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The pseudokinase domain of JAK2 is a dual-specificity protein kinase that negatively regulates cytokine signaling.

ABSTRACT: Human JAK2 tyrosine kinase mediates signaling through numerous cytokine receptors. The JAK2 JH2 domain functions as a negative regulator and is presumed to be a catalytically inactive pseudokinase, but the mechanism(s) for its inhibition of JAK2 remains unknown. Mutations in JH2 lead to increased JAK2 activity, contributing to myeloproliferative neoplasms (MPNs). Here we show that JH2 is a dual-specificity protein kinase that phosphorylates two negative regulatory sites in JAK2: Ser523 and Tyr570. Inactivation of JH2 catalytic activity increased JAK2 basal activity and downstream signaling. Notably, different MPN mutations abrogated JH2 activity in cells, and in MPN (V617F) patient cells phosphorylation of Tyr570 was reduced, suggesting that loss of JH2 activity contributes to the pathogenesis of MPNs. These results identify the catalytic activity of JH2 as a previously unrecognized mechanism to control basal activity and signaling of JAK2.

SUBMITTER: Ungureanu D

PROVIDER: S-EPMC4504201 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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The pseudokinase domain of JAK2 is a dual-specificity protein kinase that negatively regulates cytokine signaling.

Ungureanu Daniela D Wu Jinhua J Pekkala Tuija T Niranjan Yashavanthi Y Young Clifford C Jensen Ole N ON Xu Chong-Feng CF Neubert Thomas A TA Skoda Radek C RC Hubbard Stevan R SR Silvennoinen Olli O

Nature structural & molecular biology 20110814 9

Human JAK2 tyrosine kinase mediates signaling through numerous cytokine receptors. The JAK2 JH2 domain functions as a negative regulator and is presumed to be a catalytically inactive pseudokinase, but the mechanism(s) for its inhibition of JAK2 remains unknown. Mutations in JH2 lead to increased JAK2 activity, contributing to myeloproliferative neoplasms (MPNs). Here we show that JH2 is a dual-specificity protein kinase that phosphorylates two negative regulatory sites in JAK2: Ser523 and Tyr57 ...[more]

PMID: 21841788

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Project description:The Janus kinase-signal transducer and activator of transcription protein (JAK-STAT) pathway mediates essential biological functions from immune responses to haematopoiesis. Deregulated JAK-STAT signaling causes myeloproliferative neoplasms, leukaemia, and lymphomas, as well as autoimmune diseases. Thereby JAKs have gained significant relevance as therapeutic targets. However, there is still a clinical need for better JAK inhibitors and novel strategies targeting regions outside the conserved kinase domain have gained interest. In-depth knowledge about the molecular details of JAK activation is required. For example, whether the function and regulation between receptors is conserved remains an open question. We used JAK-deficient cell-lines and structure-based mutagenesis to study the function of JAK1 and its pseudokinase domain (JH2) in cytokine signaling pathways that employ JAK1 with different JAK heterodimerization partner. In interleukin-2 (IL-2)-induced STAT5 activation JAK1 was dominant over JAK3 but in interferon-γ (IFNγ) and interferon-α (IFNα) signaling both JAK1 and heteromeric partner JAK2 or TYK2 were both indispensable for STAT1 activation. Moreover, IL-2 signaling was strictly dependent on both JAK1 JH1 and JH2 but in IFNγ signaling JAK1 JH2 rather than kinase activity was required for STAT1 activation. To investigate the regulatory function, we focused on two allosteric regions in JAK1 JH2, the ATP-binding pocket and the αC-helix. Mutating L633 at the αC reduced basal and cytokine induced activation of STAT in both JAK1 wild-type (WT) and constitutively activated mutant backgrounds. Moreover, biochemical characterization and comparison of JH2s let us depict differences in the JH2 ATP-binding and strengthen the hypothesis that de-stabilization of the domain disturbs the regulatory JH1-JH2 interaction. Collectively, our results bring mechanistic understanding about the function of JAK1 in different receptor complexes that likely have relevance for the design of specific JAK modulators.

Dataset Information

The pseudokinase domain of JAK2 is a dual-specificity protein kinase that negatively regulates cytokine signaling.

Publications

The pseudokinase domain of JAK2 is a dual-specificity protein kinase that negatively regulates cytokine signaling.

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