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RNA variants that emerge from editing and alternative splicing form important regulatory stages in protein signalling. In this report, we apply an integrated DNA and RNA variant detection workbench to define the range of RNA variants that deviate from the reference genome in a human melanoma cell model. The RNA variants can be grouped into (i) classic ADAR-like or APOBEC-like RNA editing events and (ii) multiple-nucleotide variants (MNVs) including three and six base pair in-frame non-canonical unmapped exons. We focus on validating representative genes of these classes. First, clustered non-synonymous RNA edits (A-I) in the CDK13 gene were validated by Sanger sequencing to confirm the integrity of the RNA variant detection workbench. Second, a highly conserved RNA variant in the MAP4K5 gene was detected that results most likely from the splicing of a non-canonical three-base exon. The two RNA variants produced from the MAP4K5 locus deviate from the genomic reference sequence and produce V569E or V569del isoform variants. Low doses of splicing inhibitors demonstrated that the MAP4K5-V569E variant emerges from an SF3B1-dependent splicing event. Mass spectrometry of the recombinant SBP-tagged MAP4K5V569E and MAP4K5V569del proteins pull-downs in transfected cell systems was used to identify the protein-protein interactions of these two MAP4K5 isoforms and propose possible functions. Together these data highlight the utility of this integrated DNA and RNA variant detection platform to detect RNA variants in cancer cells and support future analysis of RNA variant detection in cancer tissue.

A comparative canine–human therapeutics model is being developed in B-cell lymphoma through the generation of a hybridoma cell that produces a murine monoclonal antibody specific for canine CD20. The hybridoma cell produces two light chains, light chain-3, and light chain-7. However, the contribution of either light chain to the authentic full-length hybridoma derived IgG is undefined. Mass spectrometry was used to identify only one of the two light chains, light chain-7, as predominating in the full-length IgG. Gene synthesis created a recombinant murine–canine chimeric monoclonal antibody expressing light chain-7 that reconstituted the IgG binding to CD20. Using light chain-7 as a reference sequence, hydrogen deuterium exchange mass spectrometry was used to identify the dominant CDR region implicated in CD20 antigen binding. Early in the deuteration reaction, the CD20 antigen suppressed deuteration at CDR3 (VH). In later time points, deuterium suppression occurred at CDR2 (VH) and CDR2 (VL), with the maintenance of the CDR3 (VH) interaction. These data suggest that CDR3 (VH) functions as the dominant antigen docking motif and that antibody aggregation is induced at later time points after antigen binding. These approaches define a methodology for fine mapping of CDR contacts using nested enzymatic reactions and hydrogen deuterium exchange mass spectrometry. These data support the further development of an engineered, synthetic canine–murine monoclonal antibody, focused on CDR3 (VH), for use as a canine lymphoma therapeutic that mimics the human–murine chimeric anti-CD20 antibody Rituximab.

A specific form of endometrial cancer (EC) can develop in breast cancer patients previously treated with tamoxifen (ET), an antagonist of estrogen receptor (ER) that inhibits proliferation of ER positive breast cancer. ET tumors have a different phenotype than endometrial tumors, which typically develop de novo without previous exposure to tamoxifen (EN). Here we aimed to identify specific protein markers that could serve as specific molecular targets in either phenotype. A set of total 45 formalin-fixed paraffin-embedded (FFPE) endometrial tumor tissues and adjacent myometrium tissue samples were analyzed using LC-MS/MS in SWATH-MS mode. We found that calcyphosin (CAPS) levels were elevated in EN tumors compared to ET tumors. The higher CAPS level in EC tissue invading to myometrium supports its relationship to EC aggressiveness. Further, stathmin (STMN1) levels were found significantly elevated in ET versus EN tumors and significantly associated with patient survival. This finding connects elevated levels of this cell cycle regulating, proliferation-associated protein with tamoxifen exposure. In summary, using SWATH-MS we show that CAPS and STMN1 should be recognized as clinicopathologically different EC markers of which STMN1 is specifically connected with a previous tamoxifen exposition.

