2 receptor, and sensitized ErbB2-dependent GC cells to trastuzumab-induced cytotoxicity through the stabilization of ErbB dimers at the cell membrane, and the decreased activation of both ErbB2 and EGFR RTKs. Overall, our data demonstrates that ST6Gal1-mediated aberrant alpha 2,6-sialylation actively tunes the resistance of ErbB2-driven GC cells to trastuzumab.Proteomic

Relativistic quantum dynamics of a charged particle in cosmic string spacetime in the presence of magnetic field and scalar potential

In this paper we analyze the relativistic quantum motion of charged spin-0 and spin-1/2 particles in the presence of a uniform magnetic field and scalar potentials in the cosmic string spacetime. In order to develop this analysis, we assume that the magnetic field is parallel to the string and the scalar potentials present a cylindrical symmetry with their center on the string. Two distinct configurations for the scalar potential, $S(r)$, are considered: $(i)$ the potential proportional to the inverse of the polar distance, i.e., $S\propto1/r$, and $(ii)$ the potential proportional to this distance, i.e., $S\propto r$. The energy spectra are explicitly computed for different physical situations and presented their dependences on the magnetic field strength and scalar coupling constants.Comment: New version with 20 pages and no figure. Some minor revisions and six references added. Accepted for publication in EJP