Photoaffinity-engineered protein scaffold for systematically exploring native phosphotyrosine signaling complexes in tumor samples

Clinical functional proteomics of intercellular signalling in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) has an atypical, highly stromal tumour microenvironment (TME) that profoundly contributes to its poor prognosis1. Here, to better understand the intercellular signalling between cancer and stromal cells directly in PDAC tumours, we developed a multidimensional proteomic strategy called TMEPro. We applied TMEPro to profile the glycosylated secreted and plasma membrane proteome of 100 human pancreatic tissue samples to a great depth, define cell type origins and identify potential paracrine cross-talk, especially that mediated through tyrosine phosphorylation. Temporal dynamics during pancreatic tumour progression were investigated in a genetically engineered PDAC mouse model. Functionally, we revealed reciprocal signalling between stromal cells and cancer cells mediated by the stromal PDGFR-PTPN11-FOS signalling axis. Furthermore, we examined the generic shedding mechanism of plasma membrane proteins in PDAC tumours and revealed that matrix-metalloprotease-mediated shedding of the AXL receptor tyrosine kinase ectodomain provides an additional dimension of intercellular signalling regulation in the PDAC TME. Importantly, the level of shed AXL has a potential correlation with lymph node metastasis, and inhibition of AXL shedding and its kinase activity showed a substantial synergistic effect in inhibiting cancer cell growth. In summary, we provide TMEPro, a generically applicable clinical functional proteomic strategy, and a comprehensive resource for better understanding the PDAC TME and facilitating the discovery of new diagnostic and therapeutic targets.

Investigation of Peptide Labeling with ortho-Phthalaldehyde and 2-Acylbenzaldehyde

ortho-Phthalaldehyde (OPA) with high reactivity to the amine group has been widely used to modify proteins. We discovered new modifications of OPA and 2-acylbenzaldehyde and proposed the reaction mechanism. Using isotope labeling mass spectrometry-based experiment, we identified new cross-linking properties of OPA and 2-acylbenzaldehyde. This reactivity revealed that OPA has the potential to probe proximal amino acids in biological systems.

[Applications of high performance liquid chromatography-mass spectrometry in proteomics]

Proteomics profiling plays an important role in biomedical studies. Proteomics studies are much more complicated than genome research, mainly because of the complexity and diversity of proteomic samples. High performance liquid chromatography-mass spectrometry (HPLC-MS) is a fundamental tool in proteomics research owing to its high speed, resolution, and sensitivity. Proteomics research targets from the peptides and individual proteins to larger protein complexes, the molecular weight of which gradually increases, leading to sustained increases in structural and compositional complexity and alterations in molecular properties. Therefore, the selection of various separation strategies and stationary-phase parameters is crucial when dealing with the different targets in proteomics research for in-depth proteomics analysis. This article provides an overview of commonly used chromatographic-separation strategies in the laboratory, including reversed-phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC), hydrophobic interaction chromatography (HIC), ion-exchange chromatography (IEC), and size-exclusion chromatography (SEC), as well as their applications and selectivity in the context of various biomacromolecules. At present, no single chromatographic or electrophoretic technology features the peak capacity required to resolve such complex mixtures into individual components. Multidimensional liquid chromatography (MDLC), which combines different orthogonal separation modes with MS, plays an important role in proteomics research. In the MDLC strategy, IEC, together with RPLC, remains the most widely used separation mode in proteomics analysis; other chromatographic methods are also frequently used for peptide/protein fractionation. MDLC technologies and their applications in a variety of proteomics analyses have undergone great development. Two strategies in MDLC separation systems are mainly used in proteomics profiling: the "bottom-up" approach and the "top-down" approach. The "shotgun" method is a typical "bottom-up" strategy that is based on the RPLC or MDLC separation of whole-protein-sample digests coupled with MS; it is an excellent technique for identifying a large number of proteins. "Top-down" analysis is based on the separation of intact proteins and provides their detailed molecular information; thus, this technique may be advantageous for analyzing the post-translational modifications (PTMs) of proteins. In this paper, the "bottom-up" "top-down" and protein-protein interaction (PPI) analyses of proteome samples are briefly reviewed. The diverse combinations of different chromatographic modes used to set up MDLC systems are described, and compatibility issues between mobile phases and analytes, between mobile phases and MS, and between mobile phases in different separation modes in multidimensional chromatography are analyzed. Novel developments in MDLC techniques, such as high-abundance protein depletion and chromatography arrays, are further discussed. In this review, the solutions proposed by researchers when encountering compatibility issues are emphasized. Moreover, the applications of HPLC-MS combined with various sample pretreatment methods in the study of exosomal and single-cell proteomics are examined. During exosome isolation, the combined use of ultracentrifugation and SEC can yield exosomes of higher purity. The use of SEC with ultra-large-pore-size packing materials (200 nm) enables the isolation of exosomal subgroups, and proteomics studies have revealed significant differences in protein composition and function between these subgroups. In the field of single-cell proteomics, researchers have addressed challenges related to reducing sample processing volumes, preventing sample loss, and avoiding contamination during sample preparation. Innovative methods and improvements, such as the utilization of capillaries for sample processing and microchips as platforms to minimize the contact area of the droplets, have been proposed. The integration of these techniques with HPLC-MS shows some progress. In summary, this article focuses on the recent advances in HPLC-MS technology for proteomics analysis and provides a comprehensive reference for future research in the field of proteomics.

