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Vissers LTW, van der Burg M, Lankester AC, Smiers FJW, Bartels M, Mohseny AB. Pediatric Bone Marrow Failure: A Broad Landscape in Need of Personalized Management. J Clin Med 2023; 12:7185. [PMID: 38002797 PMCID: PMC10672506 DOI: 10.3390/jcm12227185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 11/10/2023] [Accepted: 11/16/2023] [Indexed: 11/26/2023] Open
Abstract
Irreversible severe bone marrow failure (BMF) is a life-threatening condition in pediatric patients. Most important causes are inherited bone marrow failure syndromes (IBMFSs) and (pre)malignant diseases, such as myelodysplastic syndrome (MDS) and (idiopathic) aplastic anemia (AA). Timely treatment is essential to prevent infections and bleeding complications and increase overall survival (OS). Allogeneic hematopoietic stem cell transplantation (HSCT) provides a cure for most types of BMF but cannot restore non-hematological defects. When using a matched sibling donor (MSD) or a matched unrelated donor (MUD), the OS after HSCT ranges between 60 and 90%. Due to the introduction of post-transplantation cyclophosphamide (PT-Cy) to prevent graft versus host disease (GVHD), alternative donor HSCT can reach similar survival rates. Although HSCT can restore ineffective hematopoiesis, it is not always used as a first-line therapy due to the severe risks associated with HSCT. Therefore, depending on the underlying cause, other treatment options might be preferred. Finally, for IBMFSs with an identified genetic etiology, gene therapy might provide a novel treatment strategy as it could bypass certain limitations of HSCT. However, gene therapy for most IBMFSs is still in its infancy. This review summarizes current clinical practices for pediatric BMF, including HSCT as well as other disease-specific treatment options.
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Affiliation(s)
- Lotte T. W. Vissers
- Laboratory for Pediatric Immunology, Department of Pediatrics, Willem-Alexander Children’s Hospital, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; (L.T.W.V.); (M.v.d.B.)
| | - Mirjam van der Burg
- Laboratory for Pediatric Immunology, Department of Pediatrics, Willem-Alexander Children’s Hospital, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; (L.T.W.V.); (M.v.d.B.)
| | - Arjan C. Lankester
- Department of Pediatrics, Hematology and Stem Cell Transplantation, Willem-Alexander Children’s Hospital, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; (A.C.L.); (F.J.W.S.)
| | - Frans J. W. Smiers
- Department of Pediatrics, Hematology and Stem Cell Transplantation, Willem-Alexander Children’s Hospital, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; (A.C.L.); (F.J.W.S.)
| | - Marije Bartels
- Department of Pediatric Hematology, Wilhelmina Children’s Hospital, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands;
| | - Alexander B. Mohseny
- Department of Pediatrics, Hematology and Stem Cell Transplantation, Willem-Alexander Children’s Hospital, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands; (A.C.L.); (F.J.W.S.)
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Molecular Pathogenesis of Myeloproliferative Neoplasms: From Molecular Landscape to Therapeutic Implications. Int J Mol Sci 2022; 23:ijms23094573. [PMID: 35562964 PMCID: PMC9100530 DOI: 10.3390/ijms23094573] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 04/15/2022] [Accepted: 04/19/2022] [Indexed: 12/27/2022] Open
Abstract
Despite distinct clinical entities, the myeloproliferative neoplasms (MPN) share morphological similarities, propensity to thrombotic events and leukemic evolution, and a complex molecular pathogenesis. Well-known driver mutations, JAK2, MPL and CALR, determining constitutive activation of JAK-STAT signaling pathway are the hallmark of MPN pathogenesis. Recent data in MPN patients identified the presence of co-occurrence somatic mutations associated with epigenetic regulation, messenger RNA splicing, transcriptional mechanism, signal transduction, and DNA repair mechanism. The integration of genetic information within clinical setting is already improving patient management in terms of disease monitoring and prognostic information on disease progression. Even the current therapeutic approaches are limited in disease-modifying activity, the expanding insight into the genetic basis of MPN poses novel candidates for targeted therapeutic approaches. This review aims to explore the molecular landscape of MPN, providing a comprehensive overview of the role of drive mutations and additional mutations, their impact on pathogenesis as well as their prognostic value, and how they may have future implications in therapeutic management.
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Roy A, Shrivastva S, Naseer S. In and out: Traffic and dynamics of thrombopoietin receptor. J Cell Mol Med 2021; 25:9073-9083. [PMID: 34448528 PMCID: PMC8500957 DOI: 10.1111/jcmm.16878] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 07/27/2021] [Accepted: 08/04/2021] [Indexed: 12/17/2022] Open
Abstract
Thrombopoiesis had long been a challenging area of study due to the rarity of megakaryocyte precursors in the bone marrow and the incomplete understanding of its regulatory cytokines. A breakthrough was achieved in the early 1990s with the discovery of the thrombopoietin receptor (TpoR) and its ligand thrombopoietin (TPO). This accelerated research in thrombopoiesis, including the uncovering of the molecular basis of myeloproliferative neoplasms (MPN) and the advent of drugs to treat thrombocytopenic purpura. TpoR mutations affecting its membrane dynamics or transport were increasingly associated with pathologies such as MPN and thrombocytosis. It also became apparent that TpoR affected hematopoietic stem cell (HSC) quiescence while priming hematopoietic stem cells (HSCs) towards the megakaryocyte lineage. Thorough knowledge of TpoR surface localization, dimerization, dynamics and stability is therefore crucial to understanding thrombopoiesis and related pathologies. In this review, we will discuss the mechanisms of TpoR traffic. We will focus on the recent progress in TpoR membrane dynamics and highlight the areas that remain unexplored.
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Affiliation(s)
- Anita Roy
- Kusuma School of Biological Sciences, Indian Institute of Technology, New Delhi, India
| | - Saurabh Shrivastva
- Kusuma School of Biological Sciences, Indian Institute of Technology, New Delhi, India
| | - Saadia Naseer
- Kusuma School of Biological Sciences, Indian Institute of Technology, New Delhi, India
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Spivak JL, Moliterno AR. The Thrombopoietin Receptor, MPL, Is a Therapeutic Target of Opportunity in the MPN. Front Oncol 2021; 11:641613. [PMID: 33777803 PMCID: PMC7987816 DOI: 10.3389/fonc.2021.641613] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 01/28/2021] [Indexed: 12/12/2022] Open
Abstract
The myeloproliferative neoplasms, polycythemia vera, essential thrombocytosis and primary myelofibrosis share driver mutations that either activate the thrombopoietin receptor, MPL, or indirectly activate it through mutations in the gene for JAK2, its cognate tyrosine kinase. Paradoxically, although the myeloproliferative neoplasms are classified as neoplasms because they are clonal hematopoietic stem cell disorders, the mutations affecting MPL or JAK2 are gain-of-function, resulting in increased production of normal erythrocytes, myeloid cells and platelets. Constitutive JAK2 activation provides the basis for the shared clinical features of the myeloproliferative neoplasms. A second molecular abnormality, impaired posttranslational processing of MPL is also shared by these disorders but has not received the recognition it deserves. This abnormality is important because MPL is the only hematopoietic growth factor receptor expressed in hematopoietic stem cells; because MPL is a proto-oncogene; because impaired MPL processing results in chronic elevation of plasma thrombopoietin, and since these diseases involve normal hematopoietic stem cells, they have proven resistant to therapies used in other myeloid neoplasms. We hypothesize that MPL offers a selective therapeutic target in the myeloproliferative neoplasms since impaired MPL processing is unique to the involved stem cells, while MPL is required for hematopoietic stem cell survival and quiescent in their bone marrow niches. In this review, we will discuss myeloproliferative neoplasm hematopoietic stem cell pathophysiology in the context of the behavior of MPL and its ligand thrombopoietin and the ability of thrombopoietin gene deletion to abrogate the disease phenotype in vivo in a JAK2 V617 transgenic mouse model of PV.
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Affiliation(s)
- Jerry L Spivak
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine Baltimore, Baltimore, MD, United States
| | - Alison R Moliterno
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine Baltimore, Baltimore, MD, United States
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Abstract
Megakaryocytes give rise to platelets, which have a wide variety of functions in coagulation, immune response, inflammation, and tissue repair. Dysregulation of megakaryocytes is a key feature of in the myeloproliferative neoplasms, especially myelofibrosis. Megakaryocytes are among the main drivers of myelofibrosis by promoting myeloproliferation and bone marrow fibrosis. In vivo targeting of megakaryocytes by genetic and pharmacologic approaches ameliorates the disease, underscoring the important role of megakaryocytes in myeloproliferative neoplasms. Here we review the current knowledge of the function of megakaryocytes in the JAK2, CALR, and MPL-mutant myeloproliferative neoplasms.
