Identification Of Kinase Substrates Research Articles

Interrogating Kinase-Substrate Relationships with Proximity Labeling and Phosphorylation Enrichment.

Kinases govern many cellular responses through the reversible transfer of a phosphate moiety to their substrates. However, pairing a substrate with a kinase is challenging. In proximity labeling experiments, proteins proximal to a target protein are marked by biotinylation, and mass spectrometry can be used for their identification. Here, we combine ascorbate peroxidase (APEX) proximity labeling and a phosphorylation enrichment-based workflow, Phospho-APEX (pAPEX), to rapidly identify phosphorylated and biotinylated neighbor proteins which can be considered for candidate substrates. The pAPEX strategy enriches and quantifies differences in proximity for proteins and phosphorylation sites proximal to an APEX2-tagged kinase under the kinase "ON" and kinase "OFF" conditions. As a proof of concept, we identified candidate substrates of MAPK1 in HEK293T and HCT116 cells and candidate substrates of PKA in HEK293T cells. In addition to many known substrates, C15orf39 was identified and confirmed as a novel MAPK1 substrate. In all, we adapted the proximity labeling-based platform to accommodate phosphorylation analysis for kinase substrate identification.

An Affinity‐Based, Cysteine‐Specific ATP Analog for Kinase‐Catalyzed Crosslinking

AbstractKinases mediate cell signaling pathways by catalyzing protein phosphorylation. Irregularities in kinase activity are directly associated with disease conditions. Therefore, methods to identify substrates of a particular kinase are needed to understand signaling cascades in normal and diseased states. Photocrosslinking ATP analogs provide powerful tools to study kinases by covalently linking kinases with substrates. However, the involvement of UV light and nonspecific reactivity of current ATP‐photocrosslinkers challenge kinase–substrate identification. We report here an affinity‐based crosslinking ATP analog, ATP‐methylacrylamide (ATP‐MAc), that contains a cysteine‐reactive acrylamide crosslinking group, which avoids the UV irradiation and non‐specific reactivity of prior analogs. Using in vitro kinase assays, ATP‐MAc acts as a kinase co‐substrate and covalently crosslinks only kinases containing cysteines in the active site. ATP‐MAc was also able to crosslink cellular proteins in lysates, documenting compatibility with cell‐based studies.

The significant others: Global search for direct kinase substrates using chemical approaches.

Protein kinases function as key signaling hubs in the intricate network of biochemical signaling processes in the living cell. More than two-thirds of the human proteome is estimated to be phosphorylated at ~960,000 phosphosites, which makes it challenging to identify the direct contribution of any desired kinase in generating this phosphoproteome. In this review, we discuss some of the methods that have been developed over the years for global identification of kinase substrates. The methods are essentially categorized into two classes, namely, (i) direct tagging of kinase substrates and (ii) indirect phosphoproteomics-based approaches. We discuss the advantages and limitations entailed to each of the method introduced, with a special emphasis on the analog-sensitive (as) kinase approach method. © 2019 IUBMB Life, 71(6):721-737, 2019.

Modulation of plant growth in vivo and identification of kinase substrates using an analog-sensitive variant of CYCLIN-DEPENDENT KINASE A;1.

BackgroundModulation of protein activity by phosphorylation through kinases and subsequent de-phosphorylation by phosphatases is one of the most prominent cellular control mechanisms. Thus, identification of kinase substrates is pivotal for the understanding of many – if not all – molecular biological processes. Equally, the possibility to deliberately tune kinase activity is of great value to analyze the biological process controlled by a particular kinase.ResultsHere we have applied a chemical genetic approach and generated an analog-sensitive version of CDKA;1, the central cell-cycle regulator in Arabidopsis and homolog of the yeast Cdc2/CDC28 kinases. This variant could largely rescue a cdka;1 mutant and is biochemically active, albeit less than the wild type. Applying bulky kinase inhibitors allowed the reduction of kinase activity in an organismic context in vivo and the modulation of plant growth. To isolate CDK substrates, we have adopted a two-dimensional differential gel electrophoresis strategy, and searched for proteins that showed mobility changes in fluorescently labeled extracts from plants expressing the analog-sensitive version of CDKA;1 with and without adding a bulky ATP variant. A pilot set of five proteins involved in a range of different processes could be confirmed in independent kinase assays to be phosphorylated by CDKA;1 approving the applicability of the here-developed method to identify substrates.ConclusionThe here presented generation of an analog-sensitive CDKA;1 version is functional and represent a novel tool to modulate kinase activity in vivo and identify kinase substrates. Our here performed pilot screen led to the identification of CDK targets that link cell proliferation control to sugar metabolism, proline proteolysis, and glucosinolate production providing a hint how cell proliferation and growth are integrated with plant development and physiology.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0900-7) contains supplementary material, which is available to authorized users.

