Enhanced SH3:Linker Interaction Suppresses Activating Mutations of the c-Abl Protein-Tyrosine Kinase.

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 1208-1208
Author(s):  
Shoghag Panjarian ◽  
Shugui Chen ◽  
John Engen ◽  
Thomas Smithgall
Keyword(s):  
Tyrosine Kinase ◽  
Myristic Acid ◽  
Protein Tyrosine Kinase ◽  
Kinase Activity ◽  
Binding Pocket ◽  
Sh3 Domain ◽  
Kinase Domain ◽  
Abl Kinase ◽  
Defective Mutant ◽  
T315i Mutation

Abstract Abstract 1208 Bcr-Abl, the chimeric protein-tyrosine kinase expressed as a result of the Philadelphia chromosome translocation, plays a pivotal role in the initiation and maintenance of chronic myelogenous leukemia (CML). Imatinib (Gleevec) is an ATP-competitive Bcr-Abl inhibitor that selectively kills Bcr-Abl+ CML cells. Despite its clinical success, imatinib is less effective in the advanced stages of CML due to the emergence of drug resistance caused by point mutations in the Abl kinase domain. Second generation Bcr-Abl inhibitors such as dasatinib and nilotinib are active against most imatinib-resistant forms of Bcr-Abl, with the exception of the T315I “gatekeeper” mutant. The Abl gatekeeper residue (Thr315) is located between the ATP-binding site and an adjacent hydrophobic pocket, and forms a key hydrogen bond with imatinib. Additionally, the T315I mutation produces a strong activating effect on the downregulated c-Abl “core,” consisting of the myristoylated N-terminal Ncap, tandem SH3 and SH2 regulatory domains, the SH2-kinase linker, which forms a polyproline type II helix for internal SH3 docking, and the tyrosine kinase domain. Using hydrogen-exchange mass spectrometry, we recently found that the T315I mutation not only induced conformational changes in the Abl kinase domain as expected, but also at a distance in the RT-loop of the SH3 domain. Such changes may allosterically contribute to kinase domain activation by disturbing the negative regulatory influence of SH3:linker interaction. Recently, a new class of allosteric Bcr-Abl inhibitors has been reported that targets the myristate-binding pocket of Abl, which localizes to C-lobe of the kinase domain and away from the active site. Together with our finding that the T315I mutation perturbs SH3:linker interaction, these inhibitors support the existence of an extensive network of allosteric interactions that work together to regulate Abl kinase activity. In this project, we investigated whether enhanced SH3:linker interaction can allosterically reverse the activating effects of the T315I imatinib resistance mutation as well as mutations of the N-terminal myristoylation site and myristic acid binding pocket. We created modified versions of Abl [High Affinity Linker proteins (HALs)] by mutating multiple residues within the SH2-kinase linker to proline, thereby enhancing the SH3 domain binding affinity. Using mammalian cell-based expression assays and immunoblotting with phosphospecific antibodies, we identified five of eleven Abl-HAL proteins that did not exhibit changes in basal kinase activity. The Abl-HAL protein with the greatest enhancement of SH3:linker interaction was then combined with the T315I mutation, a myristoylation-defective mutant, and a myristic acid binding pocket mutation. Remarkably, this HAL substitution completely reversed the activating effect of the myristic acid binding pocket mutation, while substantially suppressing the activity of Abl T315I and the myristoylation-defective mutant. These results indicate that stabilization of SH3:linker interaction allosterically represses Abl activation by a wide variety of mechanisms, and suggests a new approach to allosteric control of Bcr-Abl kinase activity. Disclosures: No relevant conflicts of interest to declare.