IFITM proteins play a role in cancer cell progression through undefined mechanisms. Here, we propose an emergent role of IFITM1/3 regulating protein synthesis. SBP-tagged IFITM1 protein was used to identify an association of IFITM1 protein with the cytosolic isoform of SRSF1 that transports mRNA to the ribosome. This cytosolic association was confirmed in situ using proximity ligation assays for SRSF1 and IFITM1/3, suggesting a role associated with translation. Accordingly, IFITM1/3 were shown to interact with HLA-B mRNA in response to IFNγ stimulation using RNA-protein proximity ligation assays. In addition, shotgun RNA sequencing in IFITM1/IFITM3 null cells and wt-SiHa cells indicated that reduced HLA-B gene expression does not account for lowered HLA-B protein synthesis in response to IFNγ. Furthermore, ribosome profiling using sucrose gradient sedimentation identified a reduction in 80S ribosomal fraction an IFITM1/IFITM3 null cells compared to their wild-type counterpart, partially reverted by IFITM1/3 complementation. Our data all together link the binding of IFITM1/3 proteins to HLA-B mRNA and SRSF1 as a mechanism to catalyze the synthesis of target proteins, suggesting an RNA chaperonin role for IFITM1/3 proteins.SignificanceIFITMs are widely studied for their role in inhibiting viruses, and multiple studies have associated IFITMs with cancer progression. However, mechanistic insights are not well understood. Our study proposes that IFITMs have a role regulating protein synthesis, a pivotal function highly relevant for viral infection and cancer progression. Our results suggest that IFITM1/3 is present in the ribosomal fraction and regulates particular protein expression; among them, we identified HLA-B. Changes in HLA-B expression could impact the presentation and recognition of oncogenic antigens on the cell surface by cytotoxic T cells and, ultimately, limit tumor cell eradication. In addition, the role of IFITMs mediating protein translation is relevant, as has the potential of regulating the expression of viral and oncogenic proteins.

RNA variants that emerge from editing and alternative splicing form important regulatory stages in protein signalling. In this report, we apply an integrated DNA and RNA variant detection workbench to define the range of RNA variants that deviate from the reference genome in a human melanoma cell model. The RNA variants can be grouped into (i) classic ADAR-like or APOBEC-like RNA editing events and (ii) multiple-nucleotide variants (MNVs) including three and six base pair in-frame non-canonical unmapped exons. We focus on validating representative genes of these classes. First, clustered non-synonymous RNA edits (A-I) in the CDK13 gene were validated by Sanger sequencing to confirm the integrity of the RNA variant detection workbench. Second, a highly conserved RNA variant in the MAP4K5 gene was detected that results most likely from the splicing of a non-canonical three-base exon. The two RNA variants produced from the MAP4K5 locus deviate from the genomic reference sequence and produce V569E or V569del isoform variants. Low doses of splicing inhibitors demonstrated that the MAP4K5-V569E variant emerges from an SF3B1-dependent splicing event. Mass spectrometry of the recombinant SBP-tagged MAP4K5V569E and MAP4K5V569del proteins pull-downs in transfected cell systems was used to identify the protein-protein interactions of these two MAP4K5 isoforms and propose possible functions. Together these data highlight the utility of this integrated DNA and RNA variant detection platform to detect RNA variants in cancer cells and support future analysis of RNA variant detection in cancer tissue.

Solitary aculeate wasps are abundant and diverse hymenopteran insects that disable prey using venom. The venom may possess neuromodulation, immunomodulatory, metabolic-modulatory and antimicrobial functions. Venom analysis of transcriptomes and proteomes has been previously performed in social and parasitoid wasp species. We develop methodologies including mass spectrometry-based shotgun proteomics to analyse the protein constituents from venom sacs of the solitary aculeate wasp Cerceris rybyensis. The venom sac constituents of C. rybyensis are discussed with respect to other wasp species.