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MPN: The Molecular Drivers of Disease Initiation, Progression and Transformation and their Effect on Treatment. Cells 2020; 9:cells9081901. [PMID: 32823933 PMCID: PMC7465511 DOI: 10.3390/cells9081901] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 08/07/2020] [Accepted: 08/11/2020] [Indexed: 02/07/2023] Open
Abstract
Myeloproliferative neoplasms (MPNs) constitute a group of disorders identified by an overproduction of cells derived from myeloid lineage. The majority of MPNs have an identifiable driver mutation responsible for cytokine-independent proliferative signalling. The acquisition of coexisting mutations in chromatin modifiers, spliceosome complex components, DNA methylation modifiers, tumour suppressors and transcriptional regulators have been identified as major pathways for disease progression and leukemic transformation. They also confer different sensitivities to therapeutic options. This review will explore the molecular basis of MPN pathogenesis and specifically examine the impact of coexisting mutations on disease biology and therapeutic options.
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Spivak JL, Merchant A, Williams DM, Rogers O, Zhao W, Duffield A, Resar LS, Moliterno AR, Zhao ZJ. Thrombopoietin is required for full phenotype expression in a JAK2V617F transgenic mouse model of polycythemia vera. PLoS One 2020; 15:e0232801. [PMID: 32479500 PMCID: PMC7263591 DOI: 10.1371/journal.pone.0232801] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Accepted: 04/21/2020] [Indexed: 12/30/2022] Open
Abstract
The myeloproliferative neoplasms, polycythemia vera, essential thrombocytosis and primary myelofibrosis are hematopoietic stem cell disorders and share driver mutations that either directly activate the thrombopoietin receptor, MPL, or activate it indirectly through gain-of-function mutations in the gene for JAK2, its cognate tyrosine kinase. Paradoxically, MPL surface expression in hematopoietic stem cells is also reduced in the myeloproliferative neoplasms due to abnormal post-translational glycosylation and premature destruction of JAK2, suggesting that the myeloproliferative neoplasms are disorders of MPL processing since MPL is the only hematopoietic growth factor receptor in hematopoietic stem cells. To examine this possibility, we genetically manipulated MPL expression and maturation in a JAK2V617F transgenic mouse model of polycythemia vera. Elimination of MPL expression completely abrogated the polycythemia vera phenotype in this JAK2V617F transgenic mouse model, which could only be partially restored by expression of one MPL allele. Most importantly, elimination of thrombopoietin gene expression abrogated the polycythemia vera phenotype in this JAK2V617F transgenic mouse model, which could be completely restored by expression of a single thrombopoietin allele. These data indicate that polycythemia vera is in part a thrombopoietin-dependent disorder and that targeting the MPL-thrombopoietin axis could be an effective, nonmyelotoxic therapeutic strategy in this disorder.
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Affiliation(s)
- Jerry L. Spivak
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- * E-mail:
| | - Akil Merchant
- Samuel Oschin Comprehensive Cancer Institute, Blood and Marrow Transplant Program, Cedars-Sinai Medical Center, Los Angeles, California, United States of America
| | - Donna M. Williams
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Ophelia Rogers
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Wanke Zhao
- Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America
| | - Amy Duffield
- Department of Pathology, Hematologic Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Linda S. Resar
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Alison R. Moliterno
- Hematology Division, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Zhizhuang J. Zhao
- Department of Pathology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States of America
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Koride S, Nayak S, Banfield C, Peterson MC. Evaluating the Role of Janus Kinase Pathways in Platelet Homeostasis Using a Systems Modeling Approach. CPT-PHARMACOMETRICS & SYSTEMS PHARMACOLOGY 2019; 8:478-488. [PMID: 31044523 PMCID: PMC6656939 DOI: 10.1002/psp4.12419] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 03/02/2019] [Indexed: 02/06/2023]
Abstract
Maintaining platelet homeostasis is important to avoid spontaneous bleeding and organ damage. Thrombopoietin, the primary regulator of platelet production, is affected by and acts in part via Janus kinase (JAK)‐signal transducer and activator of transcription (STAT)–mediated mechanisms. Interleukin‐6 is also partly responsible for inducing thrombopoietin production via the JAK‐STAT pathway. Although current understanding suggests that JAK2 is a primary mediator of platelet regulation, the emerging data show that a JAK1‐specific inhibitor resulted in the modulation of platelet numbers following dosing. To gain a mechanistic understanding, a model describing platelet regulation based on known physiology and JAK‐STAT pathways was built. The model provides a tool to coalesce biological understanding of platelet physiology and an in silico experimental platform to explore drug effects on platelet homeostasis. In this article, we explain the model construction and demonstrate the use of JAK‐inhibitor programs as informing probes of the physiology, gaining insights on dosing paradigms that avoid platelet‐related safety concerns.
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Affiliation(s)
- Sarita Koride
- Early Clinical Development, Clinical Pharmacology, Pfizer Inc., Cambridge, Massachusetts, USA
| | - Satyaprakash Nayak
- Global Product Development, Pharmacometrics, Pfizer Inc., Cambridge, Massachusetts, USA
| | - Christopher Banfield
- Early Clinical Development, Clinical Pharmacology, Pfizer Inc., Cambridge, Massachusetts, USA
| | - Mark C Peterson
- Global Product Development, Pharmacometrics, Pfizer Inc., Cambridge, Massachusetts, USA
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Vainchenker W, Plo I, Marty C, Varghese LN, Constantinescu SN. The role of the thrombopoietin receptor MPL in myeloproliferative neoplasms: recent findings and potential therapeutic applications. Expert Rev Hematol 2019; 12:437-448. [PMID: 31092065 DOI: 10.1080/17474086.2019.1617129] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Introduction: Classical Myeloproliferative Neoplasms (MPNs) include three disorders: Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF). MPNs are associated with constitutive activation of JAK2 leading to persistent cell signaling downstream of the dimeric myeloid cytokine receptors due to mutations in three genes encoding JAK2, calreticulin (CALR) and the thrombopoietin (TPO) receptor (MPL or TPOR). CALR and MPL mutants induce JAK2 activation that depends on MPL expression, thus explaining why they induce megakaryocyte pathologies including ET and PMF, but not PV. In contrast, JAK2 V617F drives all three diseases as it induces persistent signaling via EPOR, G-CSFR (CSF3R) and MPL. Areas Covered: Here, we review how different pathogenic mutations of MPL are translated into active receptors by inducing stable dimerization. We focus on the unique role of MPL on the hematopoietic stem cell (HSC), explaining why MPL is indispensable for the development of all MPNs. Last but not least, we describe how CALR mutants are pathogenic via binding and activation of MPL. Expert Opinion: Altogether, we believe that MPL is an important, but challenging, therapeutic target in MPNs that requires novel strategies to interrupt the specific conformational changes induced by each mutation or pathologic interaction without compromising the key functions of wild type MPL.
