JAK2 V617F Constitutive Activation Requires JH2 Residue F595: A Pseudokinase Domain Target for Specific Inhibitors

Dusa, Alexandra; Mouton, Céline; Pecquet, Christian; Herman, Murielle; Constantinescu, Stefan N.

doi:10.1371/journal.pone.0011157

Cited by 80 publications

(96 citation statements)

References 46 publications

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“…8A, the corresponding isoleucine in Jak2 JH2 is located in the N lobe, at the end of the loop connecting the b4 and b5 strands, and is a few residues away from Val 617 (48). Interestingly, it was shown that the activating V617F mutation rigidifies the JH2 aC helix through p-stacking interactions with two phenylalanines (Phe 594,595 ), confirming previous mutational studies of Jak2 V617F by Constantinescu's group (49). Yet, the mode by which the rigidified aC helix brings about JH1 activation in Jak2 V617F remains unclear.…”

Section: Discussionsupporting

confidence: 81%

Two Rare Disease-Associated Tyk2 Variants Are Catalytically Impaired but Signaling Competent

Gakovic

Ragimbeau

et al. 2013

The Journal of Immunology

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Tyk2 belongs to the Janus protein tyrosine kinase family and is involved in signaling of immunoregulatory cytokines (type I and III IFNs, IL-6, IL-10, and IL-12 families) via its interaction with shared receptor subunits. Depending on the receptor complex, Tyk2 is coactivated with either Jak1 or Jak2, but a detailed molecular characterization of the interplay between the two enzymes is missing. In human populations, the Tyk2 gene presents high levels of genetic diversity with >100 nonsynonymous variants being detected. In this study, we characterized two rare Tyk2 variants, I684S and P1104A, which have been associated with susceptibility to autoimmune disease. Specifically, we measured their in vitro catalytic activity and their ability to mediate Stat activation in fibroblasts and genotyped B cell lines. Both variants were found to be catalytically impaired but rescued signaling in response to IFN-α/β, IL-6, and IL-10. These data, coupled with functional study of an engineered Jak1 P1084A, support a model of nonhierarchical activation of Janus kinases in which one catalytically competent Jak is sufficient for signaling provided that its partner behaves as proper scaffold, even if inactive. Through the analysis of IFN-α and IFN-γ signaling in cells with different Jak1 P1084A levels, we also illustrate a context in which a hypomorphic Jak can hamper signaling in a cytokine-specific manner. Given the multitude of Tyk2-activating cytokines, the cell context–dependent requirement for Tyk2 and the catalytic defect of the two disease-associated variants studied in this paper, we predict that these alleles are functionally significant in complex immune disorders.

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Section: Discussionsupporting

confidence: 81%

Two Rare Disease-Associated Tyk2 Variants Are Catalytically Impaired but Signaling Competent

Gakovic

Ragimbeau

et al. 2013

The Journal of Immunology

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“…Indeed, a recent structure of the JAK1 pseudokinase suggests that insertion of a phenylalanine at the analogous JAK1 position (V658) induces remodeling of a highly conserved Phe residue (F575) in the N-terminal exon 12 segment (13). It has also been shown that any number of large hydrophobic residues in place of V617 can activate JAK2 (33), whereas replacement of the V617-adjacent aromatic residue F595 with a smaller aliphatic residue can reverse the increased activity conferred by V617F (34), suggesting that simple steric disruption of the packing near JAK2 V617 and exon 12 can relieve inhibition. Bulky substitutions in the pseudokinase αC-helix (e.g., JAK1 A634D, JAK3 A572V or A573V) or exon 12 deletions and insertions may also relieve autoinhibition in a similar manner to the V617F mutation (Fig.…”

Section: Discussionmentioning

confidence: 99%

Structure of the pseudokinase–kinase domains from protein kinase TYK2 reveals a mechanism for Janus kinase (JAK) autoinhibition

Lupardus¹,

Ultsch²,

Wallweber³

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

192

241

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Janus kinases (JAKs) are receptor-associated multidomain tyrosine kinases that act downstream of many cytokines and interferons. JAK kinase activity is regulated by the adjacent pseudokinase domain via an unknown mechanism. Here, we report the 2.8-Å structure of the two-domain pseudokinase-kinase module from the JAK family member TYK2 in its autoinhibited form. We find that the pseudokinase and kinase interact near the kinase active site and that most reported mutations in cancer-associated JAK alleles cluster in or near this interface. Mutation of residues near the TYK2 interface that are analogous to those in cancer-associated JAK alleles, including the V617F and "exon 12" JAK2 mutations, results in increased kinase activity in vitro. These data indicate that JAK pseudokinases are autoinhibitory domains that hold the kinase domain inactive until receptor dimerization stimulates transition to an active state. JAK1 | JAK3H elical bundle cytokines of the interleukin and IFN families regulate a wide variety of immune and cellular growth responses (1). These signaling pathways are initiated by cytokinemediated receptor dimerization and subsequent activation of nonreceptor tyrosine kinases called Janus kinases (JAKs) that are associated with the receptor intracellular domains (2). JAK activation leads to phosphorylation of the receptor and recruitment of STAT family transcription factors, which are then phosphorylated by the JAK and translocated to the nucleus where they induce gene transcription. The JAK family consists of four members (JAK1, JAK2, JAK3, and tyrosine kinase 2 or TYK2), each of which binds a distinct set of cytokine receptor subtypes and hence has a unique gene knockout phenotype, ranging from embryonic lethality due to neuronal and erythropoietic defects (JAK1 and JAK2, respectively) (3-5), to profound immune system deficiencies (JAK3 and TYK2) (6).The JAK kinases are large (∼1,150-aa) multidomain proteins whose primary sequences were initially organized into seven JAK-homology (JH) domains that reflected distinct regions of high sequence homology (7). Subsequent structure predictions indicated that JAKs contain four distinct domains: N-terminal 4.1, Ezrin, Radixin, Moesin (FERM) and Src homology 2 (SH2) domains, followed by C-terminal pseudokinase and kinase domains (7,8) (Fig. 1A). The FERM and SH2 domains constitute the receptor-binding module (2), whereas the pseudokinase, which has a canonical kinase fold but lacks key catalytic residues, is thought to regulate kinase activity. Deletion of the pseudokinase in JAK2 and JAK3 increases basal kinase activity and deregulates signaling through cognate receptors (9, 10). Additionally, the JAK2 pseudokinase and kinase domains have been reported to coimmunoprecipitate, and coexpression of the JAK2 pseudokinase domain inhibits activity of the isolated kinase domain (10). Recent work on the JAK2 pseudokinase domain indicates that it has weak catalytic activity and autophosphorylates two inhibitory sites within the SH2-pseudokinase linker and pseudokinase...