Integrated Platform for Large-Scale Quantitative Profiling of Phosphotyrosine Signaling Complexes Based on Cofractionation/Mass Spectrometry and Complex-Centric Algorithm

The scarcity and dynamic nature of phosphotyrosine (pTyr)-modified proteins pose a challenge for researching protein complexes with pTyr modification, which are assembled through multiple protein-protein interactions. We developed an integrated complex-centric platform for large-scale quantitative profiling of pTyr signaling complexes based on cofractionation/mass spectrometry (CoFrac-MS) and a complex-centric algorithm. We initially constructed a trifunctional probe based on pTyr superbinder (SH2-S) for specifically binding and isolation of intact pTyr protein complexes. Then, the CoFrac-MS strategy was employed for the identification of pTyr protein complexes by integrating ion exchange chromatography in conjunction with data independent acquisition mass spectrometry. Furthermore, we developed a novel complex-centric algorithm for quantifying protein complexes based on the protein complex elution curve. Utilizing this algorithm, we effectively quantified 216 putative protein complexes. We further screened 21 regulated pTyr protein complexes related to the epidermal growth factor signal. Our study engenders a comprehensive framework for the intricate examination of pTyr protein complexes and presents, for the foremost occasion, a quantitative landscape delineating the composition of pTyr protein complexes in HeLa cells.

Novel dual inhibitors of PARP and HDAC induce intratumoral STING-mediated antitumor immunity in triple-negative breast cancer

PARP inhibitors and HDAC inhibitors have been approved for the clinical treatment of malignancies, but acquired resistance of or limited effects on solid tumors with a single agent remain as challenges. Bioinformatics analyses and a combination of experiments had demonstrated the synergistic effects of PARP and HDAC inhibitors in triple-negative breast cancer. A series of novel dual PARP and HDAC inhibitors were rationally designed and synthesized, and these molecules exhibited high enzyme inhibition activity with excellent antitumor effects in vitro and in vivo. Mechanistically, dual PARP and HDAC inhibitors induced BRCAness to restore synthetic lethality and promoted cytosolic DNA accumulation, which further activates the cGAS-STING pathway and produces proinflammatory chemokines through type I IFN-mediated JAK-STAT pathway. Moreover, these inhibitors promoted neoantigen generation, upregulated antigen presentation genes and PD-L1, and enhanced antitumor immunity when combined with immune checkpoint blockade therapy. These results indicated that novel dual PARP and HDAC inhibitors have antitumor immunomodulatory functions in triple-negative breast cancer. Novel dual PARP and HDAC inhibitors induce BRCAness to restore synthetic lethality, activating tumoral IFN signaling via the cGAS-STING pathway and inducing cytokine production, promoting neoantigen generation and presentation to enhance the immune response.