Leukemic Stem Cells of Chronic Phase CML Patients Possess Uniquely Elevated BCR-ABL Kinase Activity and Acquire Spontaneous BCR-ABL Kinase Domain Mutations at a High Frequency.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 438-438 ◽  
Author(s):  
Xiaoyan Jiang ◽  
Kyi Min Saw ◽  
Allen Eaves ◽  
Connie Eaves
Keyword(s):  
Stem Cells ◽  
Tyrosine Kinase ◽  
Kinase Activity ◽  
Point Mutations ◽  
Chronic Phase ◽  
Kinase Domain ◽  
Tyrosine Kinase Activity ◽  
Abl Kinase ◽  
Kinase Domain Mutations

Abstract Growing evidence indicates that the therapeutic potential of imatinib mesylate (IM) for the treatment of CML may be limited initially by a relative innate resistance of the leukemic stem cells and eventually by an accumulation of cells with BCR-ABL tyrosine kinase domain mutations. We now show that the amount and tyrosine kinase activity of p210-BCR-ABL in the most primitive and relatively IM-unresponsive lin−CD34+CD38− CML cells is 3 to 10-fold higher than in the majority of the lin−CD34+CD38+ CML progenitors (n=3). These results confirm previous BCR-ABL transcript data and identify elevated p210-BCR-ABL expression to be a likely important factor in the characteristic IM-insensitivity of very primitive CML cells. To determine whether in vivo, CML stem cells also accumulate gene mutations affecting the BCR-ABL kinase domain, cDNAs were prepared from RNA extracts of purified lin−CD34+CD38− cells isolated from 3 chronic phase patients that had not received IM therapy. Bidirectional sequencing of individually cloned cDNAs from these samples revealed BCR-ABL kinase domain mutations in 2 of the 3 patients at frequencies of 10% (1/10), 20% (2*/10,*identical mutations). Incubation of these lin−CD34+CD38− cells in vitro for 2–3 wk ± a high concentration of IM (up to 10 μM, which was sufficient to reduce the tyrosine kinase activity in the input cells by 70±12% and in their 2 wk progeny by 10±5%) selected a subpopulation of more differentiated and completely IM-resistant cells. This was shown in Western blots by the inability of 10 μM IM to reduce either their p210-BCR-ABL tyrosine kinase activity or CrkL phosphorylation and in methylcellulose assays ±5 μM IM. As predicted, IM-selected cells showed a higher frequency of kinase domain mutations (13–20% vs 0–20% of cDNA clones analyzed from 3 wk cells cultured ±IM). Analysis of individual colonies produced from CFCs in the cultured cells showed all (21/21) colonies from IM-selected cells had mutations vs 50% (5/10) in those cultured without IM. The total frequency of mutant cDNAs detected was also increased in the IM-resistant cells (35–55% vs 10–25% mutant cDNAs in selected vs control cells). Interestingly, in most cases, both wild-type and mutant cDNAs were identified in the same colony, indicating de novo generation of mutations in vitro. Overall, >50 different mutations were identified. These included 10 point mutations previously associated with clinical IM resistance (including G250 and T315), another 13 point mutations previously identified in a comprehensive mutational screen, and >20 previously undescribed mutations. Several of the latter affect the critical region of the P loop, the c-helix and the activation loop and would be predicted to confer significant IM resistance. To investigate the possibility that the observed genomic instability of very primitive CML cells might be related to their elevated innate p210-BCR-ABL activity, BCR-ABL transcript levels in individual IM-selected, fully resistant and control (similarly treated but no IM exposure) colonies were compared. This showed that BCR-ABL transcripts were ~20-fold higher (P<0.05) in the resistant colonies (30 assessed from 3 patients). These findings suggest that the increased BCR-ABL expression and activity that uniquely characterizes the most primitive CML cells may contribute not only to their innate insensitivity to IM but also to a deregulation of genomic stability leading to the emergence of IM-resistant mutants and other subclones associated with disease progression.

Dissection of Bcr-abl Structural Domains Relating to Kinase Auto-Inhibition Using a Forward Mutational Screen with the Non-ATP Competitive Inhibitor GNF-2.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1021-1021 ◽  
Author(s):  
John T. Powers ◽  
Mohammad Azam ◽  
Nathanael S. Gray ◽  
George Q. Daley
Keyword(s):  
Kinase Activity ◽  
Binding Pocket ◽  
Sh3 Domain ◽  
Binding Domain ◽  
Binding Partner ◽  
Abl Kinase ◽  
Indirect Mechanism ◽  
Resistance Model

