Megakaryocytic differentiation in human chronic myelogenous leukemia K562 cells induced by ionizing radiation in combination with phorbol 12-myristate 13-acetate

CRISPR/Cas9-Based Modeling of JAK2 V617F Mutation in K562 Cells Reveals Enhanced Proliferation and Sensitivity to Therapeutic Agents

The Janus kinase 2 (JAK2) protein fulfills an important role in hematopoiesis via the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, as it provides the genetic driver of BCR::ABL1-negative myeloproliferative neoplasms (MPNs), which are clinically manifested as polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The most common cause of MPNs is the mutation of JAK2 V617F in the JAK2 gene, which results in increased cell proliferation. However, both the pathogenesis and treatment regimen of BCR::ABL1-negative MPNs remain poorly understood. The aim of the present study was to establish K562 cell lines with a point mutation in exon 14 (JAK2p.V617F) using CRISPR/Cas9 technology. The modified JAK2 V617F cell lines were examined for the gene mutation using droplet digital PCR (DDPCR), and the presence of the mutation was confirmed by DNA sequencing. Modified cells were characterized by measuring JAK2 gene expression and the extent of cell proliferation. Interferon α2a (IFN-α2a) and arsenic trioxide were also administered to the cells to explore their potential effects. The JAK2 V617F-mutated cells were found to exhibit a higher level of JAK2 gene expression compared with the wild type. Interestingly, a significant increase in the proliferation rate was observed with the modified cells compared with the wild type cells (p < 0.001), as assessed from the JAK2 gene expression levels. Furthermore, the treatments with IFN-α2a and arsenic trioxide led to the preferential suppression of the cell proliferation rate of the K562 expressing mutant JAK2 cells compared with the wild type cells, and this suppression occurred in a dose-dependent manner(p < 0.01). Moreover, the modified cells were able to differentiate into megakaryocyte-like cells following stimulation with phorbol 12 myristate 13 acetate (PMA). Taken together, the results of the present study have shown that the CRISPR/Cas9-modified JAK2 V617F model may be used as a disease model in the search of novel therapies for MPNs.

The inhibitor of MyoD Family A (I-MFA) regulates megakaryocyte lineage commitment and terminal differentiation

Hematopoiesis and lineage commitment are regulated by several conserved cell-intrinsic signaling pathways, including MAPKs and β-catenin/TCF/LEF. The Inhibitor of MyoD Family A (I-MFA), a transcriptional repressor and tumor suppressor gene, interacts with these pathways and is dysregulated in chronic and acute myeloid leukemias, suggesting it may play a role in development and differentiation during hematopoiesis. To study this, immune cell populations in the bone marrow (BM) and periphery were analyzed in mice lacking Mdfi, encoding I-MFA (I-MFA-/-), and wild type (WT) controls. I-MFA-/- mice had reduced spleen and BM cellularity, with significant hyposplenism, compared to WT mice. In blood, total red blood cells and platelet counts were significantly reduced in I-MFA-/- mice, accompanied by a reduction in megakaryocyte (MK)/erythrocyte progenitor cells and an increase in myeloid progenitors in BM compared to WT mice. The K562 cell line exhibits PMA-induced MK differentiation, and shRNA knockdown of I-MFA resulted in reduced differentiation compared to control, with an increase and prolongation in phospho-JNK and phospho-ERK signaling. Overexpression of I-MFA promoted MK differentiation. These results suggest I-MFA plays a cell-intrinsic role in the response to differentiation signals, an effect that can be explored in the context of hematological cancers or other blood proliferative disorders.

Replication of Dengue Virus in K562-Megakaryocytes Induces Suppression in the Accumulation of Reactive Oxygen Species

Dengue virus can infect human megakaryocytes leading to decreased platelet biogenesis. In this article, we report a study of Dengue replication in human K562 cells undergoing PMA-induced differentiation into megakaryocytes. PMA-induced differentiation in these cells recapitulates steps of megakaryopoiesis including gene activation, expression of CD41/61 and CD61 platelet surface markers and accumulation of intracellular reactive oxygen species (ROS). Our results show differentiating megakaryocyte cells to support higher viral replication without any apparent increase in virus entry. Further, Dengue replication suppresses the accumulation of ROS in differentiating cells, probably by only augmenting the activity of the transcription factor NFE2L2 without influencing the expression of the coding gene. Interestingly pharmacological modulation of NFE2L2 activity showed a simultaneous but opposite effect on intracellular ROS and virus replication suggesting the former to have an inhibitory effect on the later. Also cells that differentiated while supporting intracellular virus replication showed reduced level of surface markers compared to uninfected differentiated cells.