Identification of Direct Kinase Substrates via Kinase Assay-Linked Phosphoproteomics.

Protein phosphorylation plays an essential role in the regulation of various cellular functions. Dysregulation of phosphorylation is implicated in the pathogenesis of certain cancers, diabetes, cardiovascular diseases, and central nervous system disorders. As a result, protein kinases have become potential drug targets for treating a wide variety of diseases. Identification of kinase substrates is vital not only for dissecting signaling pathways, but also for understanding disease pathologies and identifying novel therapeutic targets. However, identification of bona fide kinase substrates has remained challenging, necessitating the development of new methods and techniques. The kinase assay linked phosphoproteomics (KALIP) approach integrates in vitro kinase assays with global phosphoproteomics experiments to identify the direct substrates of protein kinases. This strategy has demonstrated outstanding sensitivity and a low false-positive rate for kinase substrate screening.

In Vitro Methods to Study AMPK.

AMPK studies in cell-free and cellular systems have significantly contributed to recent progress in the AMPK field. Biochemical characterization, structure determination and elucidation of AMPK-dependent signalling events benefit from application of state-of-the-art tools and methodology. This chapter provides a synopsis of recombinant protein expression systems and biochemical and cell-based study methods. We summarize three different expression systems for AMPK production: bacteria, insect cells and mammalian cells. In addition, kinase activity measurement, kinase substrate identification and determination of physical interaction with AMPK are discussed. The last part of this chapter focuses on the use of pharmacological activation, inhibition, and molecular genetic tools to study AMPK involvement in cellular signalling pathways.

Abstract LB-052: Kinase identification of proximal substrates (KIPS): A novel chemical genetics approach for kinase substrate identification

Abstract Protein kinases are attractive targets for pharmacological intervention through their frequent disease associated aberration of cellular signalling networks. In this context an understanding of the myriad of substrates on which a protein kinase operates can help to reveal potential pharmacodynamic and patient stratification biomarkers. Kinase Identification of Proximal Substrates (KIPS) utilises an innovative chemical genetics approach to identify novel proximal biomarkers of kinase target response. This approach relies on the generation of a desensitized mutant protein that retains its kinase function, but loses sensitivity to small-molecule mediated inhibition. Comparative phospho-proteomics is performed on immuno-complexes of tagged wild type and mutant protein kinases in the presence and absence of inhibitor to isolate specific phospho-proteomic changes in proximal substrates. To exemplify the KIPS approach we have focused on the identification of novel substrates of the atypical protein kinase C isoform, PKCι. Through structure based design we identified two acidic amino acid residues in the PKCι nucleotide binding site that are crucial for efficacy of a previously characterized PKCι inhibitor, CRT0066854. Upon mutation to non-acidic alanine residues the PKCι protein is rendered insensitive to compound-mediated inhibition, allowing a comparison of wild type and mutant responses to PKCι inhibition to be made. Using HCT116 cells, we identified Myosin X as a putative substrate for PKCι, and demonstrated its specificity to the PKCι signalling axis through alanine-scanning peptide arrays and generation of phospho-specific antibodies. We show that the key acidic amino acids utilised in KIPS are highly conserved across the AGC and CAMK kinase super families. Furthermore, extensive compound SAR, diverse kinome profiling and structural biology have identified a tool box of inhibitor compounds with a broad range of activities across these kinase families leading to broader applicability of KIPS to enable the identification of individual kinase specific substrates and response across approximately 20% of the human kinome. Citation Format: jon roffey, Andrew Turnbull, Christian Dillon, Susan Boyd, Philippe Riou, Mark Linch, Peter Parker, Sven Kjaer, Neil McDonald. Kinase identification of proximal substrates (KIPS): A novel chemical genetics approach for kinase substrate identification. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-052. doi:10.1158/1538-7445.AM2015-LB-052

A method for sporulating budding yeast cells that allows for unbiased identification of kinase substrates using stable isotope labeling by amino acids in cell culture.

