Assaying Bcr-Abl kinase activity and inhibition in whole cell extracts by phosphorylation of substrates immobilized on agarose beads

Abstract

There is a current and increasing demand for simple, robust, nonradioactive assays of protein tyrosine kinase activity with applications for clinical diagnosis and high-throughput screening of potential molecularly targeted therapeutic agents. One significant challenge is to detect and measure the activity of specific kinases with key roles in cell signaling as an approach to distinguish normal cells from cancer cells and as a means of evaluating targeted drug efficacy and resistance in cancer cells. Here, we describe a method in which kinase substrates fused to glutathione-S-transferase and immobilized on glutathione agarose beads are phosphorylated, eluted, and then assayed to detect kinase activity. The activity of recombinant, purified c-Abl kinase or Bcr-Abl kinase in whole cell extracts can be detected with equivalent specificity, sensitivity, and reproducibility. Similarly, inhibition of recombinant c-Abl or Bcr-Abl in cells or cell extracts by imatinib mesylate and other Bcr-Abl targeted kinase inhibitors is readily assayed. This simple kinase assay is sufficiently straightforward and robust for use in clinical laboratories and is potentially adaptable to high-throughput assay formats. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptExpression of the oncogenic protein tyrosine kinase (PTK) 1 Bcr-Abl is commonly observed in chronic myelogenous leukemia (CML), acute lymphocytic leukemia (ALL), and other hematopoietic stem cell disorders [1]. Reciprocal translocation of the long arms of chromosomes 9 and 22 to form the Philadelphia chromosome replaces the N terminus of cAbl with Bcr, resulting in constitutive Abl kinase activation [2,3]. Under normal conditions, c-Abl is tightly regulated, serving roles in diverse pathways that promote cell growth and survival. Deregulation of Abl kinase activity via fusion to Bcr induces cellular phenotypes associated with leukemia such as hyperproliferation and resistance to apoptosis [4].Imatinib mesylate (IM, Gleevec, STI-571) is currently the frontline therapy for CML. IM has been shown to specifically inhibit Bcr-Abl activity in vivo, decreasing proliferation, and restoring apoptosis in CML cells [5]. In the clinic, IM induces hematological remission in nearly all chronic-phase CML patients treated [6][7][8]. Nonetheless, a subset of patients either fail to respond or rapidly develop drug resistance so that circulating CML cells persist despite treatment. Resistance is associated with amplification of the Bcr-Abl gene or, more commonly, point mutations in the Abl kinase catalytic domain that antagonize IM binding [9,10]. This limitation is being addressed by novel agents that can overcome most IM resistance mutations [5,11,12]. Regardless, no clinically useful assays for CML cell sensitivity to IM or other inhibitors that can guide clinical decision making are available. An in vitro or in vivo assay for Bcr-Abl kinase activity and inhibition in CML cells would directly address this challenge.The large number of active ...

A peptide biosensor for detecting intracellular Abl kinase activity using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

“…1): a highly specific kinase substrate for c-Abl,(20) a photocleavable linker to release the substrate sequence for analysis (21), a Src-homology 3 (SH3)-binding ligand,(22) to enhance interaction with the kinase(23, 24), a TAT peptide to aid intracellular delivery of cargo across the plasma membrane, (12, 25) and a biotin tag to facilitate isolation of the peptide from the complex biological mixture of cell lysate. See supporting information for analytical data.…”

A Bead-Based Activity Screen for Small-Molecule Inhibitors of Signal Transduction in Chronic Myelogenous Leukemia Cells

“…To monitor downstream phosphorylation resulting from Bcr-Abl activity, the assay was expanded to include peptides derived from Crk (23, 49-51), CrkL (24, 49, 52), and Stat5a (25, 26, 53). These peptides were immobilized on distinct Luminex beads and combined in a single well with Abltide-conjugated beads.…”

“…Previous work has shown that Bcr-Abl activity can be measured in cell lysates using the optimized synthetic peptide substrate Abltide immobilized on beads (52) or in acrylamide hydrogels (17). Native substrates, such as Crk and CrkL, as well as native downstream effectors such as Stat5a, have regularly been used to monitor Bcr-Abl activity in cell lysates (49, 54, 58).…”

Peptide reporters of kinase activity in whole cell lysates

“…Abltide demonstrated a higher rate of reactivity with Abl kinase than with closely related kinases such as Src17 and is now routinely used to monitor Abl kinase activity in vitro . Abltide is preferentially phosphorylated by the Abelson subfamily, which includes Abl (ABL1) and Arg kinases (ABL2),40 as well as the oncogenic fusion protein Bcr‐Abl41–44 that characterizes chronic myelogenous leukemia (CML). Accordingly, Abltide can be used to report on Bcr‐Abl kinase activity in cell lysates, possibly providing an activity‐based molecular diagnostic for CML.…”

“…Indeed, Abltide phosphorylation is quantitatively reduced with the addition of the Bcr‐Abl inhibitor imatinib, the first FDA‐approved tyrosine kinase inhibitor for the treatment of CML45 (sold as Gleevec by Novartis, East Hanover, NJ). Similarly, cell lines such as the bone marrow‐derived BaF3 line,46 demonstrate that Abltide is minimally phosphorylated when Bcr‐Abl is not expressed 44. Assays that use Abltide as a reporter and imatinib as an inhibitor provide a model system for deriving general principles for the design of other peptide‐based kinase assays.…”