Interferon-induced transmembrane proteins IFITM1 and IFITM3 (IFITM1/3) play a role in both RNA viral restriction and in human cancer progression. Using immunohistochemical staining of FFPE tissue, we identified subgroups of cervical cancer patients where IFITM1/3 protein expression is inversely related to metastasis. Guide RNA-CAS9 methods were used to develop an isogenic IFITM1/IFITM3 double null cervical cancer model in order to define dominant pathways triggered by presence or absence of IFITM1/3 signalling. A pulse SILAC methodology identified IRF1, HLA-B, and ISG15 as the most dominating IFNγ inducible proteins whose synthesis was attenuated in the IFITM1/IFITM3 double-null cells. Conversely, SWATH-IP mass spectrometry of ectopically expressed SBP-tagged IFITM1 identified ISG15 and HLA-B as dominant co-associated proteins. ISG15ylation was attenuated in IFNγ treated IFITM1/IFITM3 double-null cells. Proximity ligation assays indicated that HLA-B can interact with IFITM1/3 proteins in parental SiHa cells. Cell surface expression of HLA-B was attenuated in IFNγ treated IFITM1/IFITM3 double-null cells. SWATH-MS proteomic screens in cells treated with IFITM1-targeted siRNA cells resulted in the attenuation of an interferon regulated protein subpopulation including MHC Class I molecules as well as IFITM3, STAT1, B2M, and ISG15. These data have implications for the function of IFITM1/3 in mediating IFNγ stimulated protein synthesis including ISG15ylation and MHC Class I production in cancer cells. The data together suggest that pro-metastatic growth associated with IFITM1/3 negative cervical cancers relates to attenuated expression of MHC Class I molecules that would support tumor immune escape., Graphical abstract Unlabelled Image, Highlights • IFITM1/3 expression in cervical cancers inversely correlates with metastases. • Isogenic IFITM1 and IFITM3 null cervical cancer cells were developed. • Pulse SILAC approaches were used to define IFITM1/3 dependent signalling pathways. • The major IFITM1/3-interferon-γ dependent effectors are HLA-B and ISG15. • IFITM1/3 loss would be predicted to reduce HLA expression and ISG15ylation in vivo.

Sample preparation is a key step in proteomics, however there is no consensus in the community about the standard method for preparation of proteins from clinical samples like tissues or biofluids. In this chapter, we will discuss some important steps in sample preparation used for bottom-up proteome profiling with mass spectrometry (MS). Specifically, tissues, which are an important source of biological information, are of interest because of their availability. Tissues are most often stored as fresh frozen (FF) or formalin-fixed paraffin-embedded (FFPE). While FF tissues are more readily available, paraffin embedding has historically been routinely used for tissue preservation. However, formaldehyde induced crosslinks during FFPE tissue preservation present a challenge to the protocols used for protein retrieval. Moreover, in our view, an important aspect to consider is also the amount of material available at the start of a protocol since this is directly related to the choice of protocol in order to minimize sample loss and maximize detection of peptides by MS. This “MS sensitivity” is of special importance when working with patient samples that are unique and often available in limited amounts making optimization of methods to analyze the proteins therein important given that their molecular information can be used in a patients’ diagnosis and treatment.

International audience; The fundamentals of how protein-protein/RNA/DNA interactions influence the structures and functions of the workhorses from the cells have been well documented in the 20th century. A diverse set of methods exist to determine such interactions between different components, particularly, the mass spectrometry (MS) methods, with its advanced instrumentation, has become a significant approach to analyze a diverse range of biomolecules, as well as bring insights to their biomolecular processes. This review highlights the principal role of chemistry in MS-based structural proteomics approaches, with a particular focus on the chemical cross-linking of protein-protein/DNA/RNA complexes. In addition, we discuss different methods to prepare the cross-linked samples for MS analysis and tools to identify cross-linked peptides. Cross-linking mass spectrometry (CLMS) holds promise to identify interaction sites in larger and more complex biological systems. The typical CLMS workflow allows for the measurement of the proximity in three-dimensional space of amino acids, identifying proteins in direct contact with DNA or RNA, and it provides information on the folds of proteins as well as their topology in the complexes. Principal CLMS applications, its notable successes, as well as common pipelines that bridge proteomics, molecular biology, structural systems biology, and interactomics are outlined.

Developments in quantitative proteomics and data-independent acquisition (DIA) methodology is enabling quantification of proteins in biological samples. Currently, there are a few reports on DIA mass spectrometry (MS) approaches for proteome analysis of formalin-fixed paraffin-embedded (FFPE) tissues. Therefore, to facilitate detection and quantification of immune- and glioblastoma (GBM)-relevant proteins from FFPE patient materials, we established a simple and precise DIA-MS workflow. We first evaluated different lysis buffers for their efficiency in protein extractions from FFPE GBM tissues. Our results showed that more than 1700 proteins were detected and over 1400 proteins were quantified from GBM FFPE tissue microdissections. GBM-relevant proteins (e.g., GFAP, FN1, VIM, and MBP) were quantified with high precision (median coefficient of variation