Abstract The Bcr-abl kinase is the causative agent for chronic myeloid leukemia (CML) and has been established as the primary clinical target for treatment of the disease through extensive use of Imatinib. Imatinib is the defining member of a class of ATP-binding site competitive inhibitors that lock Bcr-abl in an inactive conformation. Mutational screens of Bcr-abl using Imatinib and its derivatives as probes have been highly informative in prediction of clinically relevant mutations of Bcr-abl as well as in revealing the structure/function relationship of the kinase in general. Using compounds with a distinct mechanism of action from the Imatinib class to interrogate Bcr-abl will contribute to both more complete understanding of kinase function as well as to potential combination therapies for more effective treatment of CML. GNF-2, a recently identified inhibitor of Bcr-abl, establishes a new class of non-ATP competitive Bcr-abl family kinase inhibitors that may be developed as therapeutic agents for CML. GNF-2 effectively impairs the in vivo kinase activity of Bcr-abl and the growth of Bcr-abl transformed cells. GNF-2 functions at least in part through association with the myristate binding pocket of Bcr-abl. In order to further elucidate the mechanism of GNF-2 action as well as clinically relevant GNF-2 resistant mutants of Bcr-abl, a mutational screen coupling Bcr-abl mutagenesis to selection of drug resistance was performed using GNF-2 as probe. A number of functionally distinct resistant Bcr-abl mutations were recovered. Over half of all GNF-2 resistant clones harbored Bcr-abl mutations affecting the myristate binding pocket or the abl-SH3 domain, suggesting two potential methods of mutational resistance. The myristate binding domain mutants support a direct resistance model whereby GNF-2 association with Bcr-abl is impaired by disruption of the myristate binding pocket. Given a previous report that GNF-2 cannot inhibit Bcr-abl kinase activity in vitro, a novel model emerges for indirect resistance to GNF-2 by SH3 mutants that lose affinity for an inhibitory associated protein. The indirect resistance model specifically suggests that GNF-2 association confers a structural state of wildtype Bcr-abl which facilitates association to a putative inhibitory binding partner, thereby affecting inhibition. Indeed, the strongest of several candidate inhibitory binding partners, the Abl-SH3 domain binding inhibitor Abi-2 was observed to co-immunoprecipitate with Bcr-abl in the presence of GNF-2. This association correlated with reduced Bcr-abl auto-phosphorylation levels. These observations provide preliminary support for an indirect mechanism of Bcr-abl inhibition by GNF-2. Additional experiments involving shRNA knockdown of Abi-2 are being completed to determine the requirement of this Bcr-abl binding partner for GNF-2 activity. Further characterization of the SH3 and myristate binding domain mutants in the context of Abi-2 and GNF-2 binding affinities may establish a previously undescribed indirect mechanism of Bcr-abl inhibition by an allosteric non-ATP inhibitor.

Automated and Rapid Detection of BCR-ABL Kinase Domain Mutations in IM Resistant Patients with Ph+ Leukemias.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 2590-2590
Author(s):  
Ruriko Tanaka ◽  
Shinya Kimura ◽  
Toshiya Hosomi ◽  
Mitsuharu Hirai ◽  
Rina Nagao ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Second Generation ◽  
Direct Sequencing ◽  
Kinase Domain ◽  
Myelogenous Leukemia ◽  
Abl Kinase ◽  
T315i Mutation ◽  
Kinase Domain Mutations ◽  
Quenching Probe ◽  
Higher Sensitivity