Quantitative proteomics has been widely used to elucidate many cellular processes. In particular, stable isotope labeling by amino acids in cell culture (SILAC) has been instrumental in improving the quality of data generated from quantitative high-throughput proteomic studies. SILAC uses the cell’s natural metabolic pathways to label proteins with isotopically heavy amino acids. Incorporation of these heavy amino acids effectively labels a cell’s proteome, allowing the comparison of cell cultures treated under different conditions. SILAC has been successfully applied to a variety of model organisms including yeast, fruit flies, plants, and mice to look for kinase substrates as well as protein–protein interactions. In budding yeast, several kinases are known to play critical roles in different aspects of meiosis. Therefore, the use of SILAC to identify potential kinase substrates would be helpful in the understanding the specific mechanisms by which these kinases act. Previously, it has not been possible to use SILAC to quantitatively study the phosphoproteome of meiotic Saccharomyces cerevisiae cells, because yeast cells sporulate inefficiently after pregrowth in standard synthetic medium. In this study we report the development of a synthetic, SILAC-compatible, pre-sporulation medium (RPS) that allows for efficient sporulation of S. cerevisiae SK1 diploids. Pre-growth in RPS supplemented with heavy amino acids efficiently labels the proteome, after which cells proceed relatively synchronously through meiosis, producing highly viable spores. As proof of principle, SILAC experiments were able to identify known targets of the meiosis-specific kinase Mek1.

Experimental and analytical approaches to characterize plant kinases using protein microarrays.

Comprehensive analysis of protein kinases and cellular signaling pathways requires the identification of kinase substrates and interaction partners using large-scale amenable approaches. Here, we describe our methods for producing plant protein microarrays (PMAs) and discuss various parameters critical to the quality of PMAs. Next, we describe methods for detecting protein-protein interactions and kinase activity including auto-phosphorylation and substrate phosphorylation. We have provided a short video demonstrating how to conduct an interaction assay and how to properly handle a protein microarray. Finally, a set of analytical methods are presented as a bioinformatics pipeline for the acquisition of PMA data and for selecting PMA candidates using statistical testing. The experimental and analytical protocols described here outline the steps to produce and utilize PMAs to analyze signaling networks.

Identification of Direct Tyrosine Kinase Substrates Based on Protein Kinase Assay-Linked Phosphoproteomics

Protein kinases are implicated in multiple diseases such as cancer, diabetes, cardiovascular diseases, and central nervous system disorders. Identification of kinase substrates is critical to dissecting signaling pathways and to understanding disease pathologies. However, methods and techniques used to identify bona fide kinase substrates have remained elusive. Here we describe a proteomic strategy suitable for identifying kinase specificity and direct substrates in high throughput. This approach includes an in vitro kinase assay-based substrate screening and an endogenous kinase dependent phosphorylation profiling. In the in vitro kinase reaction route, a pool of formerly phosphorylated proteins is directly extracted from whole cell extracts, dephosphorylated by phosphatase treatment, after which the kinase of interest is added. Quantitative proteomics identifies the rephosphorylated proteins as direct substrates in vitro. In parallel, the in vivo quantitative phosphoproteomics is performed in which cells are treated with or without the kinase inhibitor. Together, proteins phosphorylated in vitro overlapping with the kinase-dependent phosphoproteome in vivo represents the physiological direct substrates in high confidence. The protein kinase assay-linked phosphoproteomics was applied to identify 25 candidate substrates of the protein-tyrosine kinase SYK, including a number of known substrates and many novel substrates in human B cells. These shed light on possible new roles for SYK in multiple important signaling pathways. The results demonstrate that this integrated proteomic approach can provide an efficient strategy to screen direct substrates for protein tyrosine kinases.

ProPeL: A method to discover specific kinase motifs and predict target substrates

Identification of kinase substrates is essential to understanding the role kinases play in normal and disease states. Kinases discriminate between potential substrates in part by recognizing linear sequence “motifs” of amino acids surrounding the phosphorylated residue. Current techniques for discovering kinase motifs are often expensive and labor intensive. The Proteomic Peptide Library (ProPeL) method is a novel approach to discover kinase specificity motifs de novo. Briefly, human kinases are expressed in E. coli and allowed to phosphorylate bacterial proteins. After enzymatic digestion of the bacterial lysate, tandem mass spectrometry is performed and motifs are extracted from the identified peptide sequences using the authors’ pLogo and motif‐x software. The ProPeL methodology successfully recapitulated the known and diverse motifs for human basophilic Protein Kinase A (PKA) and acidophilic Casein Kinase II (CK II). We then used the motifs determined using the ProPeL methodology to directly predict with high accuracy, potential target substrates of each kinase in the human proteome using the authors’ scan‐x program. We thus demonstrate the validity of the found motifs and the approach to search for potential substrates. This study was funded in part by grants from the University of Connecticut Research Foundation (DS) and Genomes to Life from US Department of Energy (GMC).