Background The identification of mutated proteins in human cancer cells-termed proteogenomics, requires several technologically independent research methodologies including DNA variant identification, RNA sequencing, and mass spectrometry. Any one of these methodologies are not optimized for identifying potential mutated proteins and any one output fails to cover completely a specific landscape. Methods An isogenic melanoma cell with a p53-null genotype was created by CRISPR/CAS9 system to determine how p53 gene inactivation affects mutant proteome expression. A mutant peptide reference database was developed by comparing two distinct DNA and RNA variant detection platforms using these isogenic cells. Chemically fractionated tryptic peptides from lysates were processed using a TripleTOF 5600+ mass spectrometer and their spectra were identified against this mutant reference database. Results Approximately 190 mutated peptides were enriched in wt-p53 cells, 187 mutant peptides were enriched in p53-null cells, with an overlap of 147 mutated peptides. STRING analysis highlighted that the wt-p53 cell line was enriched for mutant protein pathways such as CDC5L and POLR1B, whilst the p53-null cell line was enriched for mutated proteins comprising EGF/YES, Ubiquitination, and RPL26/5 nodes. Conclusion Our study produces a well annotated p53-dependent and p53-independent mutant proteome of a common melanoma cell line model. Coupled to the application of an integrated DNA and RNA variant detection platform (CLCbio) and software for identification of proteins (ProteinPilot), this pipeline can be used to detect high confident mutant proteins in cells. General significance This pipeline forms a blueprint for identifying mutated proteins in diseased cell systems.

Functional integrity of the E3-ubiquitin ligase CHIP is essential for healthy aging in the brain. By virtue of its association with the core molecular chaperone machinery, studies into the physiological role(s) of CHIP have been dominated by its involvement in the quality control (QC) and degradation of unfolded, aggregated and/or mutated proteins. To elucidate the dominant changes in protein steady state levels in human neurons where CHIP function was ablated, we conducted an unbiased proteomic analysis in genetically engineered CHIP knockout compared to wild-type iPSC-derived cortical neurons. Rather than a broad effect on protein homeostasis, loss of CHIP function impacted on a focused cohort of proteins that analysis defined as actin cytoskeleton signalling and membrane integrity pathways. In support of the pathway analysis, CHIP KO cell-lines had enhanced sensitivity to mechanical and chemical membrane damage. Consistent with recent studies on the identification of a non-canonical HSP-independent E3-activity for CHIP, the lack of general QC defects in knock-out cells suggests that the major readout of CHIP function in cortical neurons is the regulation of native folded substrates involved in maintaining cellular ‘health’. Thus, CHIP-mediated regulation of the of cytoskeletal- and membrane-related proteins is likely to make a vital contribution to the neuroprotective activity of CHIP.

Proteomics of human tissues and isolated cellular subpopulations create new opportunities for therapy and monitoring of a patients’ treatment in the clinic. Important considerations in such analysis include recovery of adequate amounts of protein for analysis and reproducibility in sample collection. In this study we compared several protocols for proteomic sample preparation: i) filter-aided sample preparation (FASP), ii) in-solution digestion (ISD) and iii) a pressure-assisted digestion (PCT) method. PCT method is known for already a decade [1], however it is not widely used in proteomic research. We assessed protocols for proteome profiling of isolated immune cell subsets and formalin-fixed paraffin embedded (FFPE) tissue samples. Our results show that the ISD method has very good efficiency of protein and peptide identification from the whole proteome, while the FASP method is particularly effective in identification of membrane proteins. Pressure-assisted digestion methods generally provide lower numbers of protein/peptide identifications, but have gained in popularity due to their shorter digestion time making them considerably faster than for ISD or FASP. Furthermore, PCT does not result in substantial sample loss when applied to samples of 50 000 cells. Analysis of FFPE tissues shows comparable results. ISD method similarly yields the highest number of identifications. Furthermore, proteins isolated from FFPE samples show a significant reduction of cleavages at lysine sites due to chemical modifications with formaldehyde-such as methylation (+14 Da) being among the most common. The data we present will be helpful for making decisions about the robust preparation of clinical samples for biomarker discovery and studies on pathomechanisms of various diseases.