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Affiliation(s)
- William Vainchenker
- a UMR1170 , INSERM , Villejuif , France.,b Université Paris-Saclay , Villejuif , France
| | - Isabelle Plo
- a UMR1170 , INSERM , Villejuif , France.,b Université Paris-Saclay , Villejuif , France
| | - Caroline Marty
- a UMR1170 , INSERM , Villejuif , France.,b Université Paris-Saclay , Villejuif , France
| | - Leila N Varghese
- c Ludwig Institute for Cancer Research Brussels , Brussels , Belgium.,d de Duve Institute, Université catholique de Louvain , Brussels , Belgium
| | - Stefan N Constantinescu
- c Ludwig Institute for Cancer Research Brussels , Brussels , Belgium.,d de Duve Institute, Université catholique de Louvain , Brussels , Belgium.,e WELBIO (Walloon Excellence in Life Sciences and Biotechnology) , Brussels , Belgium
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Stolyar MA, Gorbenko AS, Olkhovskiy IA. Platelet miR-28 expression level and thrombocytosis in MPN patients. Int J Lab Hematol 2018; 41:e43-e45. [PMID: 30480878 DOI: 10.1111/ijlh.12951] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Marina A Stolyar
- Department of Health, Krasnoyarsk Branch of the "National Research Center for Hematology", Krasnoyarsk, Russian Federation.,Federal Research Center Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
| | - Aleksey S Gorbenko
- Department of Health, Krasnoyarsk Branch of the "National Research Center for Hematology", Krasnoyarsk, Russian Federation
| | - Igor A Olkhovskiy
- Department of Health, Krasnoyarsk Branch of the "National Research Center for Hematology", Krasnoyarsk, Russian Federation.,Federal Research Center Krasnoyarsk Scientific Center of the Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
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Bellanné-Chantelot C, Mosca M, Marty C, Favier R, Vainchenker W, Plo I. Identification of MPL R102P Mutation in Hereditary Thrombocytosis. Front Endocrinol (Lausanne) 2017; 8:235. [PMID: 28979237 PMCID: PMC5611484 DOI: 10.3389/fendo.2017.00235] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 08/28/2017] [Indexed: 01/11/2023] Open
Abstract
The molecular basis of hereditary thrombocytosis is germline mutations affecting the thrombopoietin (TPO)/TPO receptor (MPL)/JAK2 signaling axis. Here, we report one family presenting two cases with a mild thrombocytosis. By sequencing JAK2 and MPL coding exons, we identified a germline MPL R102P heterozygous mutation in the proband and his daughter. Concomitantly, we detected high TPO levels in the serum of these two patients. The mutation was not found in three other unaffected cases from the family except in another proband's daughter who did not present thrombocytosis but had a high TPO level. The MPL R102P mutation was first described in congenital amegakaryocytic thrombocytopenia in a homozygous state with a loss-of-function activity. It was previously shown that MPL R102P was blocked in the endoplasmic reticulum without being able to translocate to the plasma membrane. Thus, this case report identifies for the first time that MPL R102P mutation can differently impact megakaryopoiesis: thrombocytosis or thrombocytopenia depending on the presence of the heterozygous or homozygous state, respectively. The paradoxical effect associated with heterozygous MPL R102P may be due to subnormal cell-surface expression of wild-type MPL in platelets inducing a defective TPO clearance. As a consequence, increased TPO levels may activate megakaryocyte progenitors that express a lower, but still sufficient level of MPL for the induction of proliferation.
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Affiliation(s)
- Christine Bellanné-Chantelot
- INSERM UMR1170, Gustave Roussy, Villejuif, France
- Department of Genetics, Assistance Publique-Hôpitaux de Paris (AP-HP) Hôpitaux Universitaires Pitié Salpêtrière—Charles Foix, UPMC Univ Paris 06, Paris, France
| | - Matthieu Mosca
- INSERM UMR1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
| | - Caroline Marty
- INSERM UMR1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
| | - Rémi Favier
- INSERM UMR1170, Gustave Roussy, Villejuif, France
- Assistance Publique-Hôpitaux de Paris (AP-HP), Service d’Hématologie biologique, Centre de Référence des Pathologies Plaquettaires (CRPP), Hôpital Armand Trousseau, Paris, France
| | - William Vainchenker
- INSERM UMR1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
| | - Isabelle Plo
- INSERM UMR1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
- *Correspondence: Isabelle Plo,
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Plo I, Bellanné-Chantelot C, Mosca M, Mazzi S, Marty C, Vainchenker W. Genetic Alterations of the Thrombopoietin/MPL/JAK2 Axis Impacting Megakaryopoiesis. Front Endocrinol (Lausanne) 2017; 8:234. [PMID: 28955303 PMCID: PMC5600916 DOI: 10.3389/fendo.2017.00234] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 08/28/2017] [Indexed: 12/31/2022] Open
Abstract
Megakaryopoiesis is an original and complex cell process which leads to the formation of platelets. The homeostatic production of platelets is mainly regulated and controlled by thrombopoietin (TPO) and the TPO receptor (MPL)/JAK2 axis. Therefore, any hereditary or acquired abnormality affecting this signaling axis can result in thrombocytosis or thrombocytopenia. Thrombocytosis can be due to genetic alterations that affect either the intrinsic MPL signaling through gain-of-function (GOF) activity (MPL, JAK2, CALR) and loss-of-function (LOF) activity of negative regulators (CBL, LNK) or the extrinsic MPL signaling by THPO GOF mutations leading to increased TPO synthesis. Alternatively, thrombocytosis may paradoxically result from mutations of MPL leading to an abnormal MPL trafficking, inducing increased TPO levels by alteration of its clearance. In contrast, thrombocytopenia can also result from LOF THPO or MPL mutations, which cause a complete defect in MPL trafficking to the cell membrane, impaired MPL signaling or stability, defects in the TPO/MPL interaction, or an absence of TPO production.
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Affiliation(s)
- Isabelle Plo
- INSERM UMR 1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
| | - Christine Bellanné-Chantelot
- INSERM UMR 1170, Gustave Roussy, Villejuif, France
- Department of Genetics, AP-HP Hôpitaux Universitaires Pitié Salpêtrière - Charles Foix, UPMC Univ Paris 06, Paris, France
| | - Matthieu Mosca
- INSERM UMR 1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
| | - Stefania Mazzi
- INSERM UMR 1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Université Paris-Diderot, Paris, France
| | - Caroline Marty
- INSERM UMR 1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
| | - William Vainchenker
- INSERM UMR 1170, Gustave Roussy, Villejuif, France
- Université Paris-Saclay, UMR1170, Gustave Roussy, Villejuif, France
- Gustave Roussy, UMR1170, Villejuif, France
- *Correspondence: William Vainchenker,
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Varghese LN, Defour JP, Pecquet C, Constantinescu SN. The Thrombopoietin Receptor: Structural Basis of Traffic and Activation by Ligand, Mutations, Agonists, and Mutated Calreticulin. Front Endocrinol (Lausanne) 2017; 8:59. [PMID: 28408900 PMCID: PMC5374145 DOI: 10.3389/fendo.2017.00059] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 03/17/2017] [Indexed: 12/13/2022] Open
Abstract
A well-functioning hematopoietic system requires a certain robustness and flexibility to maintain appropriate quantities of functional mature blood cells, such as red blood cells and platelets. This review focuses on the cytokine receptor that plays a significant role in thrombopoiesis: the receptor for thrombopoietin (TPO-R; also known as MPL). Here, we survey the work to date to understand how this receptor functions at a molecular level throughout its lifecycle, from traffic to the cell surface, dimerization and binding cognate cytokine via its extracellular domain, through to its subsequent activation of associated Janus kinases and initiation of downstream signaling pathways, as well as the regulation of these processes. Atomic level resolution structures of TPO-R have remained elusive. The identification of disease-causing mutations in the receptor has, however, offered some insight into structure and function relationships, as has artificial means of receptor activation, through TPO mimetics, transmembrane-targeting receptor agonists, and engineering in dimerization domains. More recently, a novel activation mechanism was identified whereby mutated forms of calreticulin form complexes with TPO-R via its extracellular N-glycosylated domain. Such complexes traffic pathologically in the cell and persistently activate JAK2, downstream signal transducers and activators of transcription (STATs), and other pathways. This pathologic TPO-R activation is associated with a large fraction of human myeloproliferative neoplasms.
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Affiliation(s)
- Leila N. Varghese
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- SIGN Pole, de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Jean-Philippe Defour
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- SIGN Pole, de Duve Institute, Université catholique de Louvain, Brussels, Belgium
- Department of Clinical Biology, Cliniques universitaires St Luc, Université catholique de Louvain, Brussels, Belgium
| | - Christian Pecquet
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- SIGN Pole, de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - Stefan N. Constantinescu
- Ludwig Institute for Cancer Research, Brussels Branch, Brussels, Belgium
- SIGN Pole, de Duve Institute, Université catholique de Louvain, Brussels, Belgium
- *Correspondence: Stefan N. Constantinescu,
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14
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An incomplete trafficking defect to the cell-surface leads to paradoxical thrombocytosis for human and murine MPL P106L. Blood 2016; 128:3146-3158. [PMID: 28034873 DOI: 10.1182/blood-2016-06-722058] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Accepted: 11/03/2016] [Indexed: 12/30/2022] Open
Abstract
The mechanisms behind the hereditary thrombocytosis induced by the thrombopoietin (THPO) receptor MPL P106L mutant remain unknown. A complete trafficking defect to the cell surface has been reported, suggesting either weak constitutive activity or nonconventional THPO-dependent mechanisms. Here, we report that the thrombocytosis phenotype induced by MPL P106L belongs to the paradoxical group, where low MPL levels on platelets and mature megakaryocytes (MKs) lead to high serum THPO levels, whereas weak but not absent MPL cell-surface localization in earlier MK progenitors allows response to THPO by signaling and amplification of the platelet lineage. MK progenitors from patients showed no spontaneous growth and responded to THPO, and MKs expressed MPL on their cell surface at low levels, whereas their platelets did not respond to THPO. Transduction of MPL P106L in CD34+ cells showed that this receptor was more efficiently localized at the cell surface on immature than on mature MKs, explaining a proliferative response to THPO of immature cells and a defect in THPO clearance in mature cells. In a retroviral mouse model performed in Mpl-/- mice, MPL P106L could induce a thrombocytosis phenotype with high circulating THPO levels. Furthermore, we could select THPO-dependent cell lines with more cell-surface MPL P106L localization that was detected by flow cytometry and [125I]-THPO binding. Altogether, these results demonstrate that MPL P106L is a receptor with an incomplete defect in trafficking, which induces a low but not absent localization of the receptor on cell surface and a response to THPO in immature MK cells.
