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Haematologica 2021 Volume 106(7):1968-1978
Platelet Biology & its Disorders
Antiplatelet properties of Pim kinase inhibition are mediated through disruption of thromboxane A2 receptor signaling
Amanda J. Unsworth,1,2* Alexander P. Bye,1 Tanya Sage,1 Renato S. Gaspar,1 Nathan Eaton,3,4 Caleb Drew,3 Alexander Stainer,1 Neline Kriek,1
Peter J. Volberding,3,4,5 James L. Hutchinson,6 Ryan Riley,2 Sarah Jones,2 Stuart J. Mundell,6 Weiguo Cui,3,4,5 Hervé Falet3,4 and Jonathan M. Gibbins1*
1Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, UK; 2Department of Life Sciences, Faculty of Science and Engineering, Manchester, Metropolitan University, Manchester, UK; 3Blood Research Institute, Versiti, Milwaukee, WI, USA; 4Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI, USA; 5Department of Microbiology and Immunology, Medical College of Wisconsin. Milwaukee, WI, USA and 6School of Physiology, Pharmacology & Neuroscience, Bristol, UK
*AJU and JMG contributed equally to this work.
ABSTRACT
Pim kinases are upregulated in several forms of cancer, contributing to cell survival and tumor development, but their role in platelet function and thrombotic disease has not been explored. We report for the first time that Pim-1 kinase is expressed in human and mouse platelets. Genetic deletion or pharmacological inhibition of Pim kinase results in reduced thrombus formation but is not associated with impaired hemostasis. Attenuation of thrombus formation was found to be due to inhibition of the thromboxane A2 receptor as effects on platelet function were non-addi- tive to inhibition caused by the cyclo-oxygenase inhibitor indomethacin or the thromboxane A2 receptor antagonist GR32191. Treatment with Pim kinase inhibitors caused reduced surface expression of the thromboxane A2 receptor and resulted in reduced responses to thromboxane A2 receptor agonists, indicating a role for Pim kinase in the regulation of thromboxane A2 receptor function. Our research identifies a novel, Pim kinase-dependent regulatory mechanism for the thromboxane A2 receptor and represents a new targeting strategy that is independent of cyclo-oxygenase-1 inhibition or direct antagonism of the thromboxane A2 receptor that, while attenuat- ing thrombosis, does not increase bleeding.
Introduction
The family of Pim (proviral insertion in murine lymphoma) kinases, Pim-1, -2, and -3, are highly homologous serine/threonine kinases that are widely expressed across several cell types, and are highly expressed in hematopoietic cells. Pim kinases are constitutively active and are linked with cancer progression,1,2 with overexpression and upregulation of Pim kinase activity associated with both hematologic cancers and solid tumors. They function by phosphorylating their tar- get proteins on serine/threonine residues located within the common consensus sequence ARKRRHPS*GPPTA.1 A number of proteins that have important roles in the regulation of cellular proliferation and survival have been identified as phos- phorylation targets of the Pim kinases.3-6 Expressed as a short (32 kDa) or long (44 kDa) variant, the longer variant of Pim-1 kinase, Pim-1L, kinase has also been found to regulate adenosine triphosphate-binding cassette drug transporters.7-9 Pim-1 phosphorylates both BCRP/ABCG2 and Pgp transporters enabling, through different mechanisms, the formation of drug efflux pumps.7,9
Pim kinases are highly expressed in hematopoietic cells where they are impor- tant for differentiation and development of blood cells and blood cell precursors including megakaryocytes10 and platelets.11 Whether Pim kinases are involved in the regulation of platelet function has not been explored. Analysis of the mouse
Correspondence:
AMANDA J. UNSWORTH
a.unsworth@mmu.ac.uk
Received: April 1, 2019. Accepted: May 27, 2020. Pre-published: May 28, 2020.
https://doi.org/10.3324/haematol.2019.223529
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