Abstract Abstract 2590 Poster Board II-566 Chronic myelogenous leukemia (CML) is caused by a consistent genetic abnormality, termed the Philadelphia chromosome (Ph). It results in the production of BCR-ABL fusion protein, a constitutively active tyrosine kinase. Imatinib mesylate (IM, Gleevec®), the first generation tyrosine kinase inhibitor (TKI), has revolutionized therapy for CML patients. However, resistance for IM develops in a significant proportion of cases, and is predominantly mediated by single point mutations within the BCR-ABL kinase domain. Second generation TKIs such as dasatinib (Sprycel®) and nilotinib (Tasigna®) represent viable alternatives for IM-resistant or intolerant CML patients. Each mutated BCR-ABL has different sensitivity to those TKIs. Thus, it is significantly important to detect early the existence of BCR-ABL mutations and their specificities in treating Ph+ leukemias. We have developed a novel automated method that has high sensitivity to detect a few copies of mutation sequences that are mixed in many copies of normal sequences. This method consists of PCR amplification step and Tm (melting temperature) analysis step that uses a quenching probe. And we have already shown that this system has clinical efficacy in JAK2V617F mutation that is one of the genetic hallmarks of chronic myeloproliferative diseases. (Tanaka R, et al. Leuk Res, 2008). When a whole blood sample or a purified DNA sample reacts with reagents, PCR and Tm analysis automatically processed in the same tube, and whole procedure finishes in approximately 1 hour. The detection of mutation is extremely accurate because the quenching probe is designed perfectly matched for mutated sequence. As Tm value of mutation sequence is higher than that of normal one, it is easy to detect the existence of mutation from the Tm analysis data. We have constructed the probes for 14 mutations concerned for IM-resistance (M244V, G250E, Q252H, Y253F, Y253H, E255V, E255K, T315I, T315A, F317L, M351T, E355G, F359V, and H396R). Considering the clinical significance of T315I mutation, which renders resistance to all currently available TKIs, we refined this method to higher sensitivity for detecting T315I mutation. First, we analyzed the sensitivity of this system on BCR-ABL. In dilution assays using wt and mutated plasmid, the system reliably quantified the mutation in a population containing as few as 3.0% mutant. Moreover, for T315I setting, we successfully detected as few as 0.3% (30 copies from 10,000 copies) mutations by a higher-sensitive assay. Next, we examined the clinical samples. Each sample was also examined by direct sequencing in comparison to our method. Kinase domain mutations were identified in 24 of the 50 (48%) patients. Our automated analysis was enabled to detect mutations in 19 patients, including p-loop mutations (G250E: n=3; E255K: n= 5), IM-binding domain mutations (T315I: n=10), and an activation-loop mutation (H396R: n=1). And all the positive cases (19 of 19) showed a concordance with the result of direct sequencing. On the other hand, 5 cases were detected just by direct sequencing, but all that cases were out of our setting mutations (Q252E, V379I, S417F, E459K). Impressively, in one case, only higher-sensitivity assay could reveal T315I mutation, although it was detected as a wild type both by direct sequence and our usual method. It suggests that the higher-sensitive system could detect low amount of T315I mutation in the earlier stage of disease. In conclusion, sensitivity of our system (3%) is significantly greater than that of direct sequencing (15 – 25%), and results can be obtained within one hour. By the serial monitoring, it is demonstrated the availability of the higher-sensitive analysis (0.3%) to detect T315I mutation. This rapid and accurate detection of clinically significant mutations enables us to contribute to better clinical practice in treating Ph+ leukemia patients, such as in selecting alternative strategies of IM dose escalation, second generation TKIs, or allogeneic stem cell transplantation. Disclosures: No relevant conflicts of interest to declare.

The Most Common Dasatinib-Resistant BCR-ABL Kinase Domain Mutations in Patients with Chronic Myeloid Leukemia Are Sensitive to VX-680: Rationale for Early Combination Kinase Inhibitor Therapy.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2175-2175 ◽  
Author(s):  
Neil P. Shah ◽  
Brian Skaggs ◽  
Susan Branford ◽  
Timothy P. Hughes ◽  
John M. Nicoll ◽  
...  
Keyword(s):  
Kinase Activity ◽  
Kinase Inhibitors ◽  
Kinase Inhibitor ◽  
Kinase Domain ◽  
Aurora A ◽  
Abl Kinase ◽  
Micromolar Concentration ◽  
T315i Mutation ◽  
Contact Residues ◽  
Kinase Domain Mutations

