10pj
JAK2 kinase (JH1 domain) in complex with povorcitinib
Structural highlights
DiseaseJAK2_HUMAN Note=Chromosomal aberrations involving JAK2 are found in both chronic and acute forms of eosinophilic, lymphoblastic and myeloid leukemia. Translocation t(8;9)(p22;p24) with PCM1 links the protein kinase domain of JAK2 to the major portion of PCM1. Translocation t(9;12)(p24;p13) with ETV6. Defects in JAK2 are a cause of susceptibility to Budd-Chiari syndrome (BDCHS) [MIM:600880. A syndrome caused by obstruction of hepatic venous outflow involving either the hepatic veins or the terminal segment of the inferior vena cava. Obstructions are generally caused by thrombosis and lead to hepatic congestion and ischemic necrosis. Clinical manifestations observed in the majority of patients include hepatomegaly, right upper quadrant pain and abdominal ascites. Budd-Chiari syndrome is associated with a combination of disease states including primary myeloproliferative syndromes and thrombophilia due to factor V Leiden, protein C deficiency and antithrombin III deficiency. Budd-Chiari syndrome is a rare but typical complication in patients with polycythemia vera. Defects in JAK2 are a cause of polycythemia vera (PV) [MIM:263300. A myeloproliferative disorder characterized by abnormal proliferation of all hematopoietic bone marrow elements, erythroid hyperplasia, an absolute increase in total blood volume, but also by myeloid leukocytosis, thrombocytosis and splenomegaly.[1] [2] [3] [4] Defects in JAK2 gene may be the cause of thrombocythemia type 3 (THCYT3) [MIM:614521. A myeloproliferative disorder characterized by elevated platelet levels due to sustained proliferation of megakaryocytes, and frequently lead to thrombotic and haemorrhagic complications.[5] [6] Defects in JAK2 are a cause of myelofibrosis (MYELOF) [MIM:254450. Myelofibrosis is a disorder characterized by replacement of the bone marrow by fibrous tissue, occurring in association with a myeloproliferative disorder. Clinical manifestations may include anemia, pallor, splenomegaly, hypermetabolic state, petechiae, ecchymosis, bleeding, lymphadenopathy, hepatomegaly, portal hypertension. Defects in JAK2 are a cause of acute myelogenous leukemia (AML) [MIM:601626. AML is a malignant disease in which hematopoietic precursors are arrested in an early stage of development.[7] FunctionJAK2_HUMAN Non-receptor tyrosine kinase involved in various processes such as cell growth, development, differentiation or histone modifications. Mediates essential signaling events in both innate and adaptive immunity. In the cytoplasm, plays a pivotal role in signal transduction via its association with type I receptors such as growth hormone (GHR), prolactin (PRLR), leptin (LEPR), erythropoietin (EPOR), thrombopoietin (THPO); or type II receptors including IFN-alpha, IFN-beta, IFN-gamma and multiple interleukins. Following ligand-binding to cell surface receptors, phosphorylates specific tyrosine residues on the cytoplasmic tails of the receptor, creating docking sites for STATs proteins. Subsequently, phosphorylates the STATs proteins once they are recruited to the receptor. Phosphorylated STATs then form homodimer or heterodimers and translocate to the nucleus to activate gene transcription. For example, cell stimulation with erythropoietin (EPO) during erythropoiesis leads to JAK2 autophosphorylation, activation, and its association with erythropoietin receptor (EPOR) that becomes phosphorylated in its cytoplasmic domain. Then, STAT5 (STAT5A or STAT5B) is recruited, phosphorylated and activated by JAK2. Once activated, dimerized STAT5 translocates into the nucleus and promotes the transcription of several essential genes involved in the modulation of erythropoiesis. In addition, JAK2 mediates angiotensin-2-induced ARHGEF1 phosphorylation. Plays a role in cell cycle by phosphorylating CDKN1B. Cooperates with TEC through reciprocal phosphorylation to mediate cytokine-driven activation of FOS transcription. In the nucleus, plays a key role in chromatin by specifically mediating phosphorylation of 'Tyr-41' of histone H3 (H3Y41ph), a specific tag that promotes exclusion of CBX5 (HP1 alpha) from chromatin.[8] [9] [10] [11] Publication Abstract from PubMedAberrant JAK2 signaling is a key driver in cancers such as myeloproliferative neoplasms (MPNs), whereas JAK1 acts as a central mediator of autoimmune and inflammatory diseases. Since JAK2 supports blood cell production, its inhibition can lead to anemia and other cytopenias, making selective JAK1 inhibition a potentially safer therapeutic strategy opposed to dual JAK1/JAK2 inhibition. We initially identified novel scaffold 9, which selectively inhibited JAK1 over JAK2. Iterative breakthroughs led to the discovery of povorcitinib (INCB054707, 22), which showed improved pharmacokinetics due to intramolecular hydrogen bonding of the amide moiety and a reduced ring size in the hinge binding motif. Protein crystallography suggested that JAK1 selectivity was conferred by the amide's alkyl group accessing a small lipophilic groove formed by the P-loop conformation of JAK1 that was distinct from JAK2. In murine arthritis models, povorcitinib demonstrated dose-dependent efficacy and reduced inflammatory signaling, supporting its therapeutic potential in immunological disorders. Discovery of the Orally Bioavailable Isoform Selective Janus Kinase 1 (JAK1) Compound Povorcitinib (INCB054707) for the Treatment of Inflammatory and Autoimmune Diseases.,Zhuo J, Li YL, Qian DQ, Burns DM, Mei S, Rafalski M, Xu M, Cao G, Pan Y, Jia Z, Jalluri R, Epling LB, Fenalti G, Deller MC, Procak J, Covington M, He X, Collins R, Stubbs M, Burke K, Oliver J, Margulis A, Boer J, Wynn R, Scherle P, Diamond S, Newton R, Zhang Y, Metcalf B, Yao W J Med Chem. 2026 May 27. doi: 10.1021/acs.jmedchem.5c03753. PMID:42202255[12] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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