Preparation of Recombinant Protein Spotted Arrays for Proteome‐Wide Identification of Kinase Targets

Protein microarrays allow unique approaches for interrogating global protein interaction networks. Protein arrays can be divided into two categories: antibody arrays and functional protein arrays. Antibody arrays consist of various antibodies and are appropriate for profiling protein abundance and modifications. Functional full-length protein arrays employ full-length proteins with various post-translational modifications. A key advantage of the latter is rapid parallel processing of large number of proteins for studying highly controlled biochemical activities, protein-protein interactions, protein-nucleic acid interactions, and protein-small molecule interactions. This unit presents a protocol for constructing functional yeast protein microarrays for global kinase substrate identification. This approach enables the rapid determination of protein interaction networks in yeast on a proteome-wide level. The same methodology can be readily applied to higher eukaryotic systems with careful consideration of overexpression strategy.

Current technologies to identify protein kinase substrates in high throughput.

Since the discovery of protein phosphorylation as an important modulator of many cellular processes, the involvement of protein kinases in diseases, such as cancer, diabetes, cardiovascular diseases, and central nervous system pathologies, has been extensively documented. Our understanding of many disease pathologies at the molecular level, therefore, requires the comprehensive identification of substrates targeted by protein kinases. In this review, we focus on recent techniques for kinase substrate identification in high throughput, in particular on genetic and proteomic approaches. Each method with its inherent advantages and limitations is discussed.

In Vivo Conditions to Identify Prkci Phosphorylation Targets Using the Analog-Sensitive Kinase Method in Zebrafish

Protein kinase C iota is required for various cell biological processes including epithelial tissue polarity and organ morphogenesis. To gain mechanistic insight into different roles of this kinase, it is essential to identify specific substrate proteins in their cellular context. The analog-sensitive kinase method provides a powerful tool for the identification of kinase substrates under in vivo conditions. However, it has remained a major challenge to establish screens based on this method in multicellular model organisms. Here, we report the methodology for in vivo conditions using the analog-sensitive kinase method in a genetically-tractable vertebrate model organism, the zebrafish. With this approach, kinase substrates can uniquely be labeled in the developing zebrafish embryo using bulky ATPγS analogs which results in the thiophosphorylation of substrates. The labeling of kinase substrates with a thiophosphoester epitope differs from phosphoesters that are generated by all other kinases and allows for an enrichment of thiophosphopeptides by immunoaffinity purification. This study provides the foundation for using the analog-sensitive kinase method in the context of complex vertebrate development, physiology, or disease.

Identification of kinase substrates by bimolecular complementation assays

As a consequence of the transient nature of kinase-substrate interactions, the detection of kinase targets, although central for understanding many biological processes, has remained challenging. Here we present a straightforward procedure that relies on the comparison of wild type with activation-loop mutants in the kinase of interest by bimolecular complementation assays. As a proof of functionality, we present the identification and in vivo confirmation of substrates of the major cell-cycle kinase in Arabidopsis, revealing a direct link between cell proliferation and the control of the redox state.

Deubiquitylase, DeSUMOylase, and DeISGylase Activity Microarrays for Assay of Substrate Preference and Functional Modifiers

Microarray-based proteomics expanded the information potential of DNA arrays to the level of protein translation and interaction, but so far, not much beyond. Although enzymatic activity from immobilized proteins has been reliably studied using surface plasmon resonance, a microarray of catalytically competent enzymes would facilitate high throughput, parallel study of their function. The ability to localize activity from soluble substrates has frustrated development of such an array. Here, we report the novel use of previously developed, highly specific suicide substrates for three families of enzymes: deubiquitylases, deSUMOylases, and deISGylases. We show specificity of each family to its cognate substrate, and demonstrate utility of the array in a secondary screen of small molecule inhibitors.

QIKS – Quantitative identification of kinase substrates

Signaling networks regulate cellular responses to external stimuli through post-translational modifications such as protein phosphorylation. Phosphoproteomics facilitate the large-scale identification of kinase substrates. Yet, the characterization of critical connections within these networks and the identification of respective kinases remain the major analytical challenge. To address this problem, we present a novel approach for the identification of direct kinase substrates using chemical genetics in combination with quantitative phosphoproteomics. Quantitative identification of kinase substrates (QIKS) is a novel-screening platform developed for the proteome-wide substrate-analysis of specific kinases. Here, we aimed to identify substrates of mitogen-activated protein kinase/Erk kinase (Mek1), an essential kinase in the mitogen-activated protein kinase cascade. An ATP analog-sensitive mutant of Mek1 (Mek1-as) was incubated with a cell extract from Mek1 deficient cells. Phosphorylated proteins were analyzed by LC-MS/MS of IMAC-enriched phosphopeptides, labeled differentially for relative quantification. The identification of extracellular regulated kinase 1/2 as the sole cytoplasmic substrates of MEK1 validates the applicability of this approach and suggests that QIKS could be used to identify substrates of a wide variety of kinases.