Abstract Selection for CML cells with BCR-ABL kinase domain mutations represents the predominant molecular mechanism responsible for loss of response to imatinib. Similarly, we have found acquired resistance to dasatinib to be associated with kinase domain mutations in 100% of cases (n=15). However, unlike the multitude of imatinib resistant mutations, which to a large extent occur at non-contact residues and destabilize the inactive confirmation to which imatinib binds, only two mutations appear to be responsible for nearly all cases of dasatinib resistance, T315I and V299L (Shah et al, submitted, ASH 2006). Both of these mutations occur at critical contact residues between the ABL kinase domain and dasatinib. Successful treatment of dasatinib-resistant cases will therefore require strategies to successfully eliminate cells that harbor these mutations. Use of a combination of kinase inhibitors with the ability to collectively suppress all BCR-ABL kinase domain mutants would be predicted to lead to profoundly minimize disease resistance and relapse on targeted therapy. Although the combination of imatinib and dasatinib may prevent selection of the dasatinib-resistant V299L mutation, these agents share many targets, and their combination may therefore result in substantial toxicity. Moreover, the combination of imatinib and dasatinib is not predicted to effectively inhibit the growth of cells harboring BCR-ABL/T315I. We previously have shown that the Aurora kinase inhibitor VX-680 can bind to the ABL kinase domain and inhibit the kinase activity of the T315I mutation at low micromolar concentration. VX-680 is showing early signs of efficacy in CML cases associated with the T315I mutation. Interestingly, the co-crystal structure of VX-680 reveals that V299 is one of 14 contact residues within the ABL kinase domain. Substitution of leucine at this residue might therefore be expected to diminish the potential affinity of VX-680 for BCR-ABL/V299L. However, analysis of the amino acid sequence of Aurora-A revealed divergence from native BCR-ABL at this the corresponding amino acid position due to the presence of a leucine in Aurora-A. BCR-ABL/V299L is therefore a mimetic of Aurora-A, and as a result, predicted to retain sensitivity to VX-680. We therefore assessed VX-680 for its ability to inhibit the kinase activity of BCR-ABL/V299L in Ba/F3 cells and found effective inhibition of the kinase activity at low micromolar concentration. Consistent with predictions based upon structural considerations, the V299L mutation is somewhat more sensitive to VX-680 than BCR-ABL/T315I. We confirmed these results in an analysis of primary human PBMCs obtained from a dasatinib-resistant patient who had evolved the V299L mutation on therapy. Our findings suggest that early combination therapy with two kinase inhibitors, dasatinib and VX-680, may successfully suppress resistant disease by collectively eliminating BCR-ABL kinase domain mutation as a mechanism of resistance, and thereby achieve effective long-term disease control in the vast majority of patients.

Clinical Characteristics and Outcome of Patients (pts) with T315I Mutation after Imatinib Failure.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2189-2189
Author(s):  
Elias Jabbour ◽  
Hagop Kantarjian ◽  
Dan Jones ◽  
Francis Giles ◽  
Gautam Borthakur ◽  
...  
Keyword(s):  
Overall Survival ◽  
Tyrosine Kinase ◽  
Tyrosine Kinase Inhibitors ◽  
Clinical Characteristics ◽  
Kinase Inhibitors ◽  
Cytogenetic Response ◽  
Kinase Domain ◽  
Abl Kinase ◽  
Hematologic Response ◽  
T315i Mutation

Point mutations of the Bcr-Abl kinase domain are the most frequently identified mechanism of resistance in patients (pts) with CML who failed imatinib. T315I is an imatinib pocket binding mutation within the Bcr-Abl kinase domain that is highly resistant to imatinib as well as to the novel tyrosine kinase inhibitors (NTKIs) (eg, dasatinib, nilotinib) both in vitro and in vivo. It has thus been suggested that these pts have a very poor prognosis. To define the clinical characteristics and outcome of these pts, we reviewed all pts with this mutations identified at our institution after failure to imatinib. T315I was detected in 15 of 112 patients (13%) harboring kinase domain mutations. Median age was 49 years (range, 34-66 years). At the time imatinib was started, 12 pts were in chronic (CP) and 3 in accelerated (AP). Ten pts had received prior interferon therapy. The best response to imatinib was major molecular response in 1, major cytogenetic response in 5 (complete in 2), and complete hematologic response in 8. One patient was intolerant to imatinib. The median duration of response was 37 months (range, 10–60 months). T315I was identified after a median of 48 months (range, 10–83 months). At the time the mutation was identified, 9 patients had transformed (7 to AP, 2 to BP). Clonal evolution was observed in only 1 pt. Fourteen patients received subsequent NTKIs; 3 of them received both nilotinib and dasatinib. Among them, 1 patient achieved a partial hematologic response with nilotinib that lasted for 3 months and 1 other had T315I identified while in complete cytogenetic response induced by nilotinib that has been sustained for 16+ months. After a median follow-up of 27 months (range, 3–42 months), 11 pts (73%) are alive: 8 are alive with active disease, and 3 patients are alive with ongoing response: 1 in complete molecular remission following allogeneic stem cell transplantation, 1 in partial cytogenetic response following treatment with aurora kinase inhibtor MK0457, and one in sustained complete cytogenetic response with ongoing treatment with nilotinib. Four patients have died of disease progression. Except for previous treatment with interferon (more frequent in patients harboring the T315I mutation; p=0.024) and the lack of response to the NTKI (p=0.001), there was no difference in patients characteristics and previous response to imatinib compared to patients with other mutations. Similarly, there was no difference in overall survival among patients with T315I mutations or other mutations (p=0.71). In conclusion T315I is a highly resistant mutation to conventional tyrosine kinase inhibitors; however occasional responses can be observed and overall survival may not be as poor as previously reported.

