Phosphoproteome Profiling Using an Isobaric Carrier without the Need for Phosphoenrichment

The application of proteomics and phosphoproteomics to reveal the molecular mechanism of salidroside in ameliorating myocardial hypoxia

Salidroside (SAL), belonging to a kind of the main active ingredient of Rhodiola rosea, is extensively utilized for anti-hypoxia and prevention of altitude sickness in the plateau region of China. However, the research on the systemic changes induced by SAL at intracellular protein level is still limited, especially at protein phosphorylation level. These limitations hinder a comprehensive understanding of the regulatory mechanisms of SAL. This study aimed to investigate the potential molecular mechanism of SAL in ameliorating the acute myocardial hypoxia induced by cobalt chloride using integrated proteomics and phosphoproteomics. We successfully identified 165 differentially expressed proteins and 266 differentially expressed phosphosites in H9c2 cells following SAL treatment under hypoxic conditions. Bioinformatics analysis and biological experiment validation revealed that SAL significantly antagonized CoCl2-mediated cell cycle arrest by downregulating CCND1 expression and upregulating AURKA, AURKAB, CCND3 and PLK1 expression. Additionally, SAL can stabilize the cytoskeleton through upregulating the Kinesin Family (KIF) members expression. Our study systematically revealed that SAL had the ability to protect myocardial cells against CoCl2-induced hypoxia through multiple biological pathways, including enhancing the spindle stability, maintaining the cell cycle, relieving DNA damage, and antagonizing cell apoptosis. This study supplies a comprehension perspective on the alterations at protein and protein phosphorylation levels induced by SAL treatment, thereby expanded our knowledge of the anti-hypoxic mechanisms of SAL. Moreover, this study provides a valuable resource for further investigating the effects of SAL.

Identification of a novel potent CDK inhibitor degrading cyclinK with a superb activity to reverse trastuzumab-resistance in HER2-positive breast cancer in vivo

CDK12 is overexpressed in HER2-positive breast cancers and promotes tumorigenesis and trastuzumab resistance. Thus CDK12 is a good therapeutic target for the HER2-positive breast tumors resistant to trastuzumab. We previously reported a novel purine-based CDK inhibitor with an ability to degrade cyclinK. Herein, we further explored and synthesized new derivatives, and identified a new potent pan-CDK inhibitor degrading cyclinK (32e). Compound 32e potently inhibited CDK12/cyclinK with IC50 = 3 nM, and suppressed the growth of the both trastuzumab-sensitive and trastuzumab-resistant HER2-positive breast cancer cell lines (GI50's = 9-21 nM), which is superior to a potent, clinical pan-CDK inhibitor dinaciclib. Moreover, 32e (10, 20 mg/kg, ip, twice a week) showed a dose-dependent inhibition of tumor growth and a more dramatic anti-cancer effect than dinaciclib in mouse in vivo orthotopic breast cancer model of trastuzumab-resistant HCC1954 cells. Kinome-wide inhibition profiling revealed that 32e at 1 μM exhibits a decent selectivity toward CDK-family kinases including CDK12 over other wildtype protein kinases. Quantitative global proteomic analysis of 32e-treated HCC1954 cells demonstrated that 32e also showed a decent selectivity in degrading cyclinK over other cyclins. Compound 32e could be developed as a drug for intractable trastuzumab-resistant HER2-positive breast cancers. Our current study would provide a useful insight in designing potent cyclinK degraders.

Cerium ions immobilized magnetic graphite nitride decorated with L-Alanyl-L-Glutamine as new chelator for enrichment of phosphopeptides

Cerium ions immobilized magnetic graphite nitride material have been prepared using L-Alanyl-L-Glutamine as the new chelator. The resulting Fe3O4/g-C3N4-L-Ala-L-Gln-Ce4+, as an immobilized metal ion affinity chromatography (IMAC) sorbent, was reusable. This is due to the strong coordination interaction between L-Alanyl-L-Glutamine and cerium ions. After a series of characterizations, the magnetic nanocomposite showed high surface area, good hydrophilicity, positive electricity, and magnetic response. Fe3O4/g-C3N4-L-Ala-L-Gln-Ce4+ had high sensitivity (0.1 fmol), selectivity (α-/β-casein/bovine serum albumin, 1:1:5000), and good recyclability (10 cycles). A total of 647 unique phosphopeptides mapped to 491 phosphoproteins were identified from A549 cell lysate by nano LC-MS analysis.