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15
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Establishment of a congenital amegakaryocytic thrombocytopenia model and a thrombocyte–specific reporter line in zebrafish. Leukemia 2016; 31:1206-1216. [DOI: 10.1038/leu.2016.320] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Revised: 10/06/2016] [Accepted: 10/10/2016] [Indexed: 11/08/2022]
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16
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A thrombopoietin receptor antagonist is capable of depleting myelofibrosis hematopoietic stem and progenitor cells. Blood 2016; 127:3398-409. [PMID: 27114459 DOI: 10.1182/blood-2015-10-674465] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 04/21/2016] [Indexed: 01/12/2023] Open
Abstract
Recently, interactions between thrombopoietin (TPO) and its receptor, the myeloproliferative leukemia (MPL) virus oncogene, have been shown to play a role in the development and progression of myeloproliferative neoplasms including myelofibrosis (MF). These observations have led to the development of strategies to disrupt the association of TPO with its receptor as a means of targeting MF hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). In this report, we show that although both splenic and peripheral blood MF CD34(+) cells expressed lower levels of MPL than normal CD34(+) cells, TPO promoted the proliferation of MF CD34(+) cells and HPCs in a dose-dependent fashion. Furthermore, the treatment of MF but not normal CD34(+) cells with a synthesized MPL antagonist, LCP4, decreased the number of CD34(+)Lin(-) cells and all classes of assayable HPCs (colony-forming unit-megakaryocyte [CFU-MK], CFU-granulocyte/macrophage, burst-forming unit-erythroid/CFU-erythroid, and CFU-granulocyte/erythroid/macrophage/MK) irrespective of their mutational status. In addition, LCP4 treatment resulted in the depletion of the number of MF HPCs that were JAK2V617F(+) Moreover, the degree of human cell chimerism and the proportion of malignant donor cells were significantly reduced in immunodeficient mice transplanted with MF CD34(+) cell grafts treated with LCP4. These effects of LCP4 on MF HSCs/HPCs were associated with inhibition of JAK-STAT activity, leading to the induction of apoptosis. These findings demonstrate that such specific anti-cytokine receptor antagonists represent a new class of drugs that are capable of targeting MF HSCs.
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17
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Kollek M, Müller A, Egle A, Erlacher M. Bcl-2 proteins in development, health, and disease of the hematopoietic system. FEBS J 2016; 283:2779-810. [DOI: 10.1111/febs.13683] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2015] [Revised: 01/29/2016] [Accepted: 02/12/2016] [Indexed: 12/20/2022]
Affiliation(s)
- Matthias Kollek
- Division of Pediatric Hematology and Oncology; Department of Pediatrics and Adolescent Medicine; University Medical Center of Freiburg; Germany
- Faculty of Biology; University of Freiburg; Germany
| | - Alexandra Müller
- Division of Pediatric Hematology and Oncology; Department of Pediatrics and Adolescent Medicine; University Medical Center of Freiburg; Germany
| | - Alexander Egle
- Laboratory for Immunological and Molecular Cancer Research; 3rd Medical Department for Hematology; Paracelsus Private Medical University Hospital; Salzburg Austria
| | - Miriam Erlacher
- Division of Pediatric Hematology and Oncology; Department of Pediatrics and Adolescent Medicine; University Medical Center of Freiburg; Germany
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18
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Presence of atypical thrombopoietin receptor (MPL) mutations in triple-negative essential thrombocythemia patients. Blood 2016; 127:333-42. [DOI: 10.1182/blood-2015-07-661983] [Citation(s) in RCA: 118] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 09/24/2015] [Indexed: 01/06/2023] Open
Abstract
Key Points
Enrichment of atypical MPL mutations in essential thrombocythemia. MPLS204P and MPLY591N mutants are weak gain-of-function mutants.
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19
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Fu H, Zhang X, Xu L, Liu K, Huang X. Characterization of thrombopoietin kinetics within 60 days after allogeneic hematopoietic stem cell transplantation and its correlation with megakaryocyte ploidy distribution. Clin Transplant 2015; 30:170-8. [PMID: 26589669 DOI: 10.1111/ctr.12673] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/12/2015] [Indexed: 02/05/2023]
Affiliation(s)
- Haixia Fu
- Peking University People's Hospital; Institute of Hematology; Beijing China
| | - Xiaohui Zhang
- Peking University People's Hospital; Institute of Hematology; Beijing China
| | - Lanping Xu
- Peking University People's Hospital; Institute of Hematology; Beijing China
| | - Kaiyan Liu
- Peking University People's Hospital; Institute of Hematology; Beijing China
| | - Xiaojun Huang
- Peking University People's Hospital; Institute of Hematology; Beijing China
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20
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The thrombopoietin receptor P106L mutation functionally separates receptor signaling activity from thrombopoietin homeostasis. Blood 2014; 125:1159-69. [PMID: 25538044 DOI: 10.1182/blood-2014-07-587170] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The interaction between thrombopoietin (THPO) and its receptor c-Mpl regulates downstream cytokine signaling and platelet homeostasis. Hereditary mutations of c-Mpl can either result in loss-of-function and thrombocytopenia or in gain-of-function and thrombocythemia (HT), and are important models to analyze the mechanism of c-Mpl activity. We have analyzed the effect of the c-Mpl P106L gain-of-function and the nearby loss-of-function R102P and F104S mutations, which cause HT or thrombocytopenia, respectively, on posttranslational processing, intracellular trafficking, cell surface expression, and cell proliferation. In contrast to R102P and F104S, the P106L mutant confers cytokine-independent growth and stimulates downstream signaling after THPO treatment in Ba/F3 cells. Despite their opposite function, R102P and P106L, both lead to abnormal subcellular receptor distribution, lack of membrane localization, impaired glycosylation, and elevated THPO serum levels in effected patients. These findings indicate that the activation of downstream signaling by c-Mpl P106L does not require correct processing, trafficking, and cell surface expression of c-Mpl, whereas the negative feedback loop controlling THPO serum levels requires cell surface expression of the receptor. Thus, we propose that the P106L mutation functionally separates the activity of c-Mpl in downstream signaling from that in maintaining platelet homeostasis.
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21
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22
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Ott1 (Rbm15) regulates thrombopoietin response in hematopoietic stem cells through alternative splicing of c-Mpl. Blood 2014; 125:941-8. [PMID: 25468569 DOI: 10.1182/blood-2014-08-593392] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Thrombopoietin (Thpo) signaling through the c-Mpl receptor promotes either quiescence or proliferation of hematopoietic stem cells (HSCs) in a concentration-dependent manner; however, in vivo Thpo serum levels are responsive to platelet mass rather than HSC demands, suggesting additional regulation exists. Ott1 (Rbm15), a spliceosomal component originally identified as a fusion partner in t(1;22)-associated acute megakaryocytic leukemia, is also essential for maintaining HSC quiescence under stress. Ott1 controls the alternative splicing of a dominant negative isoform, Mpl-TR, capable of inhibiting HSC engraftment and attenuating Thpo signaling. Ott1, which associates with Hdac3 and the histone methyltransferase, Setd1b, binds to both c-Mpl RNA and chromatin and regulates H4 acetylation and H3K4me3 marks. Histone deacetylase or histone methyltransferase inhibition also increases Mpl-TR levels, suggesting that Ott1 uses an underlying epigenetic mechanism to control alternative splicing of c-Mpl. Manipulation of Ott1-dependent alternative splicing may therefore provide a novel pharmacologic avenue for regulating HSC quiescence and proliferation in response to Thpo.