Discovery and Identification of Serine and Threonine Phosphorylated Proteins in Activated Mast Cells: Implications for Regulation of Protein Synthesis in the Rat Basophilic Leukemia Mast Cell Line RBL-2H3

Mast cells are important in allergic inflammation and innate immunity. Antigen-induced activation via cell-surface receptors initiates a series of intracellular signaling events, leading to the secretion of inflammatory mediators. While many of the kinases involved in this process have been defined, their substrates are generally unknown. This study aimed to identify proteins phosphorylated by serine or threonine kinases in the early stages of mast cell activation, using the rat basophilic leukemia cell line RBL-2H3 as a model system. Cells were activated via FcepsilonRI cross-linking, and lysed at different time points between 1-10 min. A novel, specific mixture of serine and threonine phospho-specific antibodies was utilized, and was shown to selectively detect proteins that were phosphorylated upon cell activation. The mixture of antibodies was used to immunoprecipitate such regulated phosphoproteins from cell lysates enriched in phosphoproteins by phospho-affinity chromatography. Immunoprecipitated proteins were analyzed by SDS-PAGE, Western blotting and liquid chromatography/mass spectrometry. With this approach, we highlighted a number of phosphoproteins, demonstrated differences in the phosphorylation/dephosphorylation rates among the regulated proteins, and identified eleven serine- or threonine-phosphorylated proteins that are substrates of kinases involved in mast cell intracellular signaling. Among these were proteins with functions in protein metabolism, including elongation factor 2, calnexin and heat shock proteins; and cell structure, including moesin, tubulin and actin. The novel approach applied in this study proved useful for the identification of kinase substrates, and can readily be extended for use in similar phosphoproteomic studies.

Protein kinase substrate identification on functional protein arrays

BackgroundOver the last decade, kinases have emerged as attractive therapeutic targets for a number of different diseases, and numerous high throughput screening efforts in the pharmaceutical community are directed towards discovery of compounds that regulate kinase function. The emerging utility of systems biology approaches has necessitated the development of multiplex tools suitable for proteomic-scale experiments to replace lower throughput technologies such as mass spectroscopy for the study of protein phosphorylation. Recently, a new approach for identifying substrates of protein kinases has applied the miniaturized format of functional protein arrays to characterize phosphorylation for thousands of candidate protein substrates in a single experiment. This method involves the addition of protein kinases in solution to arrays of immobilized proteins to identify substrates using highly sensitive radioactive detection and hit identification algorithms.ResultsTo date, the factors required for optimal performance of protein array-based kinase substrate identification have not been described. In the current study, we have carried out a detailed characterization of the protein array-based method for kinase substrate identification, including an examination of the effects of time, buffer compositions, and protein concentration on the results. The protein array approach was compared to standard solution-based assays for assessing substrate phosphorylation, and a correlation of greater than 80% was observed. The results presented here demonstrate how novel substrates for protein kinases can be quickly identified from arrays containing thousands of human proteins to provide new clues to protein kinase function. In addition, a pooling-deconvolution strategy was developed and applied that enhances characterization of specific kinase-substrate relationships and decreases reagent consumption.ConclusionFunctional protein microarrays are an important new tool that enables multiplex analysis of protein phosphorylation, and thus can be utilized to identify novel kinase substrates. Integrating this technology with a systems biology approach to cell signalling will help uncover new layers in our understanding of this essential class of enzymes.

A Coupled Chemical-Genetic and Bioinformatic Approach to Polo-like Kinase Pathway Exploration

Protein phosphorylation is a ubiquitous mechanism for cellular signal propagation, and signaling network complexity presents a challenge to protein kinase substrate identification. Few targets of Polo-like kinases are known, despite their significant role in coordinating cell-cycle progression. Here, we combine chemical-genetic, bioinformatic, and proteomic tools for Polo-like kinase substrate identification. Specific pharmacological inhibition of budding yeast Polo-like kinase, Cdc5, resulted in a misaligned preanaphase spindle and subsequently delayed anaphase nuclear migration, revealing a Cdc5 function. A cellular screen for Cdc5 substrates identified Spc72, a spindle pole body (SPB) component and microtubule anchor required for nuclear positioning. Spc72 bound to the Cdc5 PBD in a mitosis-specific manner, was phosphorylated by Cdc5 in vitro, and demonstrated a loss of mitotic phosphorylation in vivo upon Cdc5 inhibition. Finally, an examination of Cdc5 binding by SPB-localized proteins expanded our knowledge of Cdc5 function at the SPB.