Summary CHIP is an E3-ubiquitin ligase that contributes to healthy aging and has been characterized as neuroprotective. To elucidate dominant CHIP-dependent changes in protein steady-state levels in a patient-derived human neuronal model, CHIP function was ablated using gene-editing and an unbiased proteomic analysis conducted to compare knock-out and wild-type isogenic induced pluripotent stem cell (iPSC)-derived cortical neurons. Rather than a broad effect on protein homeostasis, loss of CHIP function impacted on a focused cohort of proteins from actin cytoskeleton signaling and membrane integrity networks. In support of the proteomics, CHIP knockout cells had enhanced sensitivity to induced membrane damage. We conclude that the major readout of CHIP function in cortical neurons derived from iPSC of a patient with elevate α-synuclein, Parkinson's disease and dementia, is the modulation of substrates involved in maintaining cellular “health”. Thus, regulation of the actin cytoskeletal and membrane integrity likely contributes to the neuroprotective function(s) of CHIP., Graphical abstract, Highlights • Cortical neurons were generated from iPSC of a patient with Parkinson's disease with ablated CHIP • SWATH-MS identified a focused cohort of CHIP modulated proteins • CHIP loss impacts actin cytoskeleton signaling and membrane integrity networks • CHIP is protective for induced membrane damage, Cell biology; Organizational aspects of cell biology; Bioinformatics; Omics; Proteomics

Tamoxifen treatment in breast cancer patients is associated with increased risk of endometrial malignancies. Significantly, higher AGR2 expression was found in endometrial cancers that developed in women previously treated with tamoxifen compared to those who had not been exposed to tamoxifen. An association of elevated AGR2 level with myometrial invasion occurrence and invasion depth was also found. In vitro analyses identified a stimulatory effect of AGR2 on cellular proliferation. Although adverse tamoxifen effects on endometrial cells remain elusive, our work identifies elevated AGR2 as a candidate tamoxifen-dependent mechanism of action responsible for increased incidence of endometrial cancer.

Ubiquitination is a vital posttranslational protein modification involved in the regulation of many eukaryotic signalling pathways. Aberrant ubiquitin signalling is known to be a molecular causality of certain cancer, neurodegenerative, immune system or cardiovascular diseases. The recent development of mass spectrometry methods enables qualitative and quantitative ubiquitination analysis in biological material from cancer patients. Research of ubiquitination may clarify the molecular cause of aberrant changes in the protein level of tumour suppressors or oncogenes.We aim to explain the meaning and importance of ubiquitination in certain molecular processes taking place in the human body. We hereby emphasise the connection between ubiquitination and malignant processes. A literature search is followed by introducing our mass spectrometry platform intended for ubiquitin identification via diglycyl remnants in the CHIP protein sequence. The aim is to introduce tandem mass spectrometry identification of ubiquitin modification, ubiquitination tandem mass spectra validation and the time-dependent manner of CHIP ubiquitination to the reader.A literature search familiarises the reader with known mechanisms of aberrant ubiquitination in malignant diseases. A successfully optimised mass spectrometry platform could serve as a potent tool for determining ubiquitin position in proteins that are a part of real tumour samples.

BACKGROUND The proteins of the cellular cytoplasmic membrane represent a heterogeneous group of proteins with different structures, localizations, and functions. They participate in many cellular processes including cellular signaling and communication with the external environment and communication between cells. Mutations and post-translational modifications alter the chemical-physical properties of membrane proteins and thus significantly affect the process of carcinogenesis. Therefore, membrane proteins represent important targets for the diagnosis and treatment of cancer. Nowadays, treatment in the form of monoclonal antibodies or low molecular weight inhibitors targets mainly receptors of growth factors on the surface of tumor cells and various types of molecules including the targets of the so-called checkpoint inhibitors on the surface of the cells of the immune system. In order to better understand the properties and functions of membrane proteins, especially with the perspective of developing new targeted approaches in therapy, mainly proteomic and molecular biological approaches are currently being used. AIM The aim of this article is to describe the properties and functions of different groups of membrane proteins and to summarize their current relevance and potential for use in oncology. Attention is focused on those groups that regulate the proliferation of tumor cells, affect the immune response, cause drug resistance and metastasis, and are already used or accepted as potential targets of biological therapy. Glycosylation and phosphorylation are described in detail as the most studied post-translational modification of membrane proteins, and mass spectrometry is presented as an effective tool for the identification and quantification of membrane proteins. Key words: membrane proteins - glycosylation - phosphorylation - proteomic analysis - targeted therapy This work was supported by the project MEYS - NPS I - LO1413. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 3. 8. 2018.