scholarly journals c-ABL tyrosine kinase activity is regulated by association with a novel SH3-domain-binding protein.

1996 ◽  
Vol 16 (12) ◽  
pp. 7054-7062 ◽  
Author(s):  
J Zhu ◽  
S K Shore
Keyword(s):  
Tyrosine Kinase ◽  
Kinase Activity ◽  
Cellular Transformation ◽  
Sh3 Domain ◽  
Cellular Protein ◽  
Glutathione S Transferase ◽  
Tyrosine Kinase Activity ◽  
Abl Kinase ◽  
Abl Tyrosine Kinase ◽  
Domain 3

The c-ABL tyrosine kinase is activated following either the loss or mutation of its Src homology domain 3 (SH3), resulting in both increased autophosphorylation and phosphorylation of cellular substrates and cellular transformation. This suggests that the SH3 domain negatively regulates c-ABL kinase activity. For several reasons this regulation is thought to involve a cellular protein that binds to the SH3 domain. Hyperexpression of c-ABL results in an activation of its kinase, the kinase activity of purified c-ABL protein in the absence of cellular proteins is independent of either the presence or absence of a SH3 domain, and point mutations and deletions within the SH3 domain are sufficient to activate c-ABL transforming ability. To identify proteins that interact with the c-ABL SH3 domain, we screened a cDNA library by the yeast two-hybrid system, using the c-ABL SH3SH2 domains as bait. We identified a novel protein, AAP1 (ABL-associated protein 1), that associates with these c-ABL domains and fails to bind to the SH3 domain in the activated oncoprotein BCRABL. Kinase experiments demonstrated that in the presence of AAP1, the ability of c-ABL to phosphorylate either glutathione S-transferase-CRK or enolase was inhibited. In contrast, AAP1 had little effect on the phosphorylation of glutathione S-transferase-CRK by the activated ABL oncoproteins v-ABL and BCRABL. We conclude that AAP1 inhibits c-ABL tyrosine kinase activity but has little effect on the tyrosine kinase activities of oncogenic BCRABL or v-ABL protein and propose that AAP1 functions as a trans regulator of c-ABL kinase. Our data also indicate that loss of susceptibility to AAP1 regulation correlates with oncogenicity of the activated forms of c-ABL.

scholarly journals The SH2 Domain of BCR-ABL1 Regulates Kinase Autophosphorylation By Controlling Activation Loop Accessibility

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2209-2209
Author(s):  
Oliver D. Hantschel ◽  
Allan Joaquim Lamontanara ◽  
Sandrine Georgeon ◽  
Giancarlo Tria ◽  
Dmitri Svergun
Keyword(s):  
Drug Resistance ◽  
Tyrosine Kinase ◽  
Tyrosine Kinases ◽  
Kinase Activity ◽  
Binding Pocket ◽  
Kinase Domain ◽  
Sh2 Domain ◽  
Activation Loop ◽  
Phosphorylation Sites

