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Platelet Biology & its Disorders
Post-translational polymodification of b1-tubulin regulates motor protein localization in platelet production and function
Abdullah O. Khan,1 Alexandre Slater,1 Annabel Maclachlan,1 Phillip L.R. Nicolson,1 Jeremy A. Pike,1,2 Jasmeet S. Reyat,1 Jack Yule,1,2 Rachel Stapley,1 Julie Rayes,1 Steven G. Thomas,1,2 and Neil V. Morgan1
1Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham and 2The Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham and University of Nottingham, Midlands, UK
ABSTRACT
In specialized cells, the expression of specific tubulin isoforms and their subsequent post-translational modifications drive and coordi- nate unique morphologies and behaviors. The mechanisms by which b1-tubulin, the platelet and megakaryocyte (MK) lineage restricted tubu- lin isoform, drives platelet production and function remains poorly understood. We investigated the roles of two key post-translational tubulin polymodifications (polyglutamylation and polyglycylation) on these processes using a cohort of thrombocytopenic patients, human induced pluripotent stem cell derived MK, and healthy human donor platelets. We find distinct patterns of polymodification in MK and platelets, mediated by the antagonistic activities of the cell specific expression of tubulin tyrosine ligase like enzymes and cytosolic car- boxypeptidase enzymes. The resulting microtubule patterning spatially regulates motor proteins to drive proplatelet formation in megakary- ocytes, and the cytoskeletal reorganization required for thrombus forma- tion. This work is the first to show a reversible system of polymodifica- tion by which different cell specific functions are achieved.
Introduction
Microtubules are large, cytoskeletal filaments vital to a host of critical functions including cell division, signaling, cargo transport, motility, and function.1,2 The ques- tion of how ubiquitously expressed filaments can facilitate complex and highly unique behaviors (such as neurotransmitter release and retinal organization) has been addressed by the concept of the tubulin code.3,4 This paradigm accounts for the spe- cialization of microtubules and their organization by describing a mechanism in which particular cells express lineage restricted isoforms of tubulin. These cell specific isoforms are then subject to a series of post-translational modifications (PTM) which alter the mechanical properties of microtubules, and their capacity to recruit accesso- ry proteins (e.g., motor proteins).1,2,4,5
A host of PTM have been reported in a range of cell types, including tyrosination, acetylation, glutamylation, glycylation, and phosphorylation. The loss of specific tubulin PTM has been linked to disease and dysfunction in motile and non-motile cilia (including respiratory cilia, retinal cells), spermatogenesis, muscular disorders, and neurological development.1,4,6–11 Despite an increasing understanding of the impor- tance of tubulin PTM in disease, the role of the tubulin code in the generation of blood platelets from their progenitors, megakaryocytes (MK) remains poorly under- stood.
Platelets are the smallest component of peripheral blood, and circulate as anucleate cells with an archetypal discoid shape maintained by a microtubule marginal band.12,13 Antagonistic motor proteins maintain the resting state of the marginal band, and dur- ing platelet activation a motor dependent mechanism results in sliding which extends the marginal band and causes the transition to a spherical shape.13–15
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Haematologica 2022 Volume 107(1):243-259
Conversely MK are the largest and rarest hematopoeitic cells of the bone marrow.
Correspondence:
ABDULLAH O. KHAN
a.khan.4@bham.ac.uk
NEIL V. MORGAN
N.V.Morgan@bham.ac.uk.
Received: August 28, 2020. Accepted: December 11, 2020. Pre-published: December 17, 2020.
https://doi.org/10.3324/haematol.2020.270793 ©2022 Ferrata Storti Foundation
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