Background Although immune responses to “cancer neoantigens” have been known for decades, the first neoantigen vaccines emerged only very recently. Current developments in genomics and proteomics have enabled descriptions of tumor mutational landscapes, and the immunogenicity of corresponding neoantigens can now be predicted either in silico or in vitro. Cancer regression could be achieved via a combination of neoantigen vaccination and an appropriate immunology approach. Research in model organisms and the results of initial clinical trials of neoantigen vaccines have shown them to be effective. Purpose We aim to emphasize the importance of neoantigen vaccines in personalized cancer treatment and describe their preparation. We summarize mutations leading to expression of an immunogenic antigen necessary for vaccine development. The processes leading to activation of T-cell anticancer immunity in a patient are briefly introduced. We especially focus on the identification of high confidence neoantigens by next-generation sequencing (NGS) and mass spectrometry (MS), which is key element in the process of designing neoantigen vaccines. Briefly, we describe a proteogenomic platform for confident identification of mutant peptides in biological material. We mention the possibility of neoantigen quantification in biological material using mass spectrometry such as SRM (selected reaction monitoring) and SWATH (sequential windowed acquisition of all theoretical fragment ion spectra). Successful clinical studies demonstrating the potential of neoantigen vaccination in personalized cancer treatment are summarized at the end of the paper. Key words: vaccination - mass spectrometry - neoplasms - organ-specific neoantigen This work was supported by the project MEYS - NPS I - LO1413. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 9. 7. 2018.

Summary Accurate classification of breast tumors is vital for patient management decisions and enables more precise cancer treatment. Here, we present a quantitative proteotyping approach based on sequential windowed acquisition of all theoretical fragment ion spectra (SWATH) mass spectrometry and establish key proteins for breast tumor classification. The study is based on 96 tissue samples representing five conventional breast cancer subtypes. SWATH proteotype patterns largely recapitulate these subtypes; however, they also reveal varying heterogeneity within the conventional subtypes, with triple negative tumors being the most heterogeneous. Proteins that contribute most strongly to the proteotype-based classification include INPP4B, CDK1, and ERBB2 and are associated with estrogen receptor (ER) status, tumor grade status, and HER2 status. Although these three key proteins exhibit high levels of correlation with transcript levels (R > 0.67), general correlation did not exceed R = 0.29, indicating the value of protein-level measurements of disease-regulated genes. Overall, this study highlights how cancer tissue proteotyping can lead to more accurate patient stratification., Graphical Abstract, Highlights • Proteotyping of 96 breast tumors by SWATH mass spectrometry • Three key proteins for breast tumor classification • Varying degrees of heterogeneity within conventional breast cancer subtypes • Generally modest correlation between protein and transcript levels in tumor tissue, Bouchal et al. explore and confirm the suitability of SWATH-MS for proteotyping of human tumor samples at relatively high throughput. Results indicate that proteotype-based classification resolves more variability than is apparent from conventional subtyping and potentially improves current classification.

Anterior Gradient-2 (AGR2) is a component of a pro-oncogenic signalling pathway that can promote p53 inhibition, metastatic cell migration, limb regeneration, and cancer drug-resistance. AGR2 is in the protein-disulphide isomerase superfamily containing a single cysteine (Cys-81) that forms covalent adducts with its client proteins. We have found that mutation of Cysteine-81 attenuates its biochemical activity in its sequence-specific peptide docking function, reduces binding to Reptin, and reduces its stability in cells. As such, we evaluated how chemical oxidation of its cysteine affects its biochemical properties. Recombinant AGR2 spontaneously forms covalent dimers in the absence of reductant whilst DTT promotes dimer to monomer conversion. Mutation of Cysteine-81 to alanine prevents peroxide catalysed dimerization of AGR2 in vitro, suggesting a reactive cysteine is central to covalent dimer formation. Both biochemical assays and ESI mass spectrometry were used to demonstrate that low levels of a chemical oxidant promote an intermolecular disulphide bond through formation of a labile sulfenic acid intermediate. However, higher levels of oxidant promote sulfinic or sulfonic acid formation thus preventing covalent dimerization of AGR2. These data together identify the single cysteine of AGR2 as an oxidant responsive moiety that regulates its propensity for oxidation and its monomeric-dimeric state. This has implications for redox regulation of the pro-oncogenic functions of AGR2 protein in cancer cells.