Virodhamine, an endocannabinoid, induces megakaryocyte differentiation by regulating MAPK activity and function of mitochondria

Endocannabinoids are well-known regulators of neurotransmission by activating the cannabinoid (CB) receptors. Endocannabinoids are being used extensively for the treatment of various neurological disorders such as Alzheimer's and Parkinson's diseases. Although endocannabinoids are well studied in cell survival, proliferation, and differentiation in various neurological disorders and several cancers, the functional role in the regulation of blood cell development is less examined. In the present study, virodhamine, which is an agonist of CB receptor-2, was used to examine its effect on megakaryocytic development from a megakaryoblastic cell. We observed that virodhamine increases cell adherence, cell size, and cytoplasmic protrusions. Interestingly, we have also observed large nucleus and increased expression of megakaryocytic marker (CD61), which are the typical hallmarks of megakaryocytic differentiation. Furthermore, the increased expression of CB2 receptor was noticed in virodhamine-induced megakaryocytic cells. The effect of virodhamine on megakaryocytic differentiation could be mediated through CB2 receptor. Therefore, we have studied virodhamine induced molecular regulation of megakaryocytic differentiation; mitogen-activated protein kinase (MAPK) activity, mitochondrial function, and reactive oxygen species (ROS) production were majorly affected. The altered mitochondrial functions and ROS production is the crucial event associated with megakaryocytic differentiation and maturation. In the present study, we report that virodhamine induces megakaryocytic differentiation by triggering MAPK signaling and ROS production either through MAPK effects on ROS-generating enzymes or by the target vanilloid receptor 1-mediated regulation of mitochondrial function.

Endoplasmic reticulum stress induced apoptosis and caspase activation is mediated through mitochondria during megakaryocyte differentiation

Megakaryocytopoiesis involves the process of the development of hematopoietic stem cells into megakaryocytes (MKs), which are the specialized cells responsible for the production of blood platelets. Platelets are one of the crucial factors for hemostasis and thrombosis. In terminally differentiated MKs, many molecular process such as caspase activation and a massive cytoskeletal rearrangement drive the formation of cytoplasmic extensions called proplatelets. These cytoplasmic extensions packed with granules and organelles are then released from the bone marrow into the blood circulation as platelets. Classically, caspase activation is associated with apoptosis and recent reports suggest their involvement in cell differentiation and maturation. There is no clear evidence about the stimulus for caspase activation during megakaryocyte development. In the current study, we attempted to understand the importance of endoplasmic reticulum stress in the caspase activation during megakaryocyte maturation. We used human megakaryoblstic cell line (Dami cells) as an experimental model. We used PMA (Phorbol 12-myristate 13 acetate) to induce megakaryocytic differentiation to understand the involvement of ER stress and caspase activation during MK maturation. Further, we used Thapsigargin, a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) as a positive control to induce ER stress. We observed larger and adherent cells with the increased expression of megakaryocytic markers (CD41 and CD61) and UPR markers in PMA or Thapsigargin treated cells as compared to control. Also, Thapsigargin treatment induced increased caspase activity and PARP cleavage. The increased expression of megakaryocyte maturation markers alongside with ER stress and caspase activation suggests the importance of ER stress in caspase activation during MK maturation.

Promoted megakaryocytic differentiation of K562 cells through oxidative stress caused by near ultraviolet irradiation

Reactive oxygen species (ROS) have been proven to be important activators for various cellular activities, including cell differentiation. Several reports showed the necessity of ROS during cell differentiation of the megakaryocytic (MK) lineage. In this study, we employed near ultraviolet (near-UV) irradiation to generate endogenous oxidative stress in an MK differentiation process of K562 cells with phorbol 12-myristate 13-acetate (PMA) induction. A significant increase in the intracellular ROS level was detected on day 1 after near-UV irradiation. In the initial stage of differentiation, a shifted fraction of G1 and G2 phase cells was obtained using near-UV irradiation, giving an increased percentage of G2 phase cells (up from 31.1 to 68.7%). The near-UV irradiation-induced upregulation of the p21 gene, which is a cell cycle inhibitor, suggested that the G2 phase cells were prevented from undergoing cell division. It was found that the percentage of high ploidy (8N and 16N) cells was enhanced significantly at the later stage of the K562 cell culture with near-UV irradiation. Moreover, time-lapse analysis showed that near-UV irradiation encouraged the expression of CD41, a specific surface marker of megakaryocytes. This is the first report that the elevated oxidative stress through the near-UV irradiation promoted the MK differentiation of PMA-induced K562 cells.

Megakaryocytic differentiation of K562 cells induced by PMA reduced the activity of respiratory chain complex IV

Mitochondria are involved in the regulation of cell differentiation processes, but its function changes and molecular mechanisms are not yet clear. In this study, we found that mitochondrial functions changed obviously when K562 cells were induced to megakaryocytic differentiation by phorbol 12-myristate 13-acetate (PMA). During the cell differentiation, the reactive oxygen species (ROS) level was increased, mitochondrial membrane potential declined and respiratory chain complex IV activity was decreased. Treatment with specific inhibitor of mitochondrial respiratory chain complex IV led to a significant inhibition in mitochondrial membrane potential and reduction of PMA-induced cell differentiation. However, treatment with cyclosporine A, a stabilization reagent of mitochondrial membrane potential, did not improve the down-regulation of mitochondrial respiratory chain complex IV induced by PMA. Furthermore, we found that the level of the complex IV core subunit COX3 and mitochondrial transport-related proteins Tim9 and Tim10 were decreased during the differentiation of K562 cells induced by PMA, suggesting an important role of these factors in mitochondrial functional changes. Our results suggest that changes in mitochondrial functions are involved in the PMA-induced K562 cell differentiation process, and the maintenance of the steady-state of mitochondrial functions plays a critical role in the regulation of cell differentiation.