Chemical Proteomic Approach for In-Depth Glycosylation Profiling of Plasma Carcinoembryonic Antigen in Cancer Patients

Carcinoembryonic antigen (CEA) of human plasma is a biomarker of many cancer diseases, and its N-glycosylation accounts for 60% of molecular mass. It is highly desirable to characterize its glycoforms for providing additional dimension of features to increase its performance in prognosis and diagnosis of cancers. However, to systematically characterize its site-specific glycosylation is challenging because of its low abundance. Here, we developed a highly sensitive strategy for in-depth glycosylation profiling of plasma CEA through chemical proteomics combined with multienzymatic digestion. A trifunctional probe was utilized to generate covalent bond of plasma CEA and its antibody upon UV irradiation. As low as 1 ng/ml CEA in plasma could be captured and digested with trypsin and chymotrypsin for intact glycopeptide characterization. Twenty six of 28 potential N-glycosylation sites were well identified, which were the most comprehensive N-glycosylation site characterization of CEA on intact glycopeptide level as far as we known. Importantly, this strategy was applied to the glycosylation analysis of plasma CEA in cancer patients. Differential site-specific glycoforms of plasma CEA were observed in patients with colorectal cancers (CRCs) and lung cancer. The distributions of site-specific glycoforms were different as the progression of CRC, and most site-specific glycoforms were overexpressed in stage II of CRC. Overall, we established a highly sensitive chemical proteomic method to profile site-specific glycosylation of plasma CEA, which should generally applicable to other well-established cancer glycoprotein biomarkers for improving their cancer diagnosis and monitoring performance.

Chemical biology tools for protein labelling: insights into cell-cell communication

Multicellular organisms require carefully orchestrated communication between and within cell types and tissues, and many unicellular organisms also sense their context and environment, sometimes coordinating their responses. This review highlights contributions from chemical biology in discovering and probing mechanisms of cell-cell communication. We focus on chemical tools for labelling proteins in a cellular context and how these can be applied to decipher the target receptor of a signalling molecule, label a receptor of interest in situ to understand its biology, provide a read-out of protein activity or interactions in downstream signalling pathways, or discover protein-protein interactions across cell-cell interfaces.

Deciphering intercellular signaling complexes by interaction-guided chemical proteomics

Indirect cell-cell interactions mediated by secreted proteins and their plasma membrane receptors play essential roles for regulating intercellular signaling. However, systematic profiling of the interactions between living cell surface receptors and secretome from neighboring cells remains challenging. Here we develop a chemical proteomics approach, termed interaction-guided crosslinking (IGC), to identify ligand-receptor interactions in situ. By introducing glycan-based ligation and click chemistry, the IGC approach via glycan-to-glycan crosslinking successfully captures receptors from as few as 0.1 million living cells using only 10 ng of secreted ligand. The unparalleled sensitivity and selectivity allow systematic crosslinking and identification of ligand-receptor complexes formed between cell secretome and surfaceome in an unbiased and all-to-all manner, leading to the discovery of a ligand-receptor interaction between pancreatic cancer cell-secreted urokinase (PLAU) and neuropilin 1 (NRP1) on pancreatic cancer-associated fibroblasts. This approach is thus useful for systematic exploring new ligand-receptor pairs and discovering critical intercellular signaling events.

Functional and Clinical Proteomic Exploration of Pancreatic Cancer

Pancreatic cancer, most cases being pancreatic ductal adenocarcinoma (PDAC), is one of the most lethal cancers with a median survival time of less than 6 months. Therapeutic options are very limited for PDAC patients, and surgery is still the most effective treatment, making improvements in early diagnosis critical. One typical characteristic of PDAC is the desmoplastic reaction of its stroma microenvironment, which actively interacts with cancer cells to orchestrate key components in tumorigenesis, metastasis, and chemoresistance. Global exploration of cancer-stroma crosstalk is essential to decipher PDAC biology and design intervention strategies. Over the past decade, the dramatic improvement of proteomics technologies has enabled profiling of proteins, post-translational modifications (PTMs), and their protein complexes at unprecedented sensitivity and dimensionality. Here, starting with our current understanding of PDAC characteristics, including precursor lesions, progression models, tumor microenvironment, and therapeutic advancements, we describe how proteomics contributes to the functional and clinical exploration of PDAC, providing insights into PDAC carcinogenesis, progression, and chemoresistance. We summarize recent achievements enabled by proteomics to systematically investigate PTMs-mediated intracellular signaling in PDAC, cancer-stroma interactions, and potential therapeutic targets revealed by these functional studies. We also highlight proteomic profiling of clinical tissue and plasma samples to discover and verify useful biomarkers that can aid early detection and molecular classification of patients. In addition, we introduce spatial proteomic technology and its applications in PDAC for deconvolving tumor heterogeneity. Finally, we discuss future prospects of applying new proteomic technologies in comprehensively understanding PDAC heterogeneity and intercellular signaling networks. Importantly, we expect advances in clinical functional proteomics for exploring mechanisms of cancer biology directly by high-sensitivity functional proteomic approaches starting from clinical samples.