Background/aim Pul-down assay is a popular in vitro method for identification of physical interactors of selected proteins. Here, for the first time, we compared three conventional variants of pull-down assay with the streptavidin-modified surface plasmon resonance (SPR) chips for the detection of PDZ and LIM domain protein 2 (PDLIM2) interaction partners. Materials and methods PDLIM2 protein-protein interactions were analysed by three variants of pull-down assay on streptavidin beads using LC-MS/MS in "Sequential Window Acquisition of all Theoretical fragment ion spectra (SWATH)" mode and compared with LC-SWATH-MS/MS data from SPR chips. Results The results showed that (i) the use of SPR chip led to comparable data compared to on-column streptavidin beads, (ii) gravity flow and microflow in wash and elution steps provided better results than centrifugation, and (iii) type and concentration of detergent did not significantly affect the interactome data of cancer-associated PDLIM2. Conclusion Our study supports further application of SPR-based affinity purification with SWATH mass spectrometry for reproducible and controlled characterization of cancer-associated interactomes.

Development of novel diagnostic and therapeutic approaches in cancer research requires sensitive and quantitative assays for determination of cancer associated proteins in clinical samples. Novel quantitative targeted proteomic approaches are overviewed in this communication. A major advantage of selected reaction monitoring (SRM) and pseudo- SRM lies in the selective and sensitive quantification of selected proteins in large sample sets. As such, they represent an alternative to immunochemical approaches. On the other hand, the potential of HRM and SWATH lies in recording of digital fingerprints, which enable post acquisition quantitative proteomic data mining on a similar basis to SRM. This article shows applications of targeted proteomics in a number of cancer research studies where they were used for quantification and validation of current or potential protein bio-markers and to study their role in cancer development and progression.

Metastases are responsible for most of the cases of death in patients with solid tumors. There is thus an urgent clinical need of better understanding the exact molecular mechanisms and finding novel therapeutics targets and biomarkers of metastatic disease of various tumors. Metastases are formed in a complicated biological process called metastatic cascade. Up to now, proteomics has enabled the identification of number of metastasis-associated proteins and potential biomarkers in cancer tissues, microdissected cells, model systems, and secretomes. Expression profiles and biological role of key proteins were confirmed in verification and functional experiments. This communication reviews these observations and analyses the methodological aspects of the proteomics approaches used. Moreover, it reviews contribution of current proteomics in the field of functional characterization and interactome analysis of proteins involved in various events in metastatic cascade. It is evident that ongoing technical progress will further increase proteome coverage and sample capacity of proteomics technologies, giving complex answers to clinical and functional questions asked.

Introduction Catechol-O-methyltransferase (COMT) plays an essential role in detoxification of catechols by transferring the methyl group from S-adenosyl-l-methionine to the substrate. In breast cancer, it catalyses methylation of oestrogen metabolites to block their oestrogenicity which prevents their oxidation to carcinogenic quinones. In this study we investigated whether its tumour suppressor role is limited to oestrogen receptor dependent breast cancer, or whether it has a general validity. Material and methods A differential cell surface proteomics analysis with SILAC-LC-MS quantification was performed on MDA-MB-231 breast cancer cell line and its clone selected for higher migration capacity. Analysis of migration and invasiveness of MCF7 cells stably transfected with COMT was performed using Transwell assay. The protein-level expression of COMT in different breast cancer subtypes was determined by next-generation, data independent acquisition based proteomics (96 patients) and immunohistochemistry (621 patients). Results and discussions A quantitative cell surface proteomics identified the membrane-bound isoform of COMT as a cell surface protein overexpressed in a more migrating clone of MDA-MB-231 cells, indicating the association of COMT with cell motility in triple negative breast cancer. On the other hand, overexpression of COMT in MCF-7 cells decreased cell migration and invasiveness, supporting tumour suppressor role in oestrogen receptor dependent breast cancer. Analysis of 96 primary breast cancer tumours using next generation proteomics showed increased COMT protein levels in more aggressive tumours: in grade 3 vs. grade 1, in luminal B vs. luminal A, in triple negative vs. luminal A, and in triple negative lymph node positive vs. triple negative lymph node negative tumours. Conclusion Based on our results, we hypothesise a dual role of COMT in breast cancer: while tumour suppressor role is further supported by our data in ER +breast cancer cells, in tissues COMT seems to be associated with more aggressive phenotype, namely in ER independent, triple negative breast cancer. It is thus evident that the dominance of catecholoestrogen methylation activity may be limited to ER dependent breast cancer. This may alter the perspective how COMT is considered as a potential diagnostic or therapeutic target. We thank Czech Science Foundation, project No. 17–05957S, for financial support.