Abstract Chronic myelogenous leukemia (CML) is caused by BCR-ABL1, which is a constitutively active form of the Abelson tyrosine kinase (ABL1). While treatment with the tyrosine kinase inhibitors imatinib, nilotinib, dasatinib, bosutinib or ponatinib that target the ATP binding pocket of BCR-ABL1 leads to durable cytogenetic and molecular remissions in the majority CML patients, primary and secondary drug resistance remains a clinical problem. Targeting additional sites in the BCR-ABL1 kinase outside the highly conserved ATP binding pocket may be an alternative strategy to restrict drug resistance and limit side effects of ATP-competitive drugs with low selectivity. Our recent work has shown that an allosteric intramolecular interaction of the BCR-ABL1 SH2 domain with its kinase domain is critical for leukemogenesis and can be targeted with an engineered high-affinity binding protein. We have now elucidated the molecular mechanisms responsible for the regulation of BCR-ABL1 kinase activity by its SH2 domain: To this end, we set-up an efficient expression system for the BCR-ABL1 SH2-kinase domain unit in E.coli with excellent yield, purity and activity. Detailed biophysical and biochemical analysis of the purified recombinant proteins in vitro recapitulated SH2-dependent regulation of BCR-ABL1 in CML cells and enabled a quantitative enzymatic analysis of BCR-ABL1 activation. Unexpectedly, we found that the interaction of the SH2 domain with the kinase domain is the critical switch that shifts the BCR-ABL1 activation loop from an otherwise closed to a fully open conformation and enables its autophosphorylation. The activation loop is a central and almost universally used control element that regulates the activity of protein kinases, as the conformation and phosphorylation status of the activation loop determines substrate binding to the active site. In BCR-ABL1, activation loop phosphorylation is required for transformation of fibroblasts and haematopoietic progenitors. We show that the SH2-kinase interaction enables autophosphorylation of the activation loop in trans by rendering a key phosphorylation site (Tyr-412) highly accessible. This requires prior phosphorylation of Tyr-245 in the SH2-kinase linker of BCR-ABL1. Mutational disruption of the SH2-kinase interaction abolished activation loop phosphorylation. Importantly, this effect was independent of the phosphotyrosine binding ability of the SH2 domain, which indicated that the SH2 domain is a true allosteric activator of BCR-ABL1 kinase activity. We also show that the spectrum of tyrosine phosphorylation sites that we mapped by mass spectrometry in vitro were vastly overlapping with the observed BCR-ABL1 phosphorylation sites in CML cells indicating that BCR-ABL1 autophosphorylation might be the major mechanism that determines its cellular phosphorylation status. In summary, our study demonstrates a novel mechanism by which a protein-protein interaction domain may allosterically mediate the transition of an inactive to an active kinase conformation in a key oncoprotein. This work may serve as an archetype to identify further allosteric regulatory mechanisms in other tyrosine kinases that are activated in haematological malignancies and facilitate the development of new allosteric inhibitors targeting oncogenic tyrosine kinases. Disclosures No relevant conflicts of interest to declare.

scholarly journals Development of the Sensing Platform for Protein Tyrosine Kinase Activity

Biosensors ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 240
Author(s):  
Lan-Yi Wei ◽  
Wei Lin ◽  
Bey-Fen Leo ◽  
Lik-Voon Kiew ◽  
Chia-Ching Chang ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Tyrosine Kinases ◽  
Protein Tyrosine Kinase ◽  
Kinase Activity ◽  
Significant Inhibition ◽  
Tyrosine Kinase Activity ◽  
Protein Tyrosine ◽  
Sensing Platform ◽  
Relative Standard ◽  
Protein Tyrosine Kinase Activity

A miniature tyrosinase-based electrochemical sensing platform for label-free detection of protein tyrosine kinase activity was developed in this study. The developed miniature sensing platform can detect the substrate peptides for tyrosine kinases, such as c-Src, Hck and Her2, in a low sample volume (1–2 μL). The developed sensing platform exhibited a high reproducibility for repetitive measurement with an RSD (relative standard deviation) of 6.6%. The developed sensing platform can detect the Hck and Her2 in a linear range of 1–200 U/mL with the detection limit of 1 U/mL. The sensing platform was also effective in assessing the specificity and efficacies of the inhibitors for protein tyrosine kinases. This is demonstrated by the detection of significant inhibition of Hck (~88.1%, but not Her2) by the Src inhibitor 1, an inhibitor for Src family kinases, as well as the significant inhibition of Her2 (~91%, but not Hck) by CP-724714 through the platform. These results suggest the potential of the developed miniature sensing platform as an effective tool for detecting different protein tyrosine kinase activity and for accessing the inhibitory effect of various inhibitors to these kinases.

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