Integrated and High-Throughput Approach for Sensitive Analysis of Tyrosine Phosphoproteome

Tyrosine phosphorylation (pTyr) regulates various signaling pathways under normal and cancerous states. Due to their low abundance and transient and dynamic natures, systematic profiling of pTyr sites is challenging. Antibody and engineered binding domain-based approaches have been well applied to pTyr peptide enrichment. However, traditional methods have the disadvantage of a long sample preparation process, which makes them unsuitable for processing limited amount of samples, especially in a high-throughput manner. In this study we developed a 96-well microplate-based approach to integrate all the sample preparation steps starting from cell culture to MS-compatible pTyr peptide enrichment in three consecutive 96-well microplates. By assembling an engineered SH2 domain onto a microplate, nonspecific adsorption of phosphopeptides is greatly reduced, which allows us to remove the Ti-IMAC purification and three C18 desalting steps (after digestion, pTyr enrichment, and Ti-IMAC purification) and, therefore, greatly simplifies the entire pTyr peptide enrichment workflow, especially when processing a large number of samples. Starting with 96-well microplate-cultured, pervanadate-stimulated cells, our approach could enrich 21% more pTyr sites than the traditional serial pTyr enrichment approach and showed good sensitivity and reproducibility in the range of 200 ng to 200 μg peptides. Importantly, we applied this approach to profile tyrosine kinase inhibitor-mediated EGFR signaling pathway and could well differentiate the distinct response of different pTyr sites. Collectively, the integrated 96-well microplate-based approach is valuable for profiling pTyr sites from limited biological samples and in a high-throughput manner.

Advances in enrichment methods for mass spectrometry-based proteomics analysis of post-translational modifications

Post-translational modifications (PTMs) occur during or after protein biosynthesis and increase the functional diversity of proteome. They comprise phosphorylation, acetylation, methylation, glycosylation, ubiquitination, sumoylation (among many other modifications), and influence all aspects of cell biology. Mass-spectrometry (MS)-based proteomics is the most powerful approach for PTM analysis. Despite this, it is challenging due to low abundance and labile nature of many PTMs. Hence, enrichment of modified peptides is required for MS analysis. This review provides an overview of most common PTMs and a discussion of current enrichment methods for MS-based proteomics analysis. The traditional affinity strategies, including immunoenrichment, chromatography and protein pull-down, are outlined together with their strengths and shortcomings. Moreover, a special attention is paid to chemical enrichment strategies, such as capture by chemoselective probes, metabolic and chemoenzymatic labelling, which are discussed with an emphasis on their recent progress. Finally, the challenges and future trends in the field are discussed.

Kindlin-2 promotes Src-mediated tyrosine phosphorylation of androgen receptor and contributes to breast cancer progression

Androgen receptor (AR) signaling plays important roles in breast cancer progression. We show here that Kindlin-2, a focal adhesion protein, is critically involved in the promotion of AR signaling and breast cancer progression. Kindlin-2 physically associates with AR and Src through its two neighboring domains, namely F1 and F0 domains, resulting in formation of a Kindlin-2-AR-Src supramolecular complex and consequently facilitating Src-mediated AR Tyr-534 phosphorylation and signaling. Depletion of Kindlin-2 was sufficient to suppress Src-mediated AR Tyr-534 phosphorylation and signaling, resulting in diminished breast cancer cell proliferation and migration. Re-expression of wild-type Kindlin-2, but not AR-binding-defective or Src-binding-defective mutant forms of Kindlin-2, in Kindlin-2-deficient cells restored AR Tyr-534 phosphorylation, signaling, breast cancer cell proliferation and migration. Furthermore, re-introduction of phosphor-mimic mutant AR-Y534D, but not wild-type AR reversed Kindlin-2 deficiency-induced inhibition of AR signaling and breast cancer progression. Finally, using a genetic knockout strategy, we show that ablation of Kindlin-2 from mammary tumors in mouse significantly reduced AR Tyr-534 phosphorylation, breast tumor progression and metastasis in vivo. Our results suggest a critical role of Kindlin-2 in promoting breast cancer progression and shed light on the molecular mechanism through which it functions in this process.

Generic Plug-and-Play Strategy for High-Throughput Analysis of PTM-Mediated Protein Complexes

Protein complexes mediated by various post-translational modifications (PTMs) play important roles in almost every aspect of biological processes. PTM-mediated protein complexes often have weak and transient binding properties, which limit their unbiased profiling especially in complex biological samples. Here, we developed a plug-and-play chemical proteomic approach for high-throughput analyis of PTM-mediated protein complexes. Taking advantage of the glutathione-S-transferase (GST) tag, which is the gold standard for protein purification and has wide access to a variety of proteins of interest (POIs), a glutathione (GSH) group- and photo-cross-linking group-containing trifunctional chemical probe was developed to tag POIs and assembled onto a streptavidin-coated 96-well plate for affinity purification, photo-cross-linking, and proteomics sample preparation in a fully integrated manner. Compared with the previously developed photo-pTyr-scaffold strategy, by assembling the tyrosine phosphorylation (pTyr) binding domain through covalent NHS chemistry, the new plug-and-play strategy using a noncovalent GST-GSH interaction has comparable enrichment efficiency for EGF stimulation-dependent pTyr protein complexes. To further prove its feasibility, we additionally assembled four pTyr-binding domains in the 96-well plate and selectively identified their pTyr-dependent interacting proteins. Importantly, we systematically optimized and applied the plug-and-play approach for exploring protein methylation-mediated protein complexes, which are difficult to be characterized due to their weak binding affinity and the lack of efficient enrichment strategies. We explored a comprehensive protein methylation-mediated interaction network assembled by five protein methylation binding domains including the chromo domain of MPP8, tandem tudor domain of KDM4A, full-length CBX1, PHD domain of RAG2, and tandem tudor domain of TP53BP1 and validated the chromo domain- and tudor domain-mediated interaction with histone H3. Collectively, this plug-and-play approach provides a convenient and generic strategy for exploring PTM-dependent protein complexes for any POIs with the GST tag.

Strategy for high-throughput identification of protein complexes by array-based multi-dimensional liquid chromatography-mass spectrometry

Comprehensive elucidation of the composition of multiprotein complexes in model organisms is essential to understand conserved biological systems, but large-scale mapping physical association networks is still challenging due to limited throughput of present methods. In this work, a strategy coupling array-based online two-dimensional liquid chromatography (array-based 2D-LC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was demonstrated for high throughput and in-depth identification of protein complexes from cultured human HeLa cell extracts. Mixed-bed ion-exchange column was employed as the first dimensional (1^stD) separating mode and an array consisting of eight reversed phase columns was developed as the second dimensional (2^ndD) mode. Taking advantage of array parallel strategy, this online system showed an 8-fold increase in throughput. After array-based online 2D-LC separation, altogether 256 × 2^ndD fractions were collected for further LC-MS/MS analysis. Public databases of protein-protein interaction (PPI) and co-elution curves identified by LC-MS were applied to reconstruct the protein complexes. A rigorous inspection was operated by cataloging the protein complexes into chromatographic fractions to minimize the number of false positives. As result, a total number of 4,436 proteins were identified and 26,092 elution curves were graphed. A network consisting of 47,745 PPIs was established among 2,201 proteins and presented 1,530 putative protein complexes with high confidence. Most of the identified PPIs were linked to diverse biological processes and may reveal further disease mechanism and therapeutic strategy.

High-Throughput and Integrated Chemical Proteomic Approach for Profiling Phosphotyrosine Signaling Complexes

Phosphotyrosine (pTyr) signaling complexes are important resources of biomarkers and drug targets which often need to be profiled with enough throughput. Current profiling approaches are not feasible to meet this need due to either biased profiling by antibody-based detection or low throughput by traditional affinity purification-mass spectrometry approach (AP-MS), as exemplified by our previously developed photo-pTyr-scaffold approach. To address these limitations, we developed a 96-well microplate-based sample preparation and fast data independent proteomic analysis workflow. By assembling the photo-pTyr-scaffold probe into a 96-well microplate, we achieved steric hindrance-free photoaffinity capture of pTyr signaling complexes, selective enrichment under denaturing conditions, and efficient in-well digestion in a fully integrated manner. EGFR signaling complex proteins could be efficiently captured and identified by using 300 times less cell lysate and 100 times less photo-pTyr-scaffold probe as compared with our previous approach operated in an Eppendorf tube. Furthermore, the lifetime of the photo-pTyr-scaffold probe in a 96-well microplate was significantly extended from 1 week up to 1 month. More importantly, by combining with high-flow nano LC separation and data independent acquisition on the Q Exactive HF-X mass spectrometer, LC-MS time could be significantly reduced to only 35 min per sample without increasing sample loading amount and compromising identification and quantification performance. This new high-throughput proteomic approach allowed us to rapidly and reproducibly profile dynamic pTyr signaling complexes with EGF stimulation at five time points and EGFR inhibitor treatment at five different concentrations. We are therefore optimized for its generic application in biomarkers discovery and drug screening in a high-throughput fashion.

Chondroitin sulfate synthase 1 enhances proliferation of glioblastoma by modulating PDGFRA stability

Chondroitin sulfate synthases, a family of enzyme involved in chondroitin sulfate (CS) polymerization, are dysregulated in various human malignancies, but their roles in glioma remain unclear. We performed database analysis and immunohistochemistry on human glioma tissue, to demonstrate that the expression of CHSY1 was frequently upregulated in glioma, and that it was associated with adverse clinicopathologic features, including high tumor grade and poor survival. Using a chondroitin sulfate-specific antibody, we showed that the expression of CHSY1 was significantly associated with CS formation in glioma tissue and cells. In addition, overexpression of CHSY1 in glioma cells enhanced cell viability and orthotopic tumor growth, whereas CHSY1 silencing suppressed malignant growth. Mechanistic investigations revealed that CHSY1 selectively regulates PDGFRA activation and PDGF-induced signaling in glioma cells by stabilizing PDGFRA protein levels. Inhibiting PDGFR activity with crenolanib decreased CHSY1-induced malignant characteristics of GL261 cells and prolonged survival in an orthotopic mouse model of glioma, which underlines the critical role of PDGFRA in mediating the effects of CHSY1. Taken together, these results provide information on CHSY1 expression and its role in glioma progression, and highlight novel insights into the significance of CHSY1 in PDGFRA signaling. Thus, our findings point to new molecular targets for glioma treatment.

High-Throughput Phosphotyrosine Protein Complexes Screening by Photoaffinity-Engineered Protein Scaffold-Based Forward-Phase Protein Array

Low-abundance phosphotyrosine (pTyr)-mediated signaling protein complexes play critical roles in cancer signaling. The precise and comprehensive profiling of these pTyr-mediated protein complexes remains challenging because of their dynamic nature and weak binding affinity. Taking advantage of the SH2 domains modified with trifunctional chemical probes and genetic mutations (termed Photo-pTyr-scaffold), we developed a Photo-pTyr-scaffold-based forward-phase protein array that can be used to specifically capture complexes by developing an engineered SH2 domain, photoaffinity cross-linking, and antibody-based measuring weak pTyr-mediated protein complexes from complex biological samples in a 96-well microplate format. This platform demonstrated good precision for quantitation (R² = 0.99) and high sensitivity by which only 5 μg of whole cell lysates is needed. We successfully applied the technology for profiling the dynamic EGF-stimulation-dependent EGFR signaling protein complexes across four different time courses (i.e., 0, 2, 5, 10, and 30 min) in a high-throughput manner. We further evaluated the modulation of EGFR-GRB2-SHC1 protein complexes by FDA-approved EGFR kinase inhibitor erlotinib, demonstrating the feasibility of this approach for high-throughput drug screening. The Photo-pTyr-scaffold-based forward-phase protein array could be generically applicable for exploring the dynamic pTyr signaling complexes in various biological systems and screening for related drugs in a high-throughput manner.