Osteosarcoma (OS) is the most common primary tumor of the bone in both humans and dogs. The dog, with its spontaneously occurring OS, shared pathogenic pathways and active immune system is one of the best models for studying novel immunotherapeutic approaches to human OS. Checkpoint blockade using antibodies against PD-1 has revolutionized the current approach to treatment of melanoma and other cancers. Recent reports have also shown that tumor intrinsic signalling plays a potential role in the success of PD-1 blockade in melanoma although studies in OS have not been published to date. PD-1/PD-L1 signalling has been reported to have role in epithelial to mesenchymal transition. In this study, we wanted to characterize intrinsic PD-1 signalling in canine osteosarcoma. We have created a canine specific PD-1 monoclonal antibody and we identified that PD-1 is intrinsically expressed in the cell line tested- OSA31. To further characterize the effects of PD-1 expression in this cell line we cloned canine PD-1 into a pcDNA 3.1 expression vector and transfected the cell line. Transfection of the cell line with PD-1 resulted in phenotypic changes characteristic for mesenchymal to epithelial transition. Interestingly overexpression of PD-1 as well as blockade of this receptor using the created antibody, resulted in decrease in cellular proliferation. To our knowledge this is the first report to identify role of PD-1 in mesenchymal to epithelial transition. These findings also suggest that PD-1 may be a promising therapeutic target in canine OS and warrant future clinical trials. Citation Format: Maciej Parys, Marta Nekulová, Bořivoj Vojtěšek, Jakub Faktor, Ana Lima, Theodore Hupp. Tumor intrinsic PD-1/PD-L1 signalling induces mesenchymal to epithelial transition in canine osteosarcoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-115.

Targeted mass spectrometry-based proteomics approaches enable the simultaneous and reproducible quantification of multiple protein analytes across numerous conditions in biology and clinical studies. These approaches involve e.g. selected reaction monitoring (SRM) typically conducted on a triple quadrupole mass spectrometer, its high-resolution variant named pseudo-SRM (p-SRM), carried out in a quadrupole coupled with an TOF analyzer (qTOF), and "sequential window acquisition of all theoretical spectra" (SWATH). Here we compared these methods in terms of signal-to-noise ratio (S/N), coefficient of variance (CV), fold change (FC), limit of detection and quantitation (LOD, LOQ). We have shown the highest S/N for p-SRM mode, followed by SRM and SWATH, demonstrating a trade-off between sensitivity and level of multiplexing for SRM, p-SRM, and SWATH. SRM was more sensitive than p-SRM based on determining their LOD and LOQ. Although SWATH has the worst S/N, it enables peptidemultiplexing with post-acquisition definition of the targets, leading to better proteome coverage. FC between breast tumors of different clinical-pathological characteristics were highly correlated (R-2>0.97) across three methods and consistent with the previous study on 96 tumor tissues. Our technical note presented here, therefore, confirmed that outputs of all the three methods were biologically relevant and highly applicable to cancer research.

Cancer research often focuses on protein quantification in model cancer cell lines and cancer tissues. SWATH (sequential windowed acquisition of all theoretical fragment ion spectra), the state of the art method, enables the quantification of all proteins included in spectral library. Spectral library contains fragmentation patterns of each detectable protein in a sample. Thorough spectral library preparation will improve quantitation of low abundant proteins which usually play an important role in cancer.Our research is focused on the optimization of spectral library preparation aimed at maximizing the number of identified proteins in MCF-7 breast cancer cell line. First, we optimized the sample preparation prior entering the mass spectrometer. We examined the effects of lysis buffer composition, peptide dissolution protocol and the material of sample vial on the number of proteins identified in spectral library. Next, we optimized mass spectrometry (MS) method for spectral library data acquisition.Our thorough optimized protocol for spectral library building enabled the identification of 1,653 proteins (FDR1%) in 1 µg of MCF-7 lysate. This work contributed to the enhancement of protein coverage in SWATH digital biobanks which enable quantification of arbitrary protein from physically unavailable samples. In future, high quality spectral libraries could play a key role in preparing of patient proteome digital fingerprints.Key words: biomarker - mass spectrometry - proteomics - digital biobanking - SWATH - protein quantificationThis work was supported by the project MEYS - NPS I - LO1413.The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study.The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers.Submitted: 7. 5. 2016Accepted: 9. 6. 2016.