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23
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Abstract
Dynamins are highly conserved large GTPases (enzymes that hydrolyze guanosine triphosphate) involved in endocytosis and vesicle transport, and mutations in the ubiquitous and housekeeping dynamin 2 (DNM2) have been associated with thrombocytopenia in humans. To determine the role of DNM2 in thrombopoiesis, we generated Dnm2(fl/fl) Pf4-Cre mice specifically lacking DNM2 in the megakaryocyte (MK) lineage. Dnm2(fl/fl) Pf4-Cre mice had severe macrothrombocytopenia with moderately accelerated platelet clearance. Dnm2-null bone marrow MKs had altered demarcation membrane system formation in vivo due to defective endocytic pathway, and fetal liver-derived Dnm2-null MKs formed proplatelets poorly in vitro, showing that DNM2-dependent endocytosis plays a major role in MK membrane formation and thrombopoiesis. Endocytosis of the thrombopoietin receptor Mpl was impaired in Dnm2-null platelets, causing constitutive phosphorylation of the tyrosine kinase JAK2 and elevated circulating thrombopoietin levels. MK-specific DNM2 deletion severely disrupted bone marrow homeostasis, as reflected by marked expansion of hematopoietic stem and progenitor cells, MK hyperplasia, myelofibrosis, and consequent extramedullary hematopoiesis and splenomegaly. Taken together, our data demonstrate that unrestrained MK growth and proliferation results in rapid myelofibrosis and establishes a previously unrecognized role for DNM2-dependent endocytosis in megakaryopoiesis, thrombopoiesis, and bone marrow homeostasis.
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The thrombopoietin receptor, MPL, is critical for development of a JAK2V617F-induced myeloproliferative neoplasm. Blood 2014; 124:3956-63. [PMID: 25339357 DOI: 10.1182/blood-2014-07-587238] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The most frequent contributing factor in Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) is the acquisition of a V617F mutation in Janus kinase 2 (JAK2) in hematopoietic stem cells (HSCs). Recent evidence has demonstrated that to drive MPN transformation, JAK2V617F needs to directly associate with a functional homodimeric type I cytokine receptor, suggesting that, although acquiring JAK2V617F may promote disease, there are additional cellular components necessary for MPN development. Here we show that loss of the thrombopoietin (TPO) receptor (MPL) significantly ameliorates MPN development in JAK2V617F(+) transgenic mice, whereas loss of TPO only mildly affects the disease phenotype. Specifically, compared with JAK2V617F(+) mice, JAK2V617F(+)Mpl(-/-) mice exhibited reduced thrombocythemia, neutrophilia, splenomegaly, and neoplastic stem cell pool. The importance of MPL is highlighted as JAK2V617FMpl(+/-) mice displayed a significantly reduced MPN phenotype, indicating that Mpl level may have a substantial effect on MPN development and severity. Splenomegaly and the increased neoplastic stem cell pool were retained in JAK2V617F(+)Tpo(-/-) mice, although thrombocytosis was reduced compared with JAK2V617F(+) mice. These results demonstrate that Mpl expression, but not Tpo, is fundamental in the development of JAK2V617F(+) MPNs, highlighting an entirely novel target for therapeutic intervention.
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25
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Cleyrat C, Darehshouri A, Steinkamp MP, Vilaine M, Boassa D, Ellisman MH, Hermouet S, Wilson BS. Mpl traffics to the cell surface through conventional and unconventional routes. Traffic 2014; 15:961-82. [PMID: 24931576 PMCID: PMC4141020 DOI: 10.1111/tra.12185] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2012] [Revised: 06/10/2014] [Accepted: 06/11/2014] [Indexed: 12/20/2022]
Abstract
Myeloproliferative neoplasms (MPNs) are often characterized by JAK2 or calreticulin (CALR) mutations, indicating aberrant trafficking in pathogenesis. This study focuses on Mpl trafficking and Jak2 association using two model systems: human erythroleukemia cells (HEL; JAK2V617F) and K562 myeloid leukemia cells (JAK2WT). Consistent with a putative chaperone role for Jak2, Mpl and Jak2 associate on both intracellular and plasma membranes (shown by proximity ligation assay) and siRNA-mediated knockdown of Jak2 led to Mpl trapping in the endoplasmic reticulum (ER). Even in Jak2 sufficient cells, Mpl accumulates in punctate structures that partially colocalize with ER-tracker, the ER exit site marker (ERES) Sec31a, the autophagy marker LC3 and LAMP1. Mpl was fused to miniSOG, a genetically encoded tag for correlated light and electron microscopy. Results suggest that a fraction of Mpl is taken up into autophagic structures from the ER and routed to autolyososomes. Surface biotinylation shows that both immature and mature Mpl reach the cell surface; in K562 cells Mpl is also released in exosomes. Both forms rapidly internalize upon ligand addition, while recovery is primarily attributed to immature Mpl. Mpl appears to reach the plasma membrane via both conventional ER-Golgi and autolysosome secretory pathways, as well as recycling.
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Affiliation(s)
- Cédric Cleyrat
- Department of Pathology & Cancer Center, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131 USA
- INSERM UMR892/CNRS UMR6299, Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), Institut de Recherche Thérapeutique-Université de Nantes, Nantes, France
| | - Anza Darehshouri
- Department of Pathology & Cancer Center, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131 USA
| | - Mara P. Steinkamp
- Department of Pathology & Cancer Center, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131 USA
| | - Mathias Vilaine
- INSERM UMR892/CNRS UMR6299, Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), Institut de Recherche Thérapeutique-Université de Nantes, Nantes, France
| | - Daniela Boassa
- National Center for Microscopy and Imaging Research, University of California at San Diego, San Diego CA 92093 USA
| | - Mark H. Ellisman
- National Center for Microscopy and Imaging Research, University of California at San Diego, San Diego CA 92093 USA
| | - Sylvie Hermouet
- INSERM UMR892/CNRS UMR6299, Centre de Recherche en Cancérologie Nantes-Angers (CRCNA), Institut de Recherche Thérapeutique-Université de Nantes, Nantes, France
| | - Bridget S. Wilson
- Department of Pathology & Cancer Center, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131 USA
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26
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JAK2 and MPL protein levels determine TPO-induced megakaryocyte proliferation vs differentiation. Blood 2014; 124:2104-15. [PMID: 25143485 DOI: 10.1182/blood-2014-03-559815] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Megakaryopoiesis is a 2-step differentiation process, regulated by thrombopoietin (TPO), on binding to its cognate receptor myeloproliferative leukemia (MPL). This receptor associates with intracytoplasmic tyrosine kinases, essentially janus kinase 2 (JAK2), which regulates MPL stability and cell-surface expression, and mediates TPO-induced signal transduction. We demonstrate that JAK2 and MPL mediate TPO-induced proliferation arrest and megakaryocytic differentiation of the human megakaryoblastic leukemia cell line UT7-MPL. A decrease in JAK2 or MPL protein expression, and JAK2 chemical inhibition, suppress this antiproliferative action of TPO. The expression of JAK2 and MPL, which progressively increases along normal human megakaryopoiesis, is decreased in platelets of patients diagnosed with JAK2- or MPL-mutated essential thrombocytemia and primary myelofibrosis, 2 myeloproliferative neoplasms in which megakaryocytes (MKs) proliferate excessively. Finally, low doses of JAK2 chemical inhibitors are shown to induce a paradoxical increase in MK production, both in vitro and in vivo. We propose that JAK2 and MPL expression levels regulate megakaryocytic proliferation vs differentiation in both normal and pathological conditions, and that JAK2 chemical inhibitors could promote a paradoxical thrombocytosis when used at suboptimal doses.
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27
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Abstract
JAK inhibitor treatment is limited by the variable development of anemia and thrombocytopenia thought to be due to on-target JAK2 inhibition. We evaluated the impact of Jak2 deletion in platelets (PLTs) and megakaryocytes (MKs) on blood counts, stem/progenitor cells, and Jak-Stat signaling. Pf4-Cre-mediated Jak2 deletion in PLTs and MKs did not compromise PLT formation but caused thrombocytosis, and resulted in expansion of MK progenitors and Lin(-)Sca1(+)Kit+ cells. Serum thrombopoietin (TPO) was maintained at normal levels in Pf4-Cre-positive Jak2(f/f) mice, consistent with reduced internalization/turnover by Jak2-deficient PLTs. These data demonstrate that Jak2 in terminal megakaryopoiesis is not required for PLT production, and that Jak2 loss in PLTs and MKs results in non-autonomous expansion of stem/progenitors and of MKs and PLTs via dysregulated TPO turnover. This suggests that the thrombocytopenia frequently seen with JAK inhibitor treatment is not due to JAK2 inhibition in PLTs and MKs, but rather due to JAK2 inhibition in stem/progenitor cells.
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28
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Mpl expression on megakaryocytes and platelets is dispensable for thrombopoiesis but essential to prevent myeloproliferation. Proc Natl Acad Sci U S A 2014; 111:5884-9. [PMID: 24711413 DOI: 10.1073/pnas.1404354111] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Thrombopoietin (TPO) acting via its receptor, the cellular homologue of the myeloproliferative leukemia virus oncogene (Mpl), is the major cytokine regulator of platelet number. To precisely define the role of specific hematopoietic cells in TPO-dependent hematopoiesis, we generated mice that express the Mpl receptor normally on stem/progenitor cells but lack expression on megakaryocytes and platelets (Mpl(PF4cre/PF4cre)). Mpl(PF4cre/PF4cre) mice displayed profound megakaryocytosis and thrombocytosis with a remarkable expansion of megakaryocyte-committed and multipotential progenitor cells, the latter displaying biological responses and a gene expression signature indicative of chronic TPO overstimulation as the underlying causative mechanism, despite a normal circulating TPO level. Thus, TPO signaling in megakaryocytes is dispensable for platelet production; its key role in control of platelet number is via generation and stimulation of the bipotential megakaryocyte precursors. Nevertheless, Mpl expression on megakaryocytes and platelets is essential to prevent megakaryocytosis and myeloproliferation by restricting the amount of TPO available to stimulate the production of megakaryocytes from the progenitor cell pool.
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29
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Suo J, Linke B, Meyer dos Santos S, Pierre S, Stegner D, Zhang DD, Denis CV, Geisslinger G, Nieswandt B, Scholich K. Neutrophils mediate edema formation but not mechanical allodynia during zymosan-induced inflammation. J Leukoc Biol 2014; 96:133-42. [PMID: 24555986 DOI: 10.1189/jlb.3a1213-628r] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Inflammatory pain is based on stimulation and sensitization of peripheral endings of sensory neurons (nociceptors) by pronociceptive mediators. These mediators can be released by resident cells, as well as invading immune cells. Although neutrophils are known to release various mediators, which can stimulate or sensitize nociceptors, the extent of their contribution to nociceptive responses is unclear. Here, we studied the contribution of neutrophils to zymosan-induced inflammatory pain, which is characterized by an early recruitment of high numbers of neutrophils. Surprisingly, antibody-mediated neutrophil depletion caused a complete loss of edema formation but had no effect on mechanical pain thresholds. Blockage of the interaction between neutrophils and platelets or endothelial cells using antibodies directed against CD11b and CD162 reduced neutrophil recruitment to the site of inflammation. Again, the treatment decreased zymosan-induced edemas without altering mechanical pain thresholds. Also, HLB-219 mice, which have five to 10 times less platelets than WT mice, showed reduced neutrophil recruitment to the site of inflammation and decreased edema sizes, whereas, again, mechanical thresholds were unaltered. The effects observed in HLB-219 mice were relatively small and not reproduced in vWF-deficient mice or after antibody-mediated blockage of GPIbα. Flow chamber and transmigration assays showed that platelets were not necessary for neutrophil adhesion to endothelial cells but increased their transmigration. Taken together, zymosan-induced mechanical allodynia is, in contrast to edema formation, independent of neutrophils, and recruitment of neutrophils is only partly influenced by interactions with platelets.
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Affiliation(s)
- Jing Suo
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany
| | - Bona Linke
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany
| | - Sascha Meyer dos Santos
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany
| | - Sandra Pierre
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany
| | - David Stegner
- Universität Würzburg, Institut für Experimentelle Biomedizin, Universitätsklinikum und Rudolf-Virchow-Zentrum für Experimentelle Biomedizin, Würzburg, Germany; and
| | - Dong Dong Zhang
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany
| | - Cecile V Denis
- Institut National de la Santé et de la Recherche Médicale U770, Le Kremlin-Bicêtre, France
| | - Gerd Geisslinger
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany
| | - Bernhard Nieswandt
- Universität Würzburg, Institut für Experimentelle Biomedizin, Universitätsklinikum und Rudolf-Virchow-Zentrum für Experimentelle Biomedizin, Würzburg, Germany; and
| | - Klaus Scholich
- Institut für Klinische Pharmakologie, Pharmazentrum Frankfurt, Zentrums für Arzneimittelforschung Entwicklung und Sicherheit, Klinikum der Goethe-Universität Frankfurt, Frankfurt, Germany;
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30
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Auer P, Johnsen J, Johnson A, Logsdon B, Lange L, Nalls M, Zhang G, Franceschini N, Fox K, Lange E, Rich S, O’Donnell C, Jackson R, Wallace R, Chen Z, Graubert T, Wilson J, Tang H, Lettre G, Reiner A, Ganesh S, Li Y. Imputation of exome sequence variants into population- based samples and blood-cell-trait-associated loci in African Americans: NHLBI GO Exome Sequencing Project. Am J Hum Genet 2012; 91:794-808. [PMID: 23103231 DOI: 10.1016/j.ajhg.2012.08.031] [Citation(s) in RCA: 102] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 06/12/2012] [Accepted: 08/27/2012] [Indexed: 01/07/2023] Open
Abstract
Researchers have successfully applied exome sequencing to discover causal variants in selected individuals with familial, highly penetrant disorders. We demonstrate the utility of exome sequencing followed by imputation for discovering low-frequency variants associated with complex quantitative traits. We performed exome sequencing in a reference panel of 761 African Americans and then imputed newly discovered variants into a larger sample of more than 13,000 African Americans for association testing with the blood cell traits hemoglobin, hematocrit, white blood count, and platelet count. First, we illustrate the feasibility of our approach by demonstrating genome-wide-significant associations for variants that are not covered by conventional genotyping arrays; for example, one such association is that between higher platelet count and an MPL c.117G>T (p.Lys39Asn) variant encoding a p.Lys39Asn amino acid substitution of the thrombopoietin receptor gene (p = 1.5 × 10(-11)). Second, we identified an association between missense variants of LCT and higher white blood count (p = 4 × 10(-13)). Third, we identified low-frequency coding variants that might account for allelic heterogeneity at several known blood cell-associated loci: MPL c.754T>C (p.Tyr252His) was associated with higher platelet count; CD36 c.975T>G (p.Tyr325(∗)) was associated with lower platelet count; and several missense variants at the α-globin gene locus were associated with lower hemoglobin. By identifying low-frequency missense variants associated with blood cell traits not previously reported by genome-wide association studies, we establish that exome sequencing followed by imputation is a powerful approach to dissecting complex, genetically heterogeneous traits in large population-based studies.
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31
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Thrombopoietin receptor down-modulation by JAK2 V617F: restoration of receptor levels by inhibitors of pathologic JAK2 signaling and of proteasomes. Blood 2012; 119:4625-35. [PMID: 22378845 DOI: 10.1182/blood-2011-08-372524] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The constitutively active JAK2 V617F mutant is the major determinant of human myeloproliferative neoplasms (MPNs). We show that coexpression of murine JAK2 V617F and the murine thrombopoietin (Tpo) receptor (TpoR, c-MPL) in hematopoietic cell lines or heterozygous knock-in of JAK2 V617F in mice leads to down-modulation of TpoR levels. Enhanced TpoR ubiquitinylation, proteasomal degradation, reduced recycling, and maturation are induced by the constitutive JAK2 V617F activity. These effects can be prevented in cell lines by JAK2 and proteasome inhibitors. Restoration of TpoR levels by inhibitors could be detected in platelets from JAK2 inhibitor-treated myelofibrosis patients that express the JAK2 V617F mutant, and in platelets from JAK2 V617F knock-in mice that were treated in vivo with JAK2 or proteasome inhibitors. In addition, we show that Tpo can induce both proliferative and antiproliferative effects via TpoR at low and high JAK2 activation levels, respectively, or on expression of JAK2 V617F. The antiproliferative signaling and receptor down-modulation by JAK2 V617F were dependent on signaling via TpoR cytosolic tyrosine 626. We propose that selection against TpoR antiproliferative signaling occurs by TpoR down-modulation and that restoration of down-modulated TpoR levels could become a biomarker for the treatment of MPNs.
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PI3Kδ inhibitor, GS-1101 (CAL-101), attenuates pathway signaling, induces apoptosis, and overcomes signals from the microenvironment in cellular models of Hodgkin lymphoma. Blood 2011; 119:1897-900. [PMID: 22210877 DOI: 10.1182/blood-2011-10-386763] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
GS-1101 (CAL-101) is an oral PI3Kδ-specific inhibitor that has shown preclinical and clinical activity in non-Hodgkin lymphoma and chronic lymphocytic leukemia. To investigate the potential role of PI3Kδ in Hodgkin lymphoma (HL), we screened 5 HL cell lines and primary samples from patients with HL for PI3Kδ isoform expression and constitutive PI3K pathway activation. Inhibition of PI3Kδ by GS-1101 resulted in the inhibition of Akt phosphorylation. Cocultures with stroma cells induced Akt activation in HL cells, and this effect was blocked by GS-1101. Conversely, production of the stroma-stimulating chemokine, CCL5, by HL cells was reduced by GS-1101. GS-1101 also induced dose-dependent apoptosis of HL cells at 48 hours. Reductions in cell viability and apoptosis were enhanced when combining GS-1101 with the mTOR inhibitor everolimus. Our findings suggest that excessive PI3Kδ activity is characteristic in HL and support clinical evaluation of GS-1101, alone and in combination, as targeted therapy for HL.
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Mouse models of diseases of megakaryocyte and platelet homeostasis. Mamm Genome 2011; 22:449-65. [PMID: 21667128 DOI: 10.1007/s00335-011-9336-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Accepted: 05/16/2011] [Indexed: 01/19/2023]
Abstract
Platelets are the small anuclear blood cells that are the product of megakaryocytopoiesis, the process of hematopoietic stem cell commitment to megakaryocyte production and the differentiation and maturation of these cells for platelet release. Deregulation or disruption of megakaryocytopoiesis can result in platelet deficiencies, the thrombocytopenias, with attendant risk of hemorrhage or thrombocytosis, a pathological excess of platelet numbers. Mouse models, particularly those engineered to carry genetic alterations modeling mutations associated with human disease, have provided important insights into megakaryocytopoiesis and deregulation of this process in disease. This review focuses on mouse models of diseases of altered megakaryocyte and platelet number, illustrating the profound contribution of these models in validating suspected roles of disease-associated genetic alterations, promoting discovery of new links between genetic mutations and specific diseases, and providing unique tools for better understanding of disease pathophysiology and progression, as well as resources to define drug action or develop new therapeutic strategies.
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Abstract
Thrombopoietin (TPO) is the cytokine that is chiefly responsible for megakaryocyte production but increasingly attention has turned to its role in maintaining hematopoietic stem cells (HSCs). HSCs are required to initiate the production of all mature hematopoietic cells, but this differentiation needs to be balanced against self-renewal and quiescence to maintain the stem cell pool throughout life. TPO has been shown to support HSC quiescence during adult hematopoiesis, with the loss of TPO signaling associated with bone marrow failure and thrombocytopenia. Recent studies have shown that constitutive activation mutations in Mpl contribute to myeloproliferative disease. In this review, we will discuss TPO signaling pathways, regulation of TPO levels and the role of TPO in normal hematopoiesis and during myeloproliferative disease.
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Lentiviral gene transfer regenerates hematopoietic stem cells in a mouse model for Mpl-deficient aplastic anemia. Blood 2011; 117:3737-47. [PMID: 21289307 DOI: 10.1182/blood-2010-09-308262] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Thpo/Mpl signaling plays an important role in the maintenance of hematopoietic stem cells (HSCs) in addition to its role in megakaryopoiesis. Patients with inactivating mutations in Mpl develop thrombocytopenia and aplastic anemia because of progressive loss of HSCs. Yet, it is unknown whether this loss of HSCs is an irreversible process. In this study, we used the Mpl knockout (Mpl(-/-)) mouse model and expressed Mpl from newly developed lentiviral vectors specifically in the physiologic Mpl target populations, namely, HSCs and megakaryocytes. After validating lineage-specific expression in vivo using lentiviral eGFP reporter vectors, we performed bone marrow transplantation of transduced Mpl(-/-) bone marrow cells into Mpl(-/-) mice. We show that restoration of Mpl expression from transcriptionally targeted vectors prevents lethal adverse reactions of ectopic Mpl expression, replenishes the HSC pool, restores stem cell properties, and corrects platelet production. In some mice, megakaryocyte counts were atypically high, accompanied by bone neo-formation and marrow fibrosis. Gene-corrected Mpl(-/-) cells had increased long-term repopulating potential, with a marked increase in lineage(-)Sca1(+)cKit(+) cells and early progenitor populations in reconstituted mice. Transcriptome analysis of lineage(-)Sca1(+)cKit(+) cells in Mpl-corrected mice showed functional adjustment of genes involved in HSC self-renewal.
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Lannutti BJ, Meadows SA, Herman SEM, Kashishian A, Steiner B, Johnson AJ, Byrd JC, Tyner JW, Loriaux MM, Deininger M, Druker BJ, Puri KD, Ulrich RG, Giese NA. CAL-101, a p110delta selective phosphatidylinositol-3-kinase inhibitor for the treatment of B-cell malignancies, inhibits PI3K signaling and cellular viability. Blood 2011; 117:591-4. [PMID: 20959606 PMCID: PMC3694505 DOI: 10.1182/blood-2010-03-275305] [Citation(s) in RCA: 587] [Impact Index Per Article: 45.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Phosphatidylinositol-3-kinase p110δ serves as a central integration point for signaling from cell surface receptors known to promote malignant B-cell proliferation and survival. This provides a rationale for the development of small molecule inhibitors that selectively target p110δ as a treatment approach for patients with B-cell malignancies. We thus identified 5-fluoro-3-phenyl-2-[(S)-1-(9H-purin-6-ylamino)-propyl]-3H-quinazolin-4-one (CAL-101), a highly selective and potent p110δ small molecule inhibitor (half-maximal effective concentration [EC(50)] = 8nM). Using tumor cell lines and primary patient samples representing multiple B-cell malignancies, we have demonstrated that constitutive phosphatidylinositol-3-kinase pathway activation is p110δ-dependent. CAL-101 blocked constitutive phosphatidylinositol-3-kinase signaling, resulting in decreased phosphorylation of Akt and other downstream effectors, an increase in poly(ADP-ribose) polymerase and caspase cleavage and an induction of apoptosis. These effects have been observed across a broad range of immature and mature B-cell malignancies, thereby providing a rationale for the ongoing clinical evaluation of CAL-101.
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Albu RI, Constantinescu SN. Extracellular domain N-glycosylation controls human thrombopoietin receptor cell surface levels. Front Endocrinol (Lausanne) 2011; 2:71. [PMID: 22649382 PMCID: PMC3355985 DOI: 10.3389/fendo.2011.00071] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Accepted: 10/21/2011] [Indexed: 01/13/2023] Open
Abstract
The thrombopoietin receptor (TpoR) is a type I transmembrane protein that mediates the signaling functions of thrombopoietin (Tpo) in regulating megakaryocyte differentiation, platelet formation, and hematopoietic stem cell renewal. We probed the role of each of the four extracellular domain putative N-glycosylation sites for cell surface localization and function of the receptor. Single N-glycosylation mutants at any of the four sites were able to acquire the mature N-glycosylated pattern, but exhibited a decreased Tpo-dependent JAK2-STAT response in stably transduced Ba/F3 or Ba/F3-JAK2 cell lines. The ability of JAK2 to promote cell surface localization and stability of TpoR required the first N-glycosylation site (Asn117). In contrast, the third N-glycosylation site (Asn298) decreased receptor maturation and stability. TpoR mutants lacking three N-glycosylation sites were defective in maturation, but N-glycosylation on the single remaining site could be detected by sensitivity to PNGaseF. The TpoR mutant defective in all four N-glycosylation sites was severely impaired in plasma membrane localization and was degraded by the proteasome. N-glycosylation receptor mutants are not misfolded as, once localized on the cell surface in overexpression conditions, they can bind and respond to Tpo. Our data indicate that extracellular domain N-glycosylation sites regulate in a combinatorial manner cell surface localization of TpoR. We discuss how mutations around TpoR N-glycosylation sites might contribute to inefficient receptor traffic and disease.
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Affiliation(s)
- Roxana I. Albu
- Ludwig Institute for Cancer ResearchBrussels, Belgium
- de Duve Institute, Université catholique de LouvainBrussels, Belgium
| | - Stefan N. Constantinescu
- Ludwig Institute for Cancer ResearchBrussels, Belgium
- de Duve Institute, Université catholique de LouvainBrussels, Belgium
- *Correspondence: Stefan N. Constantinescu, Ludwig Institute for Cancer Research, de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 74, UCL 75-4, Brussels B-1200, Belgium. e-mail:
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Glembotsky AC, Korin L, Lev PR, Chazarreta CD, Marta RF, Molinas FC, Heller PG. Screening for MPL mutations in essential thrombocythemia and primary myelofibrosis: normal Mpl expression and absence of constitutive STAT3 and STAT5 activation in MPLW515L-positive platelets. Eur J Haematol 2010; 84:398-405. [PMID: 20113333 DOI: 10.1111/j.1600-0609.2010.01421.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
OBJECTIVES To evaluate the frequency of MPL W515L, W515K and S505N mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) and to determine whether MPLW515L leads to impaired Mpl expression, constitutive STAT3 and STAT5 activation and enhanced response to thrombopoietin (TPO). METHODS Mutation detection was performed by allele-specific PCR and sequencing. Platelet Mpl expression was evaluated by flow cytometry, immunoblotting and real-time RT-PCR. Activation of STAT3 and STAT5 before and after stimulation with increasing concentrations of TPO was studied by immunoblotting. Plasma TPO was measured by ELISA. RESULTS MPLW515L was detected in 1 of 100 patients with ET and 1 of 11 with PMF. Platelets from the PMF patient showed 100% mutant allele, which was <50% in platelets from the ET patient, who also showed the mutation in granulocytes, monocytes and B cells. Mpl surface and total protein expression were normal, and TPO levels were mildly increased in the MPLW515L-positive ET patient, while MPL transcripts did not differ from controls in both MPLW515L-positive patients. Constitutive STAT3 and STAT5 phosphorylation was absent and dose response to TPO-induced phosphorylation was not enhanced. CONCLUSIONS The low frequency of MPL mutations in this cohort is in agreement with previous studies. The finding of normal Mpl levels in MPLW515L-positive platelets indicates this mutation does not lead to dysregulated Mpl expression, as frequently shown for myeloproliferative neoplasms. The lack of spontaneous STAT3 and STAT5 activation and the normal response to TPO is unexpected as MPLW515L leads to constitutive receptor activation and hypersensitivity to TPO in experimental models.
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Affiliation(s)
- Ana C Glembotsky
- Department of Hematology Research, Instituto de Investigaciones Médicas Alfredo Lanari, University of Buenos Aires, National Council for Scientific and Technological Research (CONICET), Buenos Aires, Argentina
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Wasiluk A, Mantur M, Kemona H, Szczepański M, Jasińska E, Milewski R. Thrombopoiesis in small for gestational age newborns. Platelets 2009; 20:520-4. [DOI: 10.3109/09537100903207505] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Wicke DC, Meyer J, Buesche G, Heckl D, Kreipe H, Li Z, Welte KH, Ballmaier M, Baum C, Modlich U. Gene therapy of MPL deficiency: challenging balance between leukemia and pancytopenia. Mol Ther 2009; 18:343-52. [PMID: 19844195 DOI: 10.1038/mt.2009.233] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Signaling of the thrombopoietin (THPO) receptor MPL is critical for the maintenance of hematopoietic stem cells (HSCs) and megakaryocytic differentiation. Inherited loss-of-function mutations of MPL cause severe thrombocytopenia and aplastic anemia, a syndrome called congenital amegakaryocytic thrombocytopenia (CAMT). With the aim to assess the toxicity of retroviral expression of Mpl as a basis for further development of a gene therapy for this disorder, we expressed Mpl in a murine bone marrow transplantation (BMT) model. Treated mice developed a profound yet transient elevation of multilineage hematopoiesis, which showed morphologic features of a chronic myeloproliferative disorder (CMPD) with progressive pancytopenia. Ten percent of mice (3/27) developed erythroleukemia, associated with insertional activation of Sfpi1 and Fli1. The majority of transplanted mice developed a progressive pancytopenia with histopathological features of a myelodysplastic syndrome (MDS)-like disorder. To avoid these adverse reactions, improved retroviral vectors were designed that mediate reduced and more physiological Mpl expression. Self-inactivating gamma-retroviral vectors were constructed that expressed Mpl from the phosphoglycerate kinase (PGK) or the murine Mpl promoter. Mice that received BM cells expressing Mpl from the Mpl promoter were free of any previously observed adverse reactions.
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Affiliation(s)
- Daniel C Wicke
- Department of Experimental Hematology, Hannover Medical School, Hannover, Germany
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In essential thrombocythemia, multiple JAK2-V617F clones are present in most mutant-positive patients: a new disease paradigm. Blood 2009; 114:3018-23. [PMID: 19541820 DOI: 10.1182/blood-2009-03-209916] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
In essential thrombocythemia (ET), the JAK2-V617F mutation is usually restricted to a subpopulation of neutrophils and platelets, and production of JAK2 wild-type (WT) platelets is not suppressed. Nonmutated precursor cells may, therefore, be susceptible to the acquisition of further JAK2 mutations. We used a common single nucleotide polymorphism (SNP) in the JAK2 coding sequence to genotype V617F alleles obtained either by allele-specific restriction enzyme digestion (RED) or by cloning. Both SNP alleles were detected in JAK2 mutant-positive alleles from neutrophils of 10 of 11 ET patients studied using RED compared with 0 of 5 with polycythemia vera. These results were confirmed in cloned products from 5 ET patients and indicate the occurrence of at least 2 separate JAK2 mutation events in the majority of ET patients investigated. In a further ET patient, JAK2 mutant-positive erythroid colonies with either X-allele inactivated were detected, demonstrating they could not have arisen from a common clonal precursor. These results indicate that at least 2 independent JAK2-V617F events occur commonly in ET patients, and they may arise on a polyclonal background. The presence of a JAK2 mutation in ET patients should not, therefore, be equated with a malignant disease.
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Ballmaier M, Germeshausen M. Advances in the understanding of congenital amegakaryocytic thrombocytopenia. Br J Haematol 2009; 146:3-16. [PMID: 19388932 DOI: 10.1111/j.1365-2141.2009.07706.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Congenital amegakaryocytic thrombocytopenia (MIM #604498) is an extremely rare inherited bone marrow failure syndrome, usually presenting as a severe thrombocytopenia at birth due to ineffective megakaryocytopoiesis and no characteristic physical anomalies. Usually the isolated thrombocytopenia progresses to pancytopenia during the first years of life. The only curative therapy to date is haematopoietic stem cell transplantation. Most of the cases of congenital amegakaryocytic thrombocytopenia are caused by defective expression or function of the thrombopoietin receptor due to homozygous or compound heterozygous mutations in the gene MPL. The essential roles of thrombopoietin as a lineage specific regulator of platelet production and as a regulator of haematopoietic stem cell function are reflected in the haematological defects seen in affected individuals.
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Affiliation(s)
- Matthias Ballmaier
- Department of Paediatric Haematology and Oncology, Hannover Medical School, Hannover, Germany.
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Abstract
Major progress in understanding the pathogenesis in patients with thrombocytosis has been made by identifying mutations in the key regulators of thrombopoietin: the thrombopoietin receptor MPL and JAK2. Together, these mutations can be found in 50% to 60% of patients with essential thrombocythemia or primary myelofibrosis and in 10% to 20% of hereditary thrombocytosis. A decrease in expression of the Mpl protein can cause thrombocytosis even in the absence of mutations in the coding sequence, due to a shift in the balance between stimulation of signaling in megakaryopoiesis and removal of thrombopoietin by receptor mediated internalization in platelets. When present in a heterozygous state the JAK2-V617F mutation preferentially stimulates megakaryopoiesis and in most cases manifests as essential thrombocythemia (ET), whereas homozygous JAK2-V617F reduces megakaryopoiesis in favor of increased erythropoiesis, resulting in polycythemia vera and/or myelofibrosis. In 30% to 40% of patients with ET or primary myelofibrosis (PMF) and in 80% to 90% of pedigrees with hereditary thrombocytosis the disease-causing gene remains unknown. Ongoing genetic and genomic screens have identified genes that, when mutated, can cause thrombocytosis in mouse models. A more complete picture of the pathways that regulate megakaryopoisis and platelet production will be important for finding new ways of controlling platelet production in patients with thrombocytosis.
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Affiliation(s)
- Radek C Skoda
- Experimental Hematology, Department of Biomedicine, University Hospital Basel, Basel, Switzerland.
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