The Hippo pathway regulates human megakaryocytic differentiation

Abstract

The Hippo pathway is involved in several biological processes in both flies and mammals. Recent studies have shown that the Hippo pathway regulates Drosophila's haematopoiesis; however, understanding of its role in mammalian haematopoiesis is still limited. In flies, deletion of the Hippo component gene, Warts, affects crystal cell differentiation. We explored the role of the Hippo pathway in human haematopoiesis focusing on megakaryopoiesis. To investigate the role of LATS1/2 (a mammalian homolog of Warts) in human megakaryoblastic cell differentiation and platelet formation, megakaryoblastic cell (MEG-01) line was used as a model to gain insight into mechanism of the Hippo pathway in mammalian megakaryopoiesis. Effect of LATS1/2 on megakaryoblastic cell differentiation and platelet production were determined by functional changes. We found that depletion of LATS1/2 resulted in an increase of CD41 megakaryocytes with impaired platelet biogenesis. Our study shows that the Hippo signalling pathway plays a crucial role in human megakaryoblastic cell differentiation and thrombopoiesis.

Effect of YAP/TAZ on megakaryocyte differentiation and platelet production

“…We previously showed that reduction of the Hippo core kinase LATS1/2 inhibits platelet production [4]. In the present study, we further demonstrated that high expression of the Hippo pathway effector protein YAP induces MEG-01 cells to become more mature as shown by the increasing number of CD41 + cells, but these cells did not produce platelets.…”

“…We previously demonstrated that Hippo pathway core kinase LATS1/2 plays an essential role in regulating megakaryocyte proliferation and differentiation [4]. In the present study, we further explored the role of the Hippo effector proteins YAP and TAZ on megakaryocyte differentiation and platelet production.…”

“…CD41, which is a common marker for megakaryocyte and platelets, is expressed on the plasma membrane of mature megakaryocyte cells prior to platelet release [ 10 , 11 ]. Our previous work and other studies demonstrated that 20–40% of a population of MEG-01 cells is made up of CD41 + cells, and MEG-01 cells can produce platelet-like particles (PLPs) either spontaneously or upon treatment with platelet induction agents, such as valproic acid (VPA) [ 4 , 12 ]. In this experiment, the proportions of CD41 − and CD41 + cells in each sample were counted and shown in the pie chart to indicate the differentiation capacity of MEG-01 after YAP and/or TAZ were depleted ( Figure 1 C; pie charts show an average value from three independent experiments with 30,000 events per experiment).…”

“…To confirm that YAP is required for megakaryoblastic cell differentiation, we performed gain-of-function experiments in MEG-01 cells via transfection with wild-type YAP, or site-directed mutagenized YAP S5A or YAP S127A to constitutively generate active form of YAP, or indirectly increasing endogenous YAP by inactivating the LATS1/2 kinases (LATS-KD) [4]. Significant up-regulation of YAP was observed after MEG-01 cells were transfected with YAP plasmids.…”

Association of recurrent venous thromboembolism and circulating microRNAs

“…However, the most important pathways, which could have a role in the pathophysiology of VTE, are discussed here; MAPK signaling pathways have been previously shown to be involved in the pathophysiology of thrombosis or platelet activity in a direct or indirect manner [31, 38–42]. Similarly, the Hippo signaling pathway has been shown to play an important role in megakaryocyte differentiation and platelet production [41, 43]. HIF-1 pathway is known to promote endothelial permeability and activation, coagulopathy, and recruitment of inflammatory cells, and contribute to the initiation or development of venous thrombosis through its target genes [42].…”