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“…The main structural effects due to ATP binding in JH2 are observed in αC, and mutations in αC (e.g., F594A, F595A) have been shown to reverse hyperactivation of several mutations scattered throughout the JAK2 JH2-JH1 interface (18,34,35). Although in the case of V617F, which is proximal to αC, F595A might reconstitute a disrupted autoinhibitory JH2-JH1 interface, a more likely explanation for the suppressive effects of ATP binding mutations (and of F594A, F595A) is that pathogenic hyperactivation is dependent on a yet-to-be-characterized positive regulatory interaction mediated by JH2, which probably involves αC and is therefore sensitive to its conformation.…”

Section: Discussionmentioning

confidence: 99%

ATP binding to the pseudokinase domain of JAK2 is critical for pathogenic activation

Hammarén

Ungureanu

Grisouard

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

123

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Pseudokinases lack conserved motifs typically required for kinase activity. Nearly half of pseudokinases bind ATP, but only few retain phosphotransfer activity, leaving the functional role of nucleotide binding in most cases unknown. Janus kinases (JAKs) are nonreceptor tyrosine kinases with a tandem pseudokinase-kinase domain configuration, where the pseudokinase domain (JAK homology 2, JH2) has important regulatory functions and harbors mutations underlying hematological and immunological diseases. JH2 of JAK1, JAK2, and TYK2 all bind ATP, but the significance of this is unclear. We characterize the role of nucleotide binding in normal and pathogenic JAK signaling using comprehensive structure-based mutagenesis. Disruption of JH2 ATP binding in wildtype JAK2 has only minor effects, and in the presence of type I cytokine receptors, the mutations do not affect JAK2 activation. However, JH2 mutants devoid of ATP binding ameliorate the hyperactivation of JAK2 V617F. Disrupting ATP binding in JH2 also inhibits the hyperactivity of other pathogenic JAK2 mutants, as well as of JAK1 V658F, and prevents induction of erythrocytosis in a JAK2 V617F myeloproliferative neoplasm mouse model. Molecular dynamic simulations and thermal-shift analysis indicate that ATP binding stabilizes JH2, with a pronounced effect on the C helix region, which plays a critical role in pathogenic activation of JAK2. Taken together, our results suggest that ATP binding to JH2 serves a structural role in JAKs, which is required for aberrant activity of pathogenic JAK mutants. The inhibitory effect of abrogating JH2 ATP binding in pathogenic JAK mutants may warrant novel therapeutic approaches.T he Janus kinases (JAK1-3, TYK2) are a family of nonreceptor tyrosine kinases with essential functions in the regulation of hematopoiesis, the immune system, and cellular metabolism. JAKs interact specifically with various cytokine receptors and couple cytokine binding to cytoplasmic signaling cascades, including the signal transducers and activators of transcription (STAT) pathway. JAKs consist of an N-terminal FERM domain, an SH2-like (Src homology 2) domain, a pseudokinase domain (JAK homology 2, JH2), and the C-terminal tyrosine kinase domain (JH1). JH2 mediates critical regulatory functions in JAKs and primarily serves to inhibit basal JH1 activity. Experimental deletion of JH2 increases JH1 activity in full-length JAK in the absence of stimulation (1-3), and in recombinant systems addition of JH2 suppresses JH1 activity (4-6). JH2 is, however, also required for ligand-induced activation of full-length JAKs in cell (1-3, 6, 7). The regulatory functions of JH2 are corroborated by the multitude of human disease mutations identified in the domain. The most common JAK2 mutation, V617F, leads to cytokine-independent signaling through the exclusively JAK2-dependent homotypic receptors for erythropoietin (EPO), granulocyte colony stimulating factor (G-CSF), and thrombopoietin (8). The V617F mutation is found in ∼95% of patients with polycythemia vera (PV) (9...

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JAK2 V617F Constitutive Activation Requires JH2 Residue F595: A Pseudokinase Domain Target for Specific Inhibitors

Cited by 80 publications

References 46 publications

Two Rare Disease-Associated Tyk2 Variants Are Catalytically Impaired but Signaling Competent

Two Rare Disease-Associated Tyk2 Variants Are Catalytically Impaired but Signaling Competent

Structure of the pseudokinase–kinase domains from protein kinase TYK2 reveals a mechanism for Janus kinase (JAK) autoinhibition

ATP binding to the pseudokinase domain of JAK2 is critical for pathogenic activation

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