Sensitive N-Glycopeptide Profiling of Single and Rare Cells Using an Isobaric Labeling Strategy without Enrichment

Single-cell omics is critical in revealing population heterogeneity, discovering unique features of individual cells, and identifying minority subpopulations of interest. As one of the major post-translational modifications, protein N-glycosylation plays crucial roles in various important biological processes. Elucidation of the variation in N-glycosylation patterns at single-cell resolution may largely facilitate the understanding of their key roles in the tumor microenvironment and immune therapy. However, comprehensive N-glycoproteome profiling for single cells has not been achieved due to the extremely limited sample amount and incompatibility with the available enrichment strategies. Here, we have developed an isobaric labeling-based carrier strategy for highly sensitive intact N-glycopeptide profiling for single cells or a small number of rare cells without enrichment. Isobaric labeling has unique multiplexing properties, by which the "total" signal from all channels triggers MS/MS fragmentation for N-glycopeptide identification, while the reporter ions provide quantitative information. In our strategy, a carrier channel using N-glycopeptides obtained from bulk-cell samples significantly improved the "total" signal of N-glycopeptides and, therefore, promoted the first quantitative analysis of averagely 260 N-glycopeptides from single HeLa cells. We further applied this strategy to study the regional heterogeneity of N-glycosylation of microglia in mouse brain and discovered region-specific N-glycoproteome patterns and cell subtypes. In conclusion, the glycocarrier strategy provides an attractive solution for sensitive and quantitative N-glycopeptide profiling of single/rare cells that cannot be enriched by traditional workflows.

Recent progress in quantitative phosphoproteomics

INTRODUCTION

Protein phosphorylation is a critical post-translational modification involved in the regulation of numerous cellular processes from signal transduction to modulation of enzyme activities. Knowledge of dynamic changes of phosphorylation levels during biological processes, under various treatments or between healthy and disease models is fundamental for understanding the role of each phosphorylation event. Thereby, LC-MS/MS based technologies in combination with quantitative proteomics strategies evolved as a powerful strategy to investigate the function of individual protein phosphorylation events.

AREAS COVERED

State-of-the-art labeling techniques including stable isotope and isobaric labeling provide precise and accurate quantification of phosphorylation events. Here, we review the strengths and limitations of recent quantification methods and provide examples based on current studies, how quantitative phosphoproteomics can be further optimized for enhanced analytic depth, dynamic range, site localization, and data integrity. Specifically, reducing the input material demands is key to a broader implementation of quantitative phosphoproteomics, not least for clinical samples.

EXPERT OPINION

Despite quantitative phosphoproteomics is one of the most thriving fields in the proteomics world, many challenges still have to be overcome to facilitate even deeper and more comprehensive analyses as required in the current research, especially at single cell levels and in clinical diagnostics.

One-STAGE Tip Method for TMT-Based Proteomic Analysis of a Minimal Amount of Cells

Liquid chromatography-tandem mass spectrometry (LC-MS)-based profiling of proteomes with isobaric tag labeling from low-quantity biological and clinical samples, including needle-core biopsies and laser capture microdissection, has been challenging due to the limited amount and sample loss during preparation. To address this problem, we developed OnM (On-Column from Myers et al. and mPOP)-modified on-column method combining freeze-thaw lysis of mPOP with isobaric tag labeling of On-Column method to minimize sample loss. OnM is a method that processes the sample in one-STAGE tip from cell lysis to tandem mass tag (TMT) labeling without any transfer of the sample. In terms of protein coverage, cellular components, and TMT labeling efficiency, the modified On-Column (or OnM) displayed similar performance to the results from Myers et al. To evaluate the lower-limit processing capability of OnM, we utilized OnM for multiplexing and were able to quantify 301 proteins in a TMT 9-plex with 50 cells per channel. We optimized the method as low as 5 cells per channel in which we identified 51 quantifiable proteins. OnM method is a low-input proteomics method widely applicable and capable of identifying and quantifying proteomes from limited samples, with tools that are readily available in a majority of proteomic laboratories.

A streamlined tandem tip-based workflow for sensitive nanoscale phosphoproteomics

Effective phosphoproteome of nanoscale sample analysis remains a daunting task, primarily due to significant sample loss associated with non-specific surface adsorption during enrichment of low stoichiometric phosphopeptide. We develop a tandem tip phosphoproteomics sample preparation method that is capable of sample cleanup and enrichment without additional sample transfer, and its integration with our recently developed SOP (Surfactant-assisted One-Pot sample preparation) and iBASIL (improved Boosting to Amplify Signal with Isobaric Labeling) approaches provides a streamlined workflow enabling sensitive, high-throughput nanoscale phosphoproteome measurements. This approach significantly reduces both sample loss and processing time, allowing the identification of >3000 (>9500) phosphopeptides from 1 (10) µg of cell lysate using the label-free method without a spectral library. It also enables precise quantification of ~600 phosphopeptides from 100 sorted cells (single-cell level input for the enriched phosphopeptides) and ~700 phosphopeptides from human spleen tissue voxels with a spatial resolution of 200 µm (equivalent to ~100 cells) in a high-throughput manner. The new workflow opens avenues for phosphoproteome profiling of mass-limited samples at the low nanogram level.