Proplatelet formation is regulated by the Rho/ROCK pathway.
Platelets are released by megakaryocytes (MKs) via cytoplasmic extensions called proplatelets, which require profound changes in the microtubule and actin organization. Here, we provide evidence that the Rho/ROCK pathway, a well-known regulator of actin cytoskeleton, acts as a negative regulator of proplatelet formation (PPF). Rho is expressed at a high level during the entire MK differentiation including human CD34(+) cells. Thrombopoietin stimulates its activity but at a higher extent in immature than in mature MKs. Overexpression of a dominant-negative or a spontaneously active RhoA leads to an increase or a decrease in PPF indicating that Rho activation inhibits PPF. This inhibitory effect is mediated through the main Rho effector, Rho kinase (ROCK), the inhibition of which also increases PPF. Furthermore, inhibition of Rho or ROCK in MKs leads to a decrease in myosin light chain 2 (MLC2) phosphorylation, which is required for myosin contractility. Interestingly, inhibition of the MLC kinase also decreases MLC2 phosphorylation while increasing PPF. Taken together, our results suggest that MLC2 phosphorylation is regulated by both ROCK and MLC kinase and plays an important role in platelet biogenesis by controlling PPF and fragmentation.
Chang
Yunhua
Y
Institut National de la Santé et de la Recherche Médicale, Unité U 790, Pavillon de Recherche 1, Institut Gustave Roussy, Villejuif, France.
Auradé
Frédéric
F
Larbret
Frédéric
F
Zhang
Yanyan
Y
Le Couedic
Jean-Pierre
JP
Momeux
Laurence
L
Larghero
Jerôme
J
Bertoglio
Jacques
J
Louache
Fawzia
F
Cramer
Elisabeth
E
Vainchenker
William
W
Debili
Najet
N
D001792:Blood Platelets / Q000166:cytology*; D024722:Cardiac Myosins / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation; D006410:Hematopoiesis / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D008533:Megakaryocytes / Q000166:cytology*; D018994:Myosin Light Chains / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D013926:Thrombopoietin / Q000494:pharmacology; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D054460:rho-Associated Kinases
D047908:Intracellular Signaling Peptides and Proteins; D018994:Myosin Light Chains; C107184:myosin light chain 2; D013926:Thrombopoietin; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D024722:Cardiac Myosins; D020741:rho